Forever chemicals, also known as PFAS, are one of the biggest environmental health hazards of the modern era. Far from being localised in a few contaminated areas, these dangerous substances are everywhere: in rivers, groundwater, wastewater, and even household dust.
These invisible contaminants have been connected with various cancers and developmental diseases. An estimated 98 per cent of people in the US have detectable levels of these synthetic chemicals in their blood, a pattern replicated around the world.
Cost and sustainability are barriers to scaling existing treatment solutions. Yet emerging biobased techniques could offer new tools without the disadvantages of traditional methods.
The problems with current treatments
PFAS are found everywhere because they have been used for decades in ordinary consumer items such as non-stick pans, firefighting foam, and food packaging. Companies have valued their heat-resistant, flame-retardant, hydrophobic, and friction-reducing properties.
True to their name, forever chemicals have proven almost impossible to break down at scale. This is thanks to the fact that the chemical bonds that make them up are incredibly hard to break apart.
The best-understood methods of treating PFAS contamination in soil or water involve physical or chemical approaches: adsorption, electrochemical oxidation, UV irradiation, sonochemical degradation, or nanofiltration.
Most have proven highly effective in lab settings, especially when used in combination. Yet the barrier to wide-scale PFAS treatment, whether for soil or water, is the high energy and capital costs.
The formation of toxic byproducts is another concern around existing methods. Perchlorate and chlorate result from some electrochemical PFAS removal techniques, for example, which are themselves harmful to health.
MIT’s silken membranes
Natural materials could solve some of these issues. This year, Yilin Zhang, Benedetto Marelli, and four other researchers at MIT reported on a new silk-based PFAS remediation platform that they had discovered almost by accident. It could offer a harmless and entirely degradable alternative to chemical and physical PFAS removal techniques.
For another research project on seed labelling, the researchers had silk proteins processed into uniform nanoscale crystals. Once combined with cellulose nanocrystals of a particular electrical charge, the silk proteins formed a completely new and powerful material that could remove contaminants: PFAS among them.
The material has one added advantage. Biobased membranes are already used in mediation but one challenge is that bacteria and fungi quickly take over. The gunk renders the membrane impossible to use effectively. This new material however also had high antimicrobial properties.
The platform has the added advantage of sustainability. The basic materials needed to make the device can be sourced from cheap waste feedstock that is also biodegradable and low-impact. The silk industry produces a lot of byproducts while forestry wood waste pulp can be an abundant source of the cellulose needed in the application.
A fungal and circular PFAS platform
The membrane filtration approach is just one method of tackling PFAS pollution but it is not the only one nor the most effective. Removing PFAS from soil or water raises the issue of what to do with the toxic material later. Actually breaking down the chemicals, not just filtering them out, is key.
One researcher spearheading biobased degradation methods is Susie Dai of Texas A&M Agrilife Research. Her team found that a fungus called ‘white rot’ degrades PFAS at a rapid rate. After two weeks, more than 98% and 99% of the two PFAS types PFOA and PFOS respectively were removed by the platform she and her team came up with.
As with most biotechnology, the basic mechanism was lifted from nature but the team had to modify the organism before it could be put to work as a PFAS-degrading device. Her team developed a biobased and low cost ‘matrix’ to house the fungus. It was made up of the leaves, stalks, and cobs of corn plants left in the field after harvest, forming a porous biological structure on which the fungus would grow. It was then seeded with nutrients for the fungus.
The porous corn-based structure was designed to fix the fungus and the PFAS chemicals in close contact over extended periods, speeding up the time the process took. By extending its lifespan and supporting its metabolism, the corn-waste framework would also allow the fungus to stay effective for longer, supporting the tech’s economic viability.
This biobased PFAS-treating platform could have the potential to offer a low-cost and highly sustainable approach to environmental clean-up. Fungus and post-harvest waste are two very low-impact materials. The former needs very few inputs to grow while the corn waste requires no additional resources to produce. Unlike other solutions to PFAS, the platform does not produce other toxic waste products during the process of treatment.
University researchers cultivate PFAS-eating microbes
At universities around the US, another biobased tool for PFAS degradation is taking shape: microbes that metabolise the chemicals so they become easier to treat through more conventional means.
At Northern University, the Acetobacterium bacteria group is the topic of interest among the chemists around William Dichtel. Some of these microbes in this group can split PFAS into smaller pieces that could then be treated more easily by chemicals.
At Princeton, the Acidimicrobium A6 is under investigation for its PFAS-eating properties. It is rare to find microbes that have evolved rapidly enough over the last century to deal with recalcitrant man-made synthetics, but this one can apparently break apart the carbon fluorine bond that makes PFAS so resilient. The microbe was originally found in a very particular acidic and iron-rich wildlife management area. Peter Jaffé leads the team.
Microbes best for soil contamination
Microbial approaches could be most practical and cost-effective when it comes to treating hyper-contaminated ground soil. Such an approach would be welcome in Flanders, Belgium where groundwater concentrations are so high around a major PFAS manufacturing site that residents within 10 miles have been warned they should no longer eat home-grown produce. Airports and military sites around Germany display similarly dangerous PFAS concentrations in the ground.
In these circumstances, existing approaches to PFAS treatment are difficult to apply. Soil ‘washing’ and thermal treatment have been tested at scale but are expensive and energy-intensive. A large volume of washing solvent or high temperatures are needed for these techniques to be effective.
Yet there are commercial hurdles to overcome before microbial solutions become the norm in PFAS treatment. Scientists will have to find ways of consistently producing microbial strains that break down PFAS effectively in ways that are replicable outside of the lab.
Part of the reason why this is an issue is that scientists still do not understand the exact physiological and chemical mechanisms inside these creatures that can break down these chemicals. More basic research into biological degradation works is needed before we can create reliable methods for making made-to-order PFAS-eating microbes.
A varied toolkit
The main advantage of biobased methods to PFAS degradation is that they produce much fewer harmful chemical pollutants than other approaches. The sustainability and biodegradability of biobased PFAS treatment platforms are also huge advantages when remediating large bodies of water or soil.
However, no single biobased method will be enough on its own to tackle an environmental health problem of this scale. Effectively treating PFAS contamination may require a multi-step process that combines different biobased methods while also pairing biological approaches with the better-understood physical and chemical techniques. The reason for this is that there are between 800 and 7 million chemicals within the PFAS group, making it unlikely that there will be a single solution that can address the problem.
A multi-pronged approach to PFAS remediation would go far beyond a single device in a single location. For example, a simple tap attachment in the home containing plant-based matrixes of microbes or fungi could become the first line of defence against bodily contamination. Alongside this, modular biobased treatment facilities could be installed at existing water treatment plants, tackling different classes of PFAS in a more centralised manner.
Chemical and physical PFAS treatment techniques will also have a role to play. Microbes can be the first port of call for tackling PFAS contamination, making these chemicals more tractable for conventional treatment methods. Microorganisms have proven particularly good at treating shorter-chain PFAS while the longer-chain PFAS could still be the target of chemical interventions.
Whatever the arrangement, it is clear that the sheer number of PFAS chemicals now in the environment will demand various techniques and infrastructures, biobased and circular platforms included.