Text

theses

Microbial reductive dechlorination of problematic halogenated aromatics was observed in aquatic sediments. Laboratory experiments demonstrated reductive dehalogenation of hexachlorobenzene (HCB) and pentachloroaniline (PCA) in anaerobic microcosms set up with sediment samples originating from different sites (H1 ~ H5) along the Hackensack River, NJ. The dehalogenation products and intermediates were detected by gas chromatography-mass spectrometry. HCB was dechlorinated via pentachlorobenzene (PeCB) and 1,3,5-trichlorobenzene (TriCB) to 1,3- and 1,4-dichlorobenzene (DCB), while PCA was dechlorinated via 2,3,5,6-tetrachloroaniline, 2,4,5- and 2,4,6-trichloroaniline, and 2,4-, 2,5-, 2,6-, and 3,5-dichloroaniline, to monochloroaniline. Debromination of hexabromobenzene (HBB) was not observed after up to 12 months incubation. However, when HCB was added as a co-substrate, reductive debromination of HBB occurred with 1,2,3,5-tetrabromobenzene (TeBB) and 1,3,5-tribromobenzene (TriBB) detected at low concentration. Chloroflexi specific 16S rRNA gene PCR-DGGE followed by sequence analysis detected members of the “Pinellas subgroup” of Dehalococcoides mccartyi in H1 sediment. H1 and H5 cultures had different reductive dehalogenase (rdh) gene profiles based on the analysis of a set of 12 rdh genes. Generally, more rdh genes were detected in H1 cultures, corresponding with higher dehalogenating activity and greater abundance of Dehalococcoides species in H1 sediment. Cultures amended with both HBB and HCB had all 12 tested rdh genes. Carbon compound specific isotope analysis (CSIA) was conducted to obtain isotope fractionation data for dehalogenation of HCB, PeCB, 1,2,3,5-TeCB, 1,2,3,5-TeBB, and 1,3,5-TriBB. Strong evidence of isotope fractionation coupled to dehalogenation was not observed, possibly due to the low solubility of the halobenzene substrates and a dilution of the isotope signal. However, we could detect a depletion of the δ13C value in the DCB product from dechlorination of HCB; isotope fractionation of TeCB and the sequential depletion and enrichment of δ13C value for TriCB in TeCB dechlorinating cultures; and the enrichment of δ13C during debromination of TriBB. From this study, we conclude that indigenous anaerobic microorganisms in the Hackensack River, NJ are capable of dehalogenating chloro- and bromobenzenes. Molecular community analyses demonstrated that there are different responsible microbial communities corresponding to the locations of the Hackensack River. A “priming” effect of HCB on HBB dehalogenation was observed. CSIA data for highly halogenated benzenes suggest that it may have application for assessing in situ microbial reductive dehalogenation.

ETD_6641

Ph.D.

Includes bibliographical references

by Seo Yean Sohn

doi:10.7282/T35X2BXZ

ETD doctoral

The author owns the copyright to this work.