Risk Assessment of T-Butanol for the Development of Drinking Water Action Levels Adequately Protective of Human Health. R. Sohn and G. L. Ball, NSF International, Ann Arbor, MI
A human health risk assessment was conducted by NSF International to determine short-term and long-term exposure limits for t-butanol in drinking water in accordance with ANSI/NSF Standard 60/61, Annex A. t-Butanol has been detected in laboratory extractions as a leachate resulting from decomposition of the following peroxide catalysts: di-t-butylperoxide; 2,5-dimethyl-2,5-di-t-butyl peroxyhexane; or cumyl di-t-butyl peroxide, when used as initiators in polymeric or elastomeric materials. Initial concentrations up to 4 ppm are seen, but decay over a 90-day period to 20 – 300 ppb. Published and unpublished scientific literature currently available on t-butanol, including information on sources of human and environmental exposure, comparative kinetics and metabolism, and effects on laboratory animals and in vitro test systems has been reviewed. The proposed USEPA cancer guidelines on risk assessment methods were used to assess the carcinogenic potential of the compound and to provide guidance for the derivation of appropriate drinking water action levels. The available literature on t-butanol suggests that the compound is an animal carcinogen and that there is insufficient evidence to determine the carcinogenic potential of t-butanol in humans. It is clear from both subchronic and chronic studies on t-butanol that the kidney is a target organ in both male and female rats. Male rats developed mineralization, nephropathy, and hyaline droplet formation in subchronic testing, and transitional epithelial and renal tubule hyperplasia with progression to renal tubule adenoma or carcinoma in chronic testing. Female rats developed significant mineralization and nephropathy, but no adenoma or carcinoma. The results on male rats were evaluated using EPA guidelines for evaluation of renal toxicity and neoplasia in the male rat associated with alpha-2:-globulin accumulation. The male rat kidney effects could not be discounted because one of the essential criteria, positive identification of alpha-2:-globulin in the hyaline droplets, was not met. The thyroid gland is a target organ in both male and female mice, with follicular cell hyperplasia and apparent increases in the overall rate of follicular cell adenoma in both sexes, with one adenoma progressing to carcinoma in a high-dose male. The increases in adenoma or adenoma/carcinoma were not statistically significant. These results were evaluated according to EPA guidelines for the assessment of thyroid follicular cell tumors. To be adequately protective of human health, drinking water action levels were developed using the linear extrapolation method presented in the proposed EPA cancer guidelines for both the kidney and thyroid effects, and the more conservative values were selected.
Go to . . .
1999 SRA Table of Contents
1999 SRA Author Index
Main Abstracts Menu Page
RiskWorld Home Page