New method assesses lead hazard in soil

January 21, 2019 by David Tenenbaum, University of Wisconsin-Madison
Vegetable gardens located close to buildings painted before 1978 may contain lead. The new soil placed in these raised beds should reduce any lead exposure. Credit: David Tenenbaum

As Milwaukee, Flint, Michigan and other cities grapple with the toxic impact of lead water pipes, another lead-contamination hazard lurks in soil.

The nervous-system damage of lead is irreversible and intolerable, and so preventing exposure is the only real defense.

Not all lead compounds are created equal, in terms of how easily they move from the , both inside and outside the lab. Yet standard tests for lead in soil do not give a full picture of bioaccessibility.

In a study published Oct. 12 in Environmental Science and Technology, University of Wisconsin–Madison researchers describe a way to use a common, low-cost soil test to determine how much of the lead is bioaccessible, and therefore dangerous.

A second factor in determining the hazard of lead in soil, called bioavailability, measures how easily it can move from the gastrointestinal tract into the bloodstream.

Although the terminology is confusing, Douglas Soldat, a lead expert and professor of soil science at the University of Wisconsin–Madison, says they tend to be related: A bioaccessible lead compound is usually bioavailable as well. Because lead is extremely toxic, immobilizing it in soil and reducing its uptake in the gastrointestinal tract both benefit public health.

The test described by Soldat and his former graduate student Shannon Plunkett focuses on lead phosphate, which is relatively insoluble soil. Lead carbonate, a pigment historically used in paint, binds less tightly and therefore is more mobile in the soil. "If our goal is to keep lead out of the body, the less soluble forms are more desirable," says Soldat.

Lead paint is not always as obvious as this. Paint flaking from walls can contaminate soil within 20 feet of a building. Creative Commons

The new testing approach uses the Mehlich 3, an existing and affordable soil-nutrient test, to evaluate lead bioaccessibility. By simultaneously measuring total lead and Mehlich-3 lead, it's possible to estimate what percentage is immobile.

Lead was found in house paint until 1978 and frequently remains in soil near foundations, posing a threat to vegetable gardeners and playful children.

In Southwest Wisconsin, more than a century of lead mining has left ground-level hot spots where lead ore was extracted, processed or shipped.

The analytical tactic explained in the new study could be used by homeowners or tenants concerned about lead in soil, or by landowners in areas of known or suspect lead contamination.

The new analysis based on Mehlich 3 could also be used to evaluate a growing tactic for immobilizing lead: adding phosphorus to soil to increase the formation of low-mobility lead phosphate. The strategy, called in situ (on site) remediation, has been applied to broadly polluted areas where soil removal or "capping" is not feasible.

Phosphorus addition has shown promise in hundreds of studies, notes Plunkett, but the results depend on many factors, including the type of phosphorus used and soil properties like acidity. Until now, measuring how much lead-phosphate remediation affects mobility using EPA-approved tests, which cost about $200 per sample, has been a difficult and expensive proposition.

The Mehlich 3 results that Soldat and Plunkett reported closely paralleled the Environmental Protection Agency's "1340" test, which is the accepted way to assess lead bioaccessibility, but at a much lower cost.

The Mehlich 3 and total lead tests are offered at the University of Wisconsin Soil and Forage Laboratory and the Milwaukee Health Department Laboratory.

Explore further: Soil's history: A solution to soluble phosphorus?

Related Stories

Quick soil test aims to determine nitrogen need

July 18, 2018

Healthy soil contributes to healthy crops. Farmers know this, so they do what they can to ensure their soil is in good shape. They send samples of their soil for lab testing to find out if it is low in any important nutrients. ...

Recommended for you

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

The friendly extortioner takes it all

February 15, 2019

Cooperating with other people makes many things easier. However, competition is also a characteristic aspect of our society. In their struggle for contracts and positions, people have to be more successful than their competitors ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.