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 f or six chemicals in selected tissues from four species of fish. Log-tr ansformed values were then regressed in stepwise fashion against chemi cal log octanol/water partition coefficient (K-ow) and the log of tiss ue lipid content to derive a series of linear one- and two-variable mo dels. Equations derived for fat indicate that n-octanol is a good surr ogate for nonpolar lipid in the range of chemical log K-ow tested (1.4 6 < log K-ow < 4.04). These equations also support the conclusion that previously developed K-ow-bioconcentration factor relationships are l argely 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 constit uents contributes substantially to chemical accumulation. A general eq uation is presented for prediction of tissue/water and blood/water par titioning 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 f or kinetic modeling efforts.