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A model is presented for the bioconcentration in fish of nonpolar hydrophobic chemicals that are not metabolized. The model assumes that diffusion rates through membrane‐diffusion layer barriers influence uptake and depuration kinetics in fish. For extremely hydrophobic (log Kd, oct > 3 to 4) chemicals, uptake rate constants in fish are independent of the solute's hydrophobicity, whereas for low to moderately hydrophobic chemicals proportionality between these parameters is observed. Additionally, elimination rate constants for low to moderately hydrophobic chemicals are independent of the solute's hydrophobicity. In contrast, the elimination rate constants for extremely hydrophobic chemicals, such as polychlorobenzenes and ‐naphthalenes, are inversely proportional to hydrophobicity. In the model presented, this is due to the rates of release from the lipid compartments of the fish. The general relationships between bioconcentration kinetic parameters and hydrophobicity are in agreement with experimental data.

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Hydrophobicityand bioaccumulation potential of linear and cyclic polydimethylsiloxane (PDMS) oligomers were estimated by reversed-phase liquid chromatography and feeding experiments with guppies (Poecilia reticulata). PDMS concentrations in fish were determined by capillary column gas chromatography and gas chromatography-mass spectrometry. In contrast to polychlorinated biphenyls (PCBs), only very small amounts of PDMS were retained by the fish after six weeks feeding.