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 orthoand 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 paradechlorination (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.

Development and Characterization of Stable Sediment-Free Anaerobic Bacterial Enrichment Cultures That Dechlorinate Aroclor 1260

“…We previously determined that it is necessary to stimulate PCB dechlorination in the sediments studied by the addition of a high concentration (350 M) of a single PCB congener or brominated biphenyl, a procedure that we called priming (6,11,13,64). Hence, we established active PCB-dechlorinating cultures in sediment slurries carrying out Process N dechlorination by priming with 26-BB as previously reported (11).…”

Quantifying Enhanced Microbial Dehalogenation Impacting the Fate and Transport of Organohalide Mixtures in Contaminated Sediments

“…The key reductive dechlorination products for process N are PCBs 47, 51,100, while the key dechlorination products in Anacostia sediment were tetra-CBs including PCBs 47, 49 and 53 and tri-CBs including PCBs 28 or 29 and 25 (varying according to the specific replicate). Furthermore, the fact that addition of PCB 116 as an alternate halogenated electron acceptor was not effective in stimulating the dehalogenating population in Anacostia sediment to dechlorinate weathered PCBs, but did stimulated extensive process N dechlorination of the Aroclor 1260 residue in Housatonic River sediment (Van Dort et al, 1997), provide another line of evidence that the observed dechlorination in Anacostia sediment is different from the previously described process N.…”

“…(Bedard et al, 2006;Fagervold et al, 2007;Van Dort et al, 1997). For example, in earlier studies flanked meta chlorines were preferentially removed, e.g.…”

“…One effective strategy for stimulating PCB dechlorination by sediment microorganisms is addition of alternate halogenated electron acceptors / co-substrates (haloprimers), such as 2,3,4,5,6-PCB (PCB 116) (Van Dort et al, 1997), 2,6-dibromobiphenyl (2,6-DBB) (Bedard et al, 1998), halobenzoates and chlorobenzenes and chlorophenols (Cho et al, 2002). Wu et al (1999) used a most probable number method to show that halopriming with 2,6-DBB increased the number of PCB-and PBB-dehalogenators, suggesting that halopriming works by stimulating growth of dehalorespirers.…”

“…Although anaerobic bioaugmentation studies have been successful for in situ treatment of chlorinated ethenes (Lendvay et al, 2003;Major et al, 2002), another class of organochlorines most commonly found in contaminated groundwater, effective bioaugmentation of PCB contaminated sites has not, as yet, been demonstrated. There have been reports on biostimulation of PCB dechlorination using other chlorinated compounds (halopriming) to enhance the numbers of dechlorinators and increase rates of contaminant breakdown (Bedard et al, 1996;Klasson et al, 1996;Van Dort et al, 1997) though, unfortunately, the biostimulants are often themselves persistent organic pollutants. Other studies investigated the effects of enrichment cultures on bioaugmentation Natarajan et al, 1997), but the fates of the dechlorinating microorganisms were not determined in these earlier studies because their identity was unknown.…”