Development of Risk-Based Regulatory Levels Under Proposition 65. Sara Hoover, Louise Lee, Andrew Salmon, Page Painter, and Laura Zeise, Office of Environmental Health Hazard Assessment, CalEPA, Berkeley, CA 94704
The Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65) states that a responsible party cannot expose an individual to known carcinogens without prior warning or discharge these agents to sources of drinking water unless such exposures can be demonstrated to pose "no significant risk." This statutory language motivates the regulated community to support risk-based standard setting, because their potential liability is clarified by the adoption of such standards. In response to the need for guidance on how to comply with the law, the state of California has promulgated "No Significant Risk Levels" (NSRLs), defined as lifetime intake levels associated with estimated cancer risks of 1 in 100,000,. NSRLs are based on cancer potencies which have been derived by applying expedited methods, conventional risk assessment techniques, or in some cases, more complicated procedures. These methods will be discussed and compared, with a few interesting examples of cancer potency estimation highlighted. The regulatory history of standard-setting under Proposition 65 will be described, and expected future directions outlined.