Urban brownfield land is property whose reuse or redevelopment is complicated by the actual or potential presence of contaminants. It may include former workshops, fuel facilities, factories, industrial yards, railway land, dumping areas, service stations and sites filled with demolition debris or imported soil. The contamination is rarely a single, neatly defined problem. Petroleum hydrocarbons may occur alongside metals, solvents, polycyclic aromatic hydrocarbons (PAHs), ash, slag, asbestos-containing materials or contaminated fill.
Mycoremediation—the use of fungi or fungal processes in environmental treatment—could form part of a restoration strategy for some brownfields. However, it is not a matter of spreading mushrooms or woodchips across a polluted site. Fungal treatment is an emerging option that requires professional assessment, controlled conditions, monitoring and, often, combination with established remediation technologies.
Why brownfield remediation is difficult
Former industrial land is often physically degraded as well as chemically contaminated. Soil may be compacted, waterlogged, saline, alkaline, nutrient-poor or mixed with rubble and ash. Buried structures, variable drainage and layers of imported fill can make contamination highly uneven. A sample from one part of a site may not represent conditions a few metres away or at a different depth.
Typical contaminants include:
- Petroleum hydrocarbons, including gasoline- and diesel-range compounds and BTEX (benzene, toluene, ethylbenzene and xylenes).
- PAHs associated with fuels, combustion residues, railways, manufactured-gas sites and creosote-related activities.
- Volatile organic compounds and other solvents that may migrate into groundwater or create vapour-intrusion risks.
- Metals and metalloids such as lead, arsenic, cadmium, chromium, copper, mercury, nickel and zinc.
- Contaminated fill, cinders, slag, ash, demolition debris and other anthropogenic soil materials.
- Degraded soil structure, low organic matter, poor aeration and limited biological activity.
The intended future use also matters. A paved commercial site, an industrial property, a public park and housing development can involve different exposure assumptions and cleanup requirements. Regulatory screening levels help identify areas requiring further investigation; they are not automatically the same as site-specific cleanup levels.
Assessment comes before fungal treatment
Site history is an important starting point, but it does not replace investigation. Historical maps, permits, storage-tank records, aerial photographs and previous environmental reports can help develop a conceptual site model: a working explanation of contaminant sources, affected media, migration routes and potential receptors.
A qualified environmental professional should then determine the nature and extent of contamination. This normally involves appropriately designed soil sampling, and may also require investigation of groundwater, surface water, vapour, dust and buried materials. Soil texture, pH, moisture, organic matter, nutrients, salinity, permeability, bulk density and redox conditions are relevant to biological treatment. Analytical methods and data-quality objectives should be established before sampling begins.
This information determines whether a biological approach is suitable at all. High contaminant concentrations, free petroleum product, volatile solvents, deep contamination or a direct connection to groundwater may make excavation, containment or another conventional remedy more appropriate.
Organic contaminants and metals require different strategies
Biodegradation of organic compounds
Some fungi can transform, and under favourable conditions contribute to the biodegradation of, organic contaminants. White-rot and other ligninolytic fungi are of particular interest because they produce extracellular enzymes used to break down lignin, a chemically complex plant polymer. Related enzyme systems may act on some aromatic pollutants and petroleum-related compounds.
Important systems include laccases, lignin peroxidases, manganese peroxidases and versatile peroxidases. Fungi may also use intracellular oxidative enzymes, including cytochrome-P450 systems. In co-metabolism, a fungus grows on an added carbon source while transforming a contaminant that is not its main food source. Bacteria living alongside fungi may then complete or extend degradation pathways.
These mechanisms provide a scientifically plausible basis for treating certain PAHs and hydrocarbons, but a reduction in a broad measurement such as total petroleum hydrocarbons does not by itself prove complete detoxification. Individual compounds, transformation products, toxicity and possible volatilisation or leaching must also be considered.
Biosorption and immobilisation of metals
Metals and metalloids cannot be biologically destroyed. Fungi may instead bind them to cell walls, accumulate them within living biomass, complex them with extracellular substances, precipitate them or alter their chemical form. These processes are described using terms such as biosorption, bioaccumulation, biomineralisation and immobilisation.
Immobilisation aims to reduce solubility, mobility, leaching or bioavailability. It does not remove the metal from the site. A lower dissolved concentration may mean that the metal has moved into fungal biomass, become associated with organic matter or shifted into a less soluble soil fraction. Under different conditions, fungal activity could also mobilise metals and increase leaching risk.
Where controlled fungal systems may fit
Mycoremediation is generally more controllable when contaminated soil is excavated and treated ex situ rather than inoculated in place. Potential configurations include:
- Contained treatment beds: lined cells can provide controlled drainage, moisture, aeration and sampling access.
- Biopiles or mycopiles: excavated soil can be mixed with suitable amendments and placed in managed piles with liners, leachate collection and passive or forced aeration.
- Treatability units: small cells can compare fungal strains, substrates, moisture levels and amendment rates before a larger pilot is attempted.
- Hybrid treatment trains: fungi may be combined with bacteria, plants, compost, biochar or conventional methods such as excavation, capping or soil treatment.
Fungal colonisation and contaminant transformation depend on moisture, oxygen, temperature, pH, nutrients, substrate and contact time. Lignocellulosic material may provide structure and carbon, but it can also dilute soil, change nutrient balance and complicate interpretation of laboratory results. Compaction, weathered petroleum, clay-rich soil, mixed fill, competing organisms and toxic contaminant concentrations can all restrict fungal establishment.
Laboratory promise does not guarantee field performance
Laboratory studies often use selected fungal strains, prepared soil and relatively uniform contaminant concentrations. Urban brownfields are heterogeneous, non-sterile and subject to changing weather. A fungus that produces useful enzyme activity in a flask may fail to colonise compacted field soil or may be inhibited by a mixture of metals and solvents.
Scale-up also introduces practical questions: how evenly can fungal biomass be distributed, how will moisture and oxygen be maintained, and how will runoff, dust, vapours and leachate be controlled? A field study of aged petroleum-contaminated soils reported difficulty distinguishing treatment performance because contaminant distribution was highly variable. This illustrates why sampling design can be as important as the biological treatment itself.
Monitoring, biomass safety and verification
A credible pilot should establish baseline conditions before treatment, including contaminant concentrations by relevant compound or class, contaminant distribution, soil properties and any groundwater or vapour pathways. During treatment, operators should monitor moisture, temperature, oxygen or redox conditions, pH, fungal establishment, leachate and changes in contaminant composition.
After treatment, confirmatory sampling should follow a defensible statistical plan. Treated soil, leachate, groundwater and relevant fungal biomass may all require analysis. Where chemical concentrations do not adequately describe risk, bioavailability or ecotoxicity testing may be appropriate. Results should be compared with the applicable site-specific cleanup criteria and intended land use.
Fungal biomass from contaminated soil must not enter food or animal-feed chains. Fruiting bodies can accumulate metals such as lead, arsenic, cadmium and mercury, while wildlife, insects, windblown material and plant uptake may create additional redistribution pathways. Fruiting should be prevented where practicable through containment, species selection and physical controls. Spent substrate, harvested mushrooms and contaminated mycelium should be characterised and managed under the applicable waste plan; they should not be composted, sold, fed to animals or spread on gardens without documented evidence of safety and legal suitability.
When fungi are not enough
Excavation, clean-fill replacement, capping, solidification or stabilisation, soil washing, thermal treatment, soil-vapour extraction, air sparging, chemical treatment or groundwater remedies may be necessary where risks are immediate or contamination is too concentrated, volatile, deep or inaccessible for biological treatment. Sites containing asbestos, unexploded ordnance, radioactive materials or continuing contaminant sources require controls beyond the scope of a fungal pilot.
The most responsible route is therefore incremental: assess the site, define measurable performance criteria, test the approach in a contained pilot area, monitor both benefits and unintended contaminant movement, and expand only when the evidence supports it. Mycoremediation may eventually help restore some brownfield soils, but its credible role is as a carefully engineered component of professional environmental remediation—not a substitute for investigation, risk management or conventional treatment when those are required.
Selected sources
- U.S. Environmental Protection Agency, Environmental Contamination at Brownfield Sites and Petroleum Brownfields.
- U.S. Environmental Protection Agency, guidance on biopiles and source-material treatment.
- U.S. Environmental Protection Agency, Soil Sampling and Superfund Soil Screening Guidance.
- Peer-reviewed reviews of fungal treatment mechanisms, hydrocarbon remediation, fungal biosorption and mushroom contaminant uptake.