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Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 7
Confidence and Support for AEGLs: AEGL-2 values are protective of human health. The level is based on a NOEL for inhibition of escape response in a behavioral study with rats in which concentrations in the exposure chamber were monitored. The AEGL values are supported by data from human studies in which no effects meeting the AEGL-2 definition were observed at similar concentrations.
Key Reference: Du Pont. 1966. Acute inhalation toxicity–progress report. Haskell Laboratory Report No. 161-66. EI Du Pont De Nemours and Company. Haskell Laboratory, Newark, DE.
Test Species/Strain/Number: Rats/CD/6 males.
Exposure Route/Concentrations/Durations: Inhalation, 3,500 ppm, 3,000 ppm/4 h.
Effects: 6/6 rats died at 3,500 ppm, none of 6 rats died at 3,000 ppm.
End Point/Concentration/Rationale: No lethality following 4 h of exposure to 3,000 ppm.
Total uncertainty factor: 10
Interspecies: 3, based on the similarity of acute effects seen in rodents compared with humans produced by agents affecting the CNS.
Intraspecies: 3, human data suggest that acute effects of volatile anesthetics and gases on the CNS show little intraspecies variability (about 2-3 fold).
Modifying factor: Not applicable.
Animal to Human Dosimetric Adjustment: Not applicable.
Time Scaling: Extrapolation was made to the relevant AEGL time points using the relationship Cn × t = k with the default of n = 3 for shorter exposure periods of 1 h and of 30 min and of n = 1 for longer exposure periods of 4 and 8 h (ten Berge et al. 1986; NRC 2001). The 10-min AEGL-2 was assigned the same value as that for the 30-min AEGL-2 as it was considered inapproprate to extrapolate from an experimental period of 4 h to 10 min.
Confidence and Support for AEGLs: AEGL-3 values are protective of human health. The available indicate a very steep concentration-lethality response curve and the values are based on a no-observed lethality concentration in rats. Additionally, the AEGL-3 values are supported by data from a human study in which the effects noted were milder than those defined by the AEGL-3 definition.