Need for Risk Assessment 

 Approach 



• Exposure assessment: Characterization of the populations ex- 

 posed to the toxic chemicals of concern; the environmental 

 transport and fate pathways; and the magnitude, frequency, 

 and duration of exposure 



• Risk characterization: Integration of qualitative and quantita- 

 tive information from the first three steps, leading to an es- 

 timate of risk for the health effect of concern. 



Because uncertainties are pervasive in risk assessment, uncertainty 

 analysis is a key element of each stage of the assessment process. 

 Assumptions and uncertainties are summarized in the risk charac- 

 terization step. The risk characterization includes a balanced discus- 

 sion of the strengths and weaknesses of the data presented. 



Direct measurement of human health risks is possible in certain limited 

 circumstances. Such circumstances generally involve a single high 

 exposure or repeated moderate exposures of humans to a specific 

 chemical with a clear adverse effect. For example, direct measurement 

 of the incidence of chloracne (a skin disorder) might be possible in a 

 population of workers exposed to a PCB spill. In contrast, it is virtually 

 impossible to directly measure the incidence of cancer associated with 

 consumption of chemically contaminated fish or shellfish. The long 

 latency period for cancer, the potential for contamination of fisheries 

 by multiple chemicals, and confounding exposures through other 

 routes would complicate the interpretation of such data. Mathematical 

 models are therefore used by EPA, FDA, the Agency for Toxic Sub- 

 stances and Disease Registry, states, and other regulatory agencies to 

 estimate human health risks from exposure information. Risk assess- 

 ment procedures discussed in this manual focus on estimating potential 

 health risks from long-term exposure to relatively low levels of 

 contamination. This prospective approach is also useful for developing 

 regulations to limit exposure to toxic chemicals and reduce associated 

 risks. 



Scientific knowledge of the effects of toxic chemicals on humans is still 

 rudimentary. Much of the present information is extrapolated from 

 results of laboratory tests on animals (e.g., rats and mice). For example, 

 animal test data may be used to estimate levels of chemical exposure 

 that are unlikely to cause toxic effects in human populations. 

 Toxicologists are faced with many uncertainties when estimating the 

 potential for human health risks associated with intake of toxic chemi- 

 cals. Despite these uncertainties, regulatory decisions must be made. 

 Many assumptions and subjective judgments may enter into an evalua- 

 tion of human health risk. The risk assessment approach provides a 

 framework for consistent, systematic estimation of health risks, with 

 clear statements of assumptions and uncertainties. 



The risk assessment framework offers an alternative to some common 

 approaches to evaluation of data on chemical residues in fish and 

 shellfish. As noted by Kneip (1983) and Peddicord (1984), many 

 investigators have evaluated chemical residue data in light of human 

 health concerns simply by comparing tissue concentrations of selected 



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