Science of Cities

Grow a Mushroom, Get Less Toxic Tomatoes in Your Community Garden?

A process that produces mushroom enzymes in straw may help detoxify soil in community gardens. (Photo from the Radix Ecological Sustainability Center)

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.

This method is one example of community-based bioremediation, also known as grassroots bioremediation. The rubric includes a wide variety of techniques. But the common goal is to capitalize on the natural properties of organisms to heal city soil, in simple, affordable ways.

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.

“We’re dealing with the past 150 years of industrial pollution that has accumulated,” said Kellogg, coauthor of the 2008 book Toolbox for Sustainable City Living: A Do-It-Ourselves Guide. Frequent culprits include lead, arsenic, pesticides, hydrocarbons and PCBs, among others, from a wide variety of household and commercial sources. “We’re really just beginning to understand the extent of this.”

The most conventional way of dealing with contaminated soil is to excavate it and take it to a landfill — an approach sometimes called “dig and dump.” But that method is “beyond the means of ordinary urban residents and community gardeners to afford,” said Kellogg. “We’re looking at ways that ordinary citizens who don’t have particularly extensive backgrounds in science or engineering can get involved — what sort of tools are available to them?”

Kellogg’s review of the research literature has identified a number of promising techniques — although it should be emphasized that further research is still needed. In other words, don’t try this at home and assume your soil’s problems are solved.

With that caveat, one technique, sometimes called “phytoextraction,” involves using plants such as geraniums and brassica, which are believed to accumulate lead and other metals in their stems or leaves, thus removing them from the soil. This method is not without downsides, however. The contaminated plants need to be disposed of in landfills, and the process can take years to complete.

Other resources range from fungi (mycoremediation) to earthworms (vermiremediation). Kellogg cites research indicating that through their interaction with the soil, these organisms can degrade various kinds of toxins, rendering them less harmful. Breaking apart a hydrocarbon, for example, yields carbon and hydrogen, neither of which is dangerous alone. Applying well-made compost, Kellogg says, can also contribute bacteria that can break down organic pollutants.

The concept of community-based bioremediation may be gaining traction. Kellogg, the most prominent proponent, wrote a chapter about it for a 2013 book called Earth Repair, and will present on the topic next week at the annual Northeast Organic Farming Association conference. A Worcester-based group called Toxic Soil Busters has also experimented with it. But the movement is still small and new, and, as Kellogg acknowledges, it faces a number of daunting hurdles.

The most fundamental problem may be the extent and complexity of the contamination in many city plots. According to Niall Kirkwood, a professor of landscape architecture and technology at Harvard who studies bioremediation, “The soil is actually a cocktail, a mixture of different things.” Levels of assorted toxins can vary even within a small lot, requiring fine-grained testing and remediation to fully address the problem. “There’s no silver bullet,” Kirkwood cautions.

Testing soil — to determine both the initial toxicity and the success of bioremediation efforts — can be costly. Even the Radix Center for Ecological Sustainability has not been able to carry out comprehensive testing. Although Kellogg believes that the mushroom enzymes he applies to soil, as described above, reduce toxicity, he clarifies that he doesn’t yet have the data.

Another challenge is the time scale. Toxic Soil Busters, part of the Worcester Roots Project, focuses on remediation of soil with lead levels up to 4,000 parts per million (any concentration above 400 is considered unsafe). They have tried bioremediation with geraniums. Shane Capra, co-director of the Worcester Roots Project, told me they found that it worked, but it was too time-consuming, reducing lead levels by about 10 percent per year. “The arc for environmental justice can’t take 10 years when you have a kid with elevated lead levels now,” he said.

Though our understanding of bioremediation is still spotty, Kirkwood says that some exciting research is emerging from Asia. (For example, a Chinese plant called a brake fern has shown great potential for taking up certain pesticides.) But most of the research to date has been conducted in labs. We need more field experiments to better understand how these techniques work in the uncontrolled conditions of a real urban environment. Kellogg calls for more collaboration from government and academia to help citizens with this undertaking.

Given the current challenges, bioremediation alone isn’t enough to ensure safe soil for next month’s tomato harvest. Instead, it’s a longer-term strategy that can supplement, not replace, other commonsense measures: using raised beds with purchased soil, wearing gloves while gardening, carefully washing fruits and vegetables.

“For people who want to go beyond that,” says Kellogg, “that’s where bioremediation would come in.”

And the hope is that gradually, the geraniums and worms and brake fern will lead to benign soil — and that someday, we can shun the imported stuff, take off the gloves and snack on snap peas directly from the vine.

*A previous version of this post mentioned the use of sunflowers in phytoextraction. As many experts have discredited sunflowers’ practical efficacy, we’ve removed that reference.

The Science of Cities column is made possible with the support of the John D. and Catherine T. MacArthur Foundation.

Rebecca Tuhus-Dubrow was Next City’s Science of Cities columnist in 2014. She has also written for the New York Times, Slate and Dissent, among other publications.

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Tags: urban farmingcommunity gardens