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14
Mycoremediation
such as Pleurotus, Aspergillus, Trichoderma has proven to be effective in the removal
of lead, cadmium, nickel,chromium, mercury, arsenic, copper, boron, iron and zinc in
marine environment, wastewater and on land.
Not all the individuals of a species are effective in the same way in the accumulation of toxins.
The single individuals are usually selected from an old-time polluted environment,
such as sludge or wastewater, where they had time to adapt to the circumstances, and the
selection is carried on in the laboratory. A diluition of the water can drastically improve
the ability of biosorption of the fungi.
The capacity of certain fungi to extract metals from the ground also can be useful for
bioindicator purposes, and can be a problem when the mushroom is an edible one. For
example, the Shaggy Ink Cap (Coprinus comatus), a common edible north-emisphere
mushroom, can be a very good bioindicator of mercury, and accumulate it in its body,
which can also be toxic to the consumer.
The capacity of metals uptake of mushroom has also been used to recover precious metals
from medium. VTT Technical Research Centre of Finland reported an 80% recovery of
gold from electronic waste using mycofiltration techniques.
{ Organic pollutants }
Fungi are amongst the primary saprotrophic organisms in an ecosystem, as they are efficient
in the decomposition of matter. Wood-decay fungi, especially white rot, secretes
extracellular enzymes and acids that break down lignin and cellulose, the two main
building blocks of plant fiber. These are long-chain organic (carbon-based) compounds,
structurally similar to many organic pollutants. They do so using a wide array of enzymes.
In the case of polycyclic aromatic hydrocarbons(PAHs), complex organic compounds
with fused, highly stable, polycyclic aromatic rings, fungi are very effective also
in marine environments.The enzymes involved in this degradation are ligninolytic and
include lignin peroxidase, versatile peroxidase, Manganese peroxidase, general lipase,
laccase and sometimes intracellular enzymes, especially the cytochrome.
Other toxins fungi are able to degrade into harmless compounds include petroleum fuels,
phenols in wastewater, Polychlorinated biphenyl(PCB) in contaminated soils using Pleurotus
ostreatus., polyurethane in aerobic and anaerobic conditions such as found at the
bottom of landfills using two species of the Ecuadorian fungus Pestalotiopsis, and more.
The mechanisms of degradation are not always clear, as the mushroom may be a precursor
to subsequent microbial activity rather than individually effective in the removal of
pollutants.