Polynuclear aromatic hydrocarbon metabolism in soils: Relationship to soil characteristics and preexposure

The fate of radiolabeled ([ 14 C]) phenanthrene, pyrene, benz[ a ]anthracene, chrysene, and benzo[ a ]pyrene was examined in five soils, four of which had previous exposure to polycyclic aromatic hydrocarbons (PAHs). The soils and [ 14 C]PAHs studied represent a range of characteristics (fraction of soil organic carbon [ f oc ] and PAH solubility) that can potentially impact contaminant fate. Fates of [ 14 C]PAHs examined in slurry microcosms included mineralization, production of water‐soluble metabolites and their polarity, cellular incorporation, and the association of [ 14 C]PAHs with soils, all compared to an abiotic control. The soils all contained active heterotrophic communities and the contaminated soils had sizable populations of PAH‐degrading microorganisms, measured by the [ 14 C]‐most probable number assay. All [ 14 C]PAHs, except [ 14 C]benzo[ a ]pyrene, were readily mineralized in most of the preexposed soils, whereas in the uncontaminated soil, less than 5% of each [ 14 C]PAH was mineralized. In the adapted soils, mineralization, after 8 weeks of incubation, accounted for 30 to 60% of [ 14 C]phenanthrene, 10 to 55% of [ 14 C]pyrene, 5 to 40% of [ 14 C]benz[ a ]anthracene, 10 to 50% of [ 14 C]chrysene, and 2 to 9% of [ 14 C]benzo[ a ]pyrene added to the microcosms. Metabolite production and cellular incorporation usually accounted for less than 10% of the added [ 14 C]PAH. The fate of PAHs was usually not related to measurements of microbial community size, characteristics of the PAH (water solubility and K ow ), and many characteristics of soils (soil f oc and PAH concentration). The fraction of silt and clay in the soils for each soil–PAH combination, however, was negatively related to the extent of added [ 14 C]PAH mineralized and the amount solvent extractable from the soil, and positively related to the amount of [ 14 C]PAH remaining in soils after extraction.