Whole-fish versus filet polychlorinated-biphenyl concentrations: An analysis using classification and regression tree models

Fish polychlorinated-biphenyl (PCB) measurements usually represent one of t wo different sample types: filers or homogenized whole fish. Filet measurem ents are more appropriate for use if the goal of analysis is estimating hum an PCB consumption, while whole-fish analysis may be more useful for quanti fying and understanding processes of contaminant flow and bioaccumulation. While it is generally assumed that whole-fish PCB concentrations exceed fil er concentrations because of the presence of fatty internal organs in whole -fish samples, the literature contains no reported comparisons of filet ver sus whole-fish PCB concentrations. We measured total PCB concentrations in filers and whole-fish samples from the same individuals in Lake Michigan co ho salmon (Oncorhynchus kisutch) and rainbow trout (Oncorhynchus mykiss). T he average whole-fish to filer PCB concentration ratio was 1.70 for coho sa lmon and 1.47 for rainbow trout, but it varied considerably among individua ls, with a few fish exhibiting a higher concentration in the filet than in the whole-fish sample. Classification and regression tree (CART) models ind icated that filer PCB concentration and fish length were the best predictor s of whole-fish PCB concentration, whereas filet and whole-fish lipid conce ntrations where less important predictors. Lipid normalization of the PCB d ata decreased within-individual variability, was equivocal with respect to variability among individuals, and accentuated the between-species differen ce. Both species exhibit a pronounced 1:1 relationship between the whole fi sh to filer PCB concentration ratio and the whole-fish to filer lipid conce ntration ratio; however, we point out that there is a strong spurious compo nent to this relationship, which indicates that the relationship may be mor e algebraic rather than an indication of underlying mechanisms.