Methods to Develop Inhalation Cancer Risk Estimates for Chromium and Nickel Compounds

摘要

The purpose of this paper is to discuss the methods used to develop inhalation cancer risk estimates associated with emissions of chromium and nickel compounds from coal- and oil-fired electric utility steam generating units (EGUs) in support of EPA's recently proposed Air Toxics Rule. The derivation of cancer risk estimates is based on the speciation data available from selected source types, and on the available unit risk estimates (UREs) reflecting the dose that corresponds to a specific level of cancer risk. This document includes discussions for both emissions of chromium (Section 2) and nickel (Section 3) compounds with regard to: (1) the methods and rationale used in previous analyses (where applicable), (2) the methods used in the recent analysis for the Air Toxics Rule (considering previous methods and currently available data), and (3) a discussion of the uncertainties and/or limitations of the methods used. In this document, we consider the emissions of chromium compounds from both coal- and oil-fired EGUs and the emissions of nickel compounds from oil-fired EGUs, since these are major contributors to inhalation cancer risk estimates from each these source types.