BioCycle September 2010, Vol. 51, No. 9, p. 35
Mycelium, especially the oyster mushroom, shows promise for consuming and converting environmentally toxic hydrocarbons.
Marsha W. Johnston
THE NEXT TIME you sauté a skillet of oyster mushrooms, consider this: You are eating the fruit of one of the most powerful natural agents known to science for breaking down industrial pollutants. Few people are aware of the powers of that mushroom’s primary organism, its infinitely intricate network of thready roots called the mycelium.
The oyster mushroom, Pleurotus ostreatus, is one of most common mushrooms found in riparian environments along streams and rivers. It belongs to the “decomposer” class, as do most gourmet and medicinal mushrooms. Scientists have catalogued about 14,000 species of mushroom-forming fungi. Paul Stamets, CEO of Fungi Perfecti in Olympia, Washington, says between 20 percent and 25 percent of those are “decomposers.”
When decomposer mushrooms require nourishment, their mycelial network excretes enzymes and acids that seek out organic material, typically lignin and cellulose, the two basic building blocks of plant fiber. Lignin and cellulose are composed of long chains of carbon and hydrogen. Coincidentally, so are many organic pollutants, including petroleum products, pesticides and herbicides.
Howard Sprouse is CEO of The Remediators Inc., a company using mycelium to decontaminate soil. He confirms that petroleum and lignin are structurally the same. As a result, although lignin is one of the most resistant organic compounds because it’s a polymer (used to create plastics and resins), mycelium easily breaks it down into carbon dioxide and water. Using fungal decomposition to break down toxins and decontaminate an environment (usually soil) is known as mycoremediation. It includes the use of microorganisms, green plants or their enzymes.
Stamets has been collecting strains of rare fungi in the old-growth forests of the Pacific Northwest for 30 years, and researching which strains, alone or in combinations, speed up the decomposition process of target contaminants. “We have a library of hundreds of strains that we have collected, and 99 percent of them are decomposers,” says Stamets of his work, which includes producing mushroom-based inoculant for use in soil remediation. “Oyster mushrooms have proven the most adaptive and versatile mushroom-forming fungus we know for bioremediation of petroleum products.”
An early field experiment conducted by the Washington Department of Transportation and Battelle Laboratories (1999-2000) proved the efficacy of a strain of Stamets’ Pleurotus ostreatus mycelium against bacteria and enzymes on three piles of soil each contaminated with between 10,000 to 20,000 ppm of diesel. In the space of a month, the pile of contaminated soil inoculated with oyster mushroom mycelium had sprouted 12-inch diameter oyster mushrooms. After 16 weeks, 95 percent of the hydrocarbons had broken down and the soil was deemed nontoxic enough to be used for landscaping. By contrast, neither of the sites bioremediated with bacteria or engineered bacteria showed significant changes. Furthermore, as the mushrooms rotted away, “fungus gnats” moved in to eat the spores. The gnats attracted other insects, which attracted birds, which brought in seeds. The oyster mushroom site was the only one that became an oasis of life.
When oyster mushrooms sprout on mycoremediated soil, they show no trace of hydrocarbons, which Stamets attributes to the mycelium reassembling them into fungal carbohydrates. However, because researchers don’t yet know how much the mushrooms bioaccumulate the other toxins in petroleum products – such as heavy metals and carcinogens – he advises against eating them.
Stamets is working to identify other petroleum-eating mushroom species. “We’re doing challenge tests now with 12 different species, and based on their pace of growth and response, we have other candidates that are also good for remediation of oil environments,” he says. At the same time, Sprouse is testing the efficacy of mycelium against dioxin.
Bioremediation expert and veteran EPA Environmental Response Team member Harry L. Allen II acknowledges the power of mycelium, but notes that in a recent project in Vietnam to remediate dioxin, the indigenous bacteria he used outperformed the indigenous fungi. One limiting factor, he explains, is that the fungi must be extremely stressed in order to generate the materials necessary to dispatch the chemicals.
APPLYING MYCOREMEDIATION IN THE GULF
With the oil disaster in the Gulf, both Stamets and Sprouse have submitted proposalsproposals – Stamets to the EPA and Coast Guard, Sprouse to a local parish – for cleaning up BP’s mess by using oyster mushroom-inoculated material. Stamets’ proposal centers on the use of what he calls “mycobooms,” 100-percent biodegradable hemp socks filled with straw mixed with germinated mushroom spores. To test the concept, he deployed them in three locations in the Puget Sound to determine their tolerance to saltwater. He also floated a mini mycoboom in an oil slick in a tub full of salt water to test oil absorption. After three weeks, the booms were still floating in Puget Sound and the oyster mushrooms had completely colonized the saltwater-soaked straw on both.
“The oil is absorbed above the water line,” Stamets says. “As the fungi eat the straw, they create CO2, water, acid and enzymes, and the fragrances of mycelium attract insects and fish. There is a whole domino effect of benefits. Mycobooms would keep new oil out on the outside, while on the inside they would release enzymes to remediate the oil already in the marshlands habitat.” Stamets notes that the mycobooms should be used in conjunction with repeated spreading of a debris field of straw inoculated with mushrooms over the marshlands. As of this writing, the proposals are still being evaluated.
In Washington State, the Mason County Conservation District has been working closely with Stamets for nearly three years, using mycobag filters primarily to stop e coli contamination of water from farm runoff. At some sites, more typical bioremediation best practices such as bioswales were not working, threatening the region’s multimillion-dollar shellfish operations, says Rich Geiger, district engineer for Mason, Jefferson, Thurston and Kitsap county conservation districts. One farm closest to some oyster beds was close to being shut down because its runoff was consistently over the limit for e coli contamination, explains Geiger. The soils in the healthy grass-lined bioswale did not perk well enough for it to function as intended and the area was frequented by large flocks of geese, a vector for E. coli. “We installed the first mycofilters, and he came into compliance at the very next test – with a dramatic reduction,” says Geiger.
The county conservation districts have at least 14 installations in various configurations on an “experimental” basis, because neither the districts nor Stamets have the capital to pay for the lab testing required to certify mycoremediation as a best practice. All involved parties agree that getting the certification would be an important step to growing the mycoremediation industry. “We are in the 21st century, and a lot of the best management practices that we are using now were developed early in the 20th century,” says Geiger. “There has been no real evolution. If we can understand better what is happening at the microscopic level with mycelium processes, we have the opportunity to revolutionize remediation and water-quality best practices by using mycoremediation. It needs to be investigated aggressively.”
Two major obstacles to using mycoremediation or any other kind of bioremediation are resistance to change and time constraints, according to many in the field. Charlie Butros, director of the Mason County Public Works Department, says the current grant “considers mycofilters an ‘innovative treatment option’ and will not fund them, only ‘approved’ methods. We’re not installing new ones for that reason. As soon as we get funding that will allow [lab testing], we hope to expand.”
Bioremediation efforts, including mycoremediation, take up to six to seven months to work, and many customers – particularly developers – feel they cannot afford to wait. For that reason, the two top tactics for eliminating soil contaminated with petroleum products remain hauling it away (called “hog and haul”) or paving it over, says San Diego, California, based Environmental Business International founder Grant Ferrier. Adds the EPA’s Allen: “The advantage of biological treatment is that it is cheaper than many methods, but only sometimes cheaper than hog and haul.”
Marsha W. Johnston is a freelance journalist based in Washington, D.C., specializing in wildlife conservation, sustainable development and renewable energy issues. She can be found at http://stewardingthewild.wordpress.com.
September 21, 2010 | General
Mushrooms Offer Bioremediation Options
BioCycle September 2010, Vol. 51, No. 9, p. 35