Preliminary studies on the development of a microbiological treatment for polychlorinated biphenyls

Abstract

A series of experiments comprising microbiological testing, surfactant screening and microcosm systems are described for the preliminary development of a treatment for polychlorinated biphenyls (PCBs). Microbial isolates from contaminated soil and sludge and culture collections, were screened for degradation of a defined mixture of PCB congeners in liquid culture. Initially, one group of bacteria substantially degraded the dichloro-to pentachlorobiphenyls except where chlorinated at the 4,4′ position, but not hexachlorobiphenyl; whereas other microorganisms, includingPhanerochaete chrysosporium, showed greater degradation of the apparently more recalcitrant congeners. Repeated subculturing of the most promising bacteria on biphenyl supplemented media apparently increased their ability to degrade both the range and extent of congeners tested. The non-ionic Triton^® X-100 and Tensoxid^® S50 were the most effective surfactants at desorbing PCB from sand but had varying degrees of inhibition either to the growth, or alternatively to the PCB metabolism of the isolates tested. The greatest degree of PCB metabolism in the presence of Triton^® X-100 was towards 2,3-dichlorobiphenyl, with a general reduction in the degree of degradation of trichlorinated to hexachlorinated congeners. The most effective reduction of Aroclor^® 1242 in sand systems spiked with 1,000 mg/kg was achieved through a combination of inoculating biphenyl-degrading bacterial isolates together withPh. chrysosporium. This resulted in a reduction of approximately 40% in a 20-week period, although this was attributable largely to the removal of the less chlorinated rather than the more chlorinated congeners.