We live in a beautiful world filled with vast mountain ranges, sprawling valleys, and roaring rivers. It is also a world of massive corporations, consumerism, pollution, and waste. Every day, pesticides, heavy metals, plastics, and many other contaminants are introduced to our terrestrial and marine surroundings. A push for green practices in industries and everyday life is vitally important and will only continue to become more so in the coming years. Remediation, meaning restoring balance, is critical.
Bioremediation is the use of microorganisms, either natural or introduced, to reduce pollutants. The goal is to mineralize organic pollutants and transform metals into less toxic forms or remove them. Mycoremediation, specifically, is the practice of using fungi to clean toxins and rehabilitate the environment.
Mycophobic ideology has plagued western society for far too long! Thankfully an increasing number of scientists, amateur mycologists, and everyday fungi-loving people are beginning to see that, under the umbrella of mycoremediation, a plethora of inexpensive, effective methods to decontaminate the environment are possible using fungi. Mycelium “mushroom roots” and other parts of fungi have many beneficial compounds and enzymes that researchers have found to aid in the decomposition and regeneration of certain pollutants in the environment.
Examples of mycoremediation include insertion of mycelium into compost, white-rot fungi breaking down harmful pollutants, and using myco-materials to build sustainable products. Some fungi are useful in the biodegradation of contaminants in extremely cold or radioactive environments where traditional remediation methods prove too costly or are unusable due to the extreme conditions. Mycoremediation can even be used for fire management! A process known as encapsulation uses fungal spores coated with agarose (seaweed extract) in pellet form. These pellets are introduced to substrates in the burnt areas, breaking down the toxins in the environment and stimulating growth. We will explore a few of these methods keeping in mind that as our society becomes more invested in studying fungi there is no telling what these incredible organisms can do for our planet.
How it Works
Though many people do not give it a second thought, the fact remains that the world would be a very different place without fungi. Living below our feet or high above us in the trees, everywhere in nature fungi are working as decomposers, acting as the bridge between life and death. What does that mean for us? Besides the fact we are not living on a pile of thousands of years’ worth of deceased plant and animal matter, they can also do wonders for your compost and garden but perhaps most importantly fungi can help with habitat renewal and undo some of the damage humans have caused.
When fungi are released into a substrate they secrete enzymes, ahead of the mycelium growth, and then slide through their fluids to break down the material into smaller components so they can ingest the nutrients via absorption through the cell walls. The now smaller components can then be used by other microorganisms in the soil and balance within the soil system begins to be restored. Bacteria used in traditional remediation need to come into direct contact with the toxin to break it down.
Fungi can be categorized into 2 physiological groupings in terms of what they break down: brown-rot and white-rot. Brown-rot fungi break down cellulose, found in plant cells whereas white-rot fungi are more competent in breaking down lignin, which is present in wood and bark. Most importantly for mycoremediation, white-rot species can break down complex polymers that have similar structures to lignin, including many of the compounds found in pesticides and other industrial pollutants.
Mycelium’s ability to quickly grow its biomass is another reason it has great potential for remediation. Research has shown mycoremediation is effective in degrading PCBs, aromatic hydrocarbons, oil spills, and eliminating E. coli. In addition, cleaning can also be used to prepare sites for potential future contamination, for example, at the spot of a future industrial runoff site
White-Rot Fungi and Degradation of Contaminants
Reduction of pesticide contamination is an important potential for mycoremediation. Pesticides have major long-term effects on the natural decomposition processes and nutrient cycling. They can stay in an ecosystem for a very long time because they can be transferred through the food web. Primary producers i.e., plants, pass pollutants to the herbivores that eat them, and then on to the predators that hunt the herbivores. At each link on the food chain the pollutants compound, a harmful phenomenon called biomagnification. Additionally, throughout an organism’s life contaminants compound within the body, this is referred to as bioaccumulation. Pesticides and other contaminants can also stay in an ecosystem through water-run-off, spreading to large areas in surrounding ecosystems, seeping into the roots of plants, and being consumed by animals.
White-rot fungi are a physiological grouping containing fungi that can extensively break down lignin, a key structural material in the cell wall of many plants, especially important in wood. These fungi can also use their extracellular ligninolytic enzymes like laccase and manganese peroxidase to degrade high quantities of pesticides! Oyster mushrooms (Pleurotus) are included in this group of efficient, remarkable organisms.
Insecticides like DDT, classified as organochlorines, were vastly applied in immense quantities in the 1940s to 1960s to control mosquitos and other pests. In the 60s the knowledge of their harmful effects on human and environmental health became more widespread. The use of organochlorines has mostly been discontinued in developed countries, but they are still used in several less-developed nations. These herbicides are persistent in the environment, and because of biomagnification through the food chain have caused sickness and population decrease in higher predators. White-rot fungi have huge potential to act as an agent to degrade contaminants in soil.
White-rot fungi enzymes have also proven useful in the decolouration of synthetic dyes, far superior to prokaryotes (organisms with plant cells). They can oxidize (give oxygen to change the compound) a more diverse range of compounds in dry, acidic, and low nitrogen sites that do not support prokaryotic bacteria. Although bacteria may have the advantage in areas without oxygen. Even a nylon-degrading enzyme has been found in a certain white-rot fungus!
Safe disposal of military munitions waste is a large environmental problem. Not only does the detonation risk of explosives render them hazardous, but the constituent compounds, explosive and non-explosive, are also toxic and persistent in the environment. Explosive manufacturing, including “red water” created from by-products of TNT manufacturing and underground disposal sites, leading to contact with soil and groundwater. S.B Pointing in an article published in 2001 speaks of research showing that certain white-rot basidiomycetes (mushroom producing fungi) are capable of oxidative TNT attack suggesting the possibility of mineralization of explosives. Several white-rot fungi can transform TNT into DNTs. DNT is still highly toxic but white-rot fungi have been shown as capable of DNT degradation, and mineralization to CO2.
While removal of contaminants from soil using white-rot fungi has not been fully tested in the field, scientists are getting the ball rolling by studying these astonishing organisms and looking forward to creating solutions to reduce human-introduced pollutants. While bioremediation using prokaryote is an established practice, white-rot fungi have the potential to expand the range of substrate treated. In-lab testing looking for potential soil treatments is underway. Mother Nature cannot combat us on her own; we need to collectively push for greener practices in industries.
Mycoremediation and at Home Composting
Mycoremediation is not just for top scientists working on large projects! Anyone can do a small part to give back to our earth. Colonized straw or sawdust, like FORIJ grow kits after they are finished fruiting, can be added to the soil in your garden or compost. The mycelium will help the soil maintain moisture and reduce erosion. Another example of how you can exercise mycoremediation at home, aside from planting spent blocks in your garden beds, is to treat waste--such as those excreted by pets--with spent oyster blocks. Place dog or cat waste in a bucket with spent grow blocks to inoculate waste with mycelium, and when fully colonized you can place the contents of the bucket in a composting pile after the mycelium has worked its way through. Use this super nutritious, mycelium-packed compost to create nutrient-packed topsoil for the garden! It’s great for your fruits and veggies, as well as for the environment.
Pleurotus species (oyster mushrooms) are excellent to use as they are very robust and will grow on many different substrates. If you know of contaminants that will be present in the mycoremediation site, you can test the resilience of different species by mixing a small amount of the contaminant into an agar plate and attempting to grow the mycelium. When choosing a fungi species for your project make sure it is compatible with the substrate. Like humans, not all fungi like to eat the same things. You can find a more thorough guide to small-scale mycoremediation in ‘Organic Mushroom Farming and Mycoremediation’ by Tradd Cotter.
So, take a moment to thank fungi for being the unsung heroes, restoring balance to our beautiful Earth!
S.B. Pointing (2001) Feasibility of bioremediation by white-rot fungi. Applied Microbiology and Biotechnology 57:20-30.
- Cotter (2014) Organic Mushroom Farming and Mycoremediation.