IRIS TOXICOLOGICAL REVIEW AND SUMMARY DOCUMENTS FOR HYDROGEN SULFIDE (EXTERNAL REVIEW DRAFT)
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Subchronic inhalation of H2S has been shown to mainly affect the nasal mucosa in laboratory animals and been reported to increase seminiferous tubular degeneration and epididymal changes in rats exposed to 80 ppm (111 mg/m3) H2S. Three subchronic animal studies were considered for derivation of an inhalation RfC: the study by Brenneman et al. (2000) was considered to be the best study for derivation of an inhalation RfC. Nasal lesions were identified as the critical effects. Application of the RfC methodology yielded a NOAEL of 10 ppm (14 mg/m3) and a LOAEL of 30 ppm (42mg/m3). The LOAEL and NOAEL were then converted to continuous exposure by means of a dosimetric adjustment factor derived from the regional gas dose ratio (RGDR) for H2S in the extrathoracic (ET) region. The animal NOAEL is then multiplied by the RGDRET to yield the NOAELHEC. The RfC was derived by dividing the NOAELHEC for nasal effects by a total uncertainty factor of 300, yielding an inhalation RfC of 0.002 mg/m3 or 1 ppb. No data pertaining to the potential carcinogenicity of H2S were identified.
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