PRINCIPLES OF TOXICOLOGY - Biology East Borneo

438 RISK ASSESSMENT18.1 RISK ASSESSMENT BASICSA Basic Risk Assessment ParadigmIn 1983, the National Research Council described risk assessment as a four-step analytical processconsisting of hazard identification, dose-response assessment, exposure assessment, and risk characterization.These fundamental steps have achieved a measure of universal acceptance and provide alogical framework to assemble information on the situation of potential concern and provide riskinformation to inform decision making (see Figure 18.1). The process is rigid enough to provide somemethodological consistency that promotes the reliability, utility, and credibility of risk assessmentoutcomes, while at the same time allowing for flexibility and judgment by the risk assessor to addressan endless variety of risk scenarios. Each step in the four-step process known as risk assessment isbriefly discussed below.Step 1: Hazard Identification. The process of determining whether exposure to a chemical agent,under any exposure condition, can cause an increase in the incidence or severity of an adverse healtheffect (cancer, birth defect, neurotoxicity, etc.). Although the matter of whether a chemical can, underany exposure condition, cause cancer or other adverse health effect is theoretically a yes/no question,there are few chemicals for which the human data are definitive. Therefore, not only epidemiologicalstudies but also laboratory animal studies, in vitro tests, and structural and mechanistic comparabilityto other known chemical hazards are considered. This step is common to qualitative and quantitativerisk assessment.Step 2: Dose–Response Assessment. The process of characterizing the relationship between thedose of a chemical and the incidence or severity of an adverse health effect in the exposed population.A dose–response assessment factors in not only the magnitude, duration, and frequency of exposurebut also other potential response-modifying variables such as age, sex, and certain lifestyle factors.A dose–response assessment frequently requires extrapolation from high to low doses and fromanimals to humans.Figure 18.1 Elements of risk assessment and risk management. Risk assessment provides a means to organizeand interpret research data in order to inform decisions regarding human and environmental health. Through therisk assessment process, important data gaps and research needs are often identified, assisting in the prioritizationof basic and applied toxicological research. [Adapted from NRC (1983).]