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ABSTRACT:
The microbial dechlorination of seven kinds of polychlorinated biphenyls (PCBs) by anaerobic microorganisms from river sediment was investigated. Dechlorination rates were found to be affected by the chlorine level of PCB congeners; dechlorination rates decreased as chlorine levels increased. Dechlorination rates were fastest under methanogenic conditions and slowest under nitrate-reducing conditions. The addition of individual electron donors (acetate, pyruvate, and lactate) enhanced the dechlorination of PCB congeners under methanogenic and sulfate-reducing conditions but delayed the dechlorination of PCB congeners under nitrate-reducing conditions. PCB congener dechlorination also was delayed by the addition of various polycyclic aromatic hydrocarbons (PAHs) under three reducing conditions and by surfactants, such as brij30, triton SN70, and triton N101. The results suggest that methanogen, sulfate-reducing bacteria, and nitrate-reducing bacteria all are involved in the dechlorination of PCB congeners. Water Environ. Res., 78, 764 (2006).
KEYWORDS: PCB, dechlorination, river sediment.
doi:10.2175/106143006X107380
Introduction
The hydrophobic quality of polychlorinated biphenyls (PCBs) and other anthropogenic pollutants enhances their ability to adsorb to sediments. As sediments settle, PCBs accumulate in the lower anoxic layers of the sediment column. The reductive PCB dechlorination power of anaerobic microorganisms in sediment has been demonstrated in the laboratory and in situ (Abramowicz, 1994; Bedard and May, 1996; Brown et al., 1987). Furthermore, the turnover of naturally formed halogenated compounds in marine coastal regions suggests that such environments hold significant dechlorination potential (King, 1988). The environmental transformation of PCBs in sediments has been documented (Brown and Wagner, 1990; Lake et al., 1992). Precise measurements of biodegradation rates are considered important for accurately forecasting the fates of potential pollutants and assessing risk.
The Taiwan Environmental Protection Administration (1997) found high concentrations of such PCB congeners as 2,2,5-CB; 2,4',5-CB; 2,2',5,5'-CB; 2,2',3,5-CB; 2,2',4,5,5'-CB; 2,2',4,4', 5,5'-CB; and 2,2',3,4,4',5,5'-CB in the Tanshui River. In the current study, the authors assessed the dechlorination potential for these seven PCB congeners and the effect of such factors as adding electron donors, polycyclic aromatic hydrocarbons (PAHs), nonionic surfactants, or microbial inhibitors on the dechlorination of PCB congeners in sediment samples collected from the Keelung River, a branch of the Tanshui River that also contains heavily contaminated sites. The microbial inhibitors included bromoethanesulfonic acid (BESA), molybdate, and vancomycin, which have been identified as selective inhibitors of methanogen (Lovely and Philips,...