Kimberly A. Gray, associate professor of civil and environmental engineering at Northwestern University, and her team tested a variety of plants cultivated in Chicago residential gardens rich with lead-contaminated soil. They found that leafy vegetables and herbs were highly likely to also be contaminated with lead.
The findings were published online by The Science of the Total Environment and will appear in an upcoming print issue of the journal.
The researchers harvested fruiting plants, leafy greens, herbs and root vegetables from 17 gardens, washed and dried the plants, and then separated root, shoot and fruit before analyzing them for lead content.
While the majority of the lead was concentrated in the roots, some lead was detected in shoots, which is often the portion of the plant that people eat. Gray's team calculated what amount of lead would be ingested by consuming some of the herbs such as cilantro. They found that those levels exceeded what would be excreted in children or women, which means lead would be stored in the body. These findings are very important for children and women of childbearing age.
"We are concerned about the edible portions of leafy vegetables and herbs that were found to contain lead," said Gray. "It is important that urban gardeners locate fruit and vegetable gardens away from buildings, test the lead levels in their soils and develop strategies to ensure safety for them and their children."
The lead concentration in the fruit of other plants, such as strawberries and tomatoes, was not found to be hazardous. Root vegetables, such as carrots and onions, are likely to have high levels of lead, but the very small sample size did not allow the researchers to draw a conclusion about this group.
Much of the soil's lead contamination comes from deteriorated paint, past use of lead-containing gasoline and industrial air pollution. Lead in soil does not biodegrade or decay.
The study grew out of an earlier federally funded, two-year phytoremediation project in Chicago's West Town community in which Gray and colleagues wanted to see if green plants could remove lead from contaminated soil or, at a minimum, stabilize the lead in the soil to reduce exposure of humans and animals to the toxin.
Other authors on the paper are Mary E. Finster, a Northwestern University graduate student working with Gray, and Helen Binns, M.D., an associate professor of pediatrics at Northwestern's Feinberg School of Medicine.
The research was supported by a grant from the U.S. Department of Housing and Urban Development.