permaculture

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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.

By David Kohn
Sun Staff
Originally published November 10, 2003

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."

http://www.sunspot.net/news/nationworld/bal- 
te.lead10nov10001546,0,2651411.story