Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 3 (1996) / Chapter Skim
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B8: Ethylbenzene
B8: Ethylbenzene
Pages 208-231
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From page 208... ...
Johnson Space Center Toxicology Group Biomedical Operations and Research Branch National Aeronautics and Space Administration Houston, Texas PHYSICAL AND CHEMICAL PROPERTIES Ethy~benzene (EB) is a clear, colorless, flammable liquid with an aromatic odor (Windho~z, 1976; Sandmeyer, 1981; ACGTH, 1991a)
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Although no studies were found on the rate of uptake of inhaled EB into the blood in humans exposed to known concentrations of EB, a good estimate of the time needed to reach steady-state blood concentrations can be made based on data available for xylene, a structural isomer of EB. For m-xylene, the concentration in the blood reached a steady state in about ~ h in eight subjects exposed to EB at 100 ppm (Riihimaki and Savolainen, 1980~.
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In rats inhaling ~4C-labeled EB at 230 ppm for 6 h, about 80-90% of absorbed ~4C label was excreted in the urine and about 10% was exhaled in breath (Chin et al., 1978~. TABLE S-1 Metabolism of EB in Humans and Rats Urinary Metabolites Humans Rats Mandelic acid 64% 25% Phenylglyoxylic acid 25 % Methylphenylcarbinol S % 1-Phenylethanol 25 % Benzoic acid 27%
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Toxic signs include irritation of mucous membranes, conjunctivitis, difficulty in breathing, pulmonary irritation, cramps, coordination disorders, narcosis, convulsions, and death due to respiratory center paralysis (Aldyreva, 1983~. The main pathological findings are marked edema of brain and lungs, foci of epithelial necrosis in renal tubules, and hepatic dystrophy (Al~yreva, 1983~.
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in which the metabolism of EB was studied in humans, nine subjects exposed at 100 ppm for ~ h did not complain of any problems, but toward the end of the exposure time at IS0 ppm, 11 subjects complained of headaches and sleepiness. Because blood concentrations probably reached steady state early (A 1 h)
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in a 13-w National Toxicology Program (NTP) study of rats and mice, the highest exposure concentration tested (1000 ppm)
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Glutathione levels remained constant in the liver and increased 30% in the kidney. Ultrastructural changes included slight proliferation of smooth endoplasmic reticulum, slight degranulation and splitting of the rough endoplasmic reticulum, and enlarged mitochondria.
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The study showed that some symptoms were reported by the workers if the exposure exceeded the threshold limit value of 100 ppm for EB. "The main complaints were fatigue, sleepiness, and headache, and mild irritation of the eyes and respiratory tract, particularly in the case of styrene." No detailed data were reported on the range of exposure concentrations, the duration of the exposures necessary to produce the reported effects, how EB concentrations in the workplace were determined, the numbers of individuals exposed, or whether any or all of the symptoms correlated with EB exposure concentrations.
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In the rabbit and monkey, 600 ppm induced slight histopathological changes described as degeneration of the germinal epithelium of the testes (concentration x time (C x T)
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Reproductive and Developmental Tox~city The offspring of rats inhaling EB continuously from gestation ~ 7 to t5 showed moderately increased rates of malfo~ations at 552 ppm compared with controls and increased rates of skeletal retardation and dead or resorbed fetuses at 13S, 276, and 552 ppm (Ungvary and Tatrai, 1985~. The offspring of mice inhaling EB at I l5 ppm continuously from gestation ~ 6 to 15 showed only moderately increased rates of malformations compared with controls (Ungvary and Tatrai, 1985~.
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2 ~ ~ SMACS FOR SELECTED AIRBORNE CONTAMINANTS Interactions with Other Chemicals in rats exposed to EB at a concentration of 650 ppm, coexposure to ethyl acetate at 1000 or 4000 ppm lowered the concentrations of EB in the blood by 26% (Freundt et al., 1989~. In rats exposed at iS0 ppm, coexposure to ethanol at 20 mmol/kg increased the blood concentration of EBbyI39%.
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219 Cal C)
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221 oo O O O O a~ ~ oo oo ~ O O O O O ~ O O O O O O _ _ ~ = ~a~ ~ ~_ _ ~ O%.
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TABLE 8-4 Spacecraft Maximum Allowable Concentrations Exposure Concentration, Concentration, Durationa ppm mg/m3 Target Toxicity 1 h 180 780 Eye and respiratory irrita tion, headache, sleepiness 24 h 60 260 Headache, sleepiness 7 db 30 130 Eye and respiratory irrita tion, testicular toxicity 30 d 30 130 Eye and respiratory irrita tion, testicular toxicity 180 d 12 50 Testicular toxicity aCeiling limits. bThe former 7-d SMAC is 20 ppm (86.8 mg/m3~.
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; respiratory distress (adequate protection would be achieved by ACs for less severe effects) ; neurochemical changes (no correlation to a functional deficits; developmental toxicity (not applicable to astronauts)
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In the rabbit and monkey, EB at 600 ppm for 7-8 in/d, 5 d/w, for 186 d induced slight histopathological changes described as degeneration of the germinal epithelium of the testes. No testicular toxicity was seen in the one male rabbit tested at 400 ppm.
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Spaceflight Considerations None of the toxic effects known to be induced by exposure to EB would be affected by launch, microgravity, or re-entry; thus, no spaceflight factor was used.
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of volunteers for irritation at the 100-ppm exposure concentration for 4 h or more might permit the ACs for 7 ~ and 30 ~ to be increased from 30 to 100 ppm. · Testing of volunteers for more than ~ h at several concentrations is needed to examine the effect of long (greater than 24 h)
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227 o to _ o c: ~ o .~ o V Ct at ¢ ~ Cal o Ct .= Cal V, o .~ C)
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1991a. Documentation of the Threshold Limit Values and Biological Exposure Indices, 6th Ed.
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1979. Preliminary identification of volatile flavor compounds in the neutral fraction of roast beef.
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1992. Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants.
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1930. Acute response of guinea pigs to vapors of some new commercial organic compounds.
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