About one in four American homes has flooring that exceeds the new U.S. Environmental Protection Agency’s lead screening levels of 200 parts per million (ppm), cut in half from the previous level of 400 ppm, according to found a new study. For homes with exposure to multiple sources, the EPA lowered the guidance to 100 ppm; Nearly 40% of households exceed that level, the study also found.
“I was surprised to see how many homes were above the new 200 ppm guideline,” said Gabriel Filippelli, a biochemist at Indiana University who led the new study. “I assumed it was going to be a more modest number. And the results for the 100 ppm guideline are even worse.”
Remediating the approximately 29 million affected homes using traditional “dig and dump” soil removal methods could cost more than $1 trillion, the study estimated. The study was published in GeoHealth, an open access AGU journal publishing research investigating the intersection of human and planetary health for a sustainable future. Filippelli is the former editor-in-chief of GeoHealth.
National lead problem ‘far from over’
Lead is a heavy metal that can accumulate in the human body, with 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 low-income communities and communities of color due to redlining and other discriminatory practices. Lead contamination can come from aging water pipes, old paint and gasoline residue, and industrial pollution, but today, most lead exposure comes from contaminated soil and dust, even after infrastructure has been removed. which contains lead.
The Centers for Disease Control and Prevention first set a limit on blood lead concentration in 1991 at 10 micrograms per deciliter, and lowered that limit several times until it reached the current limit of 3.5 micrograms per deciliter. But the EPA’s soil lead detection level remained unchanged for more than 30 years until the January announcement. Some states had established their own lower guidelines; California has the lowest detection level, 80 ppm.
The delay is likely due to “the immensity and ubiquity of the problem,” the study authors wrote. “The scale is staggering, and the country’s leadership and remediation efforts became substantially more complicated.” That’s because once the EPA lowers the detection limit, it must tell people what to do if their soils exceed it.
When the EPA lowered the detection level, Filippelli and his co-authors decided to use the database of 15,595 residential soil samples from the contiguous United States they had collected over the years to find out how many exceeded the new guideline.
Health hazard at home
About 25% of residential soil samples, collected from yards, gardens, alleys and other residential locations, exceeded the new 200 ppm level, the study found. (Only 12% of samples had exceeded the previous level of 400 ppm). Extrapolating to the entire country, that equates to approximately 29 million households.
The EPA issued separate guidance for homes with multiple sources of exposure, such as lead-contaminated soil and pipes, setting the level in those situations at 100 ppm. In practice, that’s most urban households, Filippelli said. Forty percent of households exceed that limit, increasing the number of affected households to nearly 50 million, according to the study.
Contaminated soils are typically remediated by removal (colloquially, “dig and dump”). But the practice is expensive and is typically only used after an area is placed on the National Priorities List for remediation, a process that can take years. Remediating all contaminated homes with “dig and dump” would cost between $290 billion and $1.2 trillion, the authors estimated.
A cheaper option is to “cap” – burying the contaminated soil with about a foot of soil or mulch. A geotechnical fabric barrier can also be installed. Most lead contamination is found 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 forever anyway, with raised beds, because they’re intuitively concerned about the history of land use in their home,” Filippelli said.
And the limitation is faster.
“A big advantage of capping is speed. It immediately reduces exposure,” Filippelli said. “You’re not waiting two years on a list to have your garden rehabilitated while your child is poisoned. It’s done in a weekend..“
Limitation still takes time and effort; Residents must find clean soil, transport it to their home and spread it. But the health benefits likely outweigh those costs, Filippelli said.
Because capping has been done more informally, there is still much to learn about its useful life and sustainability, Filippelli said. That’s where the research will go next.
Despite the “staggering” magnitude of the problem, “I’m really optimistic,” Filippelli said. “Lead is the most easily solvable problem we have. We know where it is and how to avoid it. It’s just a matter of taking action.”