If you were snuggled up with the latest Landscape Architecture on Monday, you might have missed the urban gardening bombshell that came out of the Geological Society of America’s meeting, of all places. Wellesley College researchers Emily Estes, Megan Carter-Thomas and Daniel Brabander found that the gardens owned by The Food Project in Roxbury and Dorchester are contaminated with lead.

That fact alone isn’t too surprising, as there’s plenty of lead in urban soils—but the gardens in question are raised beds, tall wooden boxes filled with fresh new soil and compost. They were specifically built to not have lead. And yet the lead arrived: as this article states,”…the soil in raised beds that starts with as little as 110 micrograms of lead per gram of soil rose to an average of 336 µg/g of lead in just four years.”

That measurement—335 µg/g— is equal to 336 parts per million (ppm). The U.S. Environmental Protection Agency’s (EPA) limit for soil lead in bare areas where children might play is 400 ppm; it doesn’t cover places where children might dig, till, and eat carrots out of the ground. The University of Massachusetts Soil Testing Lab recommends that young children and pregnant women avoid any soil with lead levels over 300 ppm.

The lead in Roxbury and Dorchester’s soil—and Somerville’s soil, and Cambridge’s soil, and every other Boston neighborhood and suburb—primarily comes from the paint on old houses and residue from ancient car exhaust from when lead was added to gasoline; the rest lurks on sites that held smelters, apple orchards that were sprayed with lead arsenate, and other artifacts of human habitation. It’s everywhere. The study suggests that the lead is making its way into the raised beds from wind and dirt splashed by rain. How are you going to prevent that?

Yet fewer and fewer children are being diagnosed with high lead levels in Boston every year, thanks to a successful collaboration between the EPA and nonprofit groups; the number of children in the Boston public school system with elevated blood lead levels decreased by 75% from 2001-2009, from 1,123 to 278. According to the EPA, the groups worked together “in part by deploying a local community tool to identify potential risks on a street-by-street, house-by-house level (e.g. presence of peeling paint, bare soil, gardens, etc.).”

And so we’re back to the sad fact that urban gardens are a lead poisoning risk, even when they’re put into raised beds. Fortunately, the study’s authors report that the lead they found isn’t very well absorbed by the body. They also state that there is an easy remedy to the increased lead; scraping out the top two inches of soil and replacing it each year will take care of the problem… if you don’t mind disposing of lead-contaminated dirt each year.

At this stage in Boston’s development, all urban parks and gardens are constructed; they’re environments created by human actions on top of land that has been used for hundreds of purposes in the past, good and ill. The urban gardeners of Roxbury and Dorchester (and Cambridge, and Somerville, and every other Boston neighborhood and suburb) can’t escape from their sites’ human history, even by starting new gardens, even by replacing the earth itself. If we are going to be good stewards of the land–and not poison our children—we need to remember what we have done… and perhaps make sure that the Wellesley Geology department gets enough funding to keep track of our local dust.

Photo credit: The Food Project, www.thefoodproject.org