Consistencies and Inconsistencies between Cal/EPA and US EPA Toxicity Values. D. Ting, T. McDonald, R. Becker, and L. Zeise, Cal/EPA Office of Environmental Health Hazard Assessment, 2151 Berkeley Way, Annex 11, Berkeley, CA 94704
Achieving consistency and harmonization in risk assessments done by State and Federal organizations while maintaining good scientific practice is a goal for evaluations done in the State of California. It has become increasing apparent that the use of divergent risk assessment methodologies for the same chemical or comparable situation by different organizations can create difficulties for managers and policy-makers inside government, and for parties interested in or otherwise affected by the assessment. We describe the extent to which toxicity values generated by the California Environmental Protection Agency (Cal/EPA) are consistent with those of the US Environmental Protection Agency (US EPA), and discuss reasons for the differences. Comparisons include cancer potency or unit risk values developed by the Cal/EPA and those listed in US EPA’s Integrated Risk Information System (IRIS). We discuss the basis for differences in toxicity values for chemicals for which relatively large differences are observed, as well as for those that are drivers for site-specific risk assessments. Some differences are due to: 1) time of derivation, typically with the more recent values reflecting the availability of more appropriate data or improved methods; 2) selection of different studies; and 3) different interpretations of the same study. The degree to which chemicals of interest are addressed by the two agencies is also discussed.