Evaluation of log K(OW) and tissue lipid content as predictors of chemical partitioning to fish tissues

In vitro equilibrium chemical partition coefficients were determined for six chemicals in selected tissues from four species of fish. Log-transformed values were then regressed in stepwise fashion against chemical log octanol/water partition coefficient (K(OW)) and the log of tissue lipid content to derive a series of linear one- and two-variable models. Equations derived for fat indicate that n-octanol is a good surrogate for nonpolar lipid in the range of chemical log K(OW) tested (1.46 < log K(OW) < 4.04). These equations also support the conclusion that previously developed K(OW- bioconcentration factor relationships are largely a reflection of chemical accumulation in fat. Fitted slope and intercept terms for 'lean' tissues differed from those expected from chemical partitioning to lipid only and were instead consistent with the suggestion that partitioning to nonlipid- nonwater cellular constituents contributes substantially to chemical accumulation. A general equation is presented for prediction of tissue/water and blood/water partitioning from chemical log K(OW) and tissue (or blood) lipid content. It is suggested, however, that tissue- and blood-specific equations be used to estimate the tissue/blood partitioning relationships needed for kinetic modeling efforts.