Helping to Make Boston’s Urban Gardens Safe

SPH associate professor Wendy Heiger-Bernays has been testing soil in urban gardens for more than a decade. Photos by Cydney Scott

A black cat crossed in front of Wendy Heiger-Bernays while she was walking along a path in the South End’s Northampton Community Garden recently. The School of Public Health associate professor of environmental health eyed it suspiciously, not because she’s the superstitious type, but because of the potential disease it carries. Cat feces host the pathogen that causes toxoplasmosis, which can result in encephalitis, neurological diseases, or problems with the heart, liver, ears, and eyes. The condition is especially dangerous for people with weak immune systems and pregnant women.

“There is no ambiguity,” Heiger-Bernays said, eyeing the cat. “That is a hazard.”

Heiger-Bernays should know. She and her graduate students have visited at least a dozen urban gardens, at the request of the Boston Natural Areas Network, to sample soil and analyze it for traces of arsenic and lead. The hands-on experience is part of the curriculum for her class, Analytical Methods in Environmental Health, and is one of several services provided by SPH’s Science Gardener Collaborative, which serves as a “resource of research and guidance for safer growing in soils, grounded in sound science.” Gardeners receive a written report of the students’ findings along with recommendations for how to remediate the soil, if high levels of pollutants are present.

Urban gardens are hardly a new phenomenon. Eleanor Roosevelt encouraged Americans to plant Victory Gardens during World War II, and Michelle Obama’s White House Kitchen Garden has inspired copycats across the nation. But the recent resurgence is not about patriotism; it’s a response to inflation and people’s increasing concerns regarding food sourcing and the impact of industrial farming on the environment. According to the American Community Gardening Association, there are an estimated 18,000 community gardens in the United States and Canada.

As these urban gardens spread into vacant city lots and sprout on front lawns, the fruits and vegetables grown there may be rooted in less than pristine soil. Lead paint is commonly found in soil surrounding houses built before 1978. Arsenic leaches from pressure-treated wood and was often used in pesticide sprayed in apple orchards. And asbestos, polychlorinated biphenyls (PCBs), and other hazardous materials are commonly found in soil where buildings have been demolished.

Heiger-Bernays first got involved with urban gardens about 10 years ago, when she was asked to test the soil of a couple of plots in Jamaica Plain after gardeners used compost from a questionable source. (Compost is not regulated by federal, state, or local governments.) Her analyses showed elevated levels of PAH (polycyclic aromatic hydrocarbons), a chemical released when trash is burned. She presented her findings at a public meeting and provided recommendations for how the gardeners could revitalize their soil.

Now, Heiger-Bernays regularly takes her students to urban gardens to test for pollutants under the umbrella of SPH’s Superfund Research Program, which conducts and communicates research on the impact of improperly managed hazardous wastes. Before students ever sink a trowel into garden soil, she teaches them “due diligence” by sending them to the Boston Public Library to research the plot’s history. Its former life as a housing complex, paint factory, or garbage dump reveals what might be found in the soil. Students then design a sampling plan, collect soil from the garden, and analyze it using X-ray fluorescence (XRF) technology in University labs.

On an overcast fall afternoon, SPH students had paired up and were carefully sampling the soil from three spots within the Northampton Community Garden. Groups collected soil from at least five locations within their chosen plots, carefully mixing the samples and sorting out large rocks or debris, before taking a cupful back to a University lab for testing.

“We actually don’t know what we’re going to find here,” said Heiger-Bernays, looking around at the brick buildings and new housing units on three sides. Towering dahlias and sunflowers occupied a good portion of the garden. Kale, Swiss chard, tomatoes, and herbs were growing as well. “Each garden has its own culture, and you can see it in what they grow,” said Heiger-Bernays, noting that this particular garden is maintained by a predominantly white community, while another garden just blocks down the road is cared for by Asian immigrants who erect elaborate stake-and-bag systems to protect and support their produce.

Candace Hubner (SPH’16) and Melissa Rodriguez-Vodak (SPH’16) were sampling the soil from a central plot where a white mannequin, its arms raised in a headless hallelujah, stood guard. They dug down six inches alongside a variety of vegetables and carefully placed each trowel full of dirt in a metal bowl. After the sample was well mixed, they sorted out large chunks of soil and shoveled a generous helping into a plastic bag labeled with their names and the plot’s location.

Rodriguez-Vodak likes the idea of urban gardening, but “if it has poor execution, then it creates more problems than it’s fixing,” considering gardeners’ potential exposure to pollutants.

Andrew Heller, a longtime Northampton gardener, stood nearby surveying the students’ work. The amateur photographer grows mostly ornamental plants he uses as props—red twig dogwood, asters, broomcorn, and three adolescent apple trees. He rarely amends his soil with compost and said that he doubted “anything horribly toxic is going to show up” in the students’ analysis.

Turns out, of the three plots students sampled that day, Heller’s contained the highest average lead and arsenic concentrations—229 mg/kg and 26 mg/kg, respectively. Both were above what the Massachusetts Department of Environmental Protection says are acceptable levels in soils in residential areas and gardens.

“Based on these results, we recommend that clean (tested) soil be placed atop the existing soil,” Heiger-Bernays’ students concluded in their report. They noted that because Heller did not do a lot of active digging or working with the soil, there was little risk of exposure, and therefore no health risk.

When lead or arsenic levels are higher, gardeners have had the option of removing the topsoil completely and trucking in healthy soil or capping the plot with landscaping fabric and building raised beds.

Whether or not gardeners know their soil’s contents, Heiger-Bernays recommends wearing gloves and always washing harvested fruits and vegetables before eating them. The general rule is “test when you need to test, remove soil only when you need to, and encourage the practice of gardening,” she says. “We think, although we don’t have data, that the actual activity of gardening and consuming this food has a greater benefit than the risk of the moderate to low contaminated soils.”