Lead In The Soil

Leaded paint and leaded gasoline aren't used anymore, but the once lead is in the soil it stays there. Exposure to lead can have serious health effects in children who might ingest that soil, or fruits and vegetables grown in it.

Andrew Margenot is an assistant professor of soil science at the University of Illinois. He says all soils naturally have some lead, which is measured in parts per million (ppm) from zero up to about 2,000. Most are 15-25 ppm. The health risks depend on the lead concentration.

"This is what the U.S. EPA calls a threshold of action if there's bare soil and there are children present - 400 ppm in an exposed soil is the threshold in which you need to do something," says Margenot. "And that typically means cover up that bare soil to reduce the pathway of direct exposure, meaning kids eating dirt or if you're a farmer, as you till breathing in those dust particles."

He says if soil testing shows a high lead concentration, there are a few ways to help mitigate the risk.

"The first is you increase soil pH. The availability of heavy metals depends on pH. In general, as the pH goes up, they're less available. A second option is to bind up those metals with a binding partner and in that case, it would be phosphate. The third one would be to use an organic matter input like compost," he says. "And compost, it appears, is emerging as an effective way to mitigate the availability of heavy metals like lead in soils."