Bacteria found in wastewater treated by many modern treatment plants can be used to break down certain types of PFAS or “permanent chemicals.”
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Bacteria that break down certain “permanent chemicals” can be found in the sludge of sewage treatment plants.
Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a class of synthetic chemicals widely used in oil, heat and water resistant coatings and foams. There are thousands of types of PFAS, some of which are known to cause adverse health effects. They are also long-term environmental pollutants, thanks to the strong carbon-fluorine bonds they contain.
One way to deal with this contamination would be to identify microbes that break down carbon-fluorine bonds, says Yujie Men of the University of California, Riverside. However, fluorine bonds are rare in nature, and microorganisms capable of breaking bonds seem to be rare as well.
Looking for such microbes, Meng and his colleagues collected sludge from a nearby city sewage treatment plant. Next, they spiked sludge samples with three types of he chlorinated PFASs with low, medium, and high carbon-chlorine bond numbers. This chlorinated PFAS is more susceptible to biodegradation than the fluorine bond. They also added methanol to feed the microbes present.
After 84 days under hypoxic conditions, 10 percent of the fluorine bonds in the low oxygen group were degraded, 20 percent in the medium group and about 80 percent in the high group. Subsequent exposure of the sludge to oxygen to activate the aerobic bacteria present resulted in an additional 12% degradation of the remaining bonds in all groups.
Researchers have isolated bacteria responsible for degrading molecules under anaerobic conditions.Their genomes were most similar to Desulfovibrio aminophyllus and sporomus spheroides, a bacterial species commonly found in aquatic environments. “They’re nothing special,” Meng says. Similar microbes may already be breaking down chlorinated PFAS contamination, she says.
Bacteria don’t directly break the tight bond between carbon and fluorine, Meng said. Instead, it breaks the weak bond between carbon and chlorine. Then replace the chlorine with oxygen and hydrogen radicals. This makes the molecule unstable and makes the fluorine bond easier to break.
Degrading chlorinated PFASs does nothing to address contamination with many other types of PFASs that do not contain chlorine. “We’re not going to have one magic bacterium to solve all our problems,” says Lawrence Wackett of the University of Minnesota.
But understanding how these molecules break down could help researchers design more readily biodegradable alternatives to PFAS by incorporating more of these chlorine ‘weaknesses’. can help, he says. However, these molecules should also be tested to ensure they are non-toxic.
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