Cleaning up mining waste with mushrooms

September 28, 2018

 

David Glenn

Zenith News

 

Mycoremediation is the use of fungi to filter bacterial pathogens, concentrate heavy metals as well as nanoparticles, and metabolize long-lived toxic chemicals.

 

Funguses comprise an entire kingdom of multi and unicellular organisms, such as yeasts, molds, mildews, and mushrooms. They are heterotrophic in that, unlike plants, they do not produce their own sources of food. Nutrients are absorbed from their surroundings via the secretion of enzymes, which act as chemical scissors, cutting up complex organic molecules into digestible chunks. They also can chelate and leach minerals from bare rock.

 

As the first multicellular creature on land, they paved the way for plants and animals by turning barren rocks into life-sustaining soils. Their role in the environment as primary decomposers and recyclers of organic material makes them well suited for the task of remediation.

 

Most fungi grow branching root-like filaments call mycelia. The individual cells of the mycelium, the hypha, often contain multiple nuclei, a kind of variable genetic toolkit. This has allowed them to adapt to a variety of extreme environments such as salt flats, the insides of nuclear power plants, and the depths of space.

 

This is advantageous when encountering new infectious agents, toxins, or food sources. There are species of fungi that are able to degrade plastics.

 

Award-winning mycologist Paul Stamets, who coined the term “mycoremediation,” has developed biorestorative strategies using fungi. In his book Mycelium Running, he tells the story of installing a mushroom bed in the central drainage depression on his farm.

 

Water runoff flowed via this depression into the ocean bay a few miles away, which was home to commercial oyster beds. Fecal coliform effluent from surrounding farms had gotten so bad that local officials gave farmers two years to install septic systems.

 

Stamets’ water was tested again a year later, and though he had not introduced a septic system, coliform levels had decreased 100-fold. The mycelia mat that had colonized the woodchip bed had filtered out the bacteria from the water flowing through it.

 

Macrofungi, such as mushrooms, tend to concentrate heavy metals in their fruiting bodies. This facet of their biology provides a cost-effective and convenient method for the removal of heavy metals in situ, i.e., without expensive excavation and transport to a treatment facility.

 

Contaminated areas can be seeded with such organisms, and the toxic substance can be harvested from the roots, shoots, and/or fruiting bodies. The concentration of metals in their tissues can often be higher (10 percent and above) than what is found in commercially mined ore.

 

This technique is sometimes referred to as agro-mining. By accumulating toxic metals within the mushroom cap and stem, near the center of the network, the entire organism is then able to grow away from harmful compounds. Ever expanding fairy rings of mushrooms that appear on an annual basis in fields and lawns are a similar example of this behavior.

 

One of the more versatile families of mushrooms that Stamets and other researchers have used for bioremediation is the Oyster mushroom. Most are found growing on dead or dying trees, breaking down the long-chain organic polymers lignin and cellulose, but they can survive on a vast array of substrates.

 

Able to digest complex organic molecules, too large for most microorganisms, they have found use in ameliorating techno-chemical and petroleum contaminated soils.  

 

Oyster mushroom varieties also possess heavy metal hyperaccumulation abilities. Pleurotus djamor, the Pink Oyster, can transport and sequester 38 percent of the mercury within its filamentous reach. Other species have shown affinities for concentrating copper, nickel, lead, as well as radioactive elements such as cesium. Even dead mycelia mats and dried mushrooms retain heavy metal binding and filtration abilities in a more limited capacity.

 

The application of mycotechologies to Minnesota’s logging and mining industry could provide a low-cost, low-maintenance, environmentally friendly method of disposing of waste and preventing pollutants from entering the surrounding environment.

 

Currently, the logging industry burns off much of the commercially non-viable trimmings such as branches and leaves, releasing CO₂. If this material were chipped, inoculated with mushroom spawn, and spread out over the area recently clear-cut, its decomposition would provide a rich loam in which other species could thrive. A smaller secondary income stream could be created through the harvest and sale of any resulting mushrooms.

 

The mining industry, applying burlap bags stuffed with inoculated wood chips or straw to all drain fields, watersheds, and especially around the perimeter of tailing ponds, could not only use that as a method to prevent acid mine drainage, heavy metal, and sulfate leaching, but it could also be used for monitoring. Collecting the mushroom bodies and analyzing their composition would provide a valuable tool for identifying potential breaches, faults, and fissures whereby metals and acids may leak.

 

The marshes and lakes where wild rice grows could be cleansed of sulfates and methyl mercury via floating partially submerged straw bales impregnated with the Pleurotus djamor species. Sulfates would be filtered out and repurposed as thiols and other compounds within its cellular matrix. It would further filter out and make use of excess dissolved organic matter in the water that may have been kicked up by the formerly exploding populations of sulfate-reducing bacteria.

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