Mycoremediation Takes on PFAS Pollution

1. Introduction

Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemicals that have been widely used in various industrial and consumer products since the 1950s (Figure 1). PFAS contributes to preventing food adhesion to packaging or cooking surfaces, making clothes and carpets resistant to stains, and improving the efficiency of firefighting foam. Moreover, these substances have been widely used in: 

• Cosmetics: for instance, in sunscreen because they exhibit heat resistance and film-forming in water properties. 
• Electronics: fluoropolymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are used in insulators, printed circuit boards, cell phones, computers, and speakers. 
• Medical devices: fluoropolymers are used as coating agents in catheters and needles to reduce friction and improve clot resistance.
• Food packaging: grease-resist,t paper, fast-food containers and wrappers, microwave bags, pizza boxes or candy wrappers. 
• Firefighting/fireproofing foams: aqueous film-forming foams (AFFF) designed to extinguish flammable liquid hydrocarbon fires frequently include PFAS in their composition for their unique properties. 
• Automotive: a wide range of mechanical components are made of fluoropolymers, including wiring and cables, fuel delivery tubing, seals, gaskets and lubricants. 

For more details, see: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6992415/pdf/nihms-1061846.pdf 

Recently, concerns have been raised about the environmental and health impacts of PFAS due to their persistence in the environment and bioaccumulative nature. These chemicals are often referred to as "forever chemicals" because they do not break down easily and can persist in the environment for (very) long periods. PFAS have been detected in air, water, soil, wildlife, and humans around the world, and have been associated with various adverse health effects, including cancer (e.g., testicular, kidney, and thyroid cancer), reproductive issues, immune system dysfunction, and developmental delays. 

Example of recent PFAS contamination incident and impacts on local communities

In 2023, residents of a small town in the Midwest were shocked to discover that their drinking water supply had been contaminated with high levels of PFAS. The contamination was traced back to a nearby industrial facility that had been manufacturing firefighting foam containing PFAS for decades. Despite the facility being shut down for several years, PFAS chemicals had leached into the groundwater, posing a significant threat to public health. Local residents were understandably alarmed by the news, as PFAS contamination has been linked to various adverse health effects, including cancer, reproductive issues, and immune system dysfunction. Many families relied on the town's groundwater for drinking, cooking, and bathing, and the revelation of contamination sparked concerns about long-term health risks. The town's authorities immediately took action to address the crisis, providing alternative sources of clean drinking water to affected residents and implementing measures to monitor and mitigate PFAS levels in the environment. However, the incident highlighted the broader issue of PFAS contamination nationwide, prompting calls for stricter regulations on PFAS use and disposal and greater accountability for industries responsible for contamination. The impact of the PFAS contamination extended beyond health concerns, affecting property values, local businesses, and community trust. Residents faced uncertainty about the long-term effects of exposure to PFAS and the effectiveness of remediation efforts, underscoring the need for comprehensive solutions to address PFAS contamination and protect public health and the environment.

The most well-known PFAS compounds include perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). These two compounds have been phased out of production in many countries due to health concerns, but they persist in the environment and continue to be detected in water supplies and human bodies. Regulatory agencies, such as the U.S. Environmental Protection Agency (EPA), have established health advisories and guidelines for PFAS contamination in drinking water. Efforts are also underway to regulate PFAS use, remediate contaminated sites, and develop safer alternatives. Research into PFAS continues to expand to understand better their environmental fate, human exposure pathways, health effects, and remediation strategies. Efforts are also being made to develop more sensitive detection methods and safer alternatives to PFAS in consumer products.

2. PFAS removal and remediation overview 

The removal of per- and polyfluoroalkyl substances (PFAS) from the environment poses considerable challenges with existing physico-chemical treatments. Techniques such as photolytic degradation, sonolysis (process using ultrasound waves to physically impact and degrade water contaminants), and electrochemical oxidation require extreme conditions, driving up treatment expenses while failing to convert PFAS into less harmful forms. Besides, methods employing activated carbon or ion exchange merely sequester PFAS without facilitating their transformation, leaving waste contaminated with these persistent compounds. Overall, these approaches often lack efficiency in situ further complicating the remediation process. 

In contrast, bioremediation emerges as a potentially more cost-effective solution for PFAS removal, harnessing the natural capabilities of microorganisms to metabolise contaminants into less toxic or inert forms. To date, remediation efforts have mainly focused on bacterial degradation owing to its perceived advantages in cost-effectiveness, resilience, and rapid growth. Bacteria are adept at utilising organic pollutants directly as sources of energy and carbon, a process that facilitates their rapid proliferation and pollutant degradation. However, this approach has its limitations. Bacterial remediation strategies are limited when confronted with complex pollutants or when suitable organic carbon sources are lacking in the environment. 

On the other hand, fungal remediation (i.e., mycoremediation) offers a distinctive and complementary approach to pollutant degradation. While fungi typically require an external energy and carbon source for degradation to occur  (i.e., co-metabolism), they possess unique enzymatic machinery capable of degrading a wide variety of toxic compounds. This enzymatic activity enables fungi to break down pollutants through the production of extracellular enzymes, providing a versatile means of targeting pollutants across a broad concentration range. With their intricate hyphal networks (Figure 2), filamentous fungi can access contaminants over large areas, enhancing remediation efficiency. Besides, using inexpensive lignocellulosic materials such as rice straw, wheat straw, or wood chips/pellets can provide the necessary energy and carbon sources for fungal degradation, making fungal remediation a cost-effective and sustainable solution for addressing environmental contamination, including PFAS pollutants.

3. PFAS mycoremediation: Case study

• Feasibility of Biodegradation of Polyfluoroalkyl and Perfluoroalkyl Substances - Tseng (2012)

The first report of fungi-mediated PFAS bioremediation date back to 2012, when Tseng (2012) investigated the capability of the white-root fungi Phanerochaete chrysosporium and the brown-root fungi Aspergillus niger to degrade several perfluoroalkyl substances, namely fluorotelomer alcohols (FTOHs - water and oil repellent properties), perfluorooctanoic acid (PFOA - industrial surfactant) and perfluorooctane sulfonic acid (PFOS - sealing agent and adhesive). Through a 35-day laboratory experiment, Tseng (2012) reported that when exposed to 6:2 FTOH under aerobic conditions, P. chrysosporium was able to significantly decrease the concentration of FTOH (45%), producing shorter-chain metabolites such as perfluorobutyric acid (PFBA) and perfluoropentanoic acid (PFPeA). Based on the results of this study, the author discusses the fact that fungi, particularly P. chrysosporium, show promising potential in biodegrading PFAS compounds. This pioneer investigation further highlights the importance of additional research to elucidate the optimal conditions (medium composition), degradation pathways, and enzymatic involved in fungal-mediated PFAS remediation. 

• Fungal biotransformation of 6: 2 fluorotelomer alcohol - Merino et al., (2018)

The findings of Tseng (2012) led other research groups to investigate the bioremediation potential of fungi in degrading PFAS. For example, Merino et al., (2018) delved into the fungal degradation of 6:2 FTOH by various wood-decaying fungal strains and isolates from PFAS-contaminated sites. The investigation revealed significant insights into fungal capabilities in transforming 6:2 FTOH, a compound increasingly utilised in FTOH-based products. Interestingly, P. chrysosporium and several isolates (i.e., Gloeophyllum trabeum and Trametes versicolor (commonly named Turkey tail)) demonstrated remarkable efficiency in biotransforming 6:2 FTOH, yielding substantial amounts of polyfluoroalkyl substances like 5:3 acid, while diverting away from terminal perfluorocarboxylic acids (PFCAs). This redirection towards alternative metabolites suggests promising mechanisms for PFCA precursor biotransformation by fungi. As discussed by Tseng (2012), the investigation highlighted the potential for medium amendments to enhance 6:2 FTOH biotransformation rates and product profiles. Besides, the fungal isolates tolerated up to 1000 mg/L of PFOA and PFOS, and some isolates even experienced improved growth with increasing concentrations. While PFAS are being called “forever chemicals”, these findings are of great significance and indicate that fungi can act as viable candidates for PFAS remediation strategies. These findings underscore the importance of further research into fungal-mediated PFAS remediation, emphasising the promising perspectives of fungi as key players in developing sustainable solutions for addressing PFAS contamination in various environments. 

• A Review: Per-and Polyfluoroalkyl Substances—Biological Degradation - Grgas et al., (2023)

In a recent review, Grgas et al., (2023) discuss the feasibility of remediation and treatment of PFAS and effective decomposition of PFOA using the enzyme-catalyzed oxidative humification reaction (ECOHR). ECOHR reactions are ubiquitous in soil systems and characterised by a series of oxidative reactions during the humification process (i.e., the breakdown of organic materials in soils and composts leading to the formation of humus). ECOHR has been proposed as a feasible method for PFAS remediation, with ECOHRs being carried out by natural extracellular enzymes secreted by white and brown root fungi, including laccases, lignin peroxidases (LiP) and manganese peroxidases (MnP). For example, Luo et al. (2015) used laccase extracted from the oyster mushroom Pleurotus ostreatus in an ECOHR system and reported approximately 50% of PFOA decomposition over a 157-day experiment. From this finding, the authors suggested that PFOA may be transformed during humification and highlight the fact that ECOHRs can potentially be used for the remediation of PFOA-contaminated environments. A few years later, Luo et al., (2018) conducted a similar experiment, this time aiming to investigate the degradation of PFOS, another persistent perfluorinated alkylated substance. Using the same laccase-induced ECOHR system, the authors reported that ~59% of the PFOS was transformed over a 162-day incubation experiment. The research conducted by Grgas et al. (2023) underscores the promising potential of enzyme-catalyzed oxidative humification reaction (ECOHR) in the environmental remediation of PFAS. With techniques like ECOHR, once-persistent "forever chemicals" could be effectively degraded, mitigating their prolonged presence in natural habitats. The findings from experiments by Luo et al., (2015, 2018) showcasing significant PFOA and PFOS transformation rates over incubation periods offer a glimpse into the impactful role ECOHR could play in addressing PFAS contamination.

4. Conclusion and future perspectives

The multifaceted nature of per- and polyfluoroalkyl substances (PFAS) contamination demands innovative and sustainable remediation strategies to mitigate its environmental and public health impacts. As highlighted in this article, emerging techniques such as mycoremediation and enzyme-catalyzed oxidative humification reaction (ECOHR) offer promising avenues for addressing PFAS pollution. Mycoremediation, leveraging the enzymatic capabilities of fungi, presents a cost-effective and environmentally friendly approach to PFAS remediation. The remarkable efficiency demonstrated by fungal species in degrading PFAS compounds underscores the potential of harnessing nature's own mechanisms to combat contamination. Further research into optimizing fungal degradation pathways, understanding the influence of environmental factors, and scaling up mycoremediation processes is essential to fully realize the potential of this approach.

Similarly, the enzyme-catalyzed oxidative humification reaction (ECOHR) holds great promise in transforming PFAS compounds into less harmful forms. The ability of natural extracellular enzymes secreted by fungi to catalyze oxidative reactions during humification offers a novel pathway for PFAS remediation. Continued exploration of ECOHR mechanisms, optimization of reaction conditions, and field-scale studies are crucial steps toward implementing this technique in real-world remediation scenarios.

Looking ahead, interdisciplinary collaboration among scientists, engineers, policymakers, and industry stakeholders will be essential to advance research and development in PFAS remediation. Integrating cutting-edge technologies with traditional remediation approaches, along with robust regulatory frameworks, will facilitate the transition toward cleaner, PFAS-free environments. Furthermore, prioritizing prevention, including the development of safer alternatives and responsible PFAS management practices, is paramount to prevent future contamination incidents.

In conclusion, while the challenges posed by PFAS contamination are significant, the opportunities for innovative solutions are equally vast. By harnessing the power of nature, leveraging technological advancements, and fostering collaborative efforts, we can pave the way toward a future where PFAS pollution is effectively remediated, safeguarding both environmental health and human well-being.

What it means for Ecomyko

At Ecomyko, we're on a mission to transform waste management using fungal enzymes. Our focus on mycoremediation perfectly aligns with tackling PFAS contamination in plastic packaging. By harnessing fungi's power, we're working to break down PFAS in plastics, offering eco-friendly waste solutions. This research highlights our commitment to a cleaner planet and drives our efforts to create sustainable waste management solutions for a better tomorrow.

Author: François Audrézet

Sources: 

https://pinellas.gov/per-and-polyfluoroalkyl-substances-pfas/ 

https://www.solvelabs.se/en/blog/34_mushrooms-hidden-allies-internet-of-the-forest-and-natural-recycling.html 

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