Time-Dependent Remobilization of Nonextractable Benzo[a]pyrene Residues in Contrasting Soils: Effects of Aging, Spiked Concentration, and Soil Properties.

Abstract

The environmental and health risks associated with "nonextractable" residues (NERs) of polycyclic aromatic hydrocarbons in soils and their potential for remobilization remain largely unexplored. In this novel study, sequential solvent extractions were employed to interrogate time-dependent remobilization of benzo[a]pyrene (B[a]P) NERs and associated kinetics after re-equilibration (REQ) periods lasting 30 d in four artificially spiked soils aged for up to 200 days. Following sequential extractions of the re-equilibrated soils, remobilization of B[a]P NERs was observed and further confirmed by decreases in the absolute amounts of B[a]P recovered following methanolic saponification after REQ. Remobilization may occur through slow intercompartmental partitioning of more sequestered into less sequestered B[a]P fractions in soils. The amounts of B[a]P remobilized in soils decreased throughout aging following first-order kinetics, and the rates of decrease were slow but 2 to 4 times faster than those of extractable B[a]P before re-equilibration. Sandy-clay-loam soils with large amounts of hard organic carbon exhibited less NER remobilization compared to sandy soils. The amounts of remobilized B[a]P decreased significantly ( p < 0.05) with aging. Specifically, butanol-remobilized B[a]P in soils spiked at 10 mg/kg and 50 mg/kg B[a]P ranged from 0.15 to 0.39 mg/kg and 0.67 to 2.30 mg/kg, respectively, after 200 d of aging.