Partitioning, extractability, and formation of nonextractable PAH residuesin soil. 1. Compound differences in aging and sequestration

This study was carried out to assess the influence of physicochemical prope rties on PAH sequestration in sterile sewage sludge-amended arable sail. Ra diolabeled phenanthrene (C-14-9-Phe), pyrene (C-14-4,5,9,10-Pyr), arid benz o[a]pyrene (C-14-7-B[a]P) were spiked and aged for up to 525 days in steril e soil microcosms. The degree of compound sequestration at various sampling times was determined by their extractability with organic solvents and rel ease from soil residues by base saponification extraction. The amount of PA H extractable by butanol and dichloromethane decreased with compound aging in the soil. The decrease in PAH extractability with aging, and the formati on of nonextractable bound residues, increased with compound molecular weig ht, Kow and Koc. The amount of total extractable PAH determined by sequenti al dichloromethane soxtec and methanolic saponification extraction decrease d from 98%, 97%, and 94% at day 10 to 95%, 91%, and 77%, respectively for C -14-9-Phe, C-14-4,5,9,10-Pyr, and C-14-7-B[a]P after 525 days aging. During the same aging period there was an increase in the amount of PAH released from the soil by base saponification extraction, suggesting a progressive d iffusion of PAHs into hydrolyzable and recalcitrant organic matter and mine ral phases of soil. Calculated half-lives for the apparent loss of PAHs by sequestration in this experiment were dependent on the method used to extra ct them from soil. These half-lives ranged from 96 to 1789 days depending o n the compound, and are in agreement with Values obtained from previous spi king experiments using nonsterile soils. These results suggest that a consi derable fraction of PAHs assumed degraded in previous studies may have been sequestered within the organic carbon and, to a lesser extent, mineral pha ses of soil.