anaerobic dehalogenation of halogenated organic compounds

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Mol % Mol % Auto Live TeCB TeCA TeCP TeCBA TrCAP Lac/Pro Mol % 514 Max M. Häggblom et al. 100 90 80 70 60 50 40 30 20 10 0 A 100 90 80 70 60 50 40 30 20 10 0 100 90 80 70 60 50 40 30 20 10 0 B 0 2 4 6 8 10 Control 1,2,3,4-TCDD 1,2,4-TCDD 1,3-DCDD 2-MCDD Time (months) C 0 2 4 6 8 10 Time (months) Figure 5. 1,2,3,4-TeCDD dechlorination in Paleta Creek sediment slurries under different electron donor and halogenated co-amendment conditions over 10 months with a 3-month reamendment interval (A) Mole percent of 1,2,3,4-TeCDD remaining after 15 months; (B) time course of 1,2,3,4-TeCDD dechlorination in TeCB plus lactate/propionate-amended slurries and (C) time course of 1,2,3,4-TeCDD dechlorination in TeCA plus lactate/propionateamended slurries (Ahn et al., 2005). Similarly, dechlorination of 1,2,3,4-TeCDF to tri-chlorinated and dichlorinated daughter products was significantly enhanced by TeCB and TeCA. These results suggest that halogenated aromatic compounds with structural similarity to 1,2,3,4-TeCDD/F stimulate bacteria with the ability to dechlorinate chlorinated dibenzo-p-dioxin and furans. Of critical importance is that these amendments stimulate the desirable lateral dechlorination of PCDD/Fs (removal of chlorines at position 2 and 3) that ultimately results in
Anaerobic Dehalogenation of Halogenated Organic Compounds 515 detoxification. This study coupled with findings that some species of dehalogenating bacteria have multiple dehalogenases and dechlorination capabilities suggests that halogenated compounds other than CDD/Fs could be used to enrich and isolate organisms that have activity on CDD/Fs. Identification of naturally-occurring or less toxic halogenated coamendments that are completely degraded in the sediment environment is desirable for field application. 5. DEHALOGENATION IN THE RHIZOSPHERE OF SALTMARSH PLANTS An additional variable affecting contaminant degradation in estuarine ecosystems is the effect of wetland plants. Microbial activity is stimulated in the rhizosphere of plants and wetlands may play an important function in remediation of contaminated sites, potentially reducing the impact of contaminants. We have examined the effect of two salt marsh macrophyte species on the sediment microbial community responsible for the biotransformation of the flame retardant tetrabromobisphenol A (TBBPA) (Ravit et al., 2005). Sediments vegetated by two grasses, Spartina alterniflora and Phragmites australis, commonly found in eastern U.S. brackish marshes differed significantly in their capacity to biotransform the halogenated contaminant TBBPA. Differences in the rates of TBBPA dehalogenation suggests that there are functional differences in sediment microbial communities in vegetated versus unvegetated habitats, as well as differences in the microbial communities associated with Spartina and Phragmites rhizosphere sediments. The final product of microbial reductive dehalogenation of TBBPA (Voordeckers et al., 2002; Figure 6) is bisphenol A (4,4'-isopropylidenediphenol), a known endocrine disrupter. We have not observed further anaerobic degradation of bisphenol A (Voordeckers et al., 2002). Microbial community diversity as measured by in situ sediment phospholipid fatty acid (PLFA) composition prior to TBBPA exposure, was found to be higher in the uncontaminated sediments; differences in microbial PLFA diversity were not seen in contaminated sediments associated with either the different plant species or unvegetated sediment. Understanding the effect estuarine vegetation has on dehalogenating microbial populations is necessary to predict the fate of TBBPA, as well as the production and accumulation of bisphenol in estuarine sediments
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anaerobic dehalogenation of halogenated organic compounds

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