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2 Methyl Mercaptan Acute Exposure Guideline Levels
Pages 44-74

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From page 44...
... Both the document and the AEGL values were then reviewed by the National Research Council (NRC) Committee on Acute Exposure Guideline Levels.
From page 45...
... Although the AEGL values represent threshold concentrations for the general public, including susceptible subpopulations, such as infants, children, the elderly, persons with asthma, and those with other illnesses, it is recognized that individuals, subject to idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL. SUMMARY Methyl mercaptan is a colorless gas with a strong odor.
From page 46...
... . To obtain conservative and protective AEGL values in the absence of a chemical-specific exponent, temporal scaling was performed using default values of n = 3 for extrapolating from longer to shorter durations (10 min, 30 min, and 1 h)
From page 47...
... HUMAN TOXICITY DATA 2.1. Acute Lethality Methyl mercaptan depresses the central nervous system and affects the respiratory center, similar to hydrogen sulfide, producing death by respiratory paralysis (Farr and Kirwin 1994)
From page 48...
... and reported methyl mercaptan concentrations ranging from 0 to 15 ppm. Thirteen to 15 mill workers reported headache and trouble concentrating; however, they were also simultaneously exposed to hydrogen sulfide, dimethyl sulfide, and dimethyl disulfide.
From page 49...
... TABLE 2-3 Odor Intensity of Methyl Mercaptan Intensity Description Concentration (ppm) 0 No odor 0.0030 1 Threshold 0.041 2 Faint 0.57 3 Median, easily noticeable 7.9 4 Strong 110 5 Most intense 1,500 Source: Adapted from Katz and Talbert 1930.
From page 50...
... Case reports of deaths from accidental exposure to methyl mercaptan were available; however, definitive exposure durations and concentrations were not reported. Nonlethal toxicity data are limited to odor detection or identification studies that had no accompanying health effects information.
From page 51...
... was determined from these exposure concentrations. Blood concentrations of methyl mercaptan found in comatose animals were greater than 0.5 nmoles/mL.
From page 52...
... 1981. TABLE 2-5 Acute Inhalation Toxicity in Rats Exposed to Methyl Mercaptan Concentration Duration (ppm)
From page 53...
... TABLE 2-6 Subchronic Inhalation Toxicity in Rats Exposed to Methyl Mercaptan Concentration (ppm) Duration Mortality Clinical Signs Necropsy Findings 100 6 h/d for 10 d 0/2 Occasional Bronchopneumonia (2 rats)
From page 54...
... . Methyl mercaptan and dimethyl sulfide were found in the expired breath of one mouse injected with methyl mercaptan (Susman et al.
From page 55...
... 4.3. Structure-Activity Relationships Rat lethality data suggest that the acute toxicity of methyl mercaptan is slightly less than that of hydrogen sulfide and more toxic than other mercaptans tested (with the exception of phenyl mercaptan, benzyl mercaptan, and tert-octyl mercaptan (see Table 2-7)
From page 56...
... To obtain conservative and protective AEGL values in the absence of a chemical-specific scaling exponent, temporal scaling was performed using a default value of n = 3 when extrapolating to shorter durations and n = 1 when extrapolating to longer durations.
From page 57...
... The only data on humans involve occupational observations in which workers were also simultaneously exposed to hydrogen sulfide, dimethyl sulfide, and dimethyl disulfide. Animal studies do not identify a suitable point of departure for calculating AEGL-1 values.
From page 58...
... . However, the workers were also simultaneously exposed to hydrogen sulfide, dimethyl sulfide, and dimethyl disulfide.
From page 59...
... Although a factor of 10 might normally be applied because of limited data on species differences, AEGL-3 values calculated using that larger factor would be inconsistent with the total database. AEGL3 values would range from 7.3 to 40 ppm if a total uncertainty factor of 30 was used; however, occupational exposures at concentrations up to 15 ppm (with simultaneous exposure to hydrogen sulfide, ≤20 ppm; dimethyl sulfide, ≤15 ppm; and dimethyl disulfide, ≤1.5 ppm)
From page 60...
... . To obtain conservative and protective AEGL values in the absence of an empirically derived chemicalspecific exponent, temporal scaling was performed using default values of n = 3 when extrapolating from longer to shorter durations (10 min, 30 min, and 1 h)
From page 61...
... . ERPG-1 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 h without experiencing other than mild, transient adverse health effects or without perceiving a clearly defined objectionable odor.
From page 62...
... ERPG-3 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 h without experiencing or developing lifethreatening health effects. ERPG-3 for methyl mercaptan is based on a 4-h acute inhalation study of rats exposed at 400 ppm (Tansy et al.
From page 63...
... American Conference of Governmental Industrial Hygienists, Cin cinnati, OH. AIHA (American Industrial Hygiene Association)
From page 64...
... 1984. Exposure to hydrogen sulfide, mercap tans and sulfur dioxide in pulp industry.
From page 65...
... 2001. Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals.
From page 66...
... 2002. Guidance for the Application of Odor in Chemical Emergency Response.
From page 67...
... 1981. Acute and subchronic toxicity studies of rats exposed to vapors of methyl mercaptan and other reduced-sulfur compounds.
From page 68...
... 68 Acute Exposure Guideline Levels Uncertainty factors: 3 for interspecies differences 3 for intraspecies variability 10-min AEGL-3: C3 × 0.167 h = 318,028,000 ppm3-h C3 = 1,904,359,281 ppm C = 1,240 ppm 1,240 ppm ÷ 10 = 120 ppm 30-min AEGL-3: C3 × 0.5 h = 318,028,000 ppm-h C3 = 636,056,000 ppm C = 860 ppm 860 ppm ÷ 10 = 86 ppm 1-h AEGL-3: C3 × 1 h = 318,028,000 ppm-h C3 = 318,028,000 ppm C = 682.7 ppm 682.7 ppm ÷ 10 = 68 ppm 4-h AEGL-3: 430.0 ppm ÷ 10 = 43 ppm 8-h AEGL-3: C1 × 8 h = 1,720 ppm-h C1 = 215 ppm C = 215 ppm 215 ppm ÷ 10 = 22 ppm
From page 69...
... 1981. Acute and subchronic toxicity of rats exposed to vapors of methyl mercaptan and other reduced-sulfur compounds.
From page 70...
... Interspecies: 3, although an interspecies uncertainty factor of 10 might normally be applied because of limited data, AEGL-3 values calculated using a total uncertainty factor of 30 would be inconsistent with the total database. AEGL-3 values would range from 7.3 to 40 ppm if the larger factor is used; however, occupational exposures of up to 15 ppm (along with hydrogen sulfide, ≤20 ppm; dimethyl sulfide, ≤15 ppm; and dimethyl disulfide, ≤1.5 ppm)
From page 71...
... represents the concentration above which it is predicted that more than half of the exposed population will experience at least a distinct odor intensity, and about 10% of the population will experience a strong odor intensity. The LOA should help chemical emergency responders in assessing the public awareness of the exposure on the basis of odor perception.
From page 72...
... 72 Accute Exposure Guideline Levels AP PPENDIX D CATEGORY PLOT FOR F METHY YL MERCAPT TAN FIGURRE D-1 Categorry plot of toxicitty data and AE GL values for m methyl mercaptan. The deccimal point is lo ost on this log-sccale plot.
From page 73...
... ; shallow breathing; hypoactivity Tansy et al. 1981 Rat Both 1 400 240 2 (Continued)
From page 74...
... , coma Latven 1977 Rat Male 1 1,000 60 2 Clinical signs Rat Male 1 1,400 60 SL Mortality (1/6) Rat Male 1 2,000 60 SL Mortality (5/6)


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