Microbial dechlorination of historically present and freshly spiked chlorinated dioxins and diversity of dioxin-dechlorinating populations

Abstract

The ability of a microbial consortium eluted from dioxin-contaminated Passaic River sediments to dechlorinate polychlorinated dibenzo-p-dioxins (PCDDs) was investigated under methanogenic conditions. Aged 2,3,7,8-tetraCDD, which had partitioned into the microbial consortium from sediments, was stoichiometrically converted to tri-and monoCDD congeners. During dechlorination, dominant microbial activity within the consortium shifted from methanogenic to nonmethanogenic activity. Freshly spiked octaCDD was converted to hepta-, hexa-, penta-, tetra-, tri-, di-, and monochlorinated isomers, but the reaction stoichiometry was not determined. No methanogenic activity was observed, and the maximum yield of protein coincided with the production of less-chlorinated DD congeners. Two distinct pathways of dechlorination were observed: the peri-dechlorination pathway of 2,3,7,8-substituted hepta-to pentaCDDs, resulting in the production of 2,3,7,8-tetraCDD, and the peri-lateral dechlorination pathway of non-2,3,7,8-substituted congeners. Direct evidence of further lateral dechlorination of 2,3,7,8-tetraCDD was obtained from the historically contaminated incubations; no isomer-specific identification of triCDDs in spiked incubations was determined. Pasteurized cells exhibited no peri-dechlorination pathway, and triCDDs were the least-chlorinated congeners produced in these treatments. These results demonstrate that (i) both freshly spiked and aged PCDDs are available to microbial reductive dechlorination, (ii) the peri and triCDD dechlorinations are attributed to activities of nonmethanogenic, non-spore-forming microbial subpopulations, and (iii) the 2,3,7,8-residue patterns in historically contaminated sediments are likely affected by microbial activity.

Co-amendment with halogenated compounds enhances anaerobic microbial dechlorination of 1,2,3,4-tetrachlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzofuran in estuarine sediments

“…A potential drawback of dechlorination is that the potential removal of chlorines from the 1-, 4-, 6-, and 9 positions from octachlorodibenzo-p-dioxin form 2,3,7,8-tetrachlorodibenzo-p-dioxin (TeCDD) and other 2,3,7,8-substituted congeners that are considered to be potential human carcinogens [3]. Dechlorination of CDD/Fs in sediments may be the result of a combination of both respiratory and cometabolic microbial processes [6,7,[9][10][11][12][13] in addition to a variety of abiotic mechanisms [7,[14][15][16]. In most cases, CDD/F contamination occurs at low concentrations.…”

Aerobic bacterial transformation and biodegradation of dioxins: a review

“…This activity was first indicated by changes in the dioxin congener patterns as well as build-up of lightly chlorinated analogues in anaerobic environments (Townsend 1983). Anaerobic microbial community was implicated in the reductive dehalogenation of highly chlorinated PCDD/Fs in contaminated sediments, sludges, and soils (Barkovskii and Adriaens 1996;Yoshida et al 2005). However, microbial dechlorination of highly chlorinated analogues produces most toxic congeners, i.e., 2,3,7,8-TCDD as an intermediate due to deletion of chlorine at positions 1, 4, 6 and/ or 9 (Barkovskii and Adriaens 1996).…”

Environmental bioavailability of hydrophobic organochlorines in sediments—A review

“…For example, the availability of DDT and DDE to the earthworm Eisenia fetida was reduced by up to 90 percent, although the chemical concentration in the soil remained relatively constant (Morrison et al, 2000). Similarly, reduced availability was also observed for other halogenated aromatic pesticides, PCDD/Fs, and PAHs (Alexander, 2000;Guthrie-Nichols et al, 2003).Toxicological studies have shown that less 2,3,7,8-TCDD was absorbed by mammals after it had been in soil for only eight days (Barkovskii & Adriaens, 1996). It was suggested that the assimilation and acute and chronic toxicity of these compounds decline with residence time as they become increasingly sequestered (Alexander, 2000).…”