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The purpose of this study was to assess the suitability of applying equilibrium partitioning (EqP) theory to predict the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) by earthworms when these are exposed to contaminated soils in the field. Studies carried out in situ in various contaminated floodplain sites showed the presence of linear relationships with intercept zero between the lipid‐normalized concentration of different PAHs in the earthworm Lumbricus rubellus and the organic‐matter‐normalized concentration of the compounds in soil. The demonstration of such an isometric relationship is in agreement with the prediction of EqP theory that the biota‐soil accumulation factor (BSAF) should be independent of the octanol/water partition coefficient, log Kow. The average BSAF of PAH compounds in the sampled 20‐cm top layer of soil was 0.10 (range, 0.03–0.26). The present study also investigated the route of uptake of PAHs for earthworms in soil. The bioconcentration factor of low‐molecular‐weight PAHs, such as phenanthrene, fluoranthene, and pyrene, was derived from bioconcentration kinetic modeling of water‐only experiments and found to be of the same order of magnitude as the bioaccumulation factor in the field when the latter was normalized to calculated concentrations in soil pore water. The results indicated that the exposure of earthworms to PAHs in soil is mediated through direct contact of the worms with the dissolved interstitial soil‐water phase, further supporting the applicability of EqP theory to PAHs. Our experimental data on the biotransformation of PAHs suggest that earthworms possess some capacity of metabolization, although this does not seem to be a major factor in the total elimination of these compounds. Even though the EqP approach was found to be applicable to low‐molecular‐weight PAHs with respect to the prediction of bioaccumulation by earthworms in the field, the results were less conclusive for high‐molecular‐weight compounds, such as benzo[a]pyrene.

Aqueous solubilities, n-octanol/water partition coefficients (K ow s), and Henry's law constants were determined for a range of polycyclic aromatic hydrocarbons (PAHs) using a generator-column, slow-stirring, and gas-purge method, respectively. The currently obtained data were compared to available literature data. For seven of the PAHs no K ow s previously were determined with the slow-stirring method. For four of the PAHs the present study reports the first experimental Henry's law constants. Relationships between subcooled liquid solubilities, K ow s, and Henry's law constants as a function of molar volume are discussed. A consistent data set was obtained, for which an excellent correlation was found between subcooled liquid solubility and molar volume. A linear fit did not accurately describe the relationship between log K ow and molar volume. This is probably due to a decreasing solubility in n-octanol with increasing molar volume. Finally, a high correlation was found between Henry's law constant and molar volume. The presently obtained dataset can be used to predict the fate and behavior of unsubstituted homocyclic PAHs.

Abstract-The purpose of this study was to assess the suitability of applying equilibrium partitioning (EqP) theory to predict the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) by earthworms when these are exposed to contaminated soils in the field. Studies carried out in situ in various contaminated floodplain sites showed the presence of linear relationships with intercept zero between the lipid-normalized concentration of different PAHs in the earthworm Lumbricus rubellus and the organic-matternormalized concentration of the compounds in soil. The demonstration of such an isometric relationship is in agreement with the prediction of EqP theory that the biota-soil accumulation factor (BSAF) should be independent of the octanol/water partition coefficient, log K ow . The average BSAF of PAH compounds in the sampled 20-cm top layer of soil was 0.10 (range, 0.03-0.26). The present study also investigated the route of uptake of PAHs for earthworms in soil. The bioconcentration factor of lowmolecular-weight PAHs, such as phenanthrene, fluoranthene, and pyrene, was derived from bioconcentration kinetic modeling of water-only experiments and found to be of the same order of magnitude as the bioaccumulation factor in the field when the latter was normalized to calculated concentrations in soil pore water. The results indicated that the exposure of earthworms to PAHs in soil is mediated through direct contact of the worms with the dissolved interstitial soil-water phase, further supporting the applicability of EqP theory to PAHs. Our experimental data on the biotransformation of PAHs suggest that earthworms possess some capacity of metabolization, although this does not seem to be a major factor in the total elimination of these compounds. Even though the EqP approach was found to be applicable to low-molecular-weight PAHs with respect to the prediction of bioaccumulation by earthworms in the field, the results were less conclusive for high-molecular-weight compounds, such as benzo [a]pyrene.