Noncarcinogenic Effects 



II 



centration (e.g., 1 mg/kg carcinogen in edible tissue of fish or 

 shellfish) 



• Dose or concentration corresponding to a specified level of 

 risk: For example, a guideline for maximum allowable con- 

 tamination of a specified medium may be derived from a 

 maximum allowable rislc value established by risk managers 



• Individual and population risks: Upper-limit estimates of 

 excess lifetime cancer risk may be expressed for individuals (as 

 a probability estimate) or for the exposed population (as an 

 estimate of the number of cancers produced within a popula- 

 tion of specified size per generation). 



Regardless of the option chosen for expressing risk, final numerical 

 estimates should be presented as one significant digit only, followed by 

 the EPA classification of the weight of evidence for carcinogenicity in 

 brackets (U.S. EPA 1986a). 



The general model for estimating a plausible upper limit to excess 

 lifetime risk of cancer at low doses for a single-species diet is: 



where: 



R ijkm — qi m Eijkm 



(9) 



R ijkm = Plausible-upper-limit risk of cancer associated with 



chemical m in fishery species i for human subpopulation 

 j in area k (dimensionless) 



qi*m = Carcinogenic Potency Factor for chemical m [(mg kg' 

 day" )' ] estimated as the upper 95 percent confidence 

 limit of the slope of a linear dose-response curve 



Eijkm = Exposure dose of chemical m from species i for sub- 

 population j in area k (mg kg" day" ). 



The actual risk is likely to be below the estimated upper-limit value 

 calculated from Equation 9, and may be zero in some instances. 

 Equation 9 corresponds to Equation 2 above, except that an estimate 

 of human exposure (Eijkm) has replaced the dose (d), which is usually 

 a known quantity administered to a bioassay animal. All Eijkm are 

 calculated as discussed above (see Exposure Dose Determination in 

 Exposure Assessment). When local consumption rate data are unavail- 

 able, a range of Eijkm and corresponding risk estimates may be calcu- 

 lated based on a range of assumed consumption values. Estimates of 

 qi*m are available in IRIS. Note that Equation 9 is only valid for 

 estimated risks below 10" . 



Estimation of upper-limit risk associated with the average mixed- 

 species diet follows a similar approach, except that the average effec- 

 tive dose (Ejkm) of chemical m from a mixed-species diet, calculated 

 from Equation 8 above, replaces the species-specific exposure (Eijkm) 

 in Equation 9. Calculation of the average effective dose was discussed 

 earlier (see Exposure Assessment, Exposure Dose Determination). 



Noncarcinogenic risk may be evaluated by calculating the ratio of the 

 estimated chemical intake to the RfD as follows: 



64 



