Getting the lead out - difficulty of removing lead from soil in gardens

Vegetarian Times, June, 1995 by Lee Reilly

TO ANSWER YOUR QUESTION in the narrowest possible terms: No. There are plants that absorb lead from the soil, but this is not a practical lead-removal solution for any home gardener. "The best Pead-absorbing plant] I know of is something you're probably not going to want to plant," says Jonathon Collinson, senior project director at Woods End Research Laboratory, an environmental consulting group based in Mt. Vernon, Maine. It's ragweed, the scourge of many allergy sufferers. In recent years, DuPont Corp.'s environmental biotechnology group, located in Glasgow, Del., has achieved limited success in experiments using ragweed to harvest lead at industrial sites in New Jersey, says principal investigator Scott Cunningham, Ph.D.

But once ragweed absorbs lead, the metal remains in the plant, leaving you with hazardous waste to dispose of. You'd also be left with poor soil, because in order for a plant to bind with lead, the soil has to have a low pH and very little organic matter, which is fine for ragweed but would make a very bad garden.

Before you worry too much about a garden that may contain lead, however, you should know there's some controversy over what lead in the soil really means for food crops. "The question is, how bio-available is it?" says Allen Irish, an attorney who works for the National Paint and Coating Association, a trade group based in Washington, D.C. In other words, does lead in the soil mean you'll end up with lead in your food-bearing plants? Does lead in the plants themselves mean lead in the food that they bear?

The answer is unclear. When consultants at Woods End recently tested the leaves of a Siberian crabapple tree, results showed lead levels at 600 parts per million--200 parts per million above the federal government's recommended maximum level allowable in soil. But they didn't test the apples, the part of the tree someone would actually eat.

DuPont's Cunningham says that most lead in the garden is not available to food crops. "The plants that do absorb lead don't translocate it upward," he adds; for example, although dicots (such as cucumbers and cabbage) will absorb lead, it generally does not migrate to the portion of the plant that someone would eat. Cunningham's claim is backed by a bevy of independent studies conducted in the 1970s that showed no correlation between lead in the soil and lead in food-bearing plants. "The exception would be root vegetables like carrots," says Cunningham, adding that they should be washed to remove any lead.

But Ilya Raskin, Ph.D., a professor of plant biology at Rutgers University in Camden, N.J., whose lab is studying bio-remediation using mustard plants, disagrees. Growing food in heavily leaded soil "is a very touchy issue," he says. Raskin points out that DuPont has a vested interest in the issue of lead and soil; indeed, industry sources are pretty much the only ones conducting research on the issue. Because there are still questions surrounding lead-contaminated soil, and because many factors--the types of plants you're working with or the composition of the soil you're planting in--can have an effect, he advises caution.

You might reasonably suspect that the soil in your garden contains lead if it is near an older building that may have been painted with lead-based paint. The Woods End crabapple tree, for instance, grew just a few yards from an aging barn. For years, my little urban garden was picturesquely situated against an aging, warping shed that had long since gone au nature. Chances are, since it was built sometime in the 1920s, it was probably painted with lead-based paint. As the shed weathered, the paint most likely made its way into the adjacent soil.

The Paint and Coating Association's Irish says he can't rule out that paint could be responsible for lead in the soil, though he points out that the paint industry reached voluntary consensus on limiting the content of lead in paint to . S percent as far back as 1953. (Current regulation, enacted in 1978, limits the content to .0 6 percent.) "The EPA has acknowledged that when you're discussing lead as a primary pigment, you're talking about pre-world War II," he says. The reason? Lead was used in the white pigment in the paint that was necessary for good coverage. Manufacturers discovered a cheaper and better substitute, titanium dioxide, right before the war. Still, in a 1990 study, the Department of Housing and Urban Development found that nearly 75 percent of the private housing built in the United States before 1980 had been painted with lead-based paint.

If you're concerned that your soil might contain lead, arrange to have it tested by calling your local agricultural extension office. Some offices test soil; others publish lists of private labs. Look for "Extension Service" under the U.S. Department of Agriculture in your phone book, or call the National Lead Information Center ([800] 424-5323) for a national list of labs. (The center also offers a brochure on lead; call [800] LEAD-FYI.)