ABSTRACT
Health risk assessment is the process wherein toxicology data from animal studies and human epidemiology are evaluated, a mathematical formula is applied to predict the response at low doses, and then information about the degree of exposure is used to predict quantitatively the likelihood that a particular adverse response will be seen in a speci•c human population.1-3 More simply, risk assessment is a process by which scientists evaluate the potential for adverse health effects from exposure to naturally occurring or synthetic agents.4 Regulatory agencies have used the risk assessment process for nearly 50 years, most notably the U.S. Food and Drug Administration (USFDA).5 However, the difference between assessments performed in the 1950s and 1960s and those performed in the 1980s and 1990s and even more currently is that dose-extrapolation models, quantitative exposure assessments, and quantitative descriptions of uncertainty have been added to the process.6 Because of increased ability to measure and predict exposures and better quantitative methods for estimating the low-dose response (such as physiologically based pharmacokinetic [PBPK] models), risk assessments conducted today provide more accurate risk estimates than in the past.3,7,8
Since 1980, most environmental regulations and some occupational health standards have, at least in part, been based on health risk assessments.3,9,10 They include standards for pesticide residues in crops, drinking water, ambient air, and food additives, as well as exposure limits for contaminants found in
indoor air, consumer products, and other media. Risk managers increasingly rely on risk assessment to decide whether a broad array of risks are signi•cant or trivial-an important task since, for example, more than 400 of the about 2000 chemicals routinely used in industry have been labeled carcinogens in various animal studies.11-13 In theory, the results of risk assessments in the United States should in¦uence virtually all regulatory decisions involving so-called toxic agents.14-16
The risk assessment process has four parts: hazard identi-•cation, dose-response assessment, exposure assessment, and risk characterization.11 Although progress has been made over the past 20+ years in how to conduct and interpret toxicology and epidemiology studies (e.g., hazard identi•cation), and scientists believe that they are doing a better job of doseresponse extrapolation than in the past, most signi•cant advances in the risk assessment process have occurred in the •eld of exposure assessment.17-19
Since about 1995, an increasing number of environmental scientists have embraced the view that “toxicology data are important, but they do not mean much without quantitative information about human exposure.”20 For this reason, the toxicology community has shown increasing interest in understanding the exposure assessment •eld.21,22 Fortunately, a signi•cant amount of research has been conducted to identify better values for many exposure parameters, and major improvements have been made in applying these exposure factors to various scenarios. This chapter is intended to familiarize toxicologists, risk assessors, and others with this evolving •eld.
