A review of microbial degradation of per- and polyfluoroalkyl substances (PFAS): Biotransformation routes and enzymes

Since the 1950s, copious amounts of per- and polyfluoroalkyl substances (PFAS) (dubbed "forever chemicals") have been dumped into the environment, causing heavy contamination of soil, surface water, and groundwater sources. Humans, animals, and the environment are frequently exposed to PFAS through food, water, consumer products, as well as waste streams from PFAS-manufacturing industries. PFAS are a large group of synthetic organic fluorinated compounds with widely diverse chemical structures that are extremely resistant to microbial degradation. Their persistence, toxicity to life on earth, bioaccumulation tendencies, and adverse health and ecological effects have earned them a "top priority pollutant" designation by regulatory bodies. Despite that a number of physicochemical methods exist for PFAS treatment, they suffer from major drawbacks regarding high costs, use of high energy and incomplete mineralization (destruction of the CF bond). Consequently, microbial degradation and enzymatic treatment of PFAS are highly sought after as they offer a complete, cheaper, sustainable, and environmentally friendly alternative. In this critical review, we provide an overview of the classification, properties, and interaction of PFAS within the environment relevant to microbial degradation. We discuss latest developments in the biodegradation of PFAS by microbes, transformation routes, transformation products and degradative enzymes. Finally, we highlight the existing challenges, limitations, and prospects of bioremediation approaches in treating PFAS and proffer possible solutions and future research directions.