Acute Exposure Guideline Levels for Selected Airborne Chemicals Volume 13 (2012) / Chapter Skim
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8 Trimethylbenzenes
8 Trimethylbenzenes
Pages 242-274
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From page 242... ...
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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Because occupational exposures are likely to involve more than one isomer, regulatory standards are for the individual isomers and any mixture thereof. For derivation of AEGL values, all available data on the individual TMB isomers were considered.
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According to Section 2.7 of the Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals (NRC 2001) , 10min values should not be scaled from experimental exposure durations of 4 h or longer.
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2.2.2. Case Reports No reports of injury or illness from accidental or intentional exposure to TMB isomers were found.
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246 TABLE 8-2 Chemical and Physical Properties of Trimethylbenzenes Parameter 1,3,5-TMB 1,2,4-TMB 1,2,3-TMB Reference Synonyms Mesitylene Pseudocumene Hemimellitene Delic et al. 1992 CAS registry no.
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From page 247... ...
Occupational exposures usually involve a complex mixture of hydrocarbons including dozens of related aromatic and aliphatic organic chemicals. Concentrations of a variety of compounds were measured in six areas of an offset printing shop to estimate emission of volatile organic compounds (Wadden et al.
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2.7. Summary Very little information is available concerning human exposure to pure TMB isomers despite the wide use of these materials.
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Male and female Wistar rats (number per sex not specified) were exposed in whole body inhalation chambers (Cameron et al.
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. Atmospheres were generated by bubbling air through a saturation unit, and the chamber atmospheres were described as being accurate during a continuous run as measured by "chemical analysis." No adverse clinical signs, deaths, or necropsy findings occurred in animals (n = 10)
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. No effects from any of the TMB isomers were noted in the radial maze or pain sensitivity assays.
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No treatment-related mortality, clinical signs of toxicity, or changes in food consumption were observed at 100 or 500 ppm. A total of 12 animals exposed at 1,500 ppm died between gestation days 8-16.
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Clinical signs of toxicity of ataxia and reduced motor activity were described in the F1 parental animals. During premating, males and females of all generations exposed at 500 and 1,500 ppm and the F2 animals exposed at100 ppm had reduced body weight and body weight gain.
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From page 254... ...
Rats exposed to the saturated atmosphere displayed nasal irritation, described as sneezing that progressed in severity to nasal discharge and bloody exudates; ocular irritation, described as eyes closed that progressed in severity to lachrymation; respiratory difficulty, such as rapid, shallow breathing that progressed to labored and slow breathing; lethargy, which included decreased activity; a lower response to noise; tremors; and decreased weight gain over the course of the experiment. Exposure at 1,000 ppm resulted in initial signs of slight ocular and nasal irritation.
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Body weight gain and food consumption were not affected by treatment. Animals exposed at 250 ppm exhibited increased liver weight relative to body weight (males)
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. TABLE 8-3 Summary of Animal Studies of Trimethylbenzenes Species Concentration (sex)
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after exposure at 400 and 800 ppm, respectively; the 1,2,4- and 1,2,3-TMB isomers were not detected in rats exposed at 400 ppm, but were measured at 0.40 and 0.07 mg/kg, respectively, in rats exposed at 800 ppm. Although the total white spirit concentration increased in the brain with
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From page 258... ...
That metabolite was not found with either 1,2,4- or 1,2,3-TMB. Both the 1,3,5- and 1,2,4-TMB isomers were mainly excreted as glycine conjugates with smaller amounts excreted as glucuronic and sulfuric acid conjugates.
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For derivation of AEGL values, all available data on the individual TMB isomers were considered. The most appropriate end point for each AEGL category was used as the point of departure for deriving AEGL values.
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Exposure of mice for 6 h/day on gestation days 8-16 to a mixture of TMB isomers and other alkyl benzenes resulted in maternal and developmental toxicity at 500 and 1,500 ppm (IRDC 1988a; McKee et al.
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According to Section 2.7 of the Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals (NRC 2001) , 10-min values should not to be scaled from an experimental duration of 4 h or longer.
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1938) , and cumulative effects on body weight and reproductive parameters were found over successive generations of rats exposed to a mixture TMB isomers and other alkyl benzenes at 1,500 ppm (McKee et al.
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DATA ANALYSIS FOR AEGL-3 7.1. Summary of Human Data Relevant to AEGL-3 Human data relevant to deriving AEGL-3 values for TMBs were not available.
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These standards have been established for the individual TMB isomers and any mixture thereof. The time-weighted average exposure concentration for workers is 25 ppm in the United States and Sweden.
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TMB isomers have a sensitizer notation. b REL-TWA (recommended exposure limit - time weighted average, National Institute for Occupational Safety and Health)
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1992. Trimethylben zenes: Criteria Document for an Occupational Exposure Limit.
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1988a. Inhalation Devel opmental Toxicity Study in Mice with C9 Aromatic Hydrocarbons (Final Report)
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2001. Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals.
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P 52 in Occupational Exposure Limit Values and Measures against Air Contaminants.
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3 × 4 h = 2.9 × 106 ppm-h (900 ppm ÷ 10) 1 × 4 h = 360 ppm-h Uncertainty factors: 3 for interspecies differences 3 for intraspecies variability Total uncertainty factor of 10 Modifying factor: None Calculations: 10-min AEGL-1: Set equal to the 30-min value of 180 ppm 30-min AEGL-1: (2.9 × 106 ppm-h ÷ 0.5 h)
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3 × 6 h = 4.8 × 107 ppm-h (2,000 ppm ÷ 10) 1 × 6 h = 1,200 ppm-h Uncertainty factors: 3 for interspecies differences 3 for intraspecies variability Total uncertainty factor of 10 Modifying factor: None Calculations: 10-min AEGL-2: Set equal to the 30-min value of 460 ppm 30-min AEGL-2: (4.8 × 107 ppm-h ÷ 0.5 h)
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According to Section 2.7 of the Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals (NRC 2001) , 10-min values are not to be scaled from an experimental exposure duration of 4 h or more.
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From page 273... ...
According to Section 2.7 of the Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals (NRC 2001) , 10-min values should not to be scaled from an experimental exposure duration of 4 h or more.
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From page 274... ...
274 Acute Exposure Guideline Levels APPENDIX C CATEGORY PLOT FOR TRIMETHYLBENZENES Chemical Toxicity - TSD Animal Data Trimethylbenzene 10000 No Effect 1000 Discomfort Disabling ppm AEGL-2 Some Lethality 100 AEGL-1 Lethal AEGL 10 0 60 120 180 240 300 360 420 480 Minutes FIGURE C-1 Category plot of toxicity data and AEGL values for trimethylbenzenes.
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