Determination of Drinking Water Action Levels for 11-aminoundecanoic Acid. N. A. Sachs, Dept. of Environmental & Industrial Health, School of Public Health, University of Michigan, Ann Arbor, MI; and A. D. Phelka and L. L. Bestervelt, NSF International, Ann Arbor, MI
A human health risk assessment was conducted on 11-aminoundecanoic acid for the purpose of determining appropriate action levels for short and long-term drinking water exposures. This project was sponsored by NSF International, and was conducted in accordance with ANSI/NSF Standard 60/61, Annex A. At NSF, 11-aminoundecanoic acid has been detected in laboratory extractions as a leachate from products containing Nylon-11, such as pipe appurtenances, fittings, pumps, and water meters used in municipal and residential water systems. The most critical evaluations in this risk assessment were made on results of acute, sub-chronic, and chronic oral administration bioassays on F344 rats and B6C3F1 mice. These evaluations were made in accordance with the criteria of the EPA’s Health Effects Testing Guidelines (1993). The kidney was both a short and long-term target organ, while the liver and urinary bladder were long-term target organs in the oral administration animal bioassays. 11-Aminoundecanoic acid was found to be carcinogenic in one sex and species following chronic oral administration of extremely high doses. The proposed USEPA Cancer Guidelines on Risk Assessment methods were used to assess the carcinogenic potential of the compound, and it was concluded that there is insufficient evidence to predict the carcinogenicity of this compound in humans. A search for metabolic information specific to this chemical provided inconclusive evidence of the anticipated metabolic pathway(s), therefore potentially sensitive subpopulations could not be clearly identified. Review of results from several in-vitro and in-vivo assays strongly suggests that this chemical is not a genotoxin. The proposed USEPA Cancer Guidelines on Risk Assessment, along with ANSI/NSF Standard 60/61, Annex A, were used to derive appropriate drinking water action levels. Anticipated human exposures to 11-aminoundecanoic acid were determined to be low, based on the nature of its use, low potential for transport in air, water, and soil, and low potential for bioaccumulation. Since the evidence of animal carcinogenicity was weak, and anticipated human exposures are several orders of magnitude lower than all doses tested, it was deemed appropriate to treat 11-aminoundecanoic acid as a non-carcinogen for purposes of calculating the drinking water action levels. Several dose-response models were examined to determine which was most appropriate for the data evaluations in this risk assessment. Use of the dichotomous data models in the EPA’s new Benchmark Dose Response Software (BMDS) were compared with the NOAEL/LOAEL approach for calculating a Reference Dose (RfD). Calculations for the long-term exposure action levels were based on the incidences of hyperplasia in the urinary bladder of the male F344/N rats in the chronic oral bioassay. The benchmark dose-response approach was preferred over the NOAEL/LOAEL approach because of the excellent fit of several of the BMDS models, and the fewer required uncertainty factors. Among the BMDS models, the Weibull was chosen as the preferred model, based on the resulting chi-square and p values.
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