When you see dirt in Chicago, you're probably looking at lead pollution. Thanks to decades of avoidable but profitable use of lead paint and leaded gasoline, this invisible toxin has penetrated the ground everywhere, especially near old houses and areas with heavy traffic.
Lead binds tightly to soil particles. Unlike pesticides, it never breaks down--and it doesn't wash away easily, either. It poses a double threat in the garden. For one, it's in the dust that sifts onto the parsley and tomatoes. More insidiously, lead from the soil builds up in plants' roots, shoots, leaves, and fruits. Exactly how much depends on the plant, and the soil.
No wonder some people won't take vegetables grown in city gardens as gifts. They're partly right to refuse. Northwestern University researchers Mary Finster, Kimberly Gray, and Helen Binns took a look at 87 vegetables grown in 17 Chicago gardens during the summers of 2000 and 2001. (Finster's a PhD candidate and Gray's an associate professor of civil and environmental engineering; Binns, an associate professor of pediatrics, is head of the lead evaluation clinic at Children's Memorial Hospital and directs the hospital's Safer Yards project.) Their small pilot study, published this spring in the journal Science of the Total Environment, found that lead accumulates most in the roots of plants, less in the stems and leaves, and hardly at all in the fruits. So if you aren't intimately acquainted with their place of origin, avoid city-grown onions, potatoes, carrots, rhubarb, and leafy greens. But go ahead and feast on the tomatoes, cucumbers, and peppers--after you've washed them thoroughly, with detergent.
Natural soil contains about 20 parts of lead per million parts of soil. That's the "background" level, but different jurisdictions have different opinions about how much should be considered safe in practice. In the squeaky-clean state of Minnesota bare soil with more than 100 parts of lead per million is supposed to be covered with sod, mulch, or tarp. In 2001 the U.S. EPA concluded from the available evidence that children shouldn't play on dirt with more than 400 parts per million. The city of Chicago considers bare soil accessible to children a hazard if it contains over 1,000 parts per million. The EPA's standard for bare soil where children won't be playing is 1,200.
There's never been a citywide soil survey for lead pollution, and even if there had been it wouldn't help gardeners much--lead levels can vary dramatically even on the same piece of property. In the ongoing battle against childhood lead poisoning, the city does track which neighborhoods have it worst. According to the map posted at www.cityofchicago.org/Health/Lead/LeadMap.html, lead poisoning afflicts more than 10 percent of the kids in 23 south- and west-side neighborhoods: Humboldt Park, Austin, West Garfield Park, East Garfield Park, Near West Side, North Lawndale, Fuller Park, Grand Boulevard, Washington Park, Woodlawn, South Shore, Chatham, Avalon Park, South Chicago, Roseland, West Pullman, New City, Chicago Lawn, Englewood, West Englewood, Greater Grand Crossing, Auburn Gresham, and Washington Heights. West Town, where the Northwestern study was conducted, comes in at 7 percent.
Gardeners in these neighborhoods should be especially wary of the earth they dig in. Those who live northeast of the intersection of Chicago and Cicero, downwind of where the city's Northwest Incinerator used to be, should also be careful. Students of Alanah Fitch, a chemist who heads up the environmental sciences program at Loyola University, found soil lead levels of over 4,000 parts per million downwind of the old trash burner--not an enormous surprise given that Ken Dunn, president of the Resource Center, a recycling, urban gardening, and environmental-education group, recalls seeing pallets full of lead-acid batteries dumped into its hopper.
The Northwestern University study by Finster, Gray, and Binn is unusual in that they measured lead in both the plants and the soil they were growing in. They found soil lead levels ranging from near background (27 parts per million) to grossly polluted (4,580 parts per million), with a median of 800 parts per million. More than three-quarters of their soil samples exceeded the EPA's play-area standard of 400 parts per million. And even though the plants' roots accumulated the most lead, the researchers also found trouble elsewhere. "Diets laden with urban-grown herbs may substantially contribute to a person's lead burden," they write, giving the example of some cilantro they found being grown in soil with 2,210 parts per million of lead. Its leaves contained much less lead than the soil--only 49 parts per million. But even that's too much to swallow. A single tablespoon of those leaves would deliver 86 micrograms of lead--more than the FDA's "total tolerable intake" of 75 micrograms per day for most adults. (It's 25 micrograms for pregnant women, 15 for children ages seven and up, and 6 for children younger than seven.) Just to put those numbers in perspective: preindustrial children are estimated to have taken in just two-thirds of one microgram of lead per day.
Children ingest lead not merely from paint chips and contaminated veggies and herbs but from dust blown and tracked in from outdoors. Research published in May in the Journal of Occupational and Environmental Hygiene proved the point, finding that the dust in doorways facing outside contained four times more lead than dust in windowsills, and over ten times that found in inside doorways. While lead paint remains the major culprit, Helen Binns says that "until we deal with both interior and exterior surfaces, children will not be fully protected" from lead poisoning.
Can you protect yourself and your kids and have your veggies too? Yes, say Finster, Gray, and Binns. But you have to garden differently:
Avoid gardening in high-risk areas, such as next to a busy street or close to an old structure, past or present.
Having picked a possible garden spot, get the soil tested. The site www.leadlisting.org gives names and phone numbers of five privately owned Illinois laboratories accredited as of April under the EPA's national lead laboratory accreditation program, four in the suburbs and one--STAT Analysis Corporation--in the city (prices range from $8 to $50). The state Department of Public Health also has a list of 108 Cook County "lead assessors," some public, some private, accessible from the search form at http://app.idph.state.il.us/Envhealth/lead/Leadinsp.asp.
If your soil tests at over 400 parts per million, don't grow root crops, stem crops, or leaf crops. Fruits like tomatoes are OK--but at the end of the season send the plants to the landfill rather than the compost heap. Grow other crops in containers or raised beds with a foot and a half of fresh lead-free soil instead. (Container gardening is the Chicago Department of Public Health's recommendation as well.)
In any case, say good-bye to grandpa's plowed-soil gardening style. Cover all bare ground with mulch or a weed tarp. And practice safe gardening in other ways, to avoid tracking lead inside. Among the recommendations of Binns's Safer Yards project (a brochure is available at www.chicagolead.org/Educational-Tools/Download.html): wear work gloves, wash your face and hands after gardening, and remove your shoes or boots before coming inside.
Dunn says the Resource Center simply doesn't grow its organic produce in actual city soil. Instead his outfit practices a variation on container gardening, laying down a clay barrier between three and six inches thick, then adding eighteen inches' worth of composted restaurant waste from the center's composting facility (at 1325 E. 70th) as a growing medium. Clay isn't impermeable forever, but Dunn estimates it should work to separate the plant roots from leaded soil for ten years or so. The Resource Center's produce is sold to some of the pickiest restaurants in town--the Dining Room at the Ritz-Carlton and Frontera Grill, among others. If you want to garden badly enough there's always a way.
And if you're curious just how it came to this, check out "The Secret History of Lead," by Jamie Lincoln Kitman (first published in the Nation in 2000 and available online), which documents the ghastly choices made 80 years ago by General Motors, DuPont, and Exxon's predecessor, Standard Oil of New Jersey.
Art accompanying story in printed newspaper (not available in this archive): illustration/Leslie Lammle.