Lead takes root in urban gardens

Hazard: A new study suggests that plants from city residential plots might contain harmful levels of the toxic metal.

Medicine & Science

November 10, 2003|By David Kohn | David Kohn,SUN STAFF

It seems like such a wholesome undertaking: tending your own little urban garden filled with fresh vegetables and herbs.

But some of those homegrown plants might contain potentially dangerous levels of lead, according to a new study of Chicago residential gardens.

The greatest hazard was associated with leafy green vegetables and herbs. Researchers found traces of the toxic metal in some of the plants' leaves - the part people normally eat.

Exposure to lead causes a variety of health problems, particularly in children. It can damage the brain, retard growth, impair hearing, and trigger mood swings and headaches.

The plants in the study absorbed lead from soil that contained high levels of the metal. The study, which appears in the latest edition of the journal The Science of the Total Environment, found that lead levels were highest in the roots, but in some plants it migrated further into the leaves.

"If you grow leafy vegetables and herbs in soil contaminated with lead, it's highly likely that those vegetables will be contaminated with lead," said Northwestern University environmental engineer Kimberly Gray, who oversaw the study.

Root vegetables such as carrots are also likely to absorb high levels of lead, she said. But the study tested very few such plants - not enough to produce a conclusion.

Although the study was small, it suggests that many urban gardens might be producing contaminated plants, said Northwestern researcher Mary Finster, a co-author.

She and her colleagues collected 87 vegetables, fruits and herbs from 17 gardens in an urban neighborhood in Chicago. The scientists looked at four kinds of plants: fruiting plants, leafy greens, herbs and root vegetables.

To find out how much lead was likely to be ingested by humans, the scientists washed the plants before measuring lead. Even after washing, some leafy greens and herbs had measurable lead, indicating that the metal was absorbed into plant tissue.

The researchers also tried to calculate whether eating normal amounts of the contaminated plants could affect human lead levels.

In some plants, the theoretical amounts of ingested lead exceeded the U.S. Food and Drug Administration's safe daily maximum. A tablespoon of one sample of dried cilantro contained more than 85 micrograms of lead, over 10 times the limit for children under six.

These levels could contribute to health problems, Gray said - especially in children, who can be harmed by much lower amounts than adults. Women of childbearing age are also at risk because lead can be transferred to a fetus.

Nearly all fruits and vegetables showed no signs of lead. While the roots of strawberry and tomato plants had high lead levels, the fruits had no measurable amount.

The researchers also measured lead in the soil. All samples from yards exceeded 400 parts per million (ppm), the Environmental Protection Agency's safe limit for children's play areas. Some soils had extraordinary amounts, as high as 55,000 ppm.

To minimize contamination risk, Gray recommends planting gardens far from lead-painted houses or other buildings - paint particles tend to settle close to the structures. She also suggests testing soil for lead and, if necessary, replacing it with uncontaminated soil.

Lead contaminates soil mainly through lead paint, which was banned in 1978, and leaded gasoline. In the century before it was outlawed in 1986, leaded gasoline deposited about 6 million tons of the metal across the country, much of it in heavily trafficked cities such as Chicago and Baltimore.

A 1983 study of Baltimore yards, for instance, found lead levels as high as 10,900 parts per million. "Urban areas are likely to have high levels of lead in yards," said Xavier University toxicologist Howard Mielke, who did the Baltimore study.

A leading expert on lead in soil, Mielke wasn't surprised by the results of the recent Chicago study. He said it underscored a larger point - that lead continues to saturate the environment in many large cities.

"It has accumulated over the years," he said. "And it's still just sitting there."

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