Risk Assessment of Melamine for the Development of Drinking Water Action Levels Adequately Protective of Human Health. L. L. Bestervelt and A. D. Phelka, NSF International, Ann Arbor, MI
A human health risk assessment was conducted by NSF International to determine safe short-term and long-term exposure limits for melamine in drinking water in accordance with ANSI/NSF Standard 60/61, Annex A. Melamine has been detected in laboratory extractions as a leachate from faucets, pumps, and other water carrying devices (Standard 61), drinking water treatment units (Standard 42/53) and dinnerware (Standard 36) at concentrations frequently exceeding 1 ppm. NSF International has reviewed all of the published and unpublished scientific literature currently available on melamine, including information on sources of human and environmental exposure, comparative kinetics and metabolism, and effects on laboratory animals and in vitro test systems. 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 melamine suggests that the compound is an animal carcinogen and that there is insufficient evidence to determine the carcinogenic potential of melamine in humans. However, it is suggested that the observed melamine-induced carcinogenicity in the urinary bladders of male F344/N rats is a response secondary to irritative stimulation of calculi and not molecular interactions between melamine or melamine metabolites with the bladder epithelium. As there was a demonstrated statistically significant association between bladder stone formation and bladder tumors in male rats, NSF suggests that by limiting the exposure to melamine to levels below that which would induce key events, such as hyperplasia and stone formation, the incidence of tumor formation would not be of statistical significance. Therefore, NSF International has chosen to treat melamine as a non-carcinogen for purposes of calculating appropriate action levels in drinking water. Reference doses (RfD) were calculated from a 13-week study reporting the key events associated with the proposed mode of action using both the standard NOAEL/LOAEL approach, as well as the Benchmark Dose (BMD) methodology. As the fit of the BMD models was acceptable, the drinking water action levels were derived from the RfD calculated with the Benchmark Dose approach.
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