Fungi are having a moment. Largely overlooked, awareness and interest in the fungal kingdom is on the rise, and some feel that an alliance with fungi will be key to a long-term sustainable future.

What is mycoremediation?

Mycoremediation is the application of fungi to decontaminate the environment. The creation of fungal biomass in the form of mycelium results in the biochemical breakdown, transformation or bioaccumulation of environmental pollutants. When fungi are used alongside other organisms such as plants and bacteria for this purpose, the process is referred to as bioremediation.

Setting the scene - the scale of the problem

Much of the pollutants derived from industry and agriculture end up in the soil. Soil pollution is a pervasive global problem, impacting at least 3.2 billion people - 40% of the world’s population. It is thought that over 80% of Europe’s soils are contaminated with pesticide residues. The global production of industrial chemicals has doubled since 2000 and looks set to nearly double again by 2030, meaning soil pollution is only likely to become a more pressing problem over time. We need to stop treating soil like dirt, given that it provides the foundation for most terrestrial ecosystems, while supporting the growth of almost all our food-producing crops.

https://youtu.be/jXmGzuQMFWM?si=NSPC6NZcSBsOSx\_e

How do fungi clean up pollution?

Fungi are master chemical alchemists, able to concoct an array of different digestive enzymes. They are important decomposers, using these enzymes to break down materials into smaller units that they can absorb through their cell walls as a food source. Fungal mycelium acts as an external gut, secreting these enzymes out into their surroundings. While enzymes are often engineered to be specific to the particular substrate they break down, fungi specialise in non-specific enzymes, which can function as a chemical multi-tool. This comes in part through the ability of fungi to break down wood.

Wood is partly composed of the complex biopolymer lignin. This forms a haphazard, interlinked matrix of molecular rings, making it impervious to breakdown by most enzymes. The non-specific enzymes that wood-eating ‘white rot’ fungi create generate highly reactive free radicals, which can split apart lignin’s tightly bonded structure. Many toxic pollutants happen to structurally resemble the products of lignin breakdown.

Fungi can break down a range of different pollutants that pose a risk to humans and other forms of life. These include crude oil, persistent aromatic hydrocarbons, pesticides, synthetic dyes, some plastics, the explosives TNT and RDX, human and veterinary drugs, antibiotics and synthetic hormones. The ultimate end breakdown product for the organic pollutants that fungi breakdown is carbon dioxide and organic matter.

While certain pollutants such as heavy metals and radioactive compounds do not break down, fungi can convert them to less toxic forms and bioaccumulate them in their tissues - or assist plants in doing so - for safe removal or disposal. One company in Finland has even employed fungal mycelium to filter electronic waste, reporting they were able to reclaim 80% of the gold within it.

Pleurotus ostreatus. Jean-Pol GRANDMONT

Cleaning TOXIC SOIL with fungi and native plants

While some fungi are “picky eaters”, having quite particular dietary preferences, others such as the fungus Phanerochaete chrysosporium have been found to degrade many forms of pollutant, and the oyster mushroom (Pleurotus ostreatus) is a ravenous omnivore, able to consume petrochemicals, PCB’s, cigarette butts and used diapers. Many can be trained to adapt to different environmental conditions, or to remediate high levels of certain contaminants, even beyond the thresholds they normally tolerate in their native environment. Fungi may be more effective than bacteria and plants in degrading certain forms of pollutants, while having the capacity to degrade particularly stable or toxic compounds.

Fungal mycelium can also be used to filter both pollutants and disease causing bacteria such as E. coli from water, a process referred to as mycofiltration. Even in death, fungi can play an effective role in pollution cleanup. It has been found that the cell walls of some species of dead fungi can be used as a filter to mop up heavy metals and radioactive compounds.

How are fungi used in mycoremediation?

The mycoremediation of a particular contaminated site benefits from a bespoke approach, with each site varying in its environmental and ecological aspects. An initial survey of the site may reveal fungi already present that may be well adapted to the local site conditions and the toxins present. These can potentially be cultured, and their growth supported by the addition of organic matter substrate or water to the site in question - it is important that the ecological demands of any fungi used be catered for. By observing what fungi appear on contaminated sites, it also allows for the discovery of new remediator fungi. Alternatively, a known and already tested fungus could be introduced to a site.

The fungal growth substrate applied may consist of wood chips, agricultural waste or spent blocks from mushroom farms, which can potentially be sourced for free as waste products, keeping costs to a minimum and enhancing the environmental efficiency of this process. Fungi can also potentially be used preemptively to prepare a site for contamination, such as processing runoff from proposed agricultural or industrial sites.

https://youtu.be/pIkZ1uQABI8?si=TcH\_TWay5bImk6qh

The Resilience of Fungi

Some fungi possess great resilience, being able to thrive in extreme environments. A number of fungal species found in Antarctica have shown promise in breaking down a number of toxic hydrocarbon pollutants found in crude oil. In spite of the inhospitable conditions, they are able to maintain activity and tolerate the low oxygen levels found in frozen soil, in addition to disruptions to their ability to transport nutrients caused by freeze-thaw cycles.

The fungus Rhodotorula taiwanensis is able to survive in highly acidic conditions, and is also able to tolerate high levels of radiation, and of the heavy metals mercury and chromium. Due to its resilience in these conditions it has been proposed that it could play a role in remediating toxic, radioactive waste.

A holistic and interconnected perspective

Fungi do not work in isolation when remediating a contaminated site, but rather in synergy with plants and bacteria and other organisms. Decomposition happens in stages, with different organisms picking up from where the previous left off in a successional sequence. Mycelial threads can provide highways for bacteria, providing access to otherwise inaccessible areas, boosting decomposition.

Mycorrhizal fungi form symbiotic associations with plants via their roots. They have been found to enhance phytoremediation using plants, enhancing plant resilience in a toxic environment. These fungi can also expand the influence of the plant’s root network, providing more access to contaminants, while also benefiting bacteria which themselves can contribute to the bioremediation process.

Beyond its effect on pollutants in the soil, fungal mycelium can also improve soil structure, helping restore ecological function in degraded soils. Following an initial remediation intervention, there is a tendency for nature to take up the reins and continue the process of regeneration.

Danielle spreading fungal inoculum. Adam Armengual

Conventional remediation vs bioremediation

Conventional remediation of contaminated soils often centers on a ‘dig and dump’ approach, with soil excavated and dumped elsewhere. Such work comes at a great cost - both financial and environmental - failing to actually solve the problem, while also coming with a hefty carbon footprint and risking spreading toxic dust elsewhere. It can cause irreversible damage to sites that may be ecologically and culturally sensitive. The cost of conventional remediation work is a barrier to it being applied in many cases, and it tends to be undertaken by reluctant companies under pressure to adhere to legal regulations.

Mycoremediation offers a cheaper, more effective and environmentally friendly alternative. According to some studies, it is 50-90% cheaper to decontaminate a site through bioremediation than a dig and dump approach. While this approach may require more time than conventional approaches, it has the potential to seed workforce development and provide local jobs, while empowering local communities to play an active role in cleaning up contaminated sites. This work can be carried with resources and agricultural skills accessible to poorer communities, enabling bioremediation to be widescale in reach.

Managing Expectations

In spite of its potential, mycoremediation is no simple fix - the complexity of ecosystems means that there is no single off-the-shelf solution that can be applied across sites and conditions. It is still early days in terms of the field research, and there is still much to learn. How a fungus performs in a lab in a petri dish (with no competition or stress) cannot be extrapolated onto a contaminated ecosystem, where it will face a toxic setting, adverse environmental conditions and competition with other organisms.

Further feasibility studies in the field are vital if mycoremediation is to be more widely adopted, and large scale investment will be needed if it is to be scaled up, with regulatory and funding barriers making such work challenging to undertake.

Highly contaminated site before and after bioremediation measures are implemented. Danielle Stevenson

Seeding hope - the road ahead

While bioremediation is still at the proof of concept stage, pioneering field trials suggest it does hold promise beyond the lab. One of the experts working hard to advance this field is ecotoxicologist Dr Danielle Stevenson, who has recently launched the Centre for Applied Ecological Remediation (CAER) in the hope of advancing research and application of bioremediation. In Danielle’s words:

“I’ve worked on such poisoned landscapes that they resembled Mordor…with limited signs of life, a stench of petrochemicals permeating the air, sites that would spontaneously catch fire in the summer. With the application of fungi and plants (and a little organic matter and water) kickstarting ecological processes I’ve witnessed with my own eyes the tremendous restorative potential these organisms hold at helping clean up polluted areas. This is what motivated me to establish CAER.”

**Resources - **https://caer.earth/