Arsenic.

The toxicity and carcinogenicity of arsenic are well known, but vexing questions remain. The current controversy over the appropriate Federal limit for arsenic in drinking water highlights some of the difficult scientific, ethical, economic, and political issues that complicate standard-setting in occupational and environmental health. These include limitations in the scientific evidence concerning the risk at low doses, uncertainty about the appropriate mathematical models for estimating the risk at low-level exposures based on data from higher-level exposures, and controversies concerning the appropriate safety margin, level of evidence required for standard-setting, and costs of remediation.