UC Riverside engineers are the first to report the selective destruction of a particularly resistant class of PFAS, called fluorinated carboxylic acids (FCAs), common microorganisms.
Under anaerobic conditions, the carbon-carbon double bond is crucial for the breakdown of the super-strong carbon-fluorine bond by microbial communities. Although the rupture of the carbon-carbon bond does not lead to complete degradation of the molecule, the resulting products can be transferred to other microorganisms for defluorination under aerobic conditions.
The achievement is based on previous work by the same researchers who first reported the successful microbial defluorination of a fully fluorinated PFAS structure by replacing carbon-fluorine bonds with carbon-hydrogen bonds.
Per- and polyfluoroalkyl substances, or PFAS, are a group of more than 9,000 chemicals used in countless industrial processes and commercial products since the 1940s. As a result, PFAS has entered the water cycle and is now found in virtually every water source. These chemicals contain a bond between fluorine and carbon atoms, which is the strongest of the known single bonds, making PFAS non-biodegradable and resistant to conventional water treatment methods. They get into the tissues of organisms, including humans, where they have been linked to certain types of cancer, thyroid and liver problems, and probably other, still understudied, health problems.
In a previous paper, Yue Meng, an associate professor of chemical and environmental engineering, and her colleagues reported the use of anaerobic microbial communities, often used for dechlorination, to degrade two specific PFASs, including one fully fluorinated or perfluorinated structure.
New work makes this study a step further, showing that the entry point for anaerobic microbes was the double bond between carbon atoms located adjacent to the carboxyl group of FCA molecules. Trifluoromethyl branches on the double bond could further enhance biodegradability.
Microbes capable of doing this type of deflation are not uncommon. Using activated sludge – a microbial community commonly used in sewage treatment plants to break down and remove organic matter – and anaerobic conditions, the researchers successfully replicated their previous experiment with a more similar PFAS structure.
“Currently, biocatalysts that can defluorine perfluorinated compounds such as PFOA are very rare. We still know very little about which microbes or enzymes can carry out PFAS in general and how, ”Maine said. “Our work is at the forefront of finding this information.”
Even though scientists are figuring out ways to break the original carbon-fluorine bond in perfluorinated compounds, their work is not complete because the molecules are likely to break down into other molecules that may also be harmful. Successful rehabilitation of PFAS-contaminated media requires the initial destruction of the parent PFAS molecule followed by complete destruction of the secondary molecules.
One recent study by a group of men demonstrated that activated sludge communities were able to completely degrade a secondary molecule from the chemical degradation of one type of perfluorinated chemicals through a process known as cometabolism. Their new study also suggests that simply through collaboration between different microbial groups such as anaerobic and aerobic bacteria, deeper defluorination of some perfluorinated chemicals can be achieved.
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