Biodegradation of [(sup14)C]Benzo[a]pyrene Added in Crude Oil to Uncontaminated Soil

To investigate the possible cometabolic biodegradation of benzo[a]pyrene (BaP), crude oil spiked with [7-(sup14)C]BaP and unlabeled BaP was added to soil with no known pollution history, to give 34 g of oil and 67 mg of BaP/kg of dry soil. The oil-soil mixture was amended with mineral nutrients and incubated in an airtight container with continuous forced aeration. Total CO(inf2) and (sup14)CO(inf2) in the off-gas were trapped and quantified. Soil samples were Soxhlet extracted with dichloromethane at seven time points during the 150-day incubation period, and the extracted soil was subjected to further fractionation in order to recover reversibly and irreversibly bound radiocarbon. Radiocarbon recovery was 100% (plusmn) 3% for each time point. During the first 50 days of incubation, no (sup14)CO(inf2) was evolved, but over the next 100 days, 50% of the BaP radiocarbon was evolved as (sup14)CO(inf2). At 150 days, only 5% of the intact BaP and 23% of the crude oil remained. Of the remaining radiolabel, 20% was found in solvent-extractable metabolites and 25% was incorporated into soil organic matter. Only 1/10 of this could be solubilized by chemical hydrolysis. An abiotic control experiment exhibited binding of only 2% of the BaP, indicating the microbial nature of the BaP transformations. We report that in soil containing suitable cosubstrates, BaP can be completely degraded.