Relationship between bioconcentration in fish and steric factors of hydrophobic chemicals

Most polychlorinated naphthalones (PCN) accumulate rapidly according to their hydrophobicity. The uptake and ellmination rate constants are comparable to those of chlorinated benzenes and biphenyls.For most PCN-congeners the resulting bioaccumulation factors show an increase with increasing hydrophobicity. For higher K_d,oct-values (>10⁵) however, no further increase of K_c is observed (K_c. max. = 3.5.10⁴).For the two hepta- and the octachloronaphthalenes no detectable concentrations are found in the fishes, although no restricted blo-availability could be expected. Based on these observations and on data obtained from the literature. a loss of membrane permeation is suggested for hydrophobic molecules with widths over 9.5 Å.In addition a membrane permeation model, as part of the accumulation process of hydrophobic chemicals. Is proposed, which is based on diffusion and partition processes.