(The video is available here)
The new EBNet Webinar series is designed to replace our annual Research Colloquium with top-quality, specialist webinars on a range of EB topics. Under the spotlight this January to share the latest in “Organohalide Bioremediation – Current Approaches in Environmental Biotech”, were Dr Sophie Holland, University of New South Wales and Professor Andy Cundy, National Oceanography Centre (NOC), University of Southampton. Dr Holland’s PhD focused on organochlorines, and her detective work on the biochemical, enzymatic and bacterial aspects of this degradation fully utilised the latest techniques to determine – from the biochemical to the community level – the precise mechanisms involved. Professor Cundy has extensive experience with large-scale bioremediation efforts exploiting physical, chemical, plant and microbe-based interventions for on-site regulatory compliance and associated wider societal gains. His latest EBNet-funded project will examine the various effects of biochar amendments. This exploration of current activity and future potential in the field of organohalides was chaired by Dr Tony Gutierrez, Heriot-Watt University.
Organochlorines are recalcitrant pollutants with widely known toxic effects. They are typically denser than water and disperse widely until trapped by bedrock or clay meaning they tend to be found in anaerobic zones known as DNAPL (dense non-aqueous phase liquid zone). Sites and interventions can now be relatively easily monitored by tracking the relevant reductive dehydrogenases – if known. Focusing on Dichloromethane (CH2Cl2 or DCM), Dr Holland worked with an enrichment culture that was more than 6 years old, having DCM as its sole substrate for over 20 transfers. This culture contained an isolate known as ‘Candidatus Formimonas Warabiya’ (DCMF). Only 3 DCM-fermenting bacteria are known, and none are known to respire. Precise C13 work combined with metagenomic profiling and comparative proteomics revealed certain enzymes (methyltransferases) which were highly conserved in DCM-degraders within the Wood-Ljungdahl pathway for this mixotrophic isolate. Moreover, DCMF was closely associated with other bacteria – known to be versatile necromass recyclers. Looking ahead, an understanding of these metabolically coherent communities (MeCoCos) will be important towards creating robust and resilient artificial consortia.
At polluted sites, the concept of integrated attenuation aims to reduce mass flux of a contaminant to a receptor to avoid negative effects to the human or environmental population at risk. Previous work on a site contaminated with tetrachloromethane (CCl4) encompassed physical interventions as well as phytoremediation and downstream pond creation. The role of trees and other planting was to encourage deep roots to access the aquifer and transfer the pollutant to the biomass or air via tree-mediated hydraulic pumping. After 6 years, this site achieved an average reduction of 99% – to the compliance point – and combined effective risk management with wider environmental/societal benefits. Another project involved perfluoro-alkylated substances (PFAS) at Southampton Water. Unlike some other contaminants such as caesium and copper, known to result from “pulsed” events, it was apparent that PFAS are generally dispersed and mixed by tidal circulation. This reduced the potential to sequester the contaminants in an “estuarine filter”. Another contaminant – mercury (Hg) – is found in brownfield sites in Colombia as a gross contaminant. Work carried out there to stabilise and “cap” the sites using less than 1% biochar soil amendment and surface planting managed to significantly reduce the water-soluble Hg. Looking forward, a new EBNet-funded project examines options for PFAS soil contamination, to investigate the benefits of biochar and zerovalent iron (ZVI) for their effects. It is hoped that a thorough understanding of the combined biotic/abiotic and sorption/degradation effects will support developments in “gentle” in situ bioremediation, rather than more disruptive physical/chemical treatments.
The properties of these widely dispersed and recalcitrant organohalide pollutants pose challenges for effective bioremediation techniques. Tools now exist that allow us to understand those rare microbial mechanisms which degrade these problem contaminants. Moving from gene to protein to microbe to microbial community structure, the ability to fully understand, design, monitor and measure our interventions will open new avenues for effective innovation. The onsite remediation of legacy pollutants down to acceptable levels, at scale, can be disruptive and costly, involving many physical and chemical steps. Therefore, integrating bioremediation interventions that “gently” rehabilitate sites is a pressing question as we look to redesign existing processes using improved or novel options.