Research Product

This paper discusses abiotic and biotic interactions of PCBs in soil and sediment, and suggests possible approaches to coupling enhanced availability to increased biodegradation. Currently field studies of the biodegradation of PCBs found in former drag strip soil in New York State exemplify problems associated with bioavailability. The PCB concentration in the soil is roughly 500 ppm, and no longer resembles commercial Aroclor 1242. Depletion of the di- and trichlorobiphenyls, probably due to the evaporation of the more volatile congeners, has resulted in a PCB congener profile that more closely resembles Aroclor 1248. In previous studies, Pseudomonas sp. LB400 incubated with the drag strip soil in the laboratory degraded 15% of the PCB in one day and 50% in 3 days. This is slower than that exhibited with laboratory-contaminated soil but still demonstrates a significant reduction in PCB concentration. In the field, PCB biodegradation was first detectable after 8-10 weeks. After 13 weeks, the soil in the top 3 cm of the test plot showed approximately 20% biodegradation of the PCB; after 18 weeks, approximately 25% of the PCB had degraded. The rate of biodegradation at the drag strip was about 50% of the rate seen in laboratory experiments. A large portion of the rate reduction can be attributed to the poor control of soil temperature and moisture content and the fragile nature of the added microorganism. However, even in optimized laboratory studies, approximately 50% of the total PCBs was unavailable to microbial degradation.