Acute Exposure Guideline Levels for Selected Airborne Chemicals Volume 15 (2013) / Chapter Skim
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1 Ethyl Mercaptan Acute Exposure Guideline Levels
1 Ethyl Mercaptan Acute Exposure Guideline Levels
Pages 13-43
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From page 13... ...
Both the document and the AEGL values were then reviewed by the National Research Council (NRC) Committee on Acute Exposure Guideline Levels.
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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 Ethyl mercaptan is an odorous, colorless liquid.
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Although an interspecies uncertainty factor of 10 might normally be applied because of the limited data, a total uncertainty factor of 30 would yield AEGL-3 values that are inconsistent with the total data set (the values would be in the range of AEGL-3 values for hydrogen sulfide [NRC 2010]
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HUMAN TOXICITY DATA 2.1. Acute Lethality No information concerning human lethality from acute exposure to ethyl mercaptan was found.
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(1.8 × 106 mg/m3) at 25°C Vapor pressure 442 mm Hg at 20°C HSDB 2011 Incompatibility Strong oxidizers NIOSH 2011 Conversion factors in air 1 mg/m3 = 0.39 ppm 1 ppm = 2.54 mg/m3 NIOSH 2011 TABLE 1-3 Odor Intensity of Ethyl Mercaptan Concentration (ppm)
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conducted a series of experiments whereby a total of nine human subjects inhaled ethyl mercaptan through a mask connected to a 1,000-L chamber in which a known concentration of ethyl mercaptan had been established. No other information on atmosphere generation or analytic methods was provided.
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The subject exposed at 112 ppm had a slightly irregular and decreased breathing rate. Minute volume and tidal volume increased in all three subjects.
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Case reports of deaths from accidental exposure to ethyl mercaptan were not available. Nonlethal toxicity data include a case report where high school students accidentally exposed to ethyl mercaptan experienced reversible dull headache, general discomfort, abdominal pain, vomiting, and diarrhea.
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, incoordinated movement, staggering gait, muscular weakness, partial skeletal muscle paralysis beginning in the hind limbs, light to severe cyanosis, tolerance of a prone position, and mild to heavy sedation. Animals exposed to "maximal lethal concentrations" typically died from respiratory arrest during exposure or shortly after removal from the chamber.
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No rats lost the righting reflex at ethyl mercaptan concentrations of about 3.0% (30,000 ppm) , but all rats lost the righting reflex at about 3.7% (37,000 ppm)
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All respiratory indicators returned to pre-exposure levels by the end of the 35-min observation period, except for the respiratory rate of animals exposed at 1,000 ppm, which was still decreased by approximately 25%. The changes in breathing rate and tidal volume in rabbits exposed to ethyl mercaptan at 100 ppm or higher for 20 min are similar to the effects reported in the human study by the same investigator (Shibata 1966b)
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, incoordinated movement, staggering gait, muscular weakness, skeletal muscle paralysis, light to severe cyanosis, and coma. Coma-induction data also suggest a steep concentration-response curve for ethyl mercaptan.
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4.2. Mechanism of Toxicity Ethyl mercaptan acts similar to hydrogen sulfide and cyanide by interrupting electron transport through inhibition of cytochrome oxidase.
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. For example, the 4-h LC50 value for ethyl mercaptan was 4,420 ppm, whereas the corresponding values for methyl mercaptan and hydrogen sulfide were 675 ppm and 444 ppm, respectively (Tansy et al.
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5.2. Animal Data Relevant to AEGL-1 Rabbits exposed to ethyl mercaptan at 100 or 1,000 ppm for 20 min exhibited decreased respiratory rate and expiratory volume, indicative of odor avoidance, but no significant effects was observed at 10 ppm (Shibata 1966a)
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DATA ANALYSIS FOR AEGL-2 6.1. Human Data Relevant to AEGL-2 Ten students complained of dull headache, general discomfort, and abdominal pain, and three students vomited and had diarrhea after accidentally being exposed to ethyl mercaptan at school (Pichler 1918)
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. Although an interspecies uncertainty factor of 10 might normally be applied because of the limited data, a total uncertainty factor of 30 would yield AEGL-3 values approaching or equivalent to the AEGL-3 values for hydrogen sulfide.
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, it would be inconsistent with the total data set to have AEGL-3 values for ethyl mercaptan that are in the range of the AEGL-3 values for hydrogen sulfide. Furthermore, use of a total uncertainty factor of 30 would yield a 30-min AEGL-3 value of 150 ppm, which is inconsistent with the finding that a single human exposed to ethyl mercaptan at 112 ppm for 20 min exhibited only a slightly irregular and decreased breathing rate (Shibata 1966b)
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b TLV-TWA (threshold limit value - time weighted average, American Conference of Governmental Industrial Hygienists [ACGIH 2004, 2012]
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of the American Conference of Governmental Industrial Hygienists, the Dutch maximal accepted concentration (MAC) , and the German maximum workplace concentration (MAK)
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American Conference of Governmental Industrial Hygienists, Cincinnati, OH. Amoore, J.E., and E
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2001. Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals.
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On the respiratory function and clinical findings in rabbits which inhaled ethyl mercaptan gas [in Japanese]
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: 834-843. Toxicity end point: No-effect level for respiratory changes associated with odor avoidance in rabbits, 10 ppm for 20 min Scaling: Values held constant across time Uncertainty factor: 3 for interspecies differences 3 for intraspecies variability All AEGL-1 durations: 10 ppm ÷ 10 = 1.0 ppm Derivation of AEGL-2 Values In the absence of relevant data to derive AEGL-2 values and because ethyl mercaptan has a steep concentration-response curve, AEGL-3 values were divided by 3 to estimate a threshold for inability to escape.
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3 × 4 h = 4.56 × 1010 ppm-h (2,250 ppm) 1 × 4 h = 9,000 ppm-h Uncertainty factors: 3 for interspecies differences 3 for intraspecies variability 10-min AEGL-3: 450 ppm (30-min AEGL-3 value adopted)
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From page 38... ...
. End point/Concentration/Rationale: No-effect level for respiratory changes associated with odor avoidance, 10 ppm Uncertainty factors/Rationale: Use of the full factor of 10 for either interspecies differences or intraspecies variability would yield AEGL-1 values of 0.3 ppm or lower, concentrations that are inconsistent with human data.
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From page 39... ...
, it would be inconsistent with the total data set to have AEGL-3 values for ethyl mercaptan that are in the range of the AEGL-3 values for hydrogen sulfide. Furthermore, use of a total uncertainty factor of 30 would yield a 30-min AEGL-3 value of 150 ppm, which is inconsistent with the finding that a single human exposed to ethyl mercaptan at 112 ppm for 20 min exhibited only a slightly irregular and decreased breathing rate (Shibata 1966b)
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From page 40... ...
40 Acute Exposure Guideline Levels AEGL-3 VALUES Continued Time scaling: Cn × t = k; default value of n = 3 was used for extrapolation to the shorter durations (30 min, 1 h, and 4 h) and n = 1 for extrapolation to the longer duration (8 h)
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leading to an odor intensity (I) of distinct odor detection (I = 3)
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42 Accute Exposure Guideline Levels AP PPENDIX D FIGUR RE D-1 Category y plot of toxicity y data and AEGL L values for ethyyl mercaptan. TABLE E D-1 Data Ussed in Category y Plot of AEGL L Values for E Ethyl Mercaptaan No.
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Ethyl Mercaptan 43 AEGL-3 360 60 AEGL AEGL-3 230 240 AEGL AEGL-3 110 480 AEGL Shibata 1966a Rabbit Male 1 10 20 0 Rabbit Male 1 100 20 1 Rabbit Male 1 1,000 20 1 Fairchild and Mouse Male 1 2,600 240 2 Stokinger 1958 Mouse Male 1 3,150 240 SL Mouse Male 1 3,573 240 3 Mouse Male 1 4,438 240 3 Mouse Male 1 4,832 240 3 Katz and Talbert 1930 Human Male 1 0.00002 0 Human Male 1 920 1 Wilby 1969 Human Male 1 0.0004 0 Blinova 1965 Human Male 1 4 180 1 Pichler 1918 Human Male Shibata 1966b Human Male 1 50 20 1 Human Male 1 112 20 1 Amoore and Hautala 1983 Human 1 0.0008 1 Nagata 2003 Human 1 0.00001 1 Zieve et al. 1974 Rats Rats Blinova 1965 Human 1 0.4 180 0 NIOSH 1978 Human 5 4.0 180 1 Human 5 0.4 180 0 Katz and Talbert 1930 Human 1 1,000.0 0.17 0 For category: 0 = no effect, 1 = discomfort, 2 = disabling, 3 = lethal; SL = some lethality.
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