A new study has found that almost a quarter of US households have soil exceeding the Environmental Protection Agency’s new lead screening levels of 200 parts per million.
For households with lead exposure from multiple sources, the EPA lowered the guidance to 100 parts per million; nearly 40% of households exceed that level.
The study was led by Gabriel Filippelli, a professor at Indiana University Indianapolis and executive director of the IU Environmental Resilience Institute.
Lead is a heavy metal that can accumulate in the human body with toxic effects. In children, exposure to lead is associated with decreased IQ and academic achievement. In the US, the burden of lead exposure has historically fallen on lower-income communities and communities of color due to redlining and other discriminatory housing practices.
Lead pollution can come from aging water pipes, old paint, and remnant gasoline and industrial pollution. Today, most lead exposure is from contaminated soils and dust, even after lead-containing infrastructure was removed.
The Centers for Disease Control and Prevention first set a limit on the concentration of lead in the bloodstream in 1991 at 10 micrograms per deciliter, and it lowered that limit several times until reaching the current limit of 3.5 micrograms per deciliter. The EPA’s soil lead screening level remained unchanged for more than 30 years until the agency’s recent announcement. Some states had established their own lower guidelines, like California, which has the lowest screening level, at 80 parts per million.
According to the study, the lag in policy change from the EPA is likely due to the ubiquity of the problem and because once the EPA lowers a screening limit, the organization will need to tell people what to do if their soils exceed it.
Health hazard
When the EPA lowered its screening level, Filippelli and his coauthors decided to make use of the database of 15,595 residential soil samples from the contiguous United States that they’d collected over the years to find out how many exceeded the new guideline.
About 25% of the residential soil samples, collected from yards, gardens, alleys and other residential spots, exceeded the new 200 parts per million level. Only 12% of samples had exceeded the previous 400 parts per million level. Extrapolating across the country, that equates to roughly 29 million households above the current recommended level.
Indianapolis and Chicago were among Midwestern cities with higher lead levels in household soil. In Indianapolis, 37% of soil sampled was above the 200 parts per million recommendation. In Chicago, 53% of soil sampled was above the recommended level.
The EPA issued separate guidance for households with multiple sources of exposure, such as both lead-contaminated soil and lead pipes, setting the level in those situations at 100 parts per million. That includes most urban households, Filippelli says. Forty percent of households exceed that limit, increasing the number of affected households to nearly 50 million, the study found.
“I was shocked at how many households were above the new 200 parts per million guideline,” Filippelli says. “I assumed it was going to be a more modest number, and results for the 100 parts per million guideline are even worse.”
Practical solutions
Typically, contaminated soils are remediated with a removal process known as “dig and dump.” However, the practice is costly and typically only used after an area is placed on the National Priority List for remediation, a process that can take years. Remediating all contaminated households with “dig and dump” would cost between $290 billion and $1.2 trillion, the study calculated.
A cheaper option is capping, or 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, 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 at their house,” Filippelli says.
Capping is also quicker.
“A huge advantage of capping is speed; it immediately reduces exposure,” Filippelli says. “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.”
Capping still requires time and effort; residents must find clean soil, transport it to their home and spread it out. Additionally, capping is done informally, so there is still much to learn about its lifespan and sustainability. Filippelli says that’s where the research will go next.
Despite the scale of the problem, Filippelli remains optimistic.
“Lead is the most easily solvable problem that we have,” Filippelli says. “We know where it is, and we know how to avoid it. It’s just a matter of taking action.”
The research appears in the journal GeoHealth.
Source: Indiana University
