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

Abstract

AbstractThe fate of radiolabeled ([14C]) 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 [14C]PAHs studied represent a range of characteristics (fraction of soil organic carbon [foc] and PAH solubility) that can potentially impact contaminant fate. Fates of [14C]PAHs examined in slurry microcosms included mineralization, production of water‐soluble metabolites and their polarity, cellular incorporation, and the association of [14C]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 [14C]‐most probable number assay. All [14C]PAHs, except [14C]benzo[a]pyrene, were readily mineralized in most of the preexposed soils, whereas in the uncontaminated soil, less than 5% of each [14C]PAH was mineralized. In the adapted soils, mineralization, after 8 weeks of incubation, accounted for 30 to 60% of [14C]phenanthrene, 10 to 55% of [14C]pyrene, 5 to 40% of [14C]benz[a]anthracene, 10 to 50% of [14C]chrysene, and 2 to 9% of [14C]benzo[a]pyrene added to the microcosms. Metabolite production and cellular incorporation usually accounted for less than 10% of the added [14C]PAH. The fate of PAHs was usually not related to measurements of microbial community size, characteristics of the PAH (water solubility and Kow), and many characteristics of soils (soil foc 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 [14C]PAH mineralized and the amount solvent extractable from the soil, and positively related to the amount of [14C]PAH remaining in soils after extraction.