1 in 4 Yards in U.S. Exceeds New EPA Limits for Lead Levels in Soil, Study Finds

A new study has found that approximately one in four households in the United States has soil lead levels exceeding the new U.S. Environmental Protection Agency (EPA)’s limit of 200 parts per million (ppm). The previous screening level was 400 ppm.

For households that have multiple sources of lead exposure, the guidance level was lowered to 100 ppm, a press release from the American Geophysical Union (AGU) said. The researchers found that almost 40 percent of households in the United States exceeded that level.

“Based on a wide network of citizen-science collected household soil samples, we find that nearly one in four households may now contain a soil lead hazard based on this new, more protective standard,” the authors of the study wrote. “Unsafe levels of lead exposure [have] occurred in many communities across the United States, with much of the burden resting on lower income communities, and communities of color. Lead exposure is prevalent due to past lead emissions and the substantial legacy lead loads that remain in soils and structures within communities.”

A lead concentration limit for human blood was first set by the Centers for Disease Control and Prevention back in 1991, AGU said. However, the lead screening level for soil set by the EPA was the same for more than three decades until early this year. By then, some states like California — which has the lowest limit at 80 ppm — had established their own guidelines.

In the study, the authors said the delay was likely due to “the immensity and ubiquity of the problem.”

“The scale is astounding, and the nation’s lead and remediation efforts just became substantially more complicated,” the authors said. This is because the lower limits mean the EPA needs to let people know the steps to take if their soils are over the appropriate threshold.

To find out how many households exceeded the updated guidelines, the researchers looked at their database of residential soil samples — 15,595 of them — collected from gardens, yards, alleys and other residential locations across the contiguous U.S.

They found that about a quarter of the samples exceeded the new limit of 200 ppm, whereas just 12 percent had exceeded the higher threshold of 400 ppm. That means about 29 million households across the country exceed the new lead limits.

For households with multiple exposure sources — like lead pipes and soil contaminated with lead — the EPA guidance level is 100 ppm. According to the study, 40 percent of households were above that limit, bringing the number to nearly 50 million.

“I was shocked at how many households were above the new 200 ppm guideline,” said Gabriel Filippelli, lead author of the study and an Indiana University biochemist, in the press release. “I assumed it was going to be a more modest number. And results for the 100 ppm guideline are even worse.”

The study, “One in Four US Households Likely Exceed New Soil Lead Guidance Levels,” was published in the journal GeoHealth.

Lead, a heavy metal, can build up in the human body and have toxic effects. It can come from old paint and water pipes, industrial pollution and remnant gasoline. Most lead exposure today is from contaminated dust and soils that remain after the removal of lead-tainted infrastructure.

In the U.S., there is a historically disproportionate burden of lead exposure in communities of color and those with lower incomes due to discriminatory practices such as redlining — a real estate practice where financial services were withheld in neighborhoods with higher numbers of ethnic and racial minorities. Lead exposure has been linked with lower educational outcomes in children.

Contaminated soils are usually remediated with traditional “dig and dump” removal, but this method is costly and requires an area to first be put on the remediation National Priority List, which can be a years-long process. The researchers calculated that the remediation of all contaminated households using the “dig and dump” method would cost from $290 to $1.2 trillion.

The process of burying lead-contaminated soil with roughly a foot of mulch or soil — called “capping” — is a less expensive option. The installation of a geotechnical fabric barrier is also a potential solution.

Filippelli pointed out that most soil lead contamination sits in the first 10 to 12 inches underground, so either of these methods dilutes or covers up the issue to a level that is acceptable.

“Urban gardeners have been doing this forever anyway, with raised beds, because they’re intuitively concerned about the history of land use at their house,” Filippelli said. “A huge advantage of capping is speed. It immediately reduces exposure. You’re not waiting two years on a list to have your yard remediated while your child is getting poisoned. It’s done in a weekend.”

Filippelli emphasized that despite the time and effort it takes to cap soil, the costs are likely outweighed by the health benefits. There is still a lot that is unknown about the sustainability and lifespan of capping, Filippelli added, and that will be a focal point of research in the future.

“I’m really optimistic,” Filippelli said in the press release. “Lead is the most easily solvable problem that we have. We know where it is, and we know how to avoid it. It’s just a matter of taking action.”