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Healthy Harvest

Research and outreach protect urban gardeners from compromised soils

periodiCALS, Vol. 7, Issue 1, 2017

Sara Perl Egendorf
Healthy Soils, Healthy Communities project collaborator Sara Perl Egendorf prepares clean soil for experimental beds in a Brooklyn community garden. Photo: Anna Minsky

An empty lot converted into a lush community garden is the epitome of urban renewal. But the soil below may still hold traces of a site’s less palatable history, in the form of contaminants from lead fuels and paints or residues from nearby building fires or industrial manufacturing. Community gardens yield more than fruits and vegetables; they are a boon to air quality, biodiversity, and neighborhood spirit among New York City’s more than 22,000 volunteer gardeners. But the potential risks from contaminated soil were a worrisome unknown until the 2008 launch of the Healthy Soils, Healthy Communities project.

“Gardens have so many demonstrated benefits, and the consumption of locally available, fresh food is really important to consider,” says Hannah Shayler, M.S. ’08, an extension associate in the School of Integrative Plant Science (SIPS) and the project’s coordinator. “But we didn’t know the scope of contamination in urban community gardens. Ultimately, the goal was to provide solid information to urban gardeners, focusing on what people can actually do—and what they can afford to do—to protect their health as they garden.”

Funding from the National Institute for Environmental Health Sciences at the National Institutes of Health brought together a statewide team of collaborators led by SIPS professor Murray McBride. In addition to Cornell scientists from the Soil and Crop Sciences Section, the Healthy Soils, Healthy Communities project tapped experts from the New York State Department of Health, Cornell Cooperative Extension, and the New York City Department of Parks and Recreation GreenThumb program, which boasts 551 community gardens across the city.

After analysis of hundreds of samples of garden soils and vegetables from more than 60 community gardens, the specific contamination risks became clear. Lead emerged as the metal of concern, both because of the levels present in samples and its well-established negative effects on human health, especially for children. About 70 percent of the gardens sampled had soil lead levels below recommended thresholds in vegetable-growing areas; however, 10 percent of gardeners and 40 percent of visiting children were estimated to exceed the recommendations for lead exposure. Controlling pH is a powerful intervention.

“The plants themselves were not taking up lead—they are really good at keeping lead out of their tissues,” Shayler says. “The exception to that is if the pH gets low. That makes the lead in the soil more available for plants to take up. So keeping your pH near neutral is a crucial gardening practice.”

Also key is preventing contaminated dirt from landing on the plants. The first line of defense is to use raised beds with clean soil and compost. Shayler also recommends barriers in two places: mulch at the soil surface on growing areas and walking paths and a fabric barrier between lead-contaminated soil and the new clean soil in the raised beds, a visual way to make sure you’re not digging down further than you think you are. The project also yielded an unexpected lesson: Urban soil quality can vary greatly over short distances.

“It’s dangerous to assume that a sample from one part of a site will be representative of what’s going on across the garden,” Shayler says. “We did some testing on a new urban farm that was starting up, and where they originally wanted to put a chicken coop turned out to have high levels of lead. With information from the soil tests, they were able to build the coop in a different spot with acceptably lower lead levels—the data really came to the rescue.”