Influence of solubility in lipid on bioconcentration of hydrophobic compounds

Superhydrophobic compounds (log K(ow) greater than 6) do not bioconcentrate as much as predicted from the extrapolation of linear relationships between the logarithms of the bioconcentration factor (KB) and the octan-1-ol/water partition coefficient (K(ow)) developed for compounds with log K(ow) from 2 to 6. Statistical analysis of the literature data on solubility in lipid for 79 hydrophobic compounds demonstrated a decrease in lipid solubility with increasing K(ow) values for superhydrophobic compounds. A similar, but more significant, relationship was obtained for the chlorinated hydrocarbons which closely corresponded with effectively the same relationship derived from fish bioconcentration data. As a result it is suggested that an important factor contributing to the lower than expected bioconcentration exhibited by superhydrophobic compounds is their relatively low solubility in lipid not reflected by the K(ow) value. It is suggested that lipid/water partition coefficients would provide more accurate descriptors of the bioconcentration process.