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Rooting out a little-known danger of urban gardening

Healing City Soils helps community gardeners test for — and clean up — hazardous materials in their plots.

By Hannah Thomasy

For stressed-out city dwellers, community gardens — plots of land where neighborhood residents tend to shared rows of lettuce, tomatoes, squash, and other crops — can have substantial benefits for health and well-being. Studies have shown they can increase fruit and vegetable consumption and relieve stress. But those potential upsides are for naught if the soil itself is dangerous.

The Problem

Growing food in highly urbanized environments can come with its own hazards. Gardens built near former industrial sites, former landfills, or roadways that existed before the 1980s, when leaded gasoline was still widely used, can have soil contaminated with dangerous heavy metals, including lead and cadmium. In inner-urban Baltimore, for example, soil lead levels were nearly ten times higher than in a nearby rural region, according to a 2015 analysis.

Danielle Stevenson, a community organizer and food systems consultant, started doing urban agriculture work in Victoria, British Columbia, in 2006. “I was helping a lot of groups set up gardens and farms,” she says. “We started getting the soil tested and we had a number of gardens that had elevated levels of lead and other toxic metals. And at the time, people didn’t know to even test the soil.”

Gardens built near former industrial sites can have soil contaminated with dangerous heavy metals, including lead and cadmium.

Even if would-be gardeners wanted it, testing was expensive, and the results could be difficult for non-experts to interpret. Nor was there a lot of readily available information on what people could do about contaminated soils. “I saw a lot of people [whose] gardens just stopped,” she says.

The Solution

Stevenson spread the news about those barriers, contacting city counselors and placing a letter in the local paper, The Times Colonist. In 2016 the Healing City Soils project — a collaboration between Victoria’s Compost Education Center and two local universities — was born, with Stevenson as coordinator. 

Since then, Healing City Soils has tested over 500 sites around the city for free and is creating a soil quality map, detailing levels of contaminants like lead, mercury and arsenic throughout Victoria.

The project also helps people figure out solutions. For low-level contamination, the fixes are pretty simple: adding organic matter to the soil, washing produce before eating, and handwashing after gardening. The project has also released recommendations for crops that are suitable for growing in moderately contaminated soil, like apples, tomatoes, and peppers. They may be less likely to accumulate contaminants in their edible parts than other crops, like leafy greens.

The Challenge

Those fixes, however, won’t work in areas with higher-level contamination — such as the site of a former sewage treatment plant, or a lot that once held a building heavily contaminated with lead paint.  Healing City Soils is now conducting experiments on three contaminated sites to see if they can be made suitable for gardening through a process called bioremediation. “We’re implementing some ecological, accessible options,” says Stevenson, “working with plants and compost and soil amendments that are easy for gardeners to access and within reach of the skills and knowledge they already have.”

Stevenson says many types of plants can remove contaminants from soil, including sunflowers and barley. One part of this pilot project is to evaluate whether plants native to Victoria, like certain species of willow and mugwort, also have these toxin-absorbing capabilities.

The Bigger Picture

Projects like Healing City Soils have important implications for cities far beyond Victoria. Soil contamination is a big problem for urban gardeners from cities around the world, from the United States to Hungary to Kenya to elsewhere in Canada.  “We’ve created a model that has been really effective,” says Stevenson. “We’d love to help other cities throughout Canada start up a similar type of program.” Healing City Soils aims to help people in cities everywhere grow food safely. “Urban agriculture can build community and build all different types of literacy,” Stevenson says. “Not just food literacy — where food comes from, how it grows — but also all the connected pieces in our food system that tie in soil with waste, land use issues, climate change, [and] food access.”

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Hannah Thomasy is a science writer based out of Toronto and Seattle. She has written for Undark, OneZero, Hakai, and Atlas Obscura.

Photo by Angela Pyne

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