Per- and polyfluoroalkyl substances (PFAS) are fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom. Accordingly, PFAS contain multiple carbon-fluorine bonds (C-F bonds). These bonds are highly stable and give rise to desirable properties, such as tolerance to high temperatures, which has led to widespread use of PFAS in foams for fire suppression. Fluorocarbons are also hydrophobic and lipophobic, and PFAS are also used as water- and oil-resistant barriers, for example in fabrics, cooking utensils or food containers.
Extensive use of PFAS has resulted in contamination of water and soil with these chemicals. In fact, recent studies have shown rainwater across the globe to be contaminated with levels of PFAS that exceed drinking water advisory levels (see also the BBC’s report on contamination of rainwater). Researchers conclude that the planetary boundary for PFAS has been exceeded and “it is of great importance to avoid further escalation of the problem of large-scale and long-term environmental and human exposure to PFAS by rapidly restricting uses of PFAS wherever possible”. Repeated exposure to low levels of PFAS has been linked to health problems including reduced fertility, reduced immune responses and cancer. PFAS are very difficult to metabolise and excrete from the body, owing to their very high stability. Consequently, PFAS bioaccumulate over time, increasing the risk of health problems.
Despite the “forever” nature of PFAS, many single-use plastic products contain PFAS. Recently, international and national regulations have been implemented that aim to reduce reliance on single use plastics and to move society away from the traditional linear plastics economy (see our previous article “Single-use plastics: a law unto themselves”).
In Europe, efforts are being made to reduce the widespread use of PFAS. In March 2022, the European Chemicals Agency (ECHA) submitted a proposal under EU Registration, Evaluation, Authorisation and Restriction of CHemicals (REACH) to restrict PFAS in firefighting foams. Several EU member states also intend to submit a broader proposal in January 2023 to restrict the manufacture, placing on the market and use of PFAS.
In the UK, the Health and Safety Executive (HSE) conducted a call for evidence as part of the ongoing Regulatory Management Options Analysis (RMOA) on PFAS under UK REACH. The recommendations from the RMOA are due to be published on the HSE website in summer 2022, and may indicate that a restriction is an appropriate measure to control the identified risks. The appropriate authorities, with HSE, will consider the recommendations as soon as possible after publication.
However, even if the widespread use of PFAS is reduced, the PFAS already contaminating drinking water and food products need to be removed and degraded into harmless products. Owing to the high stability of PFAS, degradation methods had until recently required harsh conditions, which require a high-energy input. However, B. Trang et al., of Midwestern University have recently published their research in Science on a milder way to break down PFAS (see also the BBC’s report on this research). They report that one of the largest classes of PFAS, perfluorocarboxylic acids (PFCAs), is broken down under mild conditions and with inexpensive reagents (temperatures of 80 to 120 °C, in the presence of sodium hydroxide in mixtures of water and dimethylsulfoxide under ambient pressure). The same method was also found to successfully degrade branched perfluoroalkyl ether carboxylic acids (another major class of PFAS), suggesting that it could be applicable to a host of different classes of PFAS. This research could therefore pave the way towards low-cost, facile methods of reducing contamination by PFAS, a class of chemical compounds that are (by design) relatively inert and, as such, difficult to remove from the environment.
Mentioned in the paper by B. Trang et al., is a provisional patent application (US 63/261,772, unpublished) that has been filed in the name of Midwestern University, and which describes methods to degrade PFCAs. Filing patents can be an effective way to protect new innovation where commercialisation will likely be of potential interest.
Patent filing data can be used to gauge growth and global trends in emerging technologies. In 2021, the EPO released a report summarizing a comprehensive review of innovation trends in the plastics sector. Some of the key findings in the report are discussed in our previous article “Polymers: transition to a sustainable future”. For example, chemical recycling includes breaking down polymers into smaller molecules, as in the process described by B. Trang et al., and has the potential to be used with more problematic waste streams (such as those comprising PFAS). The potential offered by chemical recycling methods appears to be reflected in the filing trends as reported by the EPO: chemical and biological recycling methods generated the highest level of patenting activities in this area over the last decade.
In summary, whilst PFAS have contaminated water and soil across the globe, a combination of new legislature to reduce widespread use of PFAS, with new-found mild chemical degradation methods to degrade existing PFAS has the potential to undo at least some of the damage done. Patent filing trends suggest a growth in the area of chemical plastic recycling: it seems the future of plastic recycling could be chemical.