DEHALOGENATION OF CHLORINATED DIOXINS BY AN ANAEROBIC MICROBIAL CONSORTIUM FROM SEDIMENT

Anaerobic microorganisms enriched from Rhine River sediments are able to remove chlorine substituents from polychlorinated dibenzo-p-dioxine s (PCDDs). A model PCDD, 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4- TeCDD) was reductively dechlorinated to both 1,2,3- and 1,2,4-trichlor odibenzo-p-dioxins (1,2,3- and 1,2,4-TrCDD). These compounds were furt her dechlorinated to 1,3- and 2,3-dichlorodibenzo-p-dioxins and traces of 2-monochlorodibenzo-p-dioxin. This is the first report in the lite rature of the anaerobic microbial dechlorination of PCDDs. The same en richment culture was previously found to dechlorinate chlorinated benz enes (CBs) and polychlorinated biphenyls (PCBs). An anaerobic culture able to remove aryl chlorines from three classes of compounds has not been reported before. The rate at which the culture dechlorinates 1,2, 3,4-TeCDD (t(1/2)=15.5 d) was between those observed for CBs and PCBs. This study shows that reductive dechlorination may have an effect on PCDDs in sediments, as has been demonstrated for CBs and PCBs. The for mation of metabolites with a conserved 2,3-substitution pattern from 1 ,2,3,4-TeCDD indicates that dechlorination of highly chlorinated diben zo-p-dioxins may result in metabolites that are potentially more toxic than the parent compounds.