In the next step of the exposure analysis, information on estimated 

 contaminant concentrations and rate of consumption of fish and 

 shellfish are combined to estimate chemical intake by exposed humans. 

 Analyses of single-species diets and mixed-species diets are discussed 

 separately in the following sections. 



The general model to calculate chemical intake for a single-species 

 diet is: 



£ijkm — 



_ Cikm^iik^m 



(6) 



W 



where: 

 Eijkm 



Cilun 



lijk 



w 



Effective ingested dose of chemical ni from fishery 

 species i for human subpopulation j in area k (mg 

 kg' day" averaged over a 70-year lifetime) 



Concentration of chemical m in edible portion of 

 species i in area k (mg/kg) 



Mean daily consumption rate of species i by subpop- 

 ulation j in area k (kg/day averaged over 70-year 

 lifetime) 



Relative absorption coefficient, or the ratio of hu- 

 man absorption efficiency to test-animal absorption 

 efficiency for chemical m (dimensionless) 



Average human weight (kg). 



Values of subscripted terms above may be estimated means or uncer- 

 tainty interval bounds (e.g., 95 percent confidence intervals) depend- 

 ing on the exposure scenario being modeled (e.g., worst case vs. 

 average case vs. lower-limit case). Note that Eijkm is analogous to the 

 dose "d" in Equations 1 and 2. The term "effective" ingested dose 

 (Eijkm) is introduced to emphasize that estimates of chemical intake 

 (i.e., ingested dose) may be modified by the term Xm to account for 

 differential absorption of contaminants by humans and bioassay 

 animals. 



Absorption coefficients (Xm) are assumed equal to 1.0 unless data for 

 absorbed dose in animal bioassays used to determine toxicological 

 indices (carcinogenic potency or RfD) are available and the human 

 absorption coefficient differs from that of the animal used in the 

 bioassay. Assuming that Xm is equal to 1.0 is equivalent to assuming 

 that the human absorption efficiency is equal to that of the animal used 

 in the bioassay. In the absence of data to the contrary, this is ap- 

 propriate. Toxicological indices are determined from bioassays that 

 usually measure administered (ingested) dose. Therefore, the es- 

 timated chemical intake by humans, Eijkm, is usually the ingested dose, 

 not the absorbed dose. If the toxicological index used to estimate risk 

 is based on the absorbed dose, then an estimate of human absorption 

 efficiency for the chemical of concern may take the place of the term 

 Xm in Equation 6 above. In most cases, however, information or 



Exposure Dose 

 Determination 



Single-Species Diets 



59 



