Whole-fish versus filet polychlorinated-biphenyl concentrations: An analysis using classification and regression tree models
James F. Amrhein, Craig A. Stow, Clay Wible · Environmental Toxicology and Chemistry · 1999
Abstract Fish polychlorinated-biphenyl (PCB) measurements usually represent one of two different sample types: filets or homogenized whole fish. Filet measurements are more appropriate for use if the goal of analysis is estimating human PCB consumption, while whole-fish analysis may be more useful for quantifying and understanding processes of contaminant flow and bioaccumulation. While it is generally assumed that whole-fish PCB concentrations exceed filet concentrations because of the presence of fatty internal organs in whole-fish samples, the literature contains no reported comparisons of filet versus whole-fish PCB concentrations. We measured total PCB concentrations in filets and whole-fish samples from the same individuals in Lake Michigan coho salmon (Oncorhynchus kisutch) and rainbow trout (Oncorhynchus mykiss). The average whole-fish to filet PCB concentration ratio was 1.70 for coho salmon and 1.47 for rainbow trout, but it varied considerably among individuals, with a few fish exhibiting a higher concentration in the filet than in the whole-fish sample. Classification and regression tree (CART) models indicated that filet PCB concentration and fish length were the best predictors of whole-fish PCB concentration, whereas filet and whole-fish lipid concentrations where less important predictors. Lipid normalization of the PCB data decreased within-individual variability, was equivocal with respect to variability among individuals, and accentuated the between-species difference. Both species exhibit a pronounced 1:1 relationship between the whole-fish to filet PCB concentration ratio and the whole-fish to filet lipid concentration ratio; however, we point out that there is a strong spurious component to this relationship, which indicates that the relationship may be more algebraic rather than an indication of underlying mechanisms.