Risk Characterization

Arguably the most important step in the risk assessment process, risk characterization involves the integration of dose–response and exposure data, as well as information to characterize the likelihood and severity of any health risks. Risk characterizations are used to inform risk managers and decision-makers. They should therefore be as accurate and thorough as possible. Over the last two decades, there has been a growing demand for more transparent and fit-for-purpose risk assessments that also incorporate advances in science and technology. Traditional default assumptions have also been re-evaluated. At a minimum, risk characterizations should present what is known (and unknown) about the toxicity of each chemical or mixture. They should describe the key parameters used in the exposure assessment along with a discussion of data, models, and statistical uncertainties. In this chapter, we provide an overview of the historical risk characterization process as practiced by regulatory agencies in the United States and some other countries and describe many new and emerging risk assessment approaches. The evolving nature of risk assessments suggests that future efforts to characterize human health risks will be held to a much higher standard than in the past. By providing explicit criteria and examples for conducting risk characterizations, we anticipate that their quality will continue to improve over time.