Risk Assessment Issues Associated with Cleaning up Inactive Hazardous Waste Sites

Abstract

The broad practice of using risk assessment approaches for the evaluation of suspected human carcinogens is about 12 years old. The primary departure point was the announcement by the U.S. Environmental Protection Agency (EPA) that adopted guidelines for assessing the risk of carcinogens and a policy to regulate suspect carcinogens based essentially on a risk management approach. The scientific basis was derived from the earlier experience of assessing the risk of health impacts from radiation exposure. From a practical standpoint, the use of risk assessment for carcinogens has received broad and general endorsement. The early use of risk assessment of carcinogens relied heavily on replacing the uncertainties in the risk assessment process with very conservative assumptions to ensure that the risk would in no case be underestimated. As the practice of risk assessment has become widespread, considerable attention has been focused on improving the scientific basis for evaluating each step of the risk assessment process: the weight-of-evidence indicating likely carcinogenicity, the dose-response relationships, and the environmental exposures. Chemicals that are thought to cause health or ecological effects through threshold mechanisms are also being evaluated by risk assessment approaches. More attention has been focused on the scientific relationships that underlie the characterization of suspect carcinogens and their dose-response relationships, including extrapolation from animals to humans and from high dose to low dose; far less attention has been focused on the exposure assessment, which can impact the outcome of the quantitative risk assessment by certainly as much as the assumptions in the dose-response extrapolation part of risk assessment.