Progress in microbial degradation of hexachlorobutadiene

Abstract:

Hexachlorobutadiene (HCBD), which is a toxic and harmful aliphatic chlorinated hydrocarbon, had been widely used as an important ingredient in industrial chemicals (e.g., pesticides, herbicides, transformer oils, heat transfer fluids). In 2015, HCBD was added to the persistent organic pollutants (POPs) list based on the fact that it met the risk screening criteria (e.g., levels of toxicity, persistence, bioaccumulation, potential for long-range environmental transport). In 2017, HCBD was added in Annex C of the Stockholm Convention to reduce its unintentional production and emission. Environmental transport and fate of HCBD remain a research focus, and a better understanding of the roles and mechanisms of microorganisms in HCBD degradation and transformation is required. Here, we review the microbial biodegradation pathways, rates, and mechanisms of HCBD biotransformation in anoxic environments (e.g., groundwater, sediments). The feasibility of anaerobic biotransformation of HCBD and its degradation products as electron acceptors by calculating the thermodynamic parameters are demonstrated. Finally, future research on the HCBD microbial degradation is discussed, including the use of multi-omics techniques to unravel microbial community structure and their syntrophic mechanisms; isolation of anaerobic microorganisms capable of HCBD reductive dechlorination; development of highly efficient degradation cultures that can be applied for in-situ bioremediation of HCBD contaminated sites.

Key words:Hexachlorobutadiene, POPs, Microbial degradation, Thermodynamics, In-situ bioremediation