Abstract
Soil samples contaminated with Aroclor 1260 were analyzed for microbial PCB dechlorination potential, which is the rate-limiting step for complete PCB degradation. The average chlorines per biphenyl varied throughout the site suggesting that different rates ofin situdechlorination had occurred over time. Analysis of PCB transforming (aerobic and anaerobic) microbial communities and dechlorinating potential revealed spatial heterogeneity of both putative PCB transforming phylotypes and dechlorination activity. Some soil samples inhibited PCB dechlorination in active sediment from Baltimore Harbor indicating that metal or organic cocontaminants might cause the observed heterogeneity ofin situdechlorination. Bioaugmentation of soil samples contaminated with PCBs ranging from 4.6 to 265 ppm with a pure culture of the PCB dechlorinating bacteriumDehalobium chlorocoerciaDF-1 also yielded heterologous results with significant dechlorination of weathered PCBs observed in one location. The detection of indigenous PCB dehalorespiring activity combined with the detection of putative dechlorinating bacteria and biphenyl dioxygenase genes in the soil aggregates suggests that the potential exists for complete mineralization of PCBs in soils. However, in contrast to sediments, the heterologous distribution of microorganisms, PCBs, and inhibitory cocontaminants is a significant challenge for the development ofin situmicrobial treatment of PCB impacted soils.
Highlights
Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are still present in the environment despite a U.S production ban in 1976 [1]
The results suggest that in situ PCB dechlorination occurred to some extent in these samples
Bacteria capable of aerobic PCB degradation are found ubiquitously in the soil environment and several have been isolated and identified that belong to genera such as Pseudomonas, Burkholderia, Ralstonia, Achromobacter, Comamonas, Bacillus and Rhodococcus [25, 44]
Summary
Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are still present in the environment despite a U.S production ban in 1976 [1]. Commercial mixtures of PCBs (trade name Aroclor in the U.S.) were used for a range of industrial applications such as high-voltage transformers, insulating materials, and hydraulic liquids [2, 3]. PCBs are hydrophobic with a high affinity for adsorption to soil particles and for bioaccumulation in lipids causing hepato- and immunotoxicity, carcinogenesis, and affecting endocrine organs and reproduction in humans [4, 5] and animals [6]. Soils contaminated with PCBs can be found worldwide as a result of industrial activity [8]. Even in cases without a specific source, the physical and environmental conditions in soil involved in formation of soil aggregates impacted the spatial distribution of PCBs leading to heterogeneity of microbial activity [12, 13].
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