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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Suggested Citation:"2 Ammonia." National Research Council. 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: The National Academies Press. doi: 10.17226/12032.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

2 Ammonia This chapter summarizes the relevant epidemiologic and toxicologic stud- ies of ammonia. Selected chemical and physical properties, toxicokinetic and mechanistic data, and inhalation-exposure levels from the National Research Council (NRC) and other agencies are also presented. The committee considered all that information in its evaluation of the Navy’s current and proposed 1-h, 24- h, and 90-day exposure guidance levels for ammonia. The committee’s recom- mendations for ammonia exposure levels are provided at the end of this chapter with a discussion of the adequacy of the data for defining the levels and the re- search needed to fill the remaining data gaps. PHYSICAL AND CHEMICAL PROPERTIES Ammonia is a corrosive alkaline gas at room temperature (Budavari et al. 1989). It is colorless and has a distinctive odor that has been described as sharp, pungent, and irritating (HSDB 2005). The odor threshold has been reported to range from 5 to 53 ppm (NRC 2002). Selected chemical and physical properties are listed in Table 2-1. OCCURRENCE AND USE Ammonia has several important industrial uses (Czuppon et al. 1992). It is a primary feedstock in the fertilizer industry, which is the largest consumer of ammonia. It is also used to synthesize explosives and products in the fibers and plastics industry. Ammonia also is a naturally occurring compound, an essential component of many biologic processes, and an intermediate in the global nitro- gen cycle. Average global ammonia concentrations are estimated to range from 0.6 ppb to 3 ppb (ATSDR 2004). 20

Ammonia 21 TABLE 2-1 Physical and Chemical Properties of Ammonia Synonyms Anhydrous ammonia, ammonia gas CAS registry number 7664-41-7 Molecular formula NH3 Molecular weight 17.03 Boiling point –33.35°C Melting point –77.7°C Flash point NA Explosive limits NA Specific gravity 0.639 at 0°C Vapor pressure 8.5 atm at 20°C Solubility Solubility in water: 47% (0EC), 38% (15EC), 28% (30EC), 18% (50EC); soluble in chloroform and ether Conversion factors 1 ppm = 0.7 mg/m3; 1 mg/m3 = 1.44 ppm Abbreviations: NA, not available or not applicable. Sources: Specific gravity from Czuppon et al. 1992; vapor pressure from Lewis 1993; all other data from Budavari et al. 1989. Sources of ammonia on submarines include the sanitary system, decompo- sition of monoethanolamine (a chemical used in the carbon dioxide removal system), and decomposition of insulation blowing agents (Crawl 2003). NRC (1988) listed ammonia as a possible air contaminant on board submarines and reported a concentration of 2 ppm. No information was provided on sampling protocol, location, operations, or duration. No other exposure data were located. SUMMARY OF TOXICITY The database to characterize ammonia toxicity is sufficient and includes human and animal data suitable for derivation of exposure guidance levels. Mul- tiple toxicologic reviews are available, including evaluations by the NRC (1966, 1987, 1994, 2002, 2007), the Agency for Toxic Substances and Disease Registry (ATSDR 2004), the American Conference of Governmental Industrial Hygien- ists (ACGIH 2001), and the National Institute for Occupational Safety and Health (NIOSH 1974). Information from those reviews is summarized in the following paragraphs. Ammonia is a corrosive, alkaline, irritant gas that produces effects imme- diately on contact with moist mucous membranes of the eyes, mouth, and respi- ratory tract. It reacts with moist tissues to form ammonium hydroxide in an exo- thermic reaction; the thermal and chemical burns resulting from high- concentration exposures are a consequence of the heat of reaction and of the corrosive properties of the alkaline reaction product ammonium hydroxide.

22 Exposure Guidance Levels for Selected Submarine Contaminants Ammonia is a respiratory and ocular irritant; high concentrations can cause res- piratory tissue injury and necrosis and penetrate the corneal epithelium. Because of its appreciable water solubility, ammonia is largely retained in the nasal mu- cosa, another common site of tissue injury after vapor exposure. Because of its widespread commercial use and transport, accidental expo- sure to ammonia during industrial, farm, or transport accidents is not uncom- mon, and the toxicology literature contains numerous case studies and accident reports involving human exposures to high, but unknown, concentrations that have caused deaths or severe and long-lasting injuries. Although they contain useful background information, such reports provide little quantitative informa- tion regarding dose-response relationships, do not characterize exposure condi- tions expected on board a modern submarine, and hence will be given little con- sideration in the present analysis. In addition to accident case reports, the ammonia database contains human experimental-exposure studies, epidemiologic studies, and laboratory animal experimental studies that characterize respiratory and ocular tissue injury, be- havioral changes, reductions in respiration rates (such as RD50 values), poten- tially increased infectivity with pathogen challenge, or lethality. As stated above, the human odor threshold for ammonia ranges from 5 to 53 ppm, and sensory fatigue (“adaptation” or “inurement”) is documented. There is some subjective debate regarding the concentration at which respiratory and ocular irritation occurs, but there is a consensus that tissue is injured at va- por concentrations in excess of those at which ammonia can be detected by odor or ocular irritation; thus odor and ocular irritation have warning value for am- monia, although sensory fatigue often occurs after continuous or repetitive exposures. Effects in Humans Accidental Exposures No reliable concentration data are available for characterizing human ex- posures sustained during the many transportation, industrial, and agricultural accidents in which injurious or lethal ammonia concentrations have been re- leased. Most case reports contain no exposure estimates but demonstrate that high vapor concentrations have caused severe damage to the respiratory tract. Death was most likely to occur when exposures were high enough to cause pul- monary edema. Nonlethal, irreversible, or long-term effects occurred when damage progressed to the tracheobronchial region, as manifested in reduced performance on pulmonary-function tests, bronchitis, bronchiolitis, emphysema, and bronchiectasis. Nondisabling, reversible effects were manifested as irritation to the eyes, throat, and nasopharyngeal region. A few of the many accident case reports are summarized below. Additional case reports and details are presented

Ammonia 23 in NRC (2002; see Table 2-5, “Human Toxicity Data, Accidental Exposure to Ammonia,” pp. 34-41) and ATSDR (2004). Caplin (1941, as cited in NIOSH 1974) reported effects observed in 47 persons accidentally exposed to ammonia in an air-raid shelter when a transfer pipe containing ammonia was ruptured. Casualties were divided into three groups according to the degree to which they were affected: “mildly” (slight upper respiratory tract and eye irritation and hoarseness), “moderately” (produc- tive cough and moist rales and more pronounced respiratory tract irritation), or “severely” (pulmonary edema with cyanosis, intense dyspnea, and persistent cough with frothy sputum). No deaths occurred among the nine “mildly” af- fected patients. Of the 27 “moderately” affected patients, three exhibited signs and symptoms similar to pulmonary edema and died within 36 h. Nine of the “moderately” affected patients developed bronchopneumonia within 2-3 days, and three died 2 days after the onset; mortality rate for the “moderately” affected patients was 22% (six of 27). The 11 “severely” affected patients developed pulmonary edema, and seven died within 48 h after exposure; mortality rate for the “severely” affected group was 64% (seven of 11). Walton (1973) reported on the death of one of seven workers exposed to ammonia for an undefined duration in an industrial accident. The autopsy report noted marked laryngeal edema, acute congestion, pulmonary edema, and denu- dation of the bronchial epithelium. Survivors exhibited difficulty in breathing and burns of the eyes, mucous membranes, and skin; reduced pulmonary gas transfer and airway damage were apparent in survivors followed for 3 years after exposure. A worker exposed to high concentrations of ammonia vapor estimated at 10,000 ppm for an undefined duration (perhaps a few minutes) experienced coughing, dyspnea, and vomiting soon after exposure (Mulder and Van der Zalm 1967). Three hours after initial exposure, the worker’s face was “red and swollen,” his mouth and throat were “red and raw,” his tongue was swollen, speech was difficult, and conjunctivitis was present; he died of cardiac arrest 6 h after exposure. An autopsy revealed marked respiratory irritation, denudation of the tracheal epithelium, and pulmonary edema (Mulder and Van der Zalm 1967). People acutely exposed to high concentrations of ammonia who survive immediate effects may die of complications weeks to months later. A 25-year- old man died 60 days after exposure to a high concentration of ammonia sus- tained in a farming accident (Sobonya 1977). The autopsy report noted damage to the bronchial epithelium, bronchiectasis, mucus plugging and mural thicken- ing of the smallest bronchi and bronchioles, fibrous obliteration of small air- ways, and a purulent cavitary pneumonia characterized by large numbers of No- cardia asteroides (nocardial pneumonia). Three co-workers exposed in the same accident died immediately. Hoeffler et al. (1982) reported on a case of a 30- year-old woman who died 3 years after exposure to ammonia during an accident involving a tanker truck carrying anhydrous ammonia in Houston, Texas. Her injuries resulted in severe immediate respiratory effects, including pulmonary

24 Exposure Guidance Levels for Selected Submarine Contaminants edema. She required mechanically assisted respiration throughout her remaining life. Bronchiectasis was detected 2 years after exposure and confirmed at au- topsy, which also showed bronchopneumonia and cor pulmonale. Experimental Studies Numerous clinical studies—summarized in NRC (1987, 2002, 2007), ATSDR (2004), and elsewhere—have been conducted in healthy human sub- jects—including allergic and nonallergic people, those with asthma, and smok- ers—exposed to monitored concentrations of ammonia for various durations in controlled settings. Clinical data on reversible and nondisabling effects include responses from resting and exercising subjects and address respiratory and car- diac function, airway resistance, granulocytes and monocytes in peripheral blood, cell concentrations in nasal lavage fluids, and various subjective meas- urements of ocular and respiratory irritancy and systemic effects. Although re- sults of some of the earlier (such as 1940s) studies may be compromised by what is now considered limited analytic characterization of exposure concentra- tions, there are sufficient multiple and well-conducted clinical studies suitable for exposure-guideline estimation. The more quantitative studies are summa- rized in Tables 2-2 and 2-3 and the following text. Verberk (1977) examined dose-response relationships of signs and symp- toms after exposure to ammonia vapor at 50-140 ppm in an exposure chamber over increasing durations (30 min to 2 h). Respiratory function and subjective responses of two groups of adults were recorded. One group consisted of eight people familiar with the literature on ammonia effects but “not accustomed…by personal contact” to ammonia exposures (the informed group, 29-53 years old). The second group consisted of eight university students unfamiliar with the lit- erature on ammonia effects and unfamiliar with experiments in laboratory situa- tions (the naive group, 18-30 years old). All subjects had the opportunity to leave the exposure chamber at any time during the test. Histamine threshold challenge tests performed on each subject before ammonia exposure docu- mented the absence of hypersusceptibility to nonspecific irritants. Four members of each group were smokers. Each group was exposed at 1-week intervals to ammonia at 50, 80, 110, or 140 ppm for 30 min, 1 h, or 2 h. Subjective re- sponses (such as smell, eye irritation, throat irritation, and cough) were recorded every 15 min, and respiratory function—vital capacity (VC), forced expiratory volume at 1 sec (FEV1), forced inspiratory volume at 1 sec (FIV1)—was meas- ured before and after each exposure. Chamber concentrations were monitored instantaneously with an infrared spectrometer. No subject inhaling any test con- centration for any exposure duration exhibited more than a 10% decrease in VC, FEV1, or FIV1. Verberk (1977) considered that small percentage to be “no ef- fect.” The committee agrees that such small differences have minimal clinical significance. Furthermore, there was no group effect on those measures. Subjec- tive-response scores did exhibit group effects and dose- and duration-response

Ammonia 25 TABLE 2-2 Subjective-Response Scoresa of Informedb and Naiveb Human Subjects Exposed to Ammonia Vapor at Various Concentrations Perception and 50 ppm (mean) 80 ppm (mean) 110 ppm (mean) 140 ppmc (mean) Exposure Duration Informed Naive Informed Naive Informed Naive Informed Naive Smell: ½h 2.0 2.5 2.0 3.0 2.2 3.0 2.0 3.8 1h 2.0 2.5 2.0 3.0 2.1 3.0 2.0 4.0 2h 2.0 3.0 1.5 3.0 2.1 3.0 2.0 WD Eye irritation: ½h 1.5 0.8 1.6 1.6 2.7 2.6 3.0 3.0 1h 1.5 0.8 1.7 1.6 2.7 2.5 2.9 3.2 2h 1.0 1.3 1.5 2.0 2.2 2.5 2.3 WD Throat irritation: ½h 0.5 0.5 0.8 1.1 1.4 2.0 1.0 3.8 1h 0.5 0.7 1.0 1.5 1.4 2.6 1.3 4.5 2h 0.7 1.6 0.8 2.0 1.0 3.0 1.2 WD Urge to cough: ½h 0.2 0.2 0.4 0.7 0.8 1.7 0.6 2.3 1h 0.2 0.1 0.5 1.0 0.7 2.0 0.9 1.8 2h 0.3 0.7 0.6 1.5 0.5 2.0 0.6 WD General discomfort: ½h 0.0 0.0 0.0 1.1 0.2 1.0 0.0 2.5 1h 0.0 0.2 0.0 1.2 0.2 1.0 0.0 3.3 2h 0.0 1.2 0.0 1.2 0.3 1.8 0.0 WD a Based on a scale of 0-5: 0 = “no sensation,” 1 = “just perceptible,” 2 = “distinctly per- ceptible,” 3 = “nuisance,” 4 = “offensive,” 5 = “unbearable.” b Informed subjects were academically familiar with the effects of ammonia but not accus- tomed to regular exposure to it; naive subjects were unfamiliar with literature document- ing effects and had not experienced regular exposure. See Table 2-3 for additional details of experimental protocol. c Only four of the naive subjects tolerated 140 ppm for 1 h; none tolerated 140 ppm for 2 h. Abbreviations: WD, self-withdrawn from chamber. Source: Adapted from NRC 2007; data from Verberk 1977. relationships and are summarized in Table 2-2. In general, the informed group submitted response scores lower than the naive group. Ihrig et al. (2006) evaluated the dose-response relationship of signs and symptoms (irritative, olfactory, and respiratory) during and after ammonia vapor exposures at 10-50 ppm in an exposure chamber according to the following ex- posure protocol: (a) 0 ppm for 4 h/day on day 1, (b) 10 ppm for 4 h/day on day 2, (c) 20 ppm for 4 h/day on day 3, (d) 20 ppm for 3 h/day with two 30-min peak exposures at 40 ppm (referred to hereafter as 20/40), and (e) 50 ppm for 4 h/day on day 5. The subjects were 43 male volunteers, 21-47 years old: 33 naive sub- jects unfamiliar with ammonia odor and 10 subjects who were regularly exposed to ammonia in the workplace; their smoking history was unreported. Subjective responses were elicited from them every hour of exposure at 10-40 ppm; at

26 TABLE 2-3 Summary of Experimentally Determined Human Nondisabling and Reversible Effects of Inhaled Ammonia Concentration (ppm) Time Subjects and Effects Reference 5 3-h exposure (1.5 h 5 males and 7 females; healthy adults, 21-28 years old (mean, 25); smoking Sundblad et al. resting + 1.5 h history unreported; n = 12 2004 exercising) When compared with 0-ppm control, no inflammatory reaction in upper respiratory tract, no alteration in exhaled nitric oxide concentration, no alteration in bronchial response to methacholine; subjective reports of eye discomfort and smell (p < 0.01), headache, dizziness, and “feeling of intoxication” (p < 0.05) significantly greater than control; tendency toward sensory adaptation to subjective “solvent smell” 10 4h 43 male volunteers (33 naive subjects, 10 ammonia workers); healthy adults, Ihrig et al. 2006 21-47 years old; smoking history unreported; n = 43. Subjects examined by physician before and after exposure; tear-flow rates measured with paper strips; lung-function examinations included bronchial responsiveness; individual attention, reaction time, and powers of concentration tested at end of each exposure day; “no relevant effects of the ammonia exposure in these physical and neurophysiological examination could be found” Median rank of olfactory symptoms 0.2 (less than 1 = “hardly at all”) in experienced subjects and 1.8 (2 = “somewhat”) in naive subjects 20 4h 43 male volunteers (33 naive subjects, 10 ammonia workers); healthy adults, Ihrig et al. 2006 21-47 years old; smoking history unreported; n = 43 Subjects examined by physician before and after exposure; tear-flow rates measured with paper strips; lung-function examinations included bronchial responsiveness; individual attention, reaction time, and powers of concentration tested at end of each exposure day; “no relevant effects of the ammonia exposure in these physical and neurophysiological examination could be found” Median rank of olfactory symptoms 0.5 (less than 1 = “hardly at all”) in experienced subjects and about 2.5 (2 = “somewhat”) in naive subjects

20, 40 20 ppm for 3 h with 43 male volunteers (33 naive subjects, 10 ammonia workers); healthy adults, Ihrig et al. 2006 two 30-min peaks at 21-47 years old; smoking history unreported; n = 43 40 ppm Subjects examined by physician before and after exposure; tear-flow rates measured with paper strips; lung-function examinations included bronchial responsiveness; individual attention, reaction time, and powers of concentration tested at end of each exposure day; “no relevant effects of the ammonia exposure in these physical and neurophysiological examination could be found” Median rank of olfactory symptoms 0.9 (less than 1 = “hardly at all”) in experienced subjects and 3 (“rather much”) in naive subjects 25 3-h exposure (1.5 h 5 males and 7 females; healthy adults, 21-28 years old (mean, 25 years); Sundblad et al. resting + 1.5 h smoking history unreported; n = 12 2004 exercising) When compared with 0-ppm control, no inflammatory reaction in upper respiratory tract, no alteration in exhaled nitric oxide concentration, no alteration in bronchial response to methacholine; subjective reports of irritation in eye and upper airways increased over control in all categories (p < 0.01); headache, dizziness, “feeling of intoxication, etc.” (p < 0.01 or p < 0.05); no tendency toward sensory adaptation to subjective reports of “solvent smell” 30 10 min 6 fit males, 23-44 years old (mean, 31 years) MacEwen et al. Odor moderately intense to highly penetrating; irritation faint or not detectable 1970 32 5 min 10 healthy volunteers Industrial Bio-Test 1 had nasal dryness Lab 1973 (as cited in ATSDR 2004 and WHO 1986) 50 5 min 10 healthy volunteers Industrial Bio-Test 2 had nasal dryness; NOAEL identified by ATSDR (2004) Lab 1973 (as cited in ATSDR 2004 and WHO 1986) (Continued) 27

28 TABLE 2-3 Continued Concentration (ppm) Time Subjects and Effects Reference 50 10 min 6 fit males, 23-44 years old (mean, 31 years) MacEwen et al. Highly penetrating odor; moderate irritation 1970 50 30 min 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.0-2.5 (5 = “unbearable”); eye irritation ranked 0.8-1.5; throat irritation ranked 0.5; slight urge to cough; slight general discomfort; pre- exposure and postexposure measurements of FVC and FEV1 exhibited no change from control; participants recorded subjective response every 15 min of exposure; in general, naive subjects rated effects more severely than informed subjects at all exposures 50 1h 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.0-2.5 (5 = “unbearable”); eye irritation ranked 0.8-1.5; throat irritation ranked 0.5-0.7; mild urge to cough; slight general discomfort; pre- expsoure and postexposure measurement of FVC and FEV1 exhibited no change from control; in general, naive subjects rated effects more severely than informed subjects at all exposures 50 2h 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.0-3.0 (5 = “unbearable”); eye irritation ranked 1.0-1.3; throat irritation ranked 0.7-1.6; mild urge to cough; mild general discomfort; pre- exposure and postexposure measurement of FVC and FEV1 exhibited no change from control; in general, naive subjects rated effects more severely than informed subjects, at all exposures

50 2-6 h/day, 6 weeks; 2 unacclimated subjects: 1 male, 1 female, 24-29 years old; 1 smoker Ferguson et al. workplace exposures, No significant difference in respiratory rates, pulse, systolic and diastolic BP, 1977 standard workplace FVC, and FEV1; physician-observed mild eye, nose, and throat irritation not physical activities significantly different from control; no evidence of abnormal chest sounds, heart murmur, neurologic change, or weight change; no impairment 50 4h 43 male volunteers (33 naive subjects, 10 ammonia workers); healthy adults, Ihrig et al. 2006 21-47 years old; smoking history unreported; n = 43 Subjects examined by physician before and after exposure; tear-flow rates measured with paper strips; lung-function examinations included bronchial responsiveness; individual attention, reaction time, and powers of concentration tested at end of each exposure day; “no relevant effects of the ammonia exposure in these physical and neurophysiological examination could be found” 3 participants exhibited “slight conjunctival hyperemia”; irritative symptom median of 1 (“hardly at all”) and largely unchanged over 4-h exposure; median rank of olfactory symptoms about 1.7 (2 = “somewhat”) in experienced workers and about 3.2 (3 = “rather much”) in naive subjects 72 5 min 10 healthy volunteers Industrial Bio-Test 3 had nasal, eye, and throat irritation; LOAEL identified by ATSDR (2004) Lab 1973 (as cited in ATSDR 2004 and WHO 1986) 80 30 min 16 adults; 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.0-3.0 (5 = “unbearable”); eye irritation ranked 1.6; throat irritation ranked 0.8-1.1; mild urge to cough; moderate general discomfort; no measurable change from control in respiratory function (FVC, FEV1); in general, naive subjects rated effects more severely than informed subjects at all exposures (Continued) 29

30 TABLE 2-3 Continued Concentration (ppm) Time Subjects and Effects Reference 80 1h 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.0-3.0 (5 = “unbearable”); eye irritation ranked 1.6-1.7; throat irritation ranked 1.0-1.5; mild urge to cough; moderate general discomfort; no measurable change from control in respiratory function (FVC, FEV1); in general, naive subjects rated effects more severely than informed subjects at all exposures 80 2h 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 1.5-3.0 (5 = “unbearable”); eye irritation ranked 1.5-2.0; throat irritation ranked 0.8-2.0; urge to cough; moderate general discomfort; no measurable change from control in respiratory function (FVC, FEV1); in general, naive subjects rated effects more severely than informed subjects at all exposures 25, 50, 100: ascending 2-6 h/day, 6 weeks; 4 unacclimated subjects: males, 26-46 years old; 2 smokers Ferguson et al. and descending workplace exposures; No adverse effects on respiratory function; no increase in frequency of eye, nose, 1977 sequentially weekly; 2 normal workplace throat irritation; only statistically significant increase was in FEV1 weeks at each physical and mental (“improvement”) with increasing ammonia concentration; no subjective reports of concentration tasks irritation; physician examinations indicate “mild” irritation of eyes, nose, and throat at 50, 100 ppm (0.11), not significantly different from control (0.09); after acclimation, continuous exposure at 100 ppm (with occasional excursions to 200 ppm) easily tolerated; exposure effects on workplace mental and physical tasks normally performed by chemical operator also evaluated (none) 100 5, 10, 15, 20, 30 sec Individual, forced-air nostril delivery at 100 ppm (at 9 newtons/cm2) for McLean et al. 1979 designated exposure periods separated by 15-min measurement of NAR; concentration-dependent increase in NAR but no significant differences between mean response in nonatopic and atopic (including those with allergic rhinitis) subjects

Mean, 102-336 (range, Apparently 95-120 18 healthy servicemen, mean 24.1 years old; exercising on cycle ergometer at Cole et al. 1977 71.5-492) min 20 to 120 W; considered “submaximal” exercise “No material discomfort” but dryness of mouth and prickling sensation in nose; reversible ventilatory responses; ventilation minute volume significantly reduced at 151-336 ppm; no effect on respiratory minute volume at 102 ppm; exercise tidal volume significantly increased at 152 ppm; average reduction in ventilation minute volume of 6% (range, 3.5-10.0%) at all concentrations 110 30 min 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.2-3.0 (5 = “unbearable”); eye irritation ranked 2.6-2.7; throat irritation ranked 1.4-2.0 of 5; mild urge to cough; moderate general discomfort; no measurable change from control in respiratory function (FVC, FEV1); in general, naive subjects rated effects more severely than informed subjects at all exposures 110 1h 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.1-3.0 (5 = “unbearable”); eye irritation ranked 2.5-2.7; throat irritation ranked 1.4-2.6; moderate urge to cough; moderate general discomfort; no measurable change from control in respiratory function (FVC, FEV1); in general, naive subjects rated effects more severely than informed subjects at all exposures 110 2h 16 adults: 8 informed (7 males, 1 female, 29-53 years old), 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.1-3.0 (5 = “unbearable”); eye irritation ranked 2.2-2.5; throat irritation ranked 1.0-3.0; urge to cough; general discomfort; no measurable change from control in respiratory function (FVC, FEV1); in general, naive subjects rated effects more severely than informed subjects at all exposures (Continued) 31

32 TABLE 2-3 Continued Concentration (ppm) Time Subjects and Effects Reference 140 30 min 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.0-3.8 (5 = “unbearable”); eye irritation ranked 3.0; throat irritation ranked 1.0-3.8; mild urge to cough; moderate general discomfort; no measurable change from control in respiratory function (FVC, FEV1); in general, naive subjects rated effects more severely than informed subjects at all exposures 140 1h 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Odor perception ranked 2.0-4.0 (5 = “unbearable”); eye irritation ranked 2.9-3.2; throat irritation ranked 1.3-4.5; moderate urge to cough; moderate general discomfort; no measurable change from control in respiratory function (FVC, FEV1); part of naive population withdrew; in general, naive subjects rated effects more severely than informed subjects at all exposures 140 2h 16 adults: 8 informed (7 males, 1 female, 29-53 years old); 8 naive (6 males, 2 Verberk 1977 females, 18-30 years old) Naive group withdrew; odor perception ranked 2.0 by informed group; eye irritation ranked 2.3 by informed group; throat irritation ranked 1.2 by informed group; urge to cough; general discomfort; no measurable change from control in respiratory function (FVC, FEV1). 143 5 min 10 healthy volunteers Industrial Bio-Test Nose, eye, throat, and chest irritation; lacrimation Lab 1973 (as cited in ATSDR 2004 and WHO 1986)

500 15, 30 min (1 for 15 7 adult males at rest Silverman et al. min, 6 for 30 min) Increase in minute volume compared with control (+50-250%); nose and throat 1949 irritation (2) with nasal dryness and stuffiness; excessive lacrimation (2); immediate hyperventilation (3); change to mouth breathing (5); transient hypoesthesia of skin around nose and mouth (7); no significant change in blood or urinary urea, ammonia, blood-protein nitrogen; “slight” increase in pulse rate, BP in 1 of 2; nasopharyngeal irritation persisted for 24 h in 2; authors consider 500 ppm “physiologically undesirable” 571 (mean NH3TR; Single breath 14 subjects, 21-30 years old from cohort of 102 healthy, nonsmoking males, Erskine et al. 1993 SEM, 41.5) females Threshold for reflex glottis closure 1,791 (mean NH3TR; Single breath 14 subjects, 86-95 years old from cohort of 102 healthy, nonsmoking males, Erskine et al. 1993 SEM, 52) females Threshold for reflex glottis closure Note: See also Table 2-4 of NRC (2002) and Table 3-1 of ATSDR (2004) for additional detail. For full description of rankings used in Verberk (1977), see Table 2-2 of this chapter. Abbreviations: ATSDR, Agency for Toxic Substances and Disease Registry; BP, blood pressure; FEV1, forced expiratory volume at 1 sec; FVC, forced vital capacity; LOAEL, lowest observed-adverse-effect level; NAR, nasal airway resistance; NOAEL, no-observed-adverse-effect level. Source: Adapted from NRC 2007. 33

34 Exposure Guidance Levels for Selected Submarine Contaminants 50 ppm, responses were elicited every 30 min. Subjective-response scores were to ammonia in the workplace; their smoking history was unreported. Subjective responses were elicited from them every hour of exposure at 10-40 ppm; at 50 ppm, responses were elicited every 30 min. Subjective-response scores were ranked as 0 = “not at all,” 1 = “hardly at all,” 3 = “somewhat,” 4 = “considera- bly,” and 5 = “very much.” Medical examinations conducted before and after each exposure assessed physical response of the eyes and respiratory tract and cognitive skills (for example, lung-function test, including bronchial responsive- ness; neuropsychologic examination for reaction time, attention, and concentra- tion; and nasal resistance and lacrimation). Ihrig et al. (2006) report that, with the exception of three subjects in the 50-ppm exposure group who exhibited “slight conjunctival hyperemia,” “no relevant effects of the ammonia exposure in these physical and neuropsychological examinations could be found.” Fur- thermore, comparison of subjective symptoms reported by naive subjects vs ammonia workers indicated that habituation strongly influenced complaint re- porting (for example, naive subjects reported more symptoms than experienced subjects at a given exposure). McLean et al. (1979) examined the effect of ammonia on nasal airway re- sistance (NAR) in atopic and nonatopic human subjects and the potential inhibi- tion of such effects by atropine or chlorpheniramine administration. Ammonia (100 ppm at 9 newtons/cm2) was serially introduced into each nostril (successive exposure durations for each subject of 5, 10, 15, 20, and 30 sec/nostril followed by 15-min intervals). Exposures were followed by NAR measurement with a pneumotachograph attached to a facemask every minute for 5 min and then every 2 min for 10 min (total of 10 measurements over a 15-min period). Nona- topic subjects were screened on the basis of strict criteria that included a ques- tionnaire, physical examination, spirometry, a nasal smear for eosinophils, and a battery of 19 prick and six intracutaneous allergen tests. Nonatopic subjects could possess no personal or immediate family history of atopic disease (allergic rhinitis, asthma, or atopic dermatitis), could have no more than 5% eosinophils in their nasal smears, and had to exhibit negative reactions on the battery of prick and intracutaneous allergen tests. Atopic subjects were screened on the basis of a characteristic history of allergic rhinitis and positive allergen-test reac- tions. Some subjects determined to be atopic had a history of asthma. All sub- jects had been symptom-free for several weeks before the study, and none was judged to be taking medications that would influence skin or mucosal tests. In- dividual baselines were obtained by collection of NAR measurements during a 15-min pre-exposure period. Additional tests included introduction of 0.1 mL of aerosolized phosphate-buffered saline, 0.1 mL of atropine sulfate, or 0.1 mL of chlorpheniramine maleate into the nostrils, each followed by exposure to 100- ppm ammonia vapor for 20 sec. NAR measurements after exposure increased significantly with increase in exposure duration from 5 to 20 sec. Negligible increases were noted in subjects exposed for 30 sec compared with 20 sec. There was no significant difference in NAR increase between atopic and nonatopic subjects exposed to ammonia, nor was there any significant difference between

Ammonia 35 the allergic-rhinitis subjects with and without a history of asthma. Atropine sul- fate administration inhibited the NAR response to ammonia in atopic and nona- topic subjects by up to 89%, whereas administration of the antihistamine chlor- pheniramine had no effect on ammonia-induced NAR. The study authors noted that the results of atropine and chlorpheniramine administration suggest that ammonia irritancy is mediated primarily by a parasympathetic reflex effect on the nasal vasculature and not by histamine release. Industrial Bio-Test Laboratories, Inc. (1973, as cited in ATSDR 2004 and WHO 1986) determined the irritation threshold in 10 human volunteers exposed to ammonia vapor at 32, 50, 72, or 143 ppm for 5 min. Irritation was subjec- tively defined as annoyance to the nose, throat, eyes, mouth, or chest. Subjects demonstrated dose-related response of those subjective end points; effect sever- ity was not noted. MacEwen et al. (1970) studied six male workers, 23-44 years old (aver- age, 31 years); all were considered “fit” in that each had passed either class II U.S. Air Force (USAF) or class II Federal Aviation Administration (FAA) physical examinations for flying. The test population included “nonsmokers, reformed smokers, and heavy smokers.” Each subject underwent head-only ex- posure to ammonia at 30 or 50 ppm for 10 min and reported the degree of inten- sity and description of irritation of the nose and eyes on a subjective scale. Study results demonstrated a dose-related increase in the subjective response to am- monia at 30 and 50 ppm. At 30 ppm, irritation was reported by two of the six subjects as faint (grade 1) and by three as not detectable (grade 0), and one gave no response; for odor characteristics at 30 ppm, three subjects reported odor as strong or highly penetrating (grade 4), two reported odor as easily noticeable or moderate (grade 3), and one gave no response. At 50 ppm, irritation was re- ported by four subjects as moderate (grade 2), by one as faint or just perceptible (grade 1), and by one as not detectable (grade 0); odor was characterized as strong or highly penetrating (grade 4) for by all six subjects at 50 ppm. Silverman et al. (1949) studied seven male subjects exposed to 500-ppm anhydrous ammonia through a nose and mouth mask for 30 min (six subjects) or 15 min (one subject). Respiratory rates, minute volumes, blood pressure, pulse rates, blood urea, serum nonprotein nitrogen, and urinary urea and ammonia were measured in each subject, and each subject provided subjective reactions. Results were as follows: increase (50-250%) of minute volume in all seven sub- jects; nose and throat irritation (two subjects) with nasal dryness and stuffiness; excessive lacrimation (two subjects); immediate hyperventilation (three sub- jects); change to mouth breathing (five subjects); transient hypoesthesia (de- creased sensitivity) of skin around nose and mouth (seven subjects); no signifi- cant change in blood or urinary urea, ammonia, or blood-protein nitrogen; and “slight” increase in pulse rate and systolic and diastolic blood pressure in one of two measured subjects. Nasopharyngeal irritation persisted for 24 h in two sub- jects. Silverman et al. (1949) concluded from their results that exposure to 500- ppm ammonia was “physiologically undesirable.” Cole et al. (1977) studied the effects of exercise on 18 servicemen exposed

36 Exposure Guidance Levels for Selected Submarine Contaminants to ammonia vapor at 102, 152, 206, and 336 ppm in an exposure chamber while cycling under a load of 20 W increased to 180 W in 20-W increments for vari- ous durations that apparently were 95-120 min (based on assumptions of “zero time” and extrapolation from figures in the report). Subjects served as their own controls. Measurements of respiratory function (respiratory rate, minute volume, tidal volume, and oxygen uptake) and cardiac frequency were taken during each experimental period and compared with control values. Measured minute vol- ume was decreased by 8%, 10%, and 6% at 152, 206, and 336 ppm, respec- tively. However, no clear dose-related trend was observed relative to the con- trols. Tidal volume was significantly decreased by 9% and 8% and respiratory frequency was increased by 10% and 8% at 206 and 336 ppm, respectively, compared with the control values. Those changes may indicate that vagal stimu- lation may have occurred; however, no clear dose-response relationship was observed. The small changes in tidal volume and respiratory frequency are unlikely to be clinically significant. During exposures, subjects noted “no mate- rial discomfort” but mouth dryness and prickling in the nose; these effects were reversible on cessation of exposure. Sundblad et al. (2004) investigated the acute effects of repeated low- concentration ammonia exposures in chamber experiments, incorporating both rest and ergometric exercise. Seven females and five male healthy atopic adults, 21-28 years old (mean, 25 years), with no reported present or past symptoms of allergy or airway disease were exposed to ammonia in randomized order at 0, 5, and 25 ppm for 3 h on three occasions; the exposures were separated by at least 1 week in which subjects did not undergo experimental ammonia exposures. During each 3-h exposure, 1.5 h was spent at seated rest and 1.5 h in exercising on a bicycle ergometer at 50 W. Subjects ranked 10 subjective and transient symptoms selected to characterize irritation—such as eye, nose, and throat dis- comfort—and systemic response—such as headache, dizziness, nausea, and “feeling of intoxication.” The latter symptoms were characterized by Sundblad and co-workers as “CNS [central nervous system] effects.” Sundblad et al. (2004) offered no neurophysiologic measurements or other experimental data to support categorization of the latter symptoms as adverse CNS responses. The committee concludes that the systemic responses may be consequences of irrita- tion or odor. Moreover, the exposure protocol meant that each subject was ex- posed to two ammonia concentrations, which may or may not have been sepa- rated by a sham exposure, depending on the randomized exposure sequence. Therefore, because of sensory fatigue, a subject’s response to the second ammo- nia exposure may have been less vigorous than it would have been in previously unexposed subjects. Sundblad et al. (2004) also evaluated changes resulting from exposure in the following parameters: lung function; bronchial responsiveness to methacho- line; exhaled nitric oxide; cell composition in nasal lavage fluids; and peripheral blood profiles for leukocytes, monocytes, lymphocytes, basophilic granulocytes, eosinophils and complement factor C3b. Under the experimental conditions, ammonia exposures at 5 or 25 ppm did not induce detectable upper airway in-

Ammonia 37 flammation or increased bronchial response to methacholine according to any analytic measure used; an observed increase in number of blood granulocytes after exposure was considered an exercise effect by the investigators and has been noted by other investigators (Hansen et al. 1991). Subjective-symptom rankings on a questionnaire exhibited a dose- response relationship. On the basis of questionnaire results, Sundblad et al. (2004) noted a tendency toward sensory adaptation to “solvent smell” in those exposed at 5 ppm but not those exposed at 25 ppm. Rankings of all 10 measured symptoms that characterized irritation and systemic response were significantly greater than in controls in the 25-ppm exposure group, but the 5-ppm exposure group exhibited higher rankings of only five symptoms. All symptomatic effects ranked were transient. In the controlled workplace-exposure study of Ferguson et al. (1977), ef- fects of ammonia vapor on three groups of two industrial workers exposed at 25, 50, or 100 ppm were evaluated after practice exposure at the same concentra- tions during a 1-week period. Subjects underwent exposure at a sodium bicar- bonate plant in areas where ammonia concentrations of 25 and 50 ppm were achieved; controlled 100-ppm exposures took place in an exposure chamber. Exposure periods ranged from 2 to 6 h/day for 5 weeks. No adverse effects on respiratory function and no increase in frequency of eye, nose, and throat irrita- tion were noted. The only statistically significant increase was an unexplained FEV1 (“improvement”) with increasing ammonia concentration. Participants contributed no subjective reports of irritation; physician examinations indicated that the resulting signs of “mild” eye, nose, and throat irritation at 50 and 100 ppm were not significantly different from control findings. After acclimation, exposure for up to 6 h at at least 100 ppm (averages of 103-140 ppm with occa- sional excursions to 200 ppm) was “easily tolerated” by subjects (Ferguson et al. 1977). Erskine et al. (1993) used an inspiratory pneumotachograph to measure the concentration of ammonia required to elicit reflex glottis closure in 102 healthy nonsmoking subjects, 17-96 years old, after single intermittent breaths of ammonia vapor at about 500 to 2,000 ppm. The results demonstrated a strong positive correlation (coefficient, 0.85) between age and the ammonia concentra- tion needed to trigger reflex glottis closure (NH3TR). The mean NH3TR for the group 86-95 years old was 1,791 ppm (SEM, 52; n = 14), and the mean NH3TR for the group 21-30 years old was 571 ppm (SEM, 41.5; n = 14). Occupational and Epidemiologic Studies Most available occupational and epidemiologic studies were not designed to discriminate between ammonia and other workplace contaminants—such as endotoxins, fungi, bacteria, and respirable dusts—in their relative contributions to the development of observed adverse respiratory effects. Minor pulmonary- function deficits have been observed in swine workers exposed to ammonia in

38 Exposure Guidance Levels for Selected Submarine Contaminants combination with dust and endotoxin (Reynolds et al. 1996). Although ammonia concentrations as high as 200 ppm have been reported (Carlile 1984), mean ex- posure concentrations of 4-7 ppm were more typical for the swine workers ex- amined (Reynolds et al. 1996; Donham et al. 1995). Other occupational cohort studies have examined farmers and farm workers employed in enclosed live- stock buildings; substances measured include not only ammonia but also dusts, endotoxins, and various microorganisms and fungi (Cormier et al. 2000; Chou- dat et al. 1994; Donham et al. 1995, 2000; Ballal et al. 1998, all as cited in ATSDR 2004). The utility of the data from those studies is limited because of confounding by multiple exposures, fragmentary exposure-duration characteri- zation, and lack of information on clinical signs and symptoms. Holness et al. (1989) compared respiratory effects in a group of 58 work- ers (51 production and six maintenance workers at an industrial soda-ash pro- duction facility) chronically exposed to airborne ammonia vapor (mean " stan- dard deviation, 9.2 " 1.4 ppm) with effects in a group of 31 plant workers with essentially no exposure to airborne ammonia (0.3 " 0.1 ppm). During a 1-week period, the workers were assessed on the basis of a questionnaire (reporting of cutaneous or respiratory symptoms), sense of smell, baseline pulmonary func- tion (FVC [forced vital capacity], FEV1, FEF50 [forced expiratory flow at 50% FVC], and FEF75), or change in lung function over a workshift at the beginning and end of a workweek. There were no differences between the two groups in the characteristics studied and no relationship between concentration and dura- tion of ammonia exposure and lung function. Holness and colleagues pointed out that study weaknesses included “lack of adequate exposure data” and the difficulties in accounting for both concentration and duration of exposure. In addition, there was no characterization of historical occupational ammonia ex- posures during years before the short period in which they measured workplace concentrations. Effects in Animals Thorough reviews of the results of controlled experimental exposures can be found in NRC (2002, 2007) and ATSDR (2004). Acute Toxicity Lethality values (LC50 and lowest experimental concentrations) for mice, rats, and cats receiving inhalation exposures are presented in Table 2-4; data on other exposure routes, such as rabbit intratracheal cannulation (Boyd et al. 1944), are not summarized here because of their limited application. Cats are the least characterized of the experimental species tested. The LC50 for rats ranged from 7,338 and 16,600 ppm for 60-min exposures to 40,300 ppm for a 10-min exposure (MacEwen and Vernot 1972; Appelman et al. 1982). The LC50 for mice ranged from 4,230 ppm for a 60-min exposure to 10,096 ppm for a 10-min

Ammonia 39 TABLE 2-4 Summary of Acute-Lethality Inhalation Data on Ammonia Exposure of Laboratory Animals Species Concentration (ppm) Time Effects Reference Rat 40,300 10 min LC50 Appelman et al. 1982 33,433 10 min 10% mortality 28,595 20 min LC50 26,155 20 min 30% mortality 20,300 40 min LC50 18,047 40 min 20% mortality 16,600 60 min LC50 14,114 60 min 30% mortality Rat 7,338 60 min LC50 MacEwen and Vernot 1972 Mouse 10,152 10 min LC50 Silver and McGrath 1948 8,723 10 min 25% mortality Mouse 4,837 60 min LC50 MacEwen and Vernot 4,550 60 min 30% mortality 1972 Mouse 4,230 60 min LC50 Kapeghian et al. 1982 3,950 60 min 25% mortality 4,380 240 min 25% mortalitya 1,350 240 min 100% survival Mouse 21,430 30 min LC50 Hilado et al. 1977, 1978 19,048 30 min 25% mortality Cat 1,000 10 min 5% mortality Dodd and Gross 1980 a No observation period after exposure. Abbreviations: LC50; statistically determined lethal concentration for 50% of sample population. Source: Adapted from NRC 2007. exposure (Silver and McGrath 1948; MacEwen and Vernot 1972; Kapeghian et al. 1982; Hilado et al. 1977, 1978). Rats exposed to lethal ammonia concentrations exhibited signs of dyspnea and of irritation of the eyes and nose and lung hemorrhage on necropsy (Appel- man et al. 1982). Mice exposed to lethal concentrations showed signs of irrita- tion of the eyes and nose, labored breathing, and gasping with tremors, ataxia, convulsions, and seizures; pathologic lesions occurred in the alveoli (Silver and McGrath 1948; MacEwen and Vernot 1972; Kapeghian et al. 1982). Signs of toxicity in cats included death, poor general condition, severe dyspnea, anorexia, dehydration, bronchial breath sounds, sonorous and sibilant rhonchi, and coarse rales (Dodd and Gross 1980). Pulmonary-function tests provided evidence of airway damage throughout the experiment and of central lung damage on obser- vation day 21. Gross lung examination showed congestion, hemorrhage, edema, and evidence of interstitial emphysema and collapse. Bronchopneumonia, which caused the death of one animal, was common after observation day 7.

40 Exposure Guidance Levels for Selected Submarine Contaminants Species comparisons of LC50 data by ten Berge et al. (1986) documented that mice are usually more sensitive to lethal concentrations of irritants in gen- eral, and ammonia in particular, than other experimental laboratory animals. ten Berge et al. also suggested that toxicity data on mice “do not provide an appro- priate basis for predicting…the mortality response in humans” to many locally irritant gases, including ammonia. Data summarized in NRC (2007) indicate that the mouse is 2.7-4 times more susceptible than the rat to the toxic effects of ammonia inhalation exposure. Acute sublethal toxicity after controlled experimental exposure to ammo- nia has been well summarized in the previous NRC (2002) report Review of Submarine Escape Action Levels for Selected Chemicals (Chapter 2, pp. 22-68, “Ammonia”; see Table 2-8, “Experimental Animal Toxicity Data…” pp. 44-56) and ATSDR report (2004; see Table 3-1, “Levels of Significant Exposure to Ammonia and Ammonium Compounds—Inhalation,” pp. 27-40) and will not be presented at the same level of detail here. The database on acute sublethal expo- sure includes studies on mice, rats, and cats exposed at various concentrations (3-1,157 ppm) of ammonia for 10 min to 24 h. In general, nondisabling, reversible effects in laboratory animals were mild after single exposure. Rats exhibited concentration-dependent cessation of tracheal ciliary activity during exposure at 3-90 ppm for 10 min (Dalhamn 1956 a,b): at 3, 6.5, and 90 ppm, ciliary activity ceased in 7-8 min, 150 sec, and 5 sec, respectively. Schaerdel et al. (1983) exposed rats to ammonia at 15-1,157 ppm for 24 h; no behavioral changes or irritation of the eyes or mucous membranes were exhibited, and no changes were noted in blood pCO2 and pH. Small changes in pO2 occurred “within the normal range for rats.” A 50% reduction in the respiration rate (RD50) was noted in mice exposed at about 300 ppm for 30 min (Barrow et al. 1978). There was no evidence of pulmonary lesions in mice or rats exposed at single nonlethal concentrations. Repeated Exposure and Subchronic Toxicity Effects in laboratory animals were mild and transient after repeated expo- sure (subchronic duration) to ammonia and are summarized in Table 2-5. Only minimal effects on respiratory epithelium of the upper respiratory tract were observed after continuous exposure at up to 714 ppm for several days (Schaerdel et al. 1983). Repeated exposure of Swiss-Webster mice to the experimental RD50 of 303 ppm for 6 h/day for 3 or 7 days was associated with reversible and mini- mal to moderate changes in respiratory epithelium that were not considered pathologic lesions (Buckley et al. 1984). Exposure of Swiss OF1 mice at 711 ppm, which is about 3 times the experimental RD50 of 257 ppm in this mouse breed, resulted in slight to moderate exfoliation, erosion, ulceration, and necrosis of the respiratory epithelium of the nasal cavity; no lower respiratory tract le-

Ammonia 41 sions were produced (Zissu 1995). Additional supportive studies (for example, Tepper et al. 1985; Manninen et al. 1988) are summarized in Table 2-5. Except for nonspecific inflammation of the lungs at 1,101 ppm, repeated daily exposure of rats at 57 ppm for 114 days or at 222 or 1,101 ppm for 6 weeks (8 h/day) produced no effects (Coon et al. 1970). Almost all rats died after continuous exposure at 651 or 672 ppm for 65 days. Repeated exposure at 1,101 ppm for 6 weeks (8 h/day) produced transient dyspnea and lacrimation in dogs and rabbits, whereas continuous exposure at 672 ppm for 90 days resulted in signs of irritation of the eyes and nose and pathologic lesions in the lungs of dogs and rabbits and pneumonitis in several species (dog, rabbit, guinea pig, and monkey) (Coon et al. 1970). Subchronic inhalation-exposure studies of male mice provide inconclusive evidence of nasal carcinoma (Gaafar et al. 1992), and gavage exposure of labo- ratory mice to ammonium ion at 42 mg/kg per day for 4 weeks provided no evi- dence of carcinogenicity (Uzvolgyi and Bojan 1980, as cited in ATSDR 2004). The longest exposure in the available literature was 114 days of continu- ous exposure of male and female Sprague-Dawley and Long-Evans rats at 57 ppm (Coon et al. 1970); this protocol resulted in no clinical signs and no signifi- cant effects when compared with the control. Done et al. (2005) evaluated continuous ammonia exposure (at 0.6, 10.0, 18.8, or 37.0 ppm) of weanling pigs (commercial herd) in combination with generated inspirable (artificial) dust (at 1.2, 2.7, 5.1, or 9.9 mg/m3) for 5 weeks in a controlled-ventilation facility. The ammonia and dust concentrations evalu- ated were considered representative of commercial piggeries in the United Kingdom. Done and co-workers used a multifactorial design incorporating a total of 560 weanling pigs over 2 years. Daily clinical examination for respira- tory, gastrointestinal, and ocular signs documented that the experimental expo- sures had no significant effects. Postmortem turbinate scores were low (for ex- ample, low clinical rhinitis), as were lung scores; neither turbinate nor lung scores were affected by exposure to ammonia or dust when compared with the controls. No significant differences in any monitored characteristic were noted when experimental pigs were compared with controls (Done et al. 2005). Overall, studies of repeated exposure indicate that mice are more suscepti- ble than other mammals tested repeatedly or for subchronic exposure durations. Chronic Toxicity No information characterizing chronic toxicity of ammonia exposure was located.

42 TABLE 2-5 Summary of Repeated and Subchronic Ammonia Exposure Studies in Laboratory Animals Concentration Exposure Species (ppm) Duration Effects Reference Rat (male, 222 8 h/day for 6 No deaths or clinical signs Coon et al. female weeks 1970 Sprague- 1,101 8 h/day for 6 Nonspecific inflammatory changes in lungs (colony infection); no deaths or clinical Dawley, weeks signs Long-Evans) 57 Continuous, 114 No clinical signs; no significant effects when compared with controls days 182 Continuous, 90 No clinical signs days 375 Continuous, 90 “Mild” nasal discharge in 25% of test population days 651 Continuous, 90 Day 25: mild dyspnea, nasal irritation, 63% mortality days Day 65: 98% mortality 672 Continuous, 90 87% mortality days Rabbit, 222 8 h/day for 6 Focal pneumonitis in one of three monkeys; no other signs or clinically significant Coon et al. guinea pig, weeks effects 1970 dog, monkey 1,101 8 h/day for 6 Dogs and rabbits exhibited transient lacrimation and dyspnea in week 1; nonspecific weeks inflammatory changes in guinea pig lungs Rabbit, 57 Continuous, 90 No signs or clinically significant effects Coon et al. guinea pig, days 1970 dog, monkey 672 Continuous, 90 Dogs: heavy lacrimation, nasal discharge, hemorrhagic lung lesions in one of two days Rabbits: erythema, discharge, corneal opacity, moderate lung congestion in two of three Guinea pigs: four of 15 died All (also in controls, but less severe): focal or diffuse interstitial pneumonitis; calcification in renal tubules and bronchial epithelium; cell proliferation in renal epithelium; myocardial fibrosis

Rat Serial 6 h/day, with 2 Measurements of running-wheel activity indicated decrease after more than 1 h at 100 Tepper et exposure at days separating ppm, decrease throughout 300-ppm exposures; authors attributed activity change to al. 1985 100, 300, 300, exposure sensory irritation; activity depression transient; running-wheel activity increased after 100 concentrations exposure cessation. Mouse Serial 6 h/day, with 2 Similar to rat experience, as described above; at comparable concentrations, activity Tepper et exposure at days separating of mice decreased less than that of rats al. 1985 100, 300, 300, exposure 100 concentrations Weanling pig 0.6, 10.0, Continuous for 5 Multifactorial experiment performed on 560 weanling pigs over 2 years; daily Done et al. (commercial 18.8, or 37.0 weeks inspections and clinical monitoring and postmortem examinations of 40 pigs in each 2005 herd) (in of eight batches revealed “minimal gross pathology and …minor pathological changes combination of little significance”; low turbinate scores (for example, low clinical rhinitis) and low with artificial lung scores observed and unaffected by exposure to ammonia and dusts; no dust at 1.2, differences between control and exposed pigs in any respiratory, gastrointestinal, or 2.7, 5.1 or 9.9 ocular measure monitored, including nasal discharge and sneezing mg/m3) Rat 4, 24, 44, 165, Continuous for 3 Minimal lesions in nasal-cavity respiratory epithelium at 7 days (undefined Schaerdel 714 or 7 days concentration); no change in trachea or lungs; no significant effects on blood gases or et al. 1983 pH Rat (female) 25, 300 6 h/day for 5, 10, No treatment-related changes observed in lung, kidney, or liver; 300 ppm considered Manninen or 15 days NOAEL et al. 1988 Mouse 303 (RD50) 6 h/day for 5 days Observed subjects exhibited no clinical signs; no lesions in tracheobronchial or Buckley et (Swiss- pulmonary areas; nasal-cavity epithelium exhibited minimal exfoliation and other al. 1984 Webster) tissue changes, moderate squamous metaplasia and inflammatory changes (Continued) 43

44 TABLE 2-5 Continued Concentration Exposure Species (ppm) Duration Effects Reference Mouse 78 (0.3 RD50); 6 h/day for 4, 9, or Observed subjects exhibited no clinical signs; respiratory tract exhibited rhinitis with Zissu (Swiss 257 (RD50), 711 14 days metaplasia and necrosis in nasal-cavity epithelium only at 3 times RD50, with 1995 OF1) (2.8 RD50) increasing severity at greater exposure duration (very severe on day 14); no lesions at RD50 for any exposure duration Abbreviations: NOAEL, no-observed-adverse-effect level; RD50; statistically estimated concentration resulting in 50% reduction in respiratory rate.

Ammonia 45 Reproductive Toxicity in Males No information characterizing reproductive toxicity of inhalation, ocular, oral, or dermal exposure to ammonia of male humans or laboratory animals was located. Immunotoxicity Although secondary infections of respiratory lesions and skin burns can occur after exposure to concentrated ammonia vapors or aerosols (Caplin 1941; Sobonya 1977; Slot 1938; O’Kane 1983), there is no evidence that ammonia exposure impairs the human immune system (ATSDR 2004). Laboratory animal studies of a variety of species indicate that repeated in- halation or whole-body exposure to some concentrations of ammonia is associ- ated with a decrease in immune response—a decrease in “cell-mediated immune response” in guinea pigs challenged with tuberculin derivative after exposure to 90-ppm ammonia 24 h/day for 3 weeks (Targowski et al. 1984, as cited in NRC 2002) or a decrease in resistance when challenged with an infective bacterial dose. Examples of the latter include increased mortality in male mice exposed to the LD50 of Pasteurella multocida after exposure to 500-ppm ammonia 24 h/day for 7 days (Richard et al. 1978, as cited in ATSDR 2004), increased severity of clinical signs in rats inoculated with Mycoplasma pulmonis either before a 4- week exposure to 25-ppm ammonia 24 h/day (Broderson et al. 1976, as cited in ATSDR 2004) or before a 3- to 9-day exposure to 100-ppm ammonia 24 h/day (Pinson et al. 1986), and increased Newcastle disease infection rate in chickens exposed to the 48-h lowest observed-adverse-effect level (LOAEL) of 50 ppm and to the 72-h LOAEL of 20 ppm (Anderson et al. 1964, as cited in NRC 2002). Neumann et al. (1987, as cited in ATSDR 2004) noted a reduced gamma globulin concentration in pigs exposed to ammonia at 100 ppm 24 h/day for 31- 45 days. It is thought that the experimental findings in laboratory animals repre- sent the consequences of an effect secondary to tissue injury and inflammation resulting from the ammonia exposure. Genotoxicity ATSDR (2004) considers that the data on ammonia and ammonium ion exposures may indicate the presence of mutagenic and clastogenic properties. A retrospective examination of fertilizer-factory workers with different occupational histories of ammonia exposure compared the frequencies of chro- mosomal aberrations and sister-chromatid exchanges (SCEs) and mitotic index; findings indicated increased chromosomal-aberration and SCE frequencies with “increasing length of exposure” (Yadav and Kaushik 1997, as cited in ATSDR 2004).

46 Exposure Guidance Levels for Selected Submarine Contaminants The frequency of mouse micronuclei increased after single intraperitoneal administration of ammonia at 12, 25, and 50 mg/kg in Swiss albino mice (Yadav and Kaushik 1997, as cited in ATSDR 2004). Among the several cellular assays that were not lethal to the test system, positive results were observed in the following: chromosomal aberrations in chick fibroblasts exposed to buffered ammonia-ammonium chloride solutions, reduced cell division in mouse fibroblasts cultured in media with added ammo- nia and ammonium chloride, DNA-repair inhibition in mouse fibroblasts in me- dia with added ammonium chloride, and decreased rate of DNA synthesis in mucosal cells of mouse ileum and colon in culture with added ammonium chlo- ride (Rosenfeld 1932; Visek 1972; Capuco 1977; Zimber and Visek 1972, all as cited in ATSDR 2004). Carcinogenicity The Environmental Protection Agency (EPA) Integrated Risk Information System (IRIS) has not evaluated ammonia for evidence of human carcinogenic potential, because there are “no data,” and so has made no formal determination regarding the carcinogenicity of ammonia (EPA 1991). The International Agency for Research on Cancer (IARC) considered “aqueous ammonia” as one of several materials used for spot removal in its monograph on dry cleaning (IARC 1995). However, ammonia was not specifi- cally examined for carcinogenic potential in the monograph, which focused on chlorinated and other industrial solvents (IARC 1995). IARC has not published an evaluation of the potential human carcinogenicity of ammonia. ATSDR reported a case of epidermal carcinoma of the nasal septum in the survivor of a serious industrial accident in which the exposed person’s upper lip and nose were accidentally splashed with a refrigeration mixture containing ammonia (Shimkin et al. 1954, as cited in ATSDR 2004). There was no evi- dence that the ammonia exposure was causal. ATSDR (2004) examined other cases of human inhalation exposure that followed ammonia spills but found no other case reports of carcinogenicity. Adult male mice repeatedly exposed to ammonia vapor (“ammonia vapour of 12% ammonia solution,” 15 min/day, 6 days/week, 8 weeks) exhibited “mi- totic figures” and nasal carcinoma (one of 10) or nasal mucosal adenocarcinoma (one of 10) (Gaafar et al. 1992). There is no conclusive evidence that the ammo- nia exposures induced the observed carcinomas (ATSDR 2004). Examination of mice exposed by gavage to ammonia dissolved in water at 42 mg of ammonium ion per kilogram per day for 4 weeks provided “no evi- dence of a carcinogenic effect” (Uzvolgyi and Bojan 1980, as cited in ATSDR 2004).

Ammonia 47 TOXICOKINETIC AND MECHANISTIC CONSIDERATIONS Toxicokinetics and mechanisms of action for ammonia have been thor- oughly summarized in recent publications—such as NRC 2002, 2007, and ATSDR 2004—and will not be detailed here. Metabolism and Toxicokinetics Ammonia is a product of amino acid and dietary-protein metabolism and is found naturally in human blood and tissues. In the large intestine, bacterial degradation of urea can also form ammonia (Diamondstone 1982, as cited in NRC 1994). Synthesis of some amino acids (glutamine, asparagine, and argin- ine) requires the presence of ammonia (White et al. 1978, as cited in NRC 1994). Depending on the route of exposure, ammonia can be metabolized to urea and glutamine in the liver (ingestion exposure; Visek 1972; Furst et al. 1969; Pitts 1971, as cited in NRC 2002) or metabolized to glutamine or protein in tis- sues (after subcutaneous or intraperitoneal exposures; Duda and Handler 1958; Furst et al. 1969, as cited in NRC 2002). Of more immediate interest to the pre- sent analysis is inhalation exposure, during which ammonia is largely retained and absorbed by tissues of the upper respiratory tract. For short-term exposure (less than 2 min), 83-92% of inhaled ammonia is retained in the nasal mucosa (Landahl and Hermann 1950), and only small amounts are absorbed in the sys- temic circulation. With longer and more concentrated inhalation exposure, reten- tion in the nasal mucosa decreases until it attains equilibrium (4-30%) with the inhaled-air concentration after exposure of 10-27 min (Silverman et al. 1949). Within 3-8 min after exposure termination, ammonia in expired air decreases to pre-exposure concentrations. After inhalation exposure during an industrial ac- cident to ammonia at concentrations sufficient to induce first- and second-degree burns, blood ammonia concentration in the exposed patient remained stable, and chest x-ray films were normal (Leduc et al. 1992); it is thought that this finding indicates either a lack of appreciable ammonia absorption from the respiratory tract or rapid detoxification of inhaled ammonia (NRC 2007). It has been speculated that people with impaired liver function may have increased blood-ammonia concentrations after inhalation exposure (Swotinsky and Chase 1990). Systemic ammonia is largely excreted by the kidney as urea and ammo- nium compounds and voided in urine. Systemic ammonia can also be excreted as urea in feces (Gay et al. 1969; Pitts 1971, both as cited in NRC 2002) and perspiration (Guyton 1981; Wands 1981, both as cited in NRC 2002). Silverman et al. (1949) reported no changes in blood or urinary ammonia, urea, or nonpro- tein nitrogen in seven human subjects exposed to ammonia vapor at 350-500 ppm for 30 min. Within the first 30 min, about 70-80% of inhaled ammonia was expired; Silverman and colleagues thought that this indicated ammonia satura-

48 Exposure Guidance Levels for Selected Submarine Contaminants tion of upper respiratory tract tissues. Depending on the subject, equilibrium was attained within 10-27 min after exposure at 350-400 ppm, when the concentra- tion of ammonia in expired air remained stable. Silverman et al. (1949) calcu- lated that if all retained ammonia had been absorbed into the blood, there would have been no significant change in blood or urinary urea, ammonia, or nonpro- tein nitrogen; this is consistent with the human experimental data. The data of Silverman et al. (1949) also indicate that retention of ammonia in the human nasopharynx is concentration- and time-dependent. Mechanism of Toxicity Ammonia is a corrosive, alkaline, locally irritant gas that produces effects immediately on contact with moist mucous membranes of the eyes, mouth, and respiratory tract. It reacts with those and other moist tissues to form ammonium hydroxide in an exothermic reaction (Wong 1994); the thermal and chemical burns that result from high-concentration exposures are considered to be a con- sequence of the heat of reaction and of the corrosive properties of the alkaline reaction product ammonium hydroxide. Ammonia is a respiratory and ocular irritant; case reports of accidental industrial and agricultural releases of high (but unquantified) concentrations document the presence of respiratory tissue injury and necrosis and penetration of corneal epithelium with resulting corneal scar- ring (Leduc et al. 1992; Mulder and van der Zalm 1967; Sobonya 1977; Hatton et al. 1979. For additional cases, see ATSDR 2004; NRC 1987, 2007). Although there is no evidence that CNS function is compromised by inha- lation exposure to ammonia at about 100 ppm, persons with depressed liver function or liver failure (for example, hepatic encephalopathy or congenital or acquired hyperammonemia) accumulate excessive ammonia in the CNS (NRC 2002). Depending on concentration, low or high CNS ammonia accumulations can induce “stupor and coma” (consistent with hyperpolarization) or seizures (consistent with depolarization), respectively (NRC 2002). Ammonia intoxica- tion in the CNS is associated with astrocyte swelling and morphologic change (for example, Alzheimer II astrocytes observed in cases of hyperammonemia) and adverse changes in astrocyte metabolism (Norenberg 1981; Albrecht 1996; Norenberg and Martinez-Hernandez 1979, as cited in NRC 2002). The human odor threshold for ammonia is about 5-53 ppm (Pierce 1994), and sensory fatigue (adaptation) occurs with prolonged exposure. The study conducted by Ferguson et al. (1977) demonstrated adaptation to ammonia at up to 150 ppm, with excursions to 200 ppm, in people acclimated to ammonia at 25-100 ppm for 1 week. When subjects were exposed to mixed odors, the odor threshold for ammonia was 10-20 ppm (Ferguson et al. 1977). At a concentra- tion of 30 ppm in a Rochester chamber (head-only exposures), fit and healthy male workers (who passed class II USAF or class II FAA flying physicals) de- scribed the odor as “easily noticeable, moderate intensity” (two of five subjects) or “strong, highly penetrating” (three of five); that indicated that the odor

Ammonia 49 threshold had been exceeded at 30 ppm (MacEwen et al. 1970). When groups of naive and informed subjects were exposed to ammonia for 30 min in a whole- body exposure chamber and mean results were compared, the naive group sub- jectively judged 50 ppm to be greater than “distinctly perceptible” but less than a “nuisance;” the judgement of informed subjects rated concentrations of 50 and 80 ppm as only “distinctly perceptible” after a 30-min exposure (Verberk 1977). After a 2-h exposure, the naive group judged 50, 80, and 110 ppm as a “nui- sance” (Verberk 1977). A more recent study of naive vs informed (workers familiar with work- place ammonia) subjects (Ihrig et al. 2006) evaluated the response of 43 male volunteers (21-47 years old) repeatedly exposed to ammonia at 10-50 ppm 4 h/day for 5 days in an exposure chamber. The median reported intensity of irrita- tive symptoms and respiratory symptoms remained below 1 (“hardly at all”) at all exposure concentrations (even at 50 ppm) for both naive and informed sub- jects. For olfactory symptoms, the median score of the naive group for the 20/40-ppm and 50-ppm exposure was between 3 and 4 (between “rather much” and “considerably”), whereas the median score of the informed group for the 20/40-ppm exposure was less than 1 (1 = “hardly at all”) and for the 50-ppm exposure was less than 2 (2 = “somewhat”) (Ihrig et al. 2006). Median annoy- ance rankings displayed by the naive group exceeded 4 (“rather much”) at 50 ppm, whereas the median annoyance rankings by the informed group exposed at 50 ppm remained under 2. Habituation was evident in the informed group of subjects. Although there are variable results and some debate regarding the concen- trations at which respiratory and ocular irritation occurs, there is a consensus that tissue injury occurs at vapor concentrations higher than those at which am- monia can be detected by odor or irritation; thus, sensitivity to the odor of am- monia vapor imparts warning properties via odor and ocular irritation. Susceptible Populations In tests of concentrations required to stimulate re- flex glottis closure (NH3TR) in healthy nonsmokers, Erskine et al. (1993) de- termined that the closure reflex of elderly people (86-95 years old) with a mean NH3TR of 1,791ppm (SEM ,52 ppm) is less responsive to ammonia vapor than that of younger people (21-30 years old) with a mean NH3TR of 571 ppm (SEM, 41.5 ppm). Erskine et al. (1993) point out that their earlier work (Erskine et al. 1992) indicated that “smokers have considerably more sensitive upper airway reflexes than non-smokers.” The human-subjects study of McLean et al. (1979) documented that nona- topic and atopic subjects, some of whom had a history of asthma, responded similarly on a NAR test to ammonia at 100 ppm introduced into each nostril under pressure for up to 30 sec. McLean and colleagues noted that experimental results suggest attenuation of NAR after ammonia exposure and that the attenua- tion is mediated primarily by parasympathetic reflex effects on the nasal vascu- lature, not by histamine release. Collectively, the results indicate that, at about 100 ppm, ammonia coming into contact with tracheobronchial or pulmonary regions would not be expected to induce a different effect on asthmatic people.

50 Exposure Guidance Levels for Selected Submarine Contaminants INHALATION EXPOSURE LEVELS FROM THE NATIONAL RESEARCH COUNCIL AND OTHER ORGANIZATIONS A number of organizations have established or proposed inhalation- exposure levels or guidelines for ammonia. Selected values are summarized in Table 2-6. COMMITTEE RECOMMENDATIONS The committee’s recommendations for EEGL and CEGL values for am- monia are summarized in Table 2-7. The current and proposed U.S. Navy values are provided for comparison. The literature contains human-exposure data derived from multiple clini- cal and monitoring studies that were carried out at ammonia concentrations and for exposure durations of interest and are thus suitable for direct estimation of exposure guidance levels. Over 100 adults were subjects of the clinical studies summarized in Tables 2-2 and 2-3, and 58 workers were monitored for the oc- cupational epidemiologic study of Holness et al. (1989). Evaluated subjects were healthy people participating in a variety of activities (and thus uptake rates), including resting, working, and exercise. Groups represented were nonatopic and atopic people, including asthmatics (McLean et al. 1979; Sundblad et al. 2004); smokers and nonsmokers (MacEwen et al. 1970; Ferguson et al. 1977); and those with various thresholds for reflex glottis closure (Erskine et al. 1993). Given the breadth of data available on ammonia that include evaluation of a variety of groups involved in various activities, the committee concludes that the uncertainty surrounding the variability in susceptibility of the submarine crew to ammonia is most likely small. 1-Hour EEGL On the basis of human data summarized in Table 2-3, the highest concen- trations (102-140 ppm) in exposures of about 1 h resulted in minimal or no physiologic change in respiratory function (FVC, FEV1, minute volume, and respiratory rate) or cardiac function (pulse rate and diastolic and systolic blood pressure) compared with control values (Verberk 1977; Ferguson et al. 1977; Cole et al. 1977). The protocol of Ferguson et al. (1977) incorporated serial daily exposures for 2 weeks. The exercise regimen incorporated into the study of Cole et al. (1977) and the workplace physical activity incorporated into the study of Ferguson et al. (1977) take into account the physical stress that may occur during an emergency situation onboard. The Ferguson et al. evaluation of potential exposure effects on a worker’s ability to perform physical and mental tasks required in the course of daily duties of a chemical-plant operator is perti- nent to tasks performed by submarine crew (for example, data-logging, compu- tational tasks, and walking up and down flights of stairs).

Ammonia 51 TABLE 2-6 Selected Inhalation Exposure Levels for Ammonia from the NRC and Other Agenciesa Organization Type of Level Exposure Level (ppm) Reference Occupational ACGIH TLV-TWA 25 ACGIH 2001 TLV-STEL 35 NIOSH REL-TWA 25 NIOSH 2005 REL-STEL 35 OSHA PEL-TWA 50 29 CFR 1910.1000 Spacecraft NASA SMAC NRC 1994 1-h 30 24-h 20 30-day 10 180-day 10 Submarine NRC EEGL NRC 1987 1-h 100 24-h 100 CEGL 90-day 50 SEAL 1 (10 days) 75 NRC 2002 SEAL 2 (24 h) 125 General Public ATSDR Acute MRL 1.7 ATSDR 2004 Chronic MRL 0.1 NAC/NRC AEGL-1 (1-h) 30 NRC 2007 AEGL-2 (1-h) 160 AEGL-1 (8-h) 30 AEGL-2 (8-h) 110 a The comparability of EEGLs and CEGLs with occupational-exposure and public-health standards or guidance levels is discussed in Chapter 1 (“Comparison with Other Regula- tory Standards or Guidance Levels”). Abbreviations: ACGIH, American Conference of Governmental Industrial Hygienists; AEGL, acute exposure guideline level; ATSDR, Agency for Toxic Substances and Dis- ease Registry; CEGL, continuous exposure guidance level; EEGL, emergency exposure guidance level; MRL, minimal risk level; NAC, National Advisory Committee; NASA, National Aeronautics and Space Administration; NIOSH, National Institute for Occupa- tional Safety and Health; NRC, National Research Council; OSHA, Occupational Safety and Health Administration; PEL, permissible exposure limit; REL, recommended expo- sure limit; SMAC, spacecraft maximum allowable concentration; STEL, short-term ex- posure limit; TLV, Threshold Limit Value; TWA, time-weighted average. The preponderance of data from clinical studies indicates that even a mul- tihour exposure to ammonia at about 100 ppm would result in few substantial

52 Exposure Guidance Levels for Selected Submarine Contaminants TABLE 2-7 Emergency and Continuous Exposure Guidance Levels for Ammonia U.S. Navy Values (ppm) Exposure Level Current Proposed Committee Recommended Values (ppm) EEGL 1-h 100 30 100 24-h 100 20 50 CEGL 90-day 50 10 10 Abbreviations: CEGL, continuous exposure guidance levels; EEGL, emergency exposure guidance level. physiologic effects. Among naive populations tested (Verberk 1977), exposure at 110 ppm for 1 h was judged to be at a “nuisance” level and to generate per- ceptible eye and throat irritation and perceptible urge to cough. Those effects are known to be reversible on cessation of exposure. Thus, a concentration of about 100 ppm is judged to be minimal and would not interfere with performance of critical tasks during an onboard emergency. The weight of evidence from the strong human experimental data, includ- ing exercising subjects (Cole et al. 1977) and exercising smoking subjects (Fer- guson et al. 1977) for the exposure duration of concern indicates a 1-h EEGL of 100 ppm for ammonia. The use of human data precludes the application of an interspecies uncertainty factor. Furthermore, that concentration does not induce significant differences in NAR when the response of atopic subjects, including asthmatics, is compared with that of nonatopic subjects in studies of direct (forced-air) ammonia-vapor contact with intranasal tissues (McLean et al. 1979). Therefore, no intraspecies uncertainty factor has been applied. 24-Hour EEGL Pertinent, multihour, human exposure studies include those of Ferguson et al. (1977), Sundblad et al. (2004), Verberk (1977), and Ihrig et al. (2006). For ammonia exposure 2-6 h/day, 5 days/week for 2 weeks at 100 ppm, Ferguson et al. (1977) observed no eye, nose, or throat irritation significantly different from controls and no other effects except for FEV1 improvement. Ferguson et al. (1977) observed that repeated exposure at 100 ppm as above, with excursion to 200 ppm, was “easily tolerated” by the human subjects. Sundblad et al. (2004) observed no detectable inflammation in upper airways (on the basis of multiple physiologic measurements) and no increased bronchial responsiveness to meth- acholine challenge in healthy and atopic subjects exposed to ammonia continu- ously for 3 h at 0, 5, or 25 ppm with exposures separated by an interval of at least a week; each subject exercised at 50 W for half of each exposure period. Sundblad et al. (2004) noted a dose-response relationship for multiple and tran- sient symptoms of irritation and systemic response as reported on subject ques-

Ammonia 53 tionnaires. Verberk (1977) exposed informed and naive subjects to ammonia for 2 h at 110 or 140 ppm. At 110 ppm, informed and naive subjects reported mar- ginally nuisance eye irritation and perceptible (informed) or nuisance (naive) odor; at 140 ppm, naive subjects withdrew from the exposure chamber before the passage of 2 h because of “offensive” concentrations, but no informed sub- jects withdrew (the informed group reported “perceptible” and “nuisance” odor and eye irritation at 140 ppm for 2 h ) (see Table 2-3). Ihrig et al. (2006) exposed naive and informed male volunteers (the latter “regularly exposed to ammonia in the workplace”) to ammonia at 10-50 ppm 4 h/day for 5 days. Habituation was noted during the course of the study, and ex- perienced subjects reported fewer symptoms than naive subjects. Medical ex- aminations were conducted for tear-flow rates, lung function, bronchial respon- siveness, cognitive function, and related end points after each exposure. Except for three subjects in the 50-ppm group who exhibited “slight conjunctival hy- peremia,” no relevant physical or neurophysiologic effects (such as reaction time, attention, and power of concentration) were observed (see Table 2-3). The short-term (10-min) exposure studies of fit, male, military or military- contractor personnel (MacEwen et al. 1970) also provide valuable background regarding irritancy. Pertinent animal studies were evaluated for valuable insight and to aug- ment the human database. Animal studies include repeat-exposure and sub- chronic-toxicity estimates in rats, mice, rabbits, guinea pigs, and rabbits (Coon et al. 1970; Tepper et al. 1985; Manninen et al. 1988; Buckley et al. 1984; and Zissu 1995) (see Table 2-5). Preference is given to consideration of the rat and mouse data because these species are obligate nose-breathers; mice are consid- ered unusually sensitive to the toxic effects of exposure to such respiratory irri- tants as ammonia (Ten Berge et al. 1986). Coon et al. (1970) reported no deaths or clinical signs after exposure of rats at 222 ppm 8 h/day for 6 weeks and no deaths or attributable clinical signs at 1,101 ppm with the same exposure regimen. Tepper et al. (1985) observed transient changes in running-wheel activity in rats with exposure durations greater than 1 h at ammonia concentrations of 100 ppm and for all exposure durations at 300 ppm; mice undergoing the same protocol exhibited a similar but smaller activity-profile change; Tepper and colleagues attributed the changes to sensory irritation. The related mouse studies of Buckley et al. (1984) and Zissu (1995) examined the effects of ammonia exposure at various fractions or multi- ples of the RD50 (Swiss-Webster mouse RD50 of 303 ppm, Buckley et al.; Swiss OF1 mouse RD50 of 257 ppm, Zissu); subjects exhibited no clinical signs. At the RD50, histopathologic examination identified minimal exfoliation and erosion, and moderate metaplasia and inflammation were exhibited in the nasal cavity epithelium. Rats continuously exposed at 182 ppm for 90 days exhibited no clinical signs and had normal hematologic, organ, and tissue values not different from control values for any measure examined (Coon et al. 1970; see Table 2-4). The weight of evidence exhibited by the experimental data—which in- clude those on exercising human subjects and smokers (Ferguson et al. 1977;

54 Exposure Guidance Levels for Selected Submarine Contaminants MacEwen et al. 1970; Sundblad et al. 2004), naive and informed human subjects (Verberk 1977; Ihrig et al. 2006), and mice and rats1 exercising for multiple hours (Tepper et al. 1985; ten Berge et al. 1986)—provides the basis for estimat- ing the 24-h EEGL for ammonia. It is important to note that close examination of data from MacEwen et al. (1970) and Verberk (1977) indicates that the hu- man irritancy response (for example, eye and throat irritation) tends to “flatten” after exposure at 50 ppm for 30 min to 1 h even among naive subjects (“nui- sance” concentrations of 50 ppm; Verberk 1977). The same naive subjects ranked exposure at 80-100 ppm as “offensive.” Such irritancy effects are fully reversible on cessation of ammonia exposure. It is further noted that the recent and carefully collected human-exposure data of Ihrig et al. (2006) indicate threshold physiologic effects at 50 ppm (4 h/day for 5 days) by documenting transient conjunctival irritation (three subjects) and olfactory irritation rankings considered moderate (“somewhat” for experienced subjects and “rather much” for naive subjects); habituation was evident (Ihrig et al. 2006). Therefore, the human data led the committee to consider 50 ppm as a protective level of am- monia exposure for 24 h during emergency situations, given the present insuffi- ciency of data for assessing human accommodation to 80-100 ppm for 24 h of continuous exposure. The use of human data precludes application of an interspecies uncertainty factor. Furthermore, it is known that exposure at 100 ppm does not induce sig- nificant differences in NAR when the response of atopic subjects, including asthmatics, is compared with that of nonatopic subjects in studies of direct (forced-air) ammonia-vapor contact with intranasal tissues (McLean et al. 1979). Therefore, no intraspecies uncertainty factor has been applied. The committee’s recommended 24-h EEGL is 50 ppm, which the committee judges sufficient to prevent a level of irritancy that could interfere with crew alertness and efficient work performance during an emergency. 90-Day CEGL There are no reliable human experimental data on exposure durations greater than about 6 weeks (Ferguson et al. 1977; see Table 2-3). The committee considered subchronic experimental data on a susceptible laboratory species (rat) in which there are no documented clinical signs after continuous exposure at 57 ppm for 114 days or at 182 ppm for 90 days (Coon et al. 1970); the study’s continuous-exposure protocol included “downtime” for animal feeding and chamber servicing equal to less than 2.2% of the experimental exposure dura- tion. After continuous exposure at 375 ppm for 90 days, Coon et al. (1970) re- ported “mild” nasal discharge as the only noteworthy sign in rats (see Table 2- 5). The committee did not use the latter finding regarding nasal tissue effects, 1 Both rodents are obligate nose breathers, and mice are considered sensitive to ammo- nia.

Ammonia 55 because Coon and colleagues did not perform histopathologic evaluations of the nasal cavity to confirm the presence or absence of irritation response. More con- temporary studies have shown that 5-week continuous exposure of weanling pigs at 37 ppm in combinations with dust at concentrations up to 9.9 mg/m3 was associated with no significant changes in turbinate or lung tissue when com- pared with controls (Done et al. 2005). Furthermore, daily clinical monitoring for respiratory, gastrointestinal, and ocular signs demonstrated that the experi- mental exposures had no significant effect. Swine are increasingly considered a reasonable surrogate for human physiologic and tissue responses; thus, the study of Done et al. (2005) adds particular insight to human-exposure considerations. It is reported that rodents exposed repeatedly to ammonia vapor at 711 ppm over a period of days develop lesions in the nasal respiratory epithelium (Zissu 1995). Human data indicate that exposure to ammonia concentrations at up to 140 ppm over a period of hours or days is unlikely to cause irreversible systemic effects. Nevertheless, it appears that exposure at over about 110 ppm would be expected to generate eye, nose, throat, and chest irritation in naive or untrained human populations exposed for 90 days (Verberk 1977), even when sensory fatigue is accounted for. Although not yet experimentally characterized in long- term human studies, available dose-response data indicate that systemic toxicity at that concentration is not expected to be clinically significant (NRC 1987). It is known that “most, if not all, individuals who are regularly exposed to ammonia develop a tolerance to its irritant effects” (Ferguson et al. 1977). Fer- guson et al. (1977) evaluated skilled and experienced repair workers at a chemi- cal manufacturing facility who underwent workplace exposure in areas where ammonia concentrations of 25 and 50 ppm were achieved; controlled 100-ppm exposure took place in an exposure chamber. Exposure periods ranged from 2 to 6 h/day for 5 weeks. No adverse effects on respiratory function and no increase in frequency of eye, nose, and throat irritation were noted by participants and examining physicians. After acclimation, up to 6 h of continuous exposure at at least 100 ppm (average, 103-140 ppm, with occasional excursions to 200 ppm) was “easily tolerated” (Ferguson et al. 1977). In the years before the Ferguson et al. study, facility workers did not voluntarily don respiratory protection until workplace ammonia reached 400-500 ppm. Persons who are naive with respect to ammonia do not exhibit such tolerance. The human-exposure study of Ihrig et al. (2006) also compared the subjec- tive and physiologic responses of naive vs experienced subjects (the latter com- monly experienced workplace exposures to ammonia) to successive concentra- tions of 0, 10, 20, 20/40, or 50 ppm 4 h/day over 5 days. At all concentrations, the experienced subjects reported fewer symptoms than naive subjects. At 10 ppm, the median ranking of olfactory symptoms by naive subjects lay between the qualitative score of 1 (“hardly at all”) and 2 (“somewhat”), whereas the me- dian ranking by naive subjects at 20 ppm lay between 2 and 3 (“rather much”). The median ranking of olfactory symptoms by experienced subjects was less than 1 at 10, 20, and 20/40 ppm (Ihrig et al. 2006). Habituation was evident.

56 Exposure Guidance Levels for Selected Submarine Contaminants On the basis of response to questionnaires, the subjects of the Sundblad et al. (2004) study exposed at 25 ppm for 3 h (serial exposures) did not appear to exhibit sensory fatigue to “solvent smell”; sensory fatigue to odor was noted in subjects exposed at 5 ppm. Subjects exposed at 25 ppm ranked perceived dis- comfort for all 10 possible questionnaire symptoms significantly higher than during the sham exposure or when exposed at 5 ppm; however, no subjects are reported to have terminated the 25-ppm exposure prematurely. Nevertheless, the committee considers the Sundblad et al. (2004) study to be flawed in that it lacked control for odor perception and is thus confounded by the potential for irritancy as a consequence of generic odor perception rather than any sensory- irritancy response peculiar to ammonia. An ideal study protocol would have masked the odor of ammonia or used subjects who had no sense of smell. Re- ported irritation effects and breathing difficulties for the 5-ppm exposure group are recognized as small, odor-related, and generic. The data of MacEwen et al. (1970) indicate that ammonia at 30 ppm was associated with “just perceptible” nasal and ocular effects in two of five naive volunteers exposed for 10 min. The data of Sundblad et al. (2004) indicate that ammonia at 25 ppm (3-h exposure) is associated with transient irritation of eyes, nose, and upper airways but no “detectable upper-airway inflammation or in- creased bronchial responsiveness to methacholine.” When compared with sham exposures, ammonia at 25 ppm was also associated with increased reports of sensations of nausea, headache, and sensation of intoxication in some subjects. The symptomatology is consistent with an odor response, and the committee considers 25 ppm to be an odor-irritancy threshold in healthy, exercising popula- tions of an appropriate age and thus comparable with the submarine-crew popu- lation of concern. It is acknowledged that rigorous measurements of sensory fatigue have not been collected for continuous exposure approaching 90 days, so some degree of speculation is appropriate. The human-subjects data of Sundblad et al. (2004), MacEwen et al. (1970), and Ihrig et al. (2006) are convergent in demonstrating irritancy in young adults in response to ammonia at about 20-30 ppm. The committee se- lects that range as the minimal LOAEL for irritancy due to odor and incorpo- rates a factor of 3 to accommodate adjustment of the minimal LOAEL to a no- observed-adverse-effect level (NOAEL) for odor perception. The resulting esti- mate of 6.7-10 ppm is rounded to 10 ppm. To minimize potential complaints regarding discomfort, annoyance, or ocular irritation among submariners confined for multiple weeks in ammonia atmospheres, the committee recommends a 90-day CEGL of 10 ppm. That CEGL should prevent potential degradation in submarine-crew performance resulting from sustained exposure to intense odor and nuisance concentrations and is below the human experimental concentrations associated with “moderate” irritation considered as an adverse effect. The Sundblad et al. (2004) data indi- cate that sensory fatigue for ammonia odor perception is likely to occur at some (undefined) ammonia concentration greater than 5 ppm but less than 25 ppm and

Ammonia 57 are indicative of the protective nature of a 10-ppm CEGL. Furthermore, the committee’s recommended CEGL of 10 ppm is supported by the results of Sundblad et al. (2004), Verberk (1977), and Ihrig et al. (2006) indicating rela- tively static effects over time at 20-50 ppm; the results of Coon et al. (1970) documenting no signs or clinically significant effects in nonhuman primates continuously exposed for 90 days at 57 ppm; and the results of Done et al. (2005) showing no signs or clinically significant effects in weanling pigs con- tinuously exposed at 37 ppm for 5 weeks. As for the previous 1-h and 24-h EEGL estimates, there is little justifica- tion for application of an intraspecies uncertainty adjustment to accommodate asthmatics exposed to ammonia. Given the weight of evidence from workplace and clinical exposure studies, an ammonia concentration of 10 ppm as the CEGL is protective for submarine crews. DATA ADEQUACY AND RESEARCH NEEDS Quantitative exposure data are available on humans—including asthmat- ics, smokers, elderly people, and children—and laboratory animals, including such susceptible species as mice and rats. Most human studies suitable for quan- titative assessment used short-term exposure (up to 2 h; one study incorporated exposure of 4 h and 6 h), which necessitate assumptions regarding the concen- tration-dependent nature of the toxic response to ammonia. Controlled human- exposure studies for extended exposure (especially 24-h continuous and multi- day exposure) are lacking in the database available for study. In addition, controlled experimental studies of humans are restricted to small numbers of subjects and exhibit incomplete protocols. Greater and more objective quantifi- cation of such subjective end points as irritation and nuisance is needed; how- ever, evaluations using appropriate psychophysical methods also need to assess cognitive and emotional factors that affect subjective responses (Dalton 2002). Finally, there are few contemporary studies of long-term ammonia exposure of laboratory animals; the 90-day studies available for assessment were published in the early 1970s. Although they are sufficient for the current evaluation, cor- roborating evidence based on modern analytic and vapor-generation techniques would have been highly useful for application to the 90-day assessment. The results of Verberk (1977; Table 2-2) and Ihrig et al. (2006) indicate that mere knowledge of and exposure experience with the irritant and odor prop- erties of ammonia vapor can effectively reduce human avoidance behavior and increase tolerance to concentrations as great as 140 ppm for exposure as long as 2 h. That finding has operational significance for naval submarine command and warrants further serious consideration as a training opportunity for submarine crews. The committee echoes the previous recommendation of the Committee on Submarine Escape Action Levels regarding application of Verberk’s (1977) findings to submarine-crew training curricula (NRC 2002) and recommends inclusion of the more recent Ihrig et al. (2006) human-exposure data.

58 Exposure Guidance Levels for Selected Submarine Contaminants REFERENCES ACGIH (American Conference of Governmental Industrial Hygienists). 2001. Ammonia. Documentation of the Threshold Limit Values and Biological Exposure Indi- ces, 7th Ed. American Conference of Governmental Industrial Hygienists, Cin- cinnati, OH. Albrecht, J. 1996. Astrocytes and ammonia neurotoxicity. Pp. 137-153 in The Role of Glia in Neurotoxicity, M. Aschner, and H.K. Kimelberg, eds. Boca Raton, FL: CRC Press. Anderson, D.P., C.W. Beard, and R.P. Hanson. 1964. The adverse effects of ammonia on chickens including resistance to infection with Newcastle disease virus. Avian Dis. 8:369-379. Appelman, L.M., W.F. ten Berge, and P.G. Reuzel. 1982. Acute inhalation toxicity study of ammonia in rats with variable exposure periods. Am. Ind. Hyg. Assoc. J. 43(9):662-665. ATSDR (Agency for Toxic Substances and Disease Registry). 2004. Toxicological Pro- file for Ammonia. Agency for Toxic Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. September 2004 [online]. Available: http://www.atsdr.cdc.gov/toxprofiles/ tp126.pdf [accessed June 5, 2007]. Ballal, S.G., B.A. Ali, A.A. Albar, H.O. Ahmed, and A.Y. al-Hasan. 1998. Bronchial asthma in two chemical fertilizer producing factories in eastern Saudi Arabia. Int. J. Tuberc. Lung Dis. 2(4):330-335. Barrow, C.S., Y. Alarie, and M.F. Stock. 1978. Sensory irritation and incapacitation evoked by thermal decomposition products of polymers and comparisons with known sensory irritants. Arch. Environ. Health 33(2):79-88. Boyd, E.M., M.L. MacLachlan, and W.F. Perry. 1944. Experimental ammonia gas poi- soning in rabbits and cats. J. Ind. Hyg. Toxicol. 26(1):29-34. Broderson, J.R., J.R. Lindsey, and J.E. Crawford. 1976. The role of environmental am- monia in respiratory mycoplasmosis of rats. Am. J. Pathol. 85(1):115:130. Buckley, L.A., X.Z. Jiang, R.A. James, K.T. Morgan, and C.S. Barrow. 1984. Respira- tory tract lesions induced by sensory irritants at the median respiratory rate de- crease concentration. Toxicol. Appl. Pharmacol. 74(3):417-429. Budavari, S., M.J. O’Neil, A. Smith, and P.E. Heckelman, eds. 1989. Ammonia. P. 81 in The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals, 11th Ed. Rahway, NJ: Merck. Caplin, M. 1941. Ammonia-gas poisoning. Forty-seven cases in a London shelter. Lancet 241(July 26):95-96. Capuco, A.V. 1977. Ammonia: A modulator of 3T3 cell growth. Diss. Abstr Int B 38(9):4085. Carlile, F.S. 1984. Ammonia in poultry houses: A literature review. World Poult. Sci. J. 40(2):99-113. Choudat, D., M. Goehen, M. Korobaeff, A. Boulet, J.D. Dewitte, and M.H. Martin. 1994. Respiratory symptoms and bronchial reactivity among pig and dairy farmers. Scand. J. Work Environ. Health 20(1):48-54. Cole, T.J., J.E. Cotes, G.R. Johnson, H.D. Martin, J.W. Reed, and M.J. Saunders. 1977. Ventilation, cardiac frequency and pattern of breathing during exercise in men exposed to o-chlorobenzylidene malonitrile (CS) and ammonia gas in low con- centrations. Q. J. Exp. Physiol. Cogn. Med. Sci. 62(4):341-351.

Ammonia 59 Coon, R.A., R.A. Jones, L.F. Jenkins, Jr., and J. Siegel. 1970. Animal inhalation studies on ammonia, ethylene glycol, formaldehyde, dimethylamine, and ethanol. Toxicol. Appl. Pharmacol. 16(3):646-655. Cormier, Y., E. Israel-Assayag, G. Racine, and C. Duchaine. 2000. Farming practices and the respiratory health risks of swine confinement buildings. Eur. Resp. J. 15(3):560-565. Crawl, J.R. 2003. Review/Updating of Limits for Submarine Air Contaminants. Presenta- tion at the First Meeting on Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants, January 23, 2003, Washington, DC. Czuppon, T.A.,S.A. Knez, and J.M. Rovner. 1992. Ammonia. Pp. 638-691 in Kirk- Othmer Encyclopedia of Chemical Technology, 4th Ed., Vol. 2. New York: Wiley. Dalhamn, T. 1956a. Mucous flow and ciliary activity in the trachea of healthy rats and rats exposed to respiratory irritant gases (S02, H3N, HCHO). A functional and morphologic (light microscopic and electron microscopic) study, with special reference to technique. VIII. The reaction of the tracheal ciliary activity to sin- gle exposure to respiratory irritant gases and studies of the pH. Acta Physiol. Scand. 36 Suppl. 123):93-105. Dalhamn, T. 1956b. Mucous flow and ciliary activity in the trachea of healthy rats and rats exposed to respiratory irritant gases (S02, H3N, HCHO). A functional and morphologic (light microscopic and electron microscopic) study, with special reference to technique. Acta Physiol. Scand. 36 (Suppl. 123):1-161. Dalton, P. 2002. Odor, irritation and perception of health risk. Int. Arch. Occup. Environ. Health 75(5):283-290. Diamondstone, T.I. 1982. Amino acid metabolism. I. P. 544 in Textbook of Biochemistry with Clinical Correlations, T.M. Devlin, ed. New York, NY: John Wiley & Sons. Dodd, K.T., and D.R. Gross. 1980. Ammonia inhalation toxicity in cats: A study of acute and chronic respiratory dysfunction. Arch. Environ. Health 35(1):6-14. Done, S.H., D. J. Chennells, A.C. Gresham, S. Williamson, B. Hunt, L.L. Taylor, V. Bland, P. Jones, D. Armstrong, R.P. White, T.G. Demmers, N. Teer, and C.M Wathes. 2005. Clinical and pathological responses of weaned pigs to atmos- pheric ammonia and dust. Vet. Rec. 157(3):71-80. Donham, K.J., S.J. Reynolds, P. Whitten, J.A. Merchant, L. Burmeister, and W.J. Popen- dorf. 1995. Respiratory dysfunction in swine production facility workers: Dose- response relationships of environmental exposures and pulmonary function. Am. J. Ind. Med. 27(3):405-418. Donham, K.J., D. Cumro, S.J. Reynolds, and J.A. Merchant. 2000. Dose-response rela- tionships between occupational aerosol exposures and cross-shift declines of lung function in poultry workers: Recommendations for exposure limits. J. Oc- cup. Environ. Med. 42(3):260-269. Duda, G.D., and P. Handler. 1958. Kinetics of ammonia metabolism in vivo. J. Biol. Chem. 232:303-314. EPA (U.S. Environmental Protection Agency). 1991. Ammonia. Integrated Risk Informa- tion System, U.S. Environmental Protection Agency [online]. Available: http:// www.epa.gov/iris/subst/0422.htm [accessed June 7, 2007]. Erskine, R.J., P.J. Murphy, J.A. Langton, and G. Smith. 1992. Upper air reactivity in smokers and non-smokers. Abstract 197 in 10th World Congress of Anesthesi- ologists, The Hague, Netherlands.

60 Exposure Guidance Levels for Selected Submarine Contaminants Erskine, R.J., P.J. Murphy, J.A. Langton, and G. Smith. 1993. Effect of age on the sensi- tivity of upper airways reflexes. Br. J. Anaesth. 70(5):574-575. Ferguson, W.S., W.C. Koch, L.B. Webster, and J.R. Gould. 1977. Human physiological response and adaptation to ammonia. J. Occup. Med. 19(5):319-326. Fürst, P., B. Josephson, G. Maschio, and E. Vinnars. 1969. Nitrogen balance after intra- venous and oral administration of ammonium salts to man. J. Appl. Physiol. 26(1):13-22. Gaafar, H., R. Girgis, M. Hussein, and F. el-Nemr. 1992. The effect of ammonia on the respiratory nasal mucosa of mice. A histological and histochemical study. Acta Otolaryngol. 112(2):339-342. Gay, W.M.B., C.W. Crane, and W.D. Stone. 1969. The metabolism of ammonia in liver disease: A comparison of urinary data following oral and intravenous loading of [15N] ammonium lactate. Clin. Sci. 37(3):815-823. Guyton, A.C. 1981. Pp. 456-458, 889 in Textbook of Medical Physiology, 6th Ed. Phila- delphia, PA: W.B. Saunders. Hansen, J.B., L. Wilsgard, and B. Osterud. 1991. Biphasic changes in leukocytes induced by strenuous exercise. Eur. J. Appl. Physiol. Occup. Physiol. 62(3):157-161. Hatton, D.V., C.S. Leach, A.L. Beaudet, R.O. Dillman, and N. Di Ferrante. 1979. Colla- gen breakdown and ammonia inhalation. Arch. Environ. Health 34(2):83-87. Hilado, C.J., C.J. Casey, and A. Fürst. 1977. Effect of ammonia on Swiss albino mice. J. Combust. Toxicol. 4:385-388. Hilado, C.J., H.G. Cumming, A.M. Machado, C.J. Casey, and A. Fürst. 1978. Effect of individual gaseous toxicants on mice. Proc. West. Pharmacol. Soc. 21:159-160. Hoeffler, H.B., H.I. Schweppe, and S.D. Greenberg. 1982. Bronchiectasis following pul- monary ammonia burn. Arch. Pathol. Lab. Med. 106(13):686-687. Holness, D.L., J.T. Purdham, and J.R. Nethercott. 1989. Acute and chronic respiratory effects of occupational exposure to ammonia. Am. Ind. Hyg. Assoc. J. 50(12):646-650. HSDB (Hazardous Substances Data Bank). 2005. Ammonia (CASRN 7664-41-7). TOXNET, Specialized Information Services, U.S. National Library of Medi- cine, Bethesda, MD [online]. Available: http://toxnet.nlm.nih.gov/cgi-bin/sis/ htmlgen?HSDB [accessed March 14, 2007]. IARC (International Agency for Research on Cancer). 1995. Dry Cleaning, Some Chlo- rinated Solvents and Other Industrial Chemicals. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Vol. 63. Lyon, France: Interna- tional Agency for Research on Cancer, World Health Organization. Ihrig, A., J. Hoffman, and G. Triebig. 2006. Examination of the influence of personal traits and habituation on the reporting of complaints at experimental exposure to ammonia. Int. Arch. Occup. Environ. Health 79(4):332-338. Industrial Bio-Test Labs, Inc. 1973. Irritation Threshold Evaluation Study with Ammo- nia. Industrial Bio-Test Laboratories, Inc. (Report to International Institute of Ammonia Refrigeration, Publication No. 663-03161) (as cited in NRC 2002). Kapeghian, J.C., H.H. Mincer, A.B. Jones, A.J. Verlangieri, and I.W. Waters. 1982. Acute inhalation toxicity of ammonia in mice. Bull. Environ. Contam. Toxicol. 29(3):371-378. Landahl, H.D., and R.G. Herrmann. 1950. Retention of vapors and gases in the human nose and lung. Arch. Ind. Hyg. Occup. Med. 1:36-45. Leduc, D., P. Gris, P. Lheureux, P.A. Gevenois, P. de Vuyst, and J.C. Yernault. 1992. Acute and long term respiratory damage following inhalation of ammonia. Thorax 47(9):755-757.

Ammonia 61 Lewis, R.J., ed. 1993. P. 62 in Hawley’s Condensed Chemical Dictionary, 12th Ed. New York: Van Nostrand Reinhold. MacEwen, J.D., and E.H. Vernot. 1972. Toxic Hazards Research Unit Annual Technical Report: 1972. AMRL-TR-72-62. NTIS AD-755 358. Aerospace Medical Re- search Laboratory, Wright-Patterson Air Force Base, OH. MacEwen, J.D., J. Theodore, and E.H. Vernot. 1970. Human exposure to EEL concentra- tions of monomethylhydrazine. Pp. 355-363 in Proceedings of the 1st Annual Conference Environmental Toxicology, September 9-11, 1970, Wright- Patterson Air Force Base, OH. AMRL-TR-70-102, Paper No 23. Aerospace Medical Research Laboratory, Wright-Patterson Air Force Base, OH. Manninen, A., S. Anttilla, and H. Savolainen. 1988. Rat metabolic adaptation to ammonia inhalation. Proc. Soc. Exp. Biol. Med. 187(3):278-281. McLean, J.A., K.P. Mathews, W.R. Solomon, P.R. Brayton, and N.K. Baynel. 1979. Effect of ammonia on nasal resistance in atopic and nonatopic subjects. Ann. Otol. Rhinol. Laryngol. 88(2 Pt.1):228-234. Mulder, J.S., and H.O. Van der Zalm. 1967. A fatal case of ammonia poisoning [in Dutch]. Tijdsch. Soc. Geneeskd. 45:458-460 (as cited in NIOSH 1974). Neumann, R., G. Mehlhorn, I. Buchholz, U. Johannsen, and D. Schimmel. 1987. Experi- mental studies of the effect of chronic exposure of suckling pigs with different ammonia concentrations. II. The reaction of cellular and humoral infection de- fense mechanisms of NH3-exposed suckling pigs under the conditions of an experimental Pasteurella multocida infection with and without thermomotor stress [in German]. Zentralbl. Veterinarmed. B. 34(4):241-253. NIOSH (National Institute for Occupational Safety and Health). 1974. Criteria for a Rec- ommended Standard Occupational Exposure to Ammonia. HEW74-136. Na- tional Institute for Occupational Safety and Health, Public Health Service, U.S. Department of Health, Education and Welfare, Cincinnati, OH. NIOSH (National Institute for Occupational Safety and Health). 2005. NIOSH Pocket Guide to Chemical Hazards. DHHS (NIOSH) Publication No. 2005-149. Na- tional Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, U.S. Department of Health and Human Services, Cincinnati, OH [online]. Available: http://www.cdc.gov/niosh/npg/ [accessed June 14, 2007]. Norenberg, M.D. 1981. The astrocyte in liver disease. Pp. 303-352 in Advances in Cellu- lar Neurobiology, Vol. 2, S. Fedoroff,, and L. Hertz, eds. New York, NY: Aca- demic Press. Norenberg, M.D., and A. Martinez-Hernandez. 1979. Fine structural localization of glutamine synthetase in astrocytes of rat brain. Brain Res. 161(2):303-310. NRC (National Research Council). 1966. Report on Advisory Center on Toxicology Pro- ject 390. Washington, DC: National Academy of Sciences. 5pp (as cited in NRC 1987). NRC (National Research Council). 1987. Ammonia. Pp. 7-15 in Emergency and Con- tinuous Exposure Guidance Levels for Selected Airborne Contaminants, Vol. 7. Ammonia, Hydrogen Chloride, Lithium Bromide, and Toluene. Washington, DC: National Academy Press. NRC (National Research Council). 1988. Submarine Air Quality: Monitoring the Air in Submarines; Health Effects in Divers of Breathing Submarine Air Under Hy- perbaric Conditions. Washington, DC: National Academy Press. NRC (National Research Council). 1994. Ammonia. Pp. 39-59 in Spacecraft Maximum

62 Exposure Guidance Levels for Selected Submarine Contaminants Allowable Concentrations for Selected Airborne Contaminants, Vol. 1. Wash- ington, DC: National Academy Press. NRC (National Research Council). 2002. Ammonia. Pp. 22-68 in Review of Submarine Escape Action Levels for Selected Chemicals. Washington, DC: National Academy Press. NRC (National Research Council). 2007. Acute Exposure Guideline Levels for Selected Airborne Chemicals, Vol. 6. Ammonia (CAS No. 7664-41-7). Washington, DC: The National Academies Press. O’Kane, G.J. 1983. Inhalation of ammonia vapor: A report on the management of eight patients during the acute stages. Anaesthesia 38(12):1208-1213. Pierce, J.O. 1994. Ammonia. Pp. 756-782 in Patty=s Industrial Hygiene and Toxicology, 4th Ed., Vol. II, Pt. A Toxicology, G.D. Clayton, and F.E. Clayton, eds. New York, NY: John Wiley & Sons. Pinson, D.M., T.R. Schoeb, J.R. Lindsey, and J.K. Davis. 1986. Evaluation of scoring and computerized morphometry of lesions of early Mycoplasma pulmonis in- fection and ammonia exposure in F344/N rats. Vet. Pathol. 23(5):550-555. Pitts, R.F. 1971. The role of ammonia production and excretion in regulation of acid-base balance. New Engl. J. Med. 284(1):32-38. Reynolds, S.J., K.J. Donham, P. Whitten, J.A. Merchant, L.F. Burmeister, and W.J. Popendorf. 1996. Longitudinal evaluation of dose-response relationships for environmental exposures and pulmonary function in swine production workers. Am. J. Ind. Med. 29(1):33-40. Richard, D., G. Bouley, and C. Boudene. 1978. Effects of continuous inhalation of am- monia in the rat and mouse [in French]. Bull. Eur. Physiopathol. Respir. 14(5):573-582. Rosenfeld, M. 1932. Experimental modification of mitosis by ammonia [in German]. Arch. Exp. Zellforsch. Besonders. Gewebezvecht. 14:1-13 (as cited in ATSDR 2004). Schaerdel, A.D, W. J. White, C.M. Lang, B.H. Dvorchik, and K. Bohner. 1983. Localized and systemic effects of environmental ammonia in rats. Lab. Anim. Sci. 33(1):40-45. Shimkin, M.B., A.A. de Lormier, J.R. Mitchell, and T.P. Burroughs. 1954. Appearance of carcinoma following single exposure to a refrigeration ammonia-oil mixture. Arch. Ind. Hyg. Occup. 9(3):186-193. Silver, S.D., and F.P. McGrath. 1948. A comparison of acute toxicities of ethylene imine and ammonia to mice. J. Ind. Hyg. Toxicol. 30(1):7-9. Silverman, L., J.L. Whittenberger, and J. Muller. 1949. Physiological response of man to ammonia in low concentrations. J. Ind. Hyg. Toxicol. 31(2):74-78. Slot, G.M. 1938. Ammonia gas burns: An account of six cases. Lancet 2(Dec.):1356- 1357. Sobonya, R. 1977. Fatal anhydrous ammonia inhalation. Hum. Pathol. 8(3):293-299. Sundblad, B.M., B.M. Larsson, F. Acevedo, L. Ernstgard, G. Johanson, K. Larsson, and L. Palmberg. 2004. Acute respiratory effects of exposure to ammonia on healthy persons. Scand. J. Work Environ. Health 30(4):313-321. Swotinsky, R.B., and K.H. Chase. 1990. Health effects of exposure to ammonia: Scant information. Am. J. Ind. Med. 17(4): 515-521. Targowski, S.P., W. Klucinski, S. Babiker, and B.J. Nonnecke. 1984. Effect of ammonia on in vivo and in vitro immune responses. Infect. Immun. 43(1):289-293.

Ammonia 63 ten Berge, W.F., A. Zwart, and L.M. Appelman. 1986. Concentration-time mortality response relationship of irritant and systemically acting vapours and gases. J. Hazard. Mater. 13(3):301-309. Tepper, J.S., B. Weiss, and R.W. Wood. 1985. Alterations in behavior produced by in- haled ozone or ammonia. Fundam. Appl. Toxicol. 5(6 Pt.1):1110-1118. Uzvölgyi, E., and F. Bojan. 1980. Possible in vivo formation of a carcinogenic substance from diethyl pryocarbonate and ammonia. J. Cancer Res. Clin. Oncol. 97(2):205-207. Verberk, M.M. 1977. Effects of ammonia on volunteers. Int. Arch. Occup. Environ. Health. 39(2):73-81. Visek, W.J. 1972. Effects of urea hydrolysis on cell life-span and metabolism. Fed. Proc. 31(3):1178-1193. Walton, M. 1973. Industrial ammonia gassing. Br. J. Ind. Med. 30(1):78-86. Wands, R.C. 1981. Alkaline materials. Pp. 3045-3070 in Patty’s Industrial Hygiene and Toxicology, Vol. 2B, Toxicology, G.D. Clayton, and F.E. Clayton, eds, 3rd Rev. Ed. New York, NY: John Wiley and Sons. White, A., P. Handler, E.L. Smith, R.L. Hill, and I.R. Lehman. 1978. Amino acid me- tabolism. II. Pp. 695-700 in Principles of Biochemistry. New York, NY: McGraw-Hill. WHO (World Health Organization). 1986. Ammonia. Environmental Health Criteria 54. IPCS International Programme on Chemical Safety. Geneva: World Health Or- ganization. Wong, K.L. 1994. Ammonia. Pp. 39-59 in Spacecraft Maximum Allowable Concentra- tions for Selected Airborne Contaminants, Vol. 1. Washington, DC: National Academy Press. Yadav, J.S., and V.K. Kaushik. 1997. Genotoxic effect of ammonia exposure on workers in a fertilizer factory. Indian J. Exp. Biol. 35(5):487-492. Zissu, D. 1995. Histopathological changes in the respiratory tract of mice exposed to ten families of airborne chemicals. J. Appl. Toxicol. 15(3):207-213. Zimber, A., and W.J. Visek. 1972. Effect of urease injections on Ehrlich ascites tumor growth in mice. Proc. Soc. Exp. Biol. Med. 139(1):143-149.

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U.S. Navy personnel who work on submarines are in an enclosed and isolated environment for days or weeks at a time when at sea. To protect workers from potential adverse health effects due to those conditions, the U.S. Navy has established exposure guidance levels for a number of contaminants. In this latest report in a series, the Navy asked the National Research Council (NRC) to review, and develop when necessary, exposure guidance levels for 11 contaminants. The report recommends exposure levels for hydrogen that are lower than current Navy guidelines. For all other contaminants (except for two for which there are insufficient data), recommended levels are similar to or slightly higher than those proposed by the Navy. The report finds that, overall, there is very little exposure data available on the submarine environment and echoes recommendations from earlier NRC reports to expand exposure monitoring in submarines.

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