Biological degradation of anthracene in soil after sorption from non-aqueous phase liquids

The availability of anthracene in soil for biological degradation was determined as a function of aging of the soil in the presence of liquid solvents, in order to simulate the conditions following contamination by non-aqueous phase liquids (NAPL). Two soils and a reference clay were aged in the presence of a solution of anthracene in a non-aqueous solvent. After evaporating the solvent, the availability of the remaining anthracene to bacteria was determined by contacting the sample with an active mixed culture in a slurry bioreactor. The parameters investigated during the aging step were moisture content, solvent polarity and time of aging the soil in the presence of the anthracene in a carrier solvent. When the non-aqueous solution of anthracene was in aged with soil for up to 90 d, the subsequent bioreactor treatment reduced the residual anthracene concentration to 4 mg kg-1 dry soil or less. The presence of soil organic material had no effect. The bioavailability of anthracene in the slurry bioreactor was only reduced when the soil had been aged for 180 d in the presence of the solvent solution. This reduction in availability was consistent with the formation of large anthracene crystals in the soil matrix, and slow diffusion within soil aggregates.