Enlisting Microbes to Break Down ‘Forever Chemicals’
By Saima S. Iqbal
A group of bacteria has proven to be effective in breaking down the tough carbon-fluorine bonds that give “forever chemicals” their name. This discovery raises hopes that microbes could potentially help eliminate these persistent pollutants from the environment.
There are nearly 15,000 chemicals, known as perfluoroalkyl and polyfluoroalkyl substances (PFASs), commonly found in everyday consumer products such as pizza boxes, rain jackets, and sunscreens. These chemicals can enter the body through drinking water or crops fertilized with sludge, and they have already contaminated the blood of almost every person in the U.S. Even low levels of chronic PFAS exposure have been linked to various health issues, including kidney cancer, thyroid disease, and ulcerative colitis.
Current methods for destroying PFASs require extreme heat or pressure and are only effective on filtered waste. Scientists have long speculated whether bacteria could break down these chemicals in natural environments, offering a more cost-effective and scalable solution. However, carbon-fluorine bonds are mainly found in human-made materials, and PFASs have not been around long enough for bacteria to evolve the specific ability to digest them. While this new study is not the first to identify a microbe that can break down carbon-fluorine bonds, it represents a significant step forward, according to William Dichtel, a chemist at Northwestern University.
To identify promising bacteria, the researchers screened various microbial communities living in wastewater. They found four strains from the Acetobacterium genus that stood out. These strains produced enzymes capable of breaking down caffeate, a plant compound similar to some PFASs. The enzymes replaced fluorine atoms in the PFASs with hydrogen atoms, and transporter proteins ferried the fluoride ion by-products out of the microbes, protecting them from harm. Over three weeks, most of the strains broke down the targeted PFAS molecules into smaller fragments that could be more easily degraded using traditional chemical methods.
The Acetobacterium bacteria targeted perfluoroalkyls, a type of PFAS that few microbes can break down, by directly attacking carbon-fluorine bonds. However, these bacteria could only work on unsaturated perfluoroalkyl compounds containing carbon-carbon double bonds adjacent to the carbon-fluorine ones. These compounds serve as building blocks for larger PFASs and are produced by chemical manufacturers or formed during PFAS destruction.
While a microbe called Acidimicrobium sp. strain A6 has previously been shown to break down carbon-fluorine bonds and completely degrade two common perfluoroalkyls, it grows slowly and requires specific conditions to function effectively. The Acetobacterium strains target a different group of PFASs, and the researchers hope to enhance their efficiency or broaden their scope, potentially to more perfluoroalkyls.
Lead study author Yujie Men of the University of California, Riverside, envisions these microbes working in tandem with other methods to degrade PFASs. She acknowledges that the complex chemical structures of these compounds mean that no single approach can solve the problem. While there are challenges to overcome before commercial use of these microbes becomes a reality, Men is optimistic about the potential of this technique. “We’re paving the road as we go,” she says with a smile.
