At least one in four residential yards in the U.S. exceeds the new EPA guideline for lead levels in soil

  • Art
  • June 20, 2024

About one in four U.S. households has soil that exceeds the new U.S. Environmental Protection Agency's screening levels of 200 parts per million (ppm), a halving from the previous level of 400 ppm, a new study shows. For households with exposure from multiple sources, the EPA lowered the guideline to 100 ppm; Nearly 40% of households exceed that level, the study also showed.

“I was shocked by the number of households that were above the new guideline of 200 ppm,” said Gabriel Filippelli, a biochemist at Indiana University who led the new study. “I assumed it would be a more modest number. And the results for the 100 ppm guideline are even worse.”

Remediating the roughly 29 million affected households using traditional 'dig and dump' methods of soil removal could cost more than $1 trillion, according to the study. The research was published in GeoHealth, an open-access AGU journal that publishes research on the intersection of human and planetary health for a sustainable future. Filippelli is the former editor-in-chief of GeoHealth.

National frontrunner problem 'far from over'

Lead is a heavy metal that can accumulate in the human body, causing toxic effects. In children, lead exposure is associated with lower educational outcomes. In the United States, the burden of lead exposure has historically fallen on lower-income communities and communities of color due to redlining and other discriminatory practices. Lead pollution can come from outdated water pipes, old paint, gasoline residue and industrial pollution, but today most lead exposure comes from contaminated soil and dust, even after lead-containing infrastructure has been removed.

The Centers for Disease Control and Prevention first set a blood lead concentration limit at 10 micrograms per deciliter in 1991, and lowered that limit several times until reaching the current limit of 3.5 micrograms per deciliter. But the EPA's soil lead screening level remained unchanged for more than 30 years until the January announcement. Some states had set their own lower guidelines; California has the lowest screening level, at 80 ppm.

The slowdown is likely due to “the immensity and pervasiveness of the problem,” the study authors wrote. “The scale is astonishing, and the country's leadership and recovery efforts have just become significantly more complicated.” That's because once the EPA lowers a screening limit, they have to tell people what to do if their soil exceeds it.

When the EPA lowered the screening level, Filippelli and his co-authors decided to tap the database of 15,595 residential soil samples from the contiguous United States that they had collected over the years to find out how many exceeded the new guideline.

Danger to household health

About 25% of residential soil samples collected from yards, gardens, alleys and other residential areas exceeded the new level of 200 ppm, the study found. (Only 12% of samples had exceeded the older level of 400 ppm.) Extrapolating across the country, that equates to about 29 million households.

The EPA has issued separate guidelines for households with multiple sources of exposure, such as both lead-contaminated soil and lead pipes, setting the level at 100 ppm in those situations. In practice, that's most urban households, Filippelli said. Forty percent of households exceed that limit, increasing the number of affected households to almost 50 million, the study shows.

Normally, contaminated soils are remediated by disposal – colloquially 'dig and dump'. But this practice is expensive and is usually only implemented after an area has been placed on the National Priorities List for restoration, a process that can take years. Cleaning up all contaminated households with 'dig and dump' would cost between $290 billion and $1.2 trillion, the authors calculated.

A cheaper option is “covering”: burying the contaminated soil with about a foot of soil or mulch. A geotechnical fabric barrier can also be installed. Most lead contamination is in the top 10 to 12 inches of soil, Filippelli said, so this simple method covers up the problem or dilutes it to an acceptable level.

“Urban gardeners have been doing this all the time anyway, with raised beds, because they are intuitively concerned about the land use history near their home,” Filippelli said.

And covering is faster.

“A big advantage of capping is its speed. It immediately reduces exposure,” Filippelli said. “You don't wait two years for a list to have your garden remediated while your child gets poisoned. It's done in a weekend.

Covering still requires time and effort; residents must find clean soil, transport it to their homes and distribute it. But the health benefits likely outweigh those costs, Filippelli said.

Because the capping has been done more informally, there is still much to learn about its lifespan and durability, Filippelli said. That's where the research will go next.

Despite the “mind-boggling” scale of the problem, “I'm very optimistic,” Filippelli said. “Lead is the easiest problem we have. We know where it is, and we know how to avoid it. It's just a matter of taking action.”

Cards: https://www.mapmyenvironment.com/

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