Priming Microbial meta-Dechlorination of Polychlorinated Biphenyls That Have Persisted in Housatonic River Sediments for Decades

Abstract

We recently demonstrated a strategy for stimulating or “priming” the indigenous microorganisms to dechlorinate weathered PCBs in sediments, but the dechlorination exhibited a very narrow para-dechlorination specificity. We tested the priming activity of various PCB congeners to discover those that would prime broader and more extensive PCB dechlorination activity. 2,3,4,5,6-Pentachlorobiphenyl (23456-CB), 2346-CB, and 236-CB primed extensive and sustained meta-dechlorination (Process N) of the Aroclor 1260 residue in Housatonic River sediment. The dechlorination targeted most of the hexa-, hepta-, and octachlorobiphenyls and converted them to tetra- and pentachlorobiphenyls containing mostly ortho- and para-chlorines. Both 234-CB and 2345-CB also primed Process N dechlorination, but the dechlorination ceased at 7 weeks and was much less extensive. 245-CB primed a narrow specificity para-dechlorination (Process P). 2356-CB, 235-CB, and 23-CB did not prime PCB dechlorination. The results indicate that the 236-substitution pattern is important for maximal priming of dechlorination Process N. A chlorine at position 5 suppressed the priming activity, but the suppression was overcome by a chlorine at position 4. The discovery of non-PCB primers that are both effective and environmentally acceptable could lead to the development of practical methods for in situ PCB bioremediation.