per day, a concentration of 2.65 mg/L was determined to be the minimal dose at which symptoms could occur. That value was ''divided by a safety factor of 2 in recognition of its essentiality" to yield the copper MCLG of 1.3 mg/L (Donohue 1997).

Several U.S. states (such as Nebraska and Delaware) have measured copper concentrations in drinking water that exceed the MCLG for copper because of the leaching of copper from plumbing. On the basis of recent data from epidemiological studies which show no adverse effects at higher levels, questions have been raised about the validity of the science on which the MCLG is based, and whether that level is appropriate. While some have argued that the level might be too conservative, others have argued that some individuals might experience adverse effects with copper levels at or below the current MCLG (Sidhu et al. 1995). A provisional drinking-water guideline of 2 mg/L was proposed for copper by the World Health Organization (WHO 1993). The basis for that value is not clear; however, an interpretation of the derivation is provided by Galal-Gorchev and Herrman (1996). The drinking-water guideline appears to originate from the provisional maximum tolerable daily intake (PMTDI) value established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). On the basis of the lack of adverse effects or copper accumulation in normal individuals with typical dietary copper intakes and the "considerable margin" between normal intakes and those with adverse effects, JECFA established a PMTDI of 0.05 mg of copper per kilogram (kg) of body weight per day (WHO 1967). Subsequent re-evaluation of that intake dose did not provide any basis for JECFA to change the recommendation. When determining the provisional guidelines for copper in drinking water, WHO assumed that a 60-kg adult would drink 2 L of water per day and that 10% of the PMTDI would come from drinking water. WHO then established the provisional drinking-water guideline of 1.5 mg/L (WHO 1991), which was later rounded to 2 mg/L (WHO 1993). Several states have also recommended exposure limits different from those proposed by EPA (summarized by the ATSDR) (ATSDR 1990). Olivares and Uauy (1996) and Fitzgerald (1998) discuss the drinking water standards for copper established by different agencies and governments.

In response to concern regarding the scientific validity of EPA's MCLG, the U.S. Congress requested that the administrator of EPA enter into a contract with the NRC to conduct a comprehensive study of the effects of copper in drinking water on human health. In response to that request, the NRC convened the Committee on Copper in Drinking Water. The committee's expertise is in the fields of toxicology, epidemiology, pathology, pharmacology, genetics, physiology, medicine, public health, exposure assessment, nutrition, chemistry, biostatistics, and risk assessment. The committee was charged to review independently the appropriateness of the

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