On a chilly Saturday afternoon in March, people trickle into Grow Pittsburgh’s Garden Resource Center in the city’s Larimer neighborhood. They’ve come to take advantage of a free lead test for soil.
First people drop off a sample of garden soil at a folding table and answer some questions — like if the soil has been mixed with any mulch. Most of the samples contain about a cup of soil. Shea Moore lives on the North Side, and she’s brought two sandwich bags full of dirt. “We have an area on the front where we grow a lot of herbs and some other tomatoes,” Moore says. “And then our main garden is in the back.” Moore and her wife hope to have a big harvest — that’s if they can keep their backyard chickens from pillaging the tomatoes like they did last year.
LISTEN: The Legacy Problem of Lead in Soil
But they’re also concerned about lead. Digging up and growing food in soil can expose gardeners of all ages to lead, though kids under six years old are most at risk. Children are more likely to put dirt near or in their mouths, and lead exposure can cause irreversible damage to kids’ developing nervous systems — even before they’re born. “My wife is seven months pregnant now,” Moore says. “So we’re more concerned than we were for us.”
While Moore waits her turn, Jonathan Burgess of the Allegheny County Conservation District performs the lead screenings. One at a time, he places the bags of soil in front of what looks like a gun from Star Trek. The XRF machine shoots an X-ray beam at the sample for about 30 seconds. “Then it’s shooting another X-ray beam at a different intensity at it, and it’s sort of measuring the energy coming off of all the different soil particles,” Burgess explains.
In about a minute, the final result is displayed on the gun’s screen. Shea Moore is happy with the number from her backyard. The soil contains 105 parts per million of lead. “We can plant leafy greens and all the stuff we want to plant,” Moore says.
Leafy greens, like kale, are of course, close to the ground, so they can come into contact with lead in soil that way. But greens and lettuces can actually take up lead from the soil through their roots, contaminating the leaves. Lead doesn’t seem to pass through flowering, fruiting plants the same way, so produce like beans or tomatoes aren’t contaminated that way. But they can be exposed to lead if they fall onto bare soil.
The Environmental Protection Agency says a soil lead level below 150 parts per million is relatively safe. At 400 parts per million of lead or higher, Burgess recommends bringing in lead-free soil and gardening in raised beds.
He’s seen a wide range of results today. “Nothing that screams off-the-chart dangerous,” he says. “It tends to be kind of middle levels, from 200 to 1,000. Across that range, you know, you could simply wash your hands, wash your vegetables. And at the upper end, it’s more ‘keep your kids out of there.’”
Land grant institutions like Penn State University also typically offer affordable lead testing, and their extension services can share advice about collecting samples and what to do when you get the results.
A Legacy Pollutant
Burgess says Pittsburgh is like a lot of industrial cities when it comes to heavy metals like lead. “It’s just historical,” he says. “You know, it’s cars in the driveways and paint on the houses.”
In 1978, lead-based paint was banned from use in homes, but old flakes and chips of paint end up in soil, especially around the perimeter of houses. Until the 1990s, gasoline also had lead in it to help engines run more smoothly. So anywhere near where cars and trucks were driven or idled is typically going to have higher lead concentrations. And lead was actually produced in Pittsburgh. “A lot of people would be surprised to know we used to have lead smelters all over the city in residential areas,” Burgess says.
All of that lead is still there. It accumulates in the soil and stays put — in that same few inches of soil under the grass where most gardeners are digging. That’s why instructions for taking soil samples from yards or gardens say to remove a couple of inches of undisturbed soil —and down to six inches of turned-over garden soil — to get an accurate level. Soil samples should be dry.
Burgess says testing soil from different sections of a yard, from multiple garden beds, or where there used to be an old shed, can help gardeners decide the best spots to plant food or determine if a play area is safe. “What we’ve discovered is in just a few feet you can go from very high levels to very low levels and back again,” Burgess says.
It’s in the Dust
Other ways to minimize risk include feeding the soil with compost, and covering bare ground in gardens — or anywhere else. “You need to put down wood chips or other barriers so that the rows that are not planted do not present themselves as bare soil that can be readily re-suspended,” says Daniel Brabander, a professor of Geosciences at Wellesley College in Massachusetts.
“Re-suspended” as in, in the air. Dust is another way lead from soil makes its way into our bodies and blood. It’s a significant issue, according to Dr. Marilyn Howarth of the Center of Excellence in Environmental Toxicology at the University of Pennsylvania’s Perelman School of Medicine. She’s looked at elevated blood lead levels in kids in Lancaster, Pennsylvania and found that children sometimes had elevated levels even when lead had been remediated in their homes. “And the only contribution that we’ve been able to find has been to soil.”
One study found that in cities all over the country, blood lead levels in kids vary by season. “The old idea was that that was because kids play outside a lot more in the summer,” says Gabriel Filippelli of Indiana University—Purdue University Indianapolis. His research indicates the problem isn’t necessarily that kids are playing in the dirt. Filippelli found when soil dries out by late summer, dust gets kicked up and can find its way into the house — on our shoes, for example. It winds up on nearly every horizontal surface kids come in contact with.
Because of this, Filippelli thinks looking at lead as a neighborhood-wide issue could be even more effective for improving public health than going house by house. “I would argue that recognizing the soil-based exposure source and dealing with it is probably going to possibly impact more kids for less cost per kid,” he says.
Jonathan Burgess is working with community gardens, nonprofits and researchers to get a better handle on where soil lead contamination exists in the Pittsburgh area — looking beyond backyards to spaces like blighted properties. “The question that we’re trying to answer is what we can do with land that isn’t slated for development that is going to continue to be sitting there in communities and could be put to better use and could be remediated over time,” Burgess says.
Remediation could be as simple as, say, planting sunflowers on vacant lots to soak up the lead in a process called phytoremediation. But it’s just one idea Burgess and others are looking into as they identify larger tracts of land to manage for lead exposure.
Sampling efforts are also happening alongside work to revitalize struggling parts Pittsburgh. Raqueeb Bey, a member of Black Urban Gardeners and Farmers Cooperative of Pittsburgh, recently worked with Jonathan Burgess to collect soil samples from a grid of 10-by-10-foot areas on two vacant properties in the city’s Homewood neighborhood, across from Westinghouse Academy.
“There are 27,000 blighted lots in Pittsburgh, and Homewood has more than any other neighborhood,” Bey says.
The properties are often places where old houses have been torn down, so there could be lead-based paint and other lead exposure risks. Her group is acquiring the lots through the city’s Adopt-a-Lot program, and so they have to be tested for lead.
This is an area that could really benefit from an urban farm. Right now, there aren’t any supermarkets to buy inexpensive fruits and vegetables. And Bey’s group plans to use this vacant lot to grow them. “This is a solution for us to take our community into our own hands,” she says.
They’ve already cleared an important first hurdle: The soil lead tests for the Homewood lots came back favorable. So Bey’s group will be able to break ground this summer on covered hoop houses and raised beds for vegetables.