Microbes could be key in PCB clean-up

Tiny bacterium could replace huge dredging machines and an empty landfill as the primary tool in cleaning up sites contaminated with toxic PCBs thanks to American research.

Polychlorinated biphenyls (PCBs) are a family of carcinogenic chemicals which were developed in the late 1920s, primarily for use in heavy-duty electrical equipment and as a lubricant in gas pipelines.

They are particularly problematic due to the long period of time they remain environment without breaking down.

Although by the early 1980s they had been banned in most developed countries, 50 years of widespread use meant that the persistent toxins had entered the environment where they accumulated in the fatty tissues of animals and in sediment on the seabed and inland waterways.

The most common way of dealing with PCB contamination remains a kind of aquatic dig and dump, with heavy dredging machinery used to collect sediment which can then be deposited in landfill.

But new research at New York’s Rensselaer Polytechnic appears to have cracked a problem which has been frustrating scientists working in this field for decades.

In the 1980s, scientists observed that naturally occurring microbes appeared to be slowly breaking down the strong atomic bonds between the chlorine and biphenyl compounds which make PCBs so persistent, but had been unable to identify exactly which bacteria were doing the job.

But a team led by Rensselaer biology professor Donna Bedard believe they have now pinpointed the microbes responsible for the biodegradation.

“For the first time we have been able to cultivate in defined media naturally occurring bacteria that can extensively dechlorinate PCBs right at the site of the contamination,” she said.

“This is a major step toward the development of cost-effective methods for on-site PCB remediation.”

Dr Bedard used sediments from the Housatonic River in Massachusetts, an area known to be contaminated with PCBs, to develop sediment-free cultures and to identify the bacteria that were breaking down the PCBs and determined they belonged to a family known as Dehalococcoides (Dhc), which are already widely used in the natural remediation of sites contaminated by various chlorine-based solvents.

“Now that we have identified the PCB-dechlorinating bacteria and learned how to cultivate them in the laboratory, we can begin to understand the processes that they use to dechlorinate PCBs and tap their unique abilities to create new technologies that efficiently and safely remove commercial PCBs from our environment,” said Dr Bedard.

The research paper detailing the findings will appear in the April edition of scientific journal Applied and Environmental Microbiology.

Sam Bond

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