Mitigating emissions of semi-volatile polychlorinated biphenyls (PCBs) from contaminated sediments using aerobic bioaugmentation
Year: 2022
Type: dissertation
Abstract: Polychlorinated biphenyls (PCBs) are semi-volatile organic compounds (SVOCs) with 209 possible molecular configurations called congeners. PCBs were used in industry as mixtures of these 209 congeners throughout the 20th century until their commercial use was banned in the United States in 1979 under the Toxic Substances Control Act (TSCA) and internationally in 2004 under the Stockholm Convention. These complex mixtures of carcinogenic compounds still contaminate the built and natural environment today. The primary route of human exposure to PCBs is through consumption of PCB-contaminated food. However, recent Iowa Superfund Research Program (ISRP) studies have shown that inhalation exposure to airborne PCBs is also a relatively significant route of human exposure for certain vulnerable populations due to PCB emissions from modern, unregulated sources of PCBs and legacy sources, such as PCB-contaminated sediments at Superfund Sites. Therefore, the most effective way to disrupt the PCB inhalation exposure pathway is through targeted remediation of specific congeners which are most likely to volatilize to the atmosphere from these major emission sources. This work investigates whether bioaugmentation of aerobic, PCB-degrading microorganisms can be an effective engineering solution to decrease PCB exposure in communities surrounding contaminated sites. The research described here focuses on evaluating whether the activity of aerobic microbes can mitigate emissions of lightly chlorinated PCB congeners (LC-PCBs) from sediment collected from a field site. Aerobic bioremediation is a desirable treatment technology because dredging, the traditional PCB cleanup method, increases emissions of LC-PCBs from sediment to air and does not destroy the highly chlorinated PCBs (HC-PCBs) that remain in displaced dredged material. Certain aerobic microorganisms have evolved the biphenyl gene locus (bph) which encodes for the expression catabolic enzymes capable of very effectively biodegrading (oxidizing) certain LC-PCBs. Paraburkholderia xenovorans strain LB400 is widely regarded as one of the most efficient at using this pathway and is the primary microorganism used in this work. This document describes the development of a lab-scale PCB biodegradation assay (BDA) which evaluated key limitations in the ability of strain LB400 to biotransform PCB congeners in the presence and absence of sediment particles. The sediment used was gathered from a decommissioned wastewater overflow lagoon in Altavista, VA which became contaminated with PCBs decades ago. Additionally, the PCB biodegradation capability of another microbial consortium isolated from the Altavista lagoon sediment was evaluated using the BDA procedure and compared to that of the non-native strain, LB400. Furthermore, the effect on LB400’s ability to degrade PCBs was evaluated when three amendments were separately introduced to the BDA: First, (1) a hybrid poplar tree root extract; second, (2) a commercial, plant-based biosurfactant, called saponin; and third, (3) a commercially available, sorptive, black carbon material called SediMite™. Finally, the ability of LB400 to mitigate emissions of PCBs from Altavista sediment to air was investigated by modifying the BDA design to measure PCBs both in the air and in the freely dissolved phase within the bioreactor by using passive samplers.
DOI: 10.17077/etd.006438
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4294100393