It should be emphasized that some variables are capable of being 

 measured relatively precisely (e.g., contaminant concentrations in fish 

 tissue), whereas others may only be estimated on an order-of-mag- 

 nitude basis (e^., Carcinogenic Potency Factor). The precision and 

 accuracy of the final risk estimates are directly related to the precision 

 and accuracy of the variables incorporated into the equations used to 

 calculate exposure and risk. 



Quantitative uncertainty analyses such as sensitivity analysis are easily 

 performed with a spreadsheet by calculating exposure estimates for 

 low, mid, and high values of key variables within their respective 

 plausible ranges. Specification of probability distributions for key 

 variables is an alternative method of uncertainty analysis requiring 

 graphical models (see below, Uncertainty Analysis). In the example 

 shown in Table 6, the average, minimum, and maximum concentrations 

 of each contaminant [PCBs and mercury (Hg)] are used to estimate 

 potential health risk, thereby accounting for uncertainty in chemical 

 analyses. Also, risks are estimated for two consumption rate estimates 

 (6.5g/day and 20 g/day). Note that spreadsheet summaries of quantita- 

 tive information should be supported by a text discussion of qualitative 

 uncertainties such as the weight of evidence for the health effect of 

 concern. 



Presentation of risk assessment results in graphic form may include: 



• Plots of estimated risk vs. consumption rate 



• Plots of estimated risk vs. contaminant concentration in edible 

 tissue of fish or shellfish 



• Summary maps of risk estimates for different geographic loca- 

 tions or individual sampling stations 



• Histograms of estimated risk by fishery species, human sub- 

 population, or geographic location. 



Because estimated risk for a given area and fishery species varies with 

 consumption rate and because consumption rates vary greatly among 

 individual humans, the first approach above is recommended as a 

 primary means of presenting risk assessment results. Actual consump- 

 tion patterns of the exposed population may or may not be estimated 

 (see above. Exposure Assessment). If they are, estimates of average 

 consumption rate (and 95 percent confidence limits) can be identified 

 in a footnote (e.g., Figure 7). Uncertainty in chemical measurements 

 can be illustrated by plotting lines corresponding to the minimum and 

 maximum (or 95 percent confidence limit) values of contaminant 

 concentrations in fishery species, as well as the mean concentration 

 (e.g., each solid Hne in Figure 7). As an interpretive aid, risk assessment 

 results for a reference area can be presented along with those for the 

 study area. 



Other approaches noted above can be used to supplement plots of risk 

 vs. consumption. Summary maps and histograms may be especially 

 useful for presentation of detailed results of spatial analyses by human 

 subpopulation or by fishery species. Plots of risk vs. contaminant 



Summary Graphics 



69 



