Risk Characterization 



In the risk characterization stage, results of the hazard, exposure and 

 the dose-response assessments are combined to estimate the prob- 

 ability and extent of adverse effects associated with consumption of 

 contaminated fish or shellfish. An overview of the risk characterization 

 process is shown in Figure 6. In human health risk assessment, car- 

 cinogens and noncarcinogens are treated separately. Indices of risk for 

 these different categories of toxicants are based on different dose- 

 response models (see above, Dose-Response Assessment). 



The procedures for generating quantitative estimates of risk are em- 

 phasized in the following sections. However, it is critical that numerical 

 estimates of risk not be presented in isolation from the assumptions 

 and uncertainties inherent in the process of risk assessment. The risk 

 characterization should include a discussion of assumptions and un- 

 certainties and their potential impact on numerical estimates of risk; 

 i.e., the degree to which the numerical estimates are likely to refiect 

 the actual magnitude of risk to humans. For example, if upper con- 

 fidence limits for mean chemical concentrations are used to develop 

 risk estimates, the effects of compounding assumptions of upper- 

 bound estimates of carcinogenic potency and conservatively high es- 

 timates of consumption rate should be evaluated. A risk 

 characterization should mclude a summary of the preceding steps of 

 the risk assessment: hazard assessment, dose-response assessment, 

 and exposure assessment. The weight-of-evidence classification and 

 other supporting information should be summarized concisely. Ap- 

 proaches to presentation of summary information to be included in risk 

 characterization are presented in the next chapter (see below. Presen- 

 tation and Interpretation of Results). 



Numerical estimates of carcinogenic risk can be presented in one or 

 more of the following ways (U.S. EPA 1986a): 



• Unit risk: The excess lifetime risk corresponding to a con- 

 tinuous constant lifetime exposiue to a unit carcinogen con- 



Carcinogenic Risk 



63 



