Kinetics of PCB Microbial Dechlorination Explained by Freely Dissolved Concentration in Sediment Microcosms

Abstract

While microbial dechlorination of polychlorinated biphenyls (PCBs) has been observed in sediments over the last 3 decades, translation to the field has been difficult due to a lack of a clear understanding of the kinetic limitations. To address this issue, the present study used passive dosing/sampling to accurately measure the biological rate of dechlorination of 2,3,4,5-tetrachlorobiphenyl (PCB 61) to 2,3,5-trichlorobiphenyl (PCB 23) by an organohalide-respiring bacterium, Dehalobium chlorocoercia (DF-1). The biological rates were measured over an environmentally relevant concentration range of 1–50 ng/L of freely dissolved concentrations with and without the presence of sediment in bench-scale microcosm studies. The rate of dechlorination was found to be linearly dependent on the freely dissolved concentration of PCB 61 both in sediment and in sediment-free microcosms. The observed rate of dechlorination in sediment microcosms could be predicted within a factor of 2 based on the kinetics measured in sediment-free microcosms. A threshold for dechlorination was not observed down to an aqueous concentration of about 1 ng/L PCB 61. We demonstrate that with the combination of an accurate measurement of the aqueous-phase dechlorination kinetics and an understanding of the site-specific partitioning characteristics, it is possible to predict PCB microbial dechlorination in sediments.

Efficient and Complete Detoxification of Polybrominated Diphenyl Ethers in Sediments Achieved by Bioaugmentation with Dehalococcoides and Microbial Ecological Insights

“…, the low bioavailability of organohalide substrates and potential inhibition by co-contaminants) could lead to less effective or even failed bioaugmentation. , The low bioavailability of polyhalogenated aromatic compounds ( e.g. , PBDEs and PCBs) is likely one crucial factor causing their slow remediation in the environment . The bioaugmented bacteria, whose growth can only be supported at a low level by these lowly bioavailable aromatic organohalide pollutants, are risky of being phased out when competing with the indigenous microorganisms for nutrients and substrates. , Various halogenated co-substrates ( e.g.…”

Accelerated Passive Dosing of Hydrophobic Complex Mixtures–Controlling the Level and Composition in Aquatic Tests

“…Lastly, passive dosing is increasingly used for setting and maintaining HOC exposure in aquatic tests. In passive dosing, a biocompatible polymer such as silicone is loaded with the test substance and then used as dominant partitioning donor to establish and control freely dissolved HOC concentrations in an aqueous medium. ,− This approach has been used in many types of toxicity studies, − bioaccumulation studies, , biodegradation studies, − and binding and sorption studies − and for solubility measurements. , Passive dosing has so far primarily been used for research on single compounds and simple mixtures and more recently for research on defined composed mixtures of more than 30 chemicals . For complex mixtures, passive dosing has only been used to dose crude oil and fuel oil into water near the saturation limit. − Table provides a comparison of the three dosing methods (solvent spiking, WAF, and passive dosing) based on their underlying principles.…”

Contaminated aquatic sediments

“…They noted that up to 94% of dioxin‐like PCB toxicity was reduced through 21 pathways resulting from the model. Needham, Payne, Sowers, and Ghosh (2019) investigated the rate of microbially mediated PCB dechlorination in sediment and sediment‐free microcosms. They concluded that the dechlorination rate was linearly dependent on concentrations of PCBs that were freely dissolved in the microcosms.…”