Mixed-Species Diets 



assumptions about absorption efficiencies has been incorporated into 

 EPA's estimates of RfDs and Carcinogenic Potency Factors. There- 

 fore, Xm is usually dropped from Equation 6 and Eijkm becomes simply 

 the ingested dose. 



W is usually assumed to be 70 kg for the "reference man" (U.S. EPA 

 1980b). Assuming other average values to account for growth from a 

 child's body weight to adult weight over a lifetime would not change 

 the results of carcinogen risk assessment substantially. Concerns about 

 exposures over a time period of less than about 15 years may require 

 modehng of early childhood exposures. Standard values for age- 

 specific body weight and other factors used in exposure assessment are 

 provided by Anderson et al. (1985). 



Estimation of chemical exposure due to a mixed-species diet is com- 

 plicated by variation in the dietary habits of individuals. The various 

 diets of individual humans may differ from one another in the kinds 

 and relative proportions of fishery species consumed. The sum of 

 species-specific exposures (Eijkm) is not equivalent to total exposure 

 for a mixed-species diet. In a diverse fishery, each individual consumer 

 is likely to consume only a subset of the total available species. Thus, 

 the sum of species-specific exposures might overestimate the average 

 consumption rate for mixed-species diets. 



To estimate average chemical exposure resulting from a mixed-species 

 diet, an exposure dose should first be estimated for each individual in 

 a subpopulation as follows: 



£hjkm = 2 



w 



(7) 



where: 



Ehjkm = Effective exposure dose of chemical m from a mixed- 

 species diet eaten by individual human h in subpopulation j in 

 area k (mg kg" day" averaged over a 70-year lifetime) 



Ihijk = Average consumption rate of species i by individual h in 

 subpopulation j in area k (kg/day averaged over a 70-year lifetime) 



and other terms are defined as above. The average exposure dose for 

 mixed species diets is: 



ijkm = 



E £hjkn 

 h 



(8) 



//jk 



where: 



Ejkm = Average effective exposure dose of chemical m from 



1 j_..-l\ 



mixed-species diet for subpopulation j in area k (mg kg' day' ) 

 Hjk = Number of persons in subpopulation] in area k. 



Uncertainty estimates can be obtained by calculating 95 percent con- 

 fidence limits for Ejkm- 



60 



