Polychlorinated Biphenyl Dechlorination in Aquatic Sediments

Abstract

The polychlorinated biphenyl (PCB) residues in the aquatic sediments from six PCB spill sites showed changes in PCB isomer and homolog (congener) distribution that indicated the occurrence of reductive dechlorination. The PCB dechlorinations exhibited several distinct congener selection patterns that indicated mediation by several different localized populations of anaerobic microorganisms. The higher (more heavily chlorinated) PCB congeners that were preferentially attacked by the observed dechlorination processes included all those that are either pharmacologically active or persistent in higher animals. All the lower (less heavily chlorinated) PCB congeners formed by the dechlorinations were species that are known to be oxidatively biodegradable by the bacteria of aerobic environments.

Aerobic and anaerobic PCB biodegradation in the environment.

“…In general, this microbial process effects the preferential removal of meta and para chlorines, resulting in a depletion of highly chlorinated PCB congeners with corresponding increases in lower chlorinated, ortho-substituted PCB congeners. The altered congener distribution of residual PCB contamination observed in several aquatic sediments was the earliest evidence of the anaerobic dechlorination of PCBs (11)(12)(13). This same activity has been observed in the laboratory (14)(15)(16), where the selective removal of meta and para chlorines was also noted.…”

A PCR-based specific assay reveals a population of bacteria within the Chloroflexi associated with the reductive dehalogenation of polychlorinated biphenyls

“…As PCBs are hydrophobic, they strongly associate with clays and silt that ultimately migrate into the marine sediments as a result of runoff from tributaries and industrial activities along ocean coastlines (Brown et al, 1987). Anaerobic dechlorination is a significant process in the environment because it results in the sequential reduction of more extensively chlorinated PCBs to lesser chlorinated congeners or complete dechlorination to biphenyl (Wiegel & Wu, 2000).…”

Poliklorlu Bifeniller ve Sucul Yaşam

“…Sucul sistemlerde PCB bileşenlerinin kompozisyonundaki farklılık aynı zamanda, muhtemel mikrobiyal parçalanma, sedimentasyon ve buharlaşma yoluyla kayıplara karşı daha hassas olan düşük klorlu PCB'lerin oranındaki azalmaya da bağlanabilir (Brown et al 1987, Quensen et al 1988. Orta ve yüksek düzeyde klorlanmış PCB'lerin sucul çevrede nispeten sabit seviyelerde kalması veya daha yüksek konsantrasyonlarda bulunmasının nedeni bu bileşiklerin daha az uçucu olmalarına, yağda çözünürlüklerinin fazla oluşuna, sediment yüzeyine tutunma eğiliminin daha fazla olmasına ve mikrobiyal parçalanmaya karşı daha dirençli olmalarına bağlanabilir (Shiu ve Mackay 1986, Tyler ve Millward 1996.…”