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Mycoremediation, a term coined by Paul Stamets, refers to the process of using fungi to degrade or sequester contaminants in the environment. It is a form of bioremediation. Mycofiltration is a similar process, using fungal mycelia to filter toxic waste and microorganisms from water in soil.

One of the primary roles of fungi in the ecosystem is decomposition, which is performed by the mycelium. Stimulating microbial and enzyme activity, mycelium reduces toxins in-situ. The architecture and development of mycelial networks complements its usefulness in bioremediation due to its pervasiveness; a single cubic inch of forest topsoil contains more than 8 miles of mycelium if laid end to end and measured. This branch-like network has an extremely high surface area to volume ratio, making its absorptive abilities unsurpassed. For example, the mycelium of saprotrophic fungi secretes extracellular enzymes and acids that break down lignin and cellulose, the two main building blocks of plant fiber. These are organic compounds composed of long chains of carbon and hydrogen, structurally similar to many organic pollutants. Some fungi are hyperaccumulators, capable of absorbing and concentrating heavy metals in the mushroom fruit bodies.

A Wide Diversity of Potential Applications
The key to mycoremediation is determining the right fungal species to target a specific pollutant. The broad diversity of Fungi lends itself well to a wide diversity of potential applications in environmental clean-up. Certain strains have been reported to successfully degrade toxic chemicals that are carbon-based, such as petrochemicals, dioxins, certain pesticides and chemical warfare agents like the nerve gases VX and sarin.

In a text dedicated specifically to the subject of mycoremediation, Harbhajan Singh lists the following as potential areas of fungal bioremediation :
 * treatment of industrial wastewaters
 * treatment of distillery and brewery wastes
 * metabolism of petroleum hydrocarbons
 * degredation of polychlorinated biphenyls
 * metabolism of phenols, chlorophenols, and pentachlorophenol
 * metabolism of polycyclic aromatic hydrocarbons
 * lignin degredation and decolorization of pulp and paper mill effluents
 * decolorization and degradation of dyes
 * biosorption of heavy metals
 * rhizosphere remediation by mycorrhizal fungi.

With respect to petroleum degradation, filamentous fungi have been found to be an ideal candidate. While other microorganisms like bacteria and yeast exhibit particular preferences for the chain-length of alkanes, filamentous fungi show no discrimination between different alkanes. Additionally, fungi can grow under environmentally stressed conditions. It is also relatively cheap to produce large quantities of fungi.

Oil Polluted Environments
An 1998 experiment conducted by Battelle Marine Sciences Laboratory and the Washington State Department of Transportation in conjuction with Dr. S. A. Thomas, a major contributor in the bioremediation industry, revolutionized the way in which fungi were viewed as agents of bioremediation. Four plots of soil were contaminated with diesel and other petroleum waste; one plot was treated with chemical enzymes, another with bacteria according to traditional bioremediation techniques, a third was inoculated with mycelia of oyster mushrooms, and the last was left uninoculated as a control. Over time, the mycelium absorbed the petroleum and excreted enzymes that broke down the carbon-hydrogen bonds of the contaminants. After six weeks, the mycelial-inoculated plot was found to be covered in large, healthy flushes of oyster mushrooms. More than 95% of many of the PAHs (polycyclic aromatic hydrocarbons) had been reduced to non-toxic components from over 20,000 ppm to less than 200 ppm, thus making the soil suitable for highway landscaping projects. The other piles remained lifeless and virtually unchanged. Within another six weeks, the mushrooms of the mycelial-inoculated plot had rotted, attracting insects, which brought birds, which brought seeds. Within 12 weeks, the previously petroleum-soaked plot had been remediated to a small berm of life.

This study inspired many similar projects in the clean-up of land-based oil spills, such as the Amazon Mycorenewal Project. One of the largest land-based oil spills in the world is located in Sucumbios province of the Ecuadorian Amazon. For over 40 years, the people of the region have lived in an environment polluted with carcinogenic PAHs in the soil, causing an above-average rate of cancer. The Amazon Mycorenewal Project, in an attempt to remediate the area, have begun a large-scale project with oyster mushroom mycelia.

However, not all oil spills have or will occur on land, prompting Stamets to explore the possibility of creating a structure to allow oyster mushrooms to grow and even fruit on water. Coined "MycoBooms," tubes of straw and mushroom mycelia are light enough to float on water and corral and absorb spilled oil.

Degradation of Diapers
A recent study by researchers in Mexico City showed a novel approach toward the problem of degrading baby diapers, a recently assumed non-biodegradable material, by inoculating the substrate with oyster mushrooms. They have been shown to rapidly increase the rate of degradation of diapers, which makes up 10-15% of the weight of urban solid waste in Mexico City; around 5 billion are disposed of each year in Mexico alone. 90% of the cellulose, a major constituent of the diapers, can be degraded within 2 months and fully degraded within 4 months. These findings, however, have not yet been applied in a large-scale manner.

Mycoremediation of a Contaminated Watershed
In 2004, Battelle Marine Sciences Laboratory was asked by the Jamestown S'Kallam Tribe of Washington State to develop a mycoremediation program for the Dungeness River Water Shed as a part of the EPA Targeted Watershed Grant Program. The Dungeness River runs 32 miles from the Olympic Mountains in northern Puget Sound to Dungeness Bay. Over years, the surrounding area was converted from forest to a more agricultural and residential community. The Dungeness River now supports an extensive irrigation network and the quality of water has suffered to the point that a ban was placed on shellfish harvesting due to high levels of fecal coliform.

A team led by Dr. S.A. Thomas constructed two bioretention cells, through which drainwater from agricultural fields and dairy farms would pass before entering the river. Both biofiltration cells were prepared with native trees and shrubs, but only one cell was prepared with preconditioned mulch inoculated with Pleurotus ostreatus, Pleurotus ulmerius, and Stropharia rugosoannulata. Over the course of several months, inflow and outflow fecal coliform levels were monitored. On average, the mycoremediation treatment removed 90% of fecal coliforms between inflow and outflow measurements, showing a 24% improved efficiency over the control bioretention cell.

Bioaccumulation of Heavy Metals & Radiation
Fungi are one of the most biogeochemically active components of soil microbiota. Due to their symbiotic relationship with plants and organisms that depend upon their superb acquisition skills, mycorrhizal fungi such as Gomphidius glutinosus, Craterellus tubaeformis, and Laccaria amethystina are particularly adept at sequestering metals from the environment at levels that would be considered toxic to other organisms.

Scientists from the Einstein College of Medicine have discovered fungi thriving within the irradiated exclusion zone of the Chernobyl disaster. Radiotrophic fungi such as Cladosporium sphaerospermum, Cryptococcus neoformans, and Wangiella dermatitidis have been shown to use [Caesium-137] to convert gamma radiation into energy by using the pigment melanin. Likewise, due to the dispersion of depleted uranium (DU) throughout the environment in Iraq and the Balkans, scientists have discovered novel fungi capable of transforming and immobilizing metallic uranium.

Limiting Factors of Mycoremediation
Despite the successes of the previous case studies, the potential for mycoremediation is site-specific. Solutions must be adaptable to various ecosystems: saltwater, freshwater, and terrestrial. Nutrition, temperature, pH, and oxygen availability are often limiting factors. If native fungi are not used in the mycoremediation treatment, the effect of exogenous fungi on the indigenous mycoflora is unknown.

Additionally, in the case of hyperaccumulation of heavy metals, it is uncertain whether it is a economically viable option to remove toxic mycelia and fruiting bodies removed from the environment.

References in Art & Culture
Hayao Miyazaki explored the concept of mycoremediation in his 1984 film Nausicaä of the Valley of the Wind, where vast tracts of fungal forest rehabilitate the planet after catastrophic human polluting and apocalypse.

Suggested Reading

 * Gadd, G.M., ed., 2001. Fungi in Bioremediation. Cambridge University Press, Cambridge.
 * Singh, H., 2006. Mycoremediation. John Wiley & Sons, Hoboken, New Jersey.
 * Stamets, Paul, 2005. Mycelium Running: How Mushrooms Can Help Save the World, Ten Speed Press, Berkeley, California.