Some Grasses Can Stop Lead From Spreading In Soil

This article is part of The State of Science, a series featuring science stories from public radio stations across the United States. This story, by NPR Midwest Newsroom and The Missouri Independent reporter Niara Savage, was originally published by KCUR.

Lead left behind in soil from mining and smelting poses a major health risk to people who live nearby. Researchers in Nebraska and Kansas believe plant life and organic material can limit lead’s spread.

In parts of the Midwest where lead mining and smelting lasted for over a century, communities are still dealing with toxic waste left behind by the industry.

Lead, a dangerous neurotoxin, persists in the environment, including in water and soil, where it can pose a threat to the health of people living nearby. The risk is especially acute for children, who can unintentionally ingest lead by putting their hands in their mouths and whose brains and bodies are still developing.

It can be spread to other areas, like yards and schools, by rainfall, and can also taint aquifers or vegetables in gardens, making them harmful to consume.

Now researchers are working to limit the impact of lead in the environment on people, and they believe they’ve found a promising solution: Plant life.

Phytostabilization involves moving lead from soil into the roots, stems and leaves of plants to prevent it from spreading and to limit people’s contact with it.

“One of the goals of phytostabilization is to take the site with lead and put it in a stable state, so that the risk is reduced, and the issues related to lead in the soil can be managed,” said Larry Erickson, a professor emeritus at Kansas State University and former director of the university’s Center for Hazardous Substance Research.

His research is focused on using miscanthus grass to stabilize lead in soil.

“One of the benefits of having vegetation in the soil, where the lead is, is that we can have an opportunity for the water to be taken up by the plant that keeps the water from moving in other directions and transporting the lead,” Erickson said.

Stabilizing lead in soil to prevent it from spreading can help avert and alleviate potentially dangerous consequences.

“In the operation of (lead smelters), lead has gone up and out of the smokestack and fallen on soil and there may be lead associated with the soil in terms of a five-mile radius of the shelter,” Erickson said.

Leftover mining waste can cause metal contaminants to spread up to 100 miles along rivers and streams when the lead is washed away by rainfall, Erickson said.

Erickson published the results of his experiments with phytostabilization in 2021. The focus was on Fort Riley, Kansas. Erickson found the root systems of miscanthus grass are complex enough to significantly limit the movement of lead on a contaminated site from rainfall in about two years.

That means lead in soil at a contaminated site can’t spread and flow to other areas and put people at risk of exposure. In an ideal situation, planting miscanthus grass would be paired with remediating the top several inches of contaminated soil to limit the spread of lead.

Researchers have known for decades that exposure to lead can cause irreversible brain damage in children, even at low levels. Children are most at risk because their bodies are still developing.

The Food and Drug Administration recommends children consume no more than 2.2 µg per day of lead from food.

“Unfortunately, a lot of those areas also have higher contamination of soils just by location, near highly trafficked areas, or railroads.”

Another plant-based solution for lead exposure being studied by researchers is biochar, a carbonized substance produced from plant materials with absorption abilities that could have applications for urban farming by reducing the amount of lead taken up by the lettuce planted in it, according to a 2020 experiment led by a student at the University of Nebraska-Lincoln.

The results of the small study showed that adding biochar to soil reduced the amount of lead taken up by the lettuce planted in it.

Biochar-treated garden soil produced lettuce with just 0.41 µg of lead per serving. Untreated soil produced lettuce with a lead level of 1.22 µg of lead per 85 grams.

Ryley Thomas, the student who led the experiment under the supervision of Michael Kaiser and Jennifer Cooper, professors with the university’s Department of Agronomy and Horticulture, said she designed it to help people who live in food deserts.

“Community Crops Lincoln is a community garden nonprofit organization, and they go into areas that have food deserts, and they tried to create community gardens where people can go and have fresh produce,” Thomas said.

“Unfortunately, a lot of those areas also have higher contamination of soils just by location, near highly trafficked areas, or railroads.”

Kaiser said food deserts are a major problem in Lincoln, Nebraska.

“This means a large distance between people and grocery stores,” he said. “A potential solution would be community crops or urban agriculture.”

Thomas and Kaiser sampled soil near railroads in the state where lead levels are often high. Adding biochar to soil could be a long-term solution for entrapment of lead because it remains in soil for hundreds of years. But they emphasized that the study was small and needs to be repeated before significant implications can be drawn from the results.

In June, Bloomberg Philanthropies awarded Lincoln $400,000 in funding to support a project to turn wood waste into biochar. The city will establish the Lincoln Biochar Initiative by working closely with the Nebraska Forest Service and the University of Nebraska.

“We are looking to build our own biochar plant and then produce about 700 tons of biochar per year,” Kaiser said.

Aside from its absorption properties with implications for lead-tainted soil, biochar also promotes plant growth, carbon sequestration and fertilizer reduction. The facility is set to be fully operational by summer 2023.

The Missouri Independent and the Midwest Newsroom are jointly exploring the issue of high levels of lead in the children in Iowa, Kansas, Missouri and Nebraska.