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 achieve this 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 in addition to 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 P450.
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 conditions 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.