of their water. Questions have been raised about the validity of the science on which the MCLG is based and whether that level is appropriate. Some believe that the level might be unnecessarily low, and others believe that some individuals might have adverse health effects with copper levels at or below the current MCLG.

THE CHARGE TO THE COMMITTEE

At the direction of Congress, EPA asked the National Research Council (NRC) to review independently the scientific and technical basis for EPA's MCLG of 1.3 mg/L for copper in drinking water. For the review, the NRC convened the Committee on Copper in Drinking Water, whose members have expertise in the fields of toxicology, epidemiology, pathology, pharmacology, genetics, physiology, medicine, public health, exposure assessment, nutrition, chemistry, biostatistics, and risk assessment. The committee reviewed available toxicological, epidemiological, and exposure data (from food and water) and determined the appropriateness of the critical study used for deriving the MCLG, end points of toxicity, and uncertainty factors used by EPA in the derivation of the MCLG for copper. The committee was also asked to identify data gaps and make recommendations for future research. The committee was not asked to address risk-management issues.

THE COMMITTEE'S APPROACH TO ITS CHARGE

The committee evaluated data relating to key elements of the risk-assessment process that led to the current MCLG. The key elements are hazard identification, dose response, exposure assessment, and risk characterization. The current MCLG is based on gastrointestinal effects following acute exposure to copper. However, effects on the liver have been observed with chronic exposure in sensitive populations. Therefore, in this report, the committee reviewed information on the health effects of copper exposure in humans following both acute and chronic oral exposure. The committee also evaluated data on the mechanisms of action of copper toxicity, the health effects associated with copper deficiencies, and factors affecting the bioavailability of copper—all data that could affect the risk assessment. The toxicity of copper was used as the basis for evaluating the safety of copper concentrations in drinking water, but the essential need for copper as a micronutrient (i.e., the dietary essentiality of copper) was taken into account when considering uncertainty factors.

To provide background information on relevant issues in copper toxicity,



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