BIOAVAILABILITY AND TRANSFORMATION OF HIGHLY CHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS IN ANAEROBIC SOILS AND SEDIMENTS

The long-term fate of environmentally relevant concentrations (ppb) of penta- to heptachlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) congeners was evaluated in both high and low organic carbon anaerobic sediments. The inocula were derived from historically contaminated environments and were amended with a mixture of aliphatic and aromatic acids to stimulate anaerobic microbial activity. The long-term (> 2 years) removal patterns of sediment-sorbed PCDD/PCDF in both sediments could be explained by labile and resistant PCDD/PCDF desorption components, presumably due to intraparticle diffusion-controlled mass transfer limitations. Mass transfer limitations were based on incubation time-dependent decreased extraction efficiencies of PCDD/PCDF from autoclaved controls. Lesser chlorinated congeners were observed in both active and autoclaved sediments, accounting for up to 30% of the PCDD/F spiked. Whereas tetra CDD accumulated from hepta-, hexa-, and pentaCDD/F in active sediments, the extent of dechlorination in autoclaved sediments was limited to removal of one to two chlorines. These observations provide the first evidence for the contribution of biologically mediated reductive dechlorination of PCDD/PCDF to the overall fate of these contaminants in the environment and may lead the way to designing in situ transformation/biodegradation systems.