Modeling the bioconcentration of organic compounds by fish: A novel approach

Bioconcentration is generally assumed to be similar to the partitioning of compounds between an aqueous and lipoid phase. In the case of bioconcentrat ion lipoid phase is thought to consist of the lipid and lipoid tissues of a n organism, e.g. a fish. However, it is frequently observed that for highly lipophilic compounds, defined as compounds with a high octanol-water parti tion coefficient, or log K-ow, that simple view seems to break down. At low and intermediate log K-ow there seems to he a linear relationship between bioconcentration, expressed as log BCF, and log K-ow. At high log K-ow devi ations are seen, generally indicating that for these compounds BCF increase s less than proportionally with increasing log K-ow. Many different explana tions and accompanying correlation models have been proposed to date. We pr esent here a model that is capable of explaining the different shapes of th e BCF/K-ow relationships empirically observed, based on the effect of the p resence of tiny amounts of different types of organic material in the aqueo us phase. The actual shape of the nonlinear curve simply depends on the amo unt of organic material in the water, the difference in "affinity" for hydr ophobic compounds of the organic material in water and lipid in fish, and t o a lesser extent the amount of lipid in fish. The model presented also fit s a large dataset of experimental BCF values with fitted parameter values t hat are consistent with the biology and physical chemistry of the described system.