eventually becomes negligible (e.g., at greater than 10 individuals per 

 composite at typical levels of data variability). For moderate levels of 

 variability in chemical residue data, 6 to 10 individual samples within 

 each of 5 replicate composite samples should be adequate to detect a 

 treatment difference equal to 100 percent of the overall mean among 

 treatments. Rohde (1976), Schaeffer et al. (1980), Brumelle et al. 

 (1984), and Gilbert (1987) also discuss statistical aspects of composite 

 sampling. 



Sample Preparation— Tissue samples should be removed from target 

 organisms and prepared for analysis according to a well-defmed 

 protocol. Tissue preparation methods can greatly affect the results of 

 bioaccumulation analyses (Smith et al. 1973; Skea et al. 1981; Puffer 

 and Gossett 1983; Landolt et al. 1987). In specifying a tissue prepara- 

 tion protocol, the following issues should be addressed: 



• Type of tissue (e.g., muscle fillet, whole body, internal organs) 



• Location of tissue in organisms' body 



• Removal of any or all of shells, scales, skin, and subcutaneous 

 fat 



• Raw vs. cooked samples and cooking method 



• Homogenization method 



• Minimum sample mass for each kind of analysis. 



The kind and location of tissue analyzed may influence the realism of 

 the exposure assessment. For example, most humans consume only 

 fillets of fish, not internal organs or whole fish. Because internal organs 

 are often more contaminated by toxic chemicals than are fillets, ex- 

 posure estimates based on chemical analyses of organs or whole fish 

 could be unrealistically high. Removal of skin and subcutaneous fat 

 from samples before chemical analysis generally reduces the mean 

 concentrations of chlorinated organic compounds. In species with a 

 subcutaneous fat layer, this practice may also reduce the variability of 

 replicate data, allowing more sensitive discrimination among statistical 

 treatments (e.g., species or sampling locations). Within the fillet tissue, 

 contaminant concentrations may vary depending on the original loca- 

 tion of the sample on the fish's body. 



The effect of cooking on the ultimate health risk from a mixture of 

 chemicals (including any transformation or degradation products 

 produced by heating) is unknown. Some studies have shown decreases 

 in concentrations of lipid-soluble organic compounds such as DDT 

 and PCBs following pan-frying, broiling, or baking offish fillets (Smith 

 et al. 1973; Skea et al. 1981; Puffer and Gossett 1983). For example, 

 cooking of fillets before chemical analysis may result in a 2 to 65 percent 

 decrease in the concentration of PCBs relative to the uncooked sample, 

 but the results vary greatly with species and cooking method. However, 

 cooking may also activate or transform chemicals to create carcinogens 

 [e.g., formation of benzo(a)pyrene during charbroiling]. Regardless of 

 method of tissue preparation, an adequate mass of each sample and 

 adequate homogenization of samples before they are analyzed are 

 necessary to obtain representative results (e.g., see Tetra Tech 1986e). 



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