EVALUATION OF THE CARCINOGENIC RISK OF BIOCHEMICALLY INERT INSOLUBLE PARTICLES BY THE EPA USING RAT INHALATION DATA

Abstract

Regulations pertaining to inhalable particulate matter are promulgated primarily by three program offices of the U.S. Environmental Protection Agency (EPA): Pollution Prevention and Toxic Substances (OPPTS), Air Quality Planning and Standards (OAQPS), and Mobile Sources (OMS). Risk assessment for these agents are carried out either by the program offices or by the National Center for Environmental Assessment (NCEA), formerly the Office of Health and Environmental Assessment (OHEA). Particular matter pollutants within the regulatory domain of OAQPS for which either quantitative or qualitative assessment of cancer risk has been carried out include asbestos, beryllium, cadmium, nickel refinery dust, nickel subsulfide, and ambient particulate matter of less than 10 µm diameter (PM10). OPPTS has qualitatively evaluated manmade mineral fibers, titanium dioxide, and vermiculite. Asbestos is the only fiber for which cancer quantitation has been carried out. For several of these agents, risk is based upon human data with animal studies providing supporting data. Both qualitative and quantitative assessment of cancer risk from exposure to diesel engine emissions is under development by NCEA for OMS. Quantitative assessment of cancer risk from exposure to this agent is described as an example of EPA's approach to the use of rats for evaluation of cancer risk. The major uncertainties relating to this assessment include the appropriateness of rat data for assessing human risk and the selection of a low-dose extrapolation model.