Urban stormwater runoff is a significant source of contamination in lakes and streams, not only from hard surfaces like streets, parking lots and roofs, but also after percolating through the contaminated soil of former industrial sites and abandoned homes.
“Bioremediation... involves the use of organisms to eliminate [or] neutralise (sic) pollutants from a contaminated site. Traditionally, naturally-occurring organisms have been used to achieve this end. One such example is the use of fungi in mycoremediation, which utilises (sic) the fungal mycelia and capitalises (sic) on its decompositional properties.”
Before planting an urban garden, the soil should be tested. Andrew Bernier reported on Phoenix Radio KJZZ, October 2, 2014:
We sift out rocks to prep the soil for chemical testing, which is then mixed with reagents, or substances that start a chemical reaction. Those reactions reveal the amount of nutrients in the soil and detect for contaminants, like heavy metals lead and arsenic, or possible solvents and oils...
But decades of urban development has changed the soil. It now needs to be cleaned with nutrients and organic life restored through a process known as bioremediation. This is done by adding compost rich with little living things like bugs and fungi, collectively called microbes...
“Microbes can bioremediate most toxins and pollutants. They’ll take everything down and break it into fractions. And this is a cross-section of what microbes should be in healthy compost,” [farmer Ken] Singh said...
Singh also stresses how time helps restore the health of soil.
Time, plus some combination of (1) a carefully chosen (additional) fungus, (2) symbiotic bacteria, (3) heat, (4) oxygen and (5) a supporting medium like sawdust, straw or corncobs will combine to hasten the demise of toxins in soil.
Even plastic isn’t safe from a fungal onslaught.
“Upon collecting multiple plant samples from the Ecuadorean Amazon rainforest containing endophytic fungi (fungi that live inside a plant) and culturing the fungi, the group discovered that certain strains of Pestalotiopsis microspora could degrade polyurethane (PUR). Polyurethane is a commonly used plastic—it is in everything from building insulation to furniture to footwear. This is a unique discovery not only because it is a plastic “eating” fungus but also because it is also the first endophytic fungus found to have these properties. The fungus uses the PUR as a carbon source to grow in both aerobic and anaerobic conditions.”
Professor Mohamed Hijri at the University of Montreal “...has collected a biological clean-up team that can turn what’s basically a moonscape into something habitable (at least by some species) over the course of just a few years. First, willow trees are planted in dense stands to soak up the heavy metal contamination and store it in the plant’s cells. Then, each season, the trees’ stems and leaves are burned, creating an ash residue full of heavy metals. Finally, specially selected (but naturally occurring) fungi and bacteria are released to metabolize the petrochemical waste. Even a highly contaminated soil, says Hiri, can be cleaned within a few seasons.”
Rebecca Tuhus-Dubrow wrote in Next City, July 29, 2014:
In Albany, New York, staff members of the Radix Ecological Sustainability Center grow oyster mushrooms in straw. After harvesting the mushrooms, they take the straw, which is replete with mushroom enzymes, and spread it on contaminated soil. These enzymes, according to the center’s educational director, Scott Kellogg, break down pollutants, helping to detoxify the soil…
In recent years, community gardens and urban farming have grown increasingly popular. But alongside that growing popularity are concerns about safety. Just a couple of months ago, reports emerged that 70 percent of New York City’s community gardens had toxic soil. A recent study of urban gardeners in Baltimore found that few were well-informed about the hazards of soil contamination or the best practices for mitigating them. Gardening aside, mere proximity to tainted dirt can pose health risks, especially for children who might play in it.
The Michigan State University Extension Service recommends:
When establishing a new garden or farm... it is always a good practice to test the soil for lead. This is due to lead being present in paint and gasoline until the late 1970s. Land close to heavy traffic and sites of old homes that may have had lead paint in them are potential sites of lead deposition, and should be tested for lead as a precaution before growing food on these sites.
Soil lead testing is available through Michigan State University Extension and the soil test kits are available for purchase at the MSU Extension bookstore.
If the potential garden site was an industrial or commercial site, it may be necessary to find out what types of businesses were there in order to know what potential contaminants to test for. Testing for contaminants can become expensive. Environmental Protection Agency brownfields grants are available to provide money for your community to assess the property you’re interested in, but the process can be time consuming.