It’s a number thousands of Palisades and Eaton fire survivors have come to depend on: 80 milligrams of lead in each kilogram of soil.
Below this concentration, California has historically deemed yards safe enough for families to rebuild and move home after a fire. Any more, state scientists say, comes with a notable risk of kids developing neurological problems from the lead they accidentally inhale, absorb through their skin and eat while playing outside.
In a new paper out Friday, Harvard environmental health researchers argue it’s not strict enough. The scientists contend that the state’s health standard is not based on sound science and should sit around 55 milligrams per kilogram of soil (a measure also referred to as “parts per million”) instead.
“We’re getting asked these questions every single day, like every other scientist … ‘Is it safe for my kids?’ ” said Joseph Allen, lead author on the paper and a Harvard T.H. Chan School of Public Health professor who has been working with fire survivors through the LA Fire HEALTH Study research program. “I can’t look at somebody in the eye any more, knowing what I know about these models, and tell them yes.”
However, other soil and health researchers said it’s a debate best confined to technical scientific papers, with few implications for fire survivors wondering if their property is safe.
Here’s what you should know:
Why a stricter standard?
Lead can cause negative health effects at virtually any level of exposure, so scientists at California’s Department of Toxic Substances Control set their health standard for lead in residential soil by first starting with a goal: The standard should prevent children from losing one IQ point due to lead exposure.
To answer this, the department uses a computer model, LeadSpread, that estimates how much lead might enter the body of a kid who plays in the dirt, primarily through accidentally eating dirt left on their hands.
Then, it determines what fraction of lead that has entered the body actually makes it into the bloodstream.
From there, DTSC estimates that 1 microgram of lead per deciliter of blood results in a loss of one IQ point.
By digging through DTSC’s papers outlining how it calculated the 80 mg/kg standard, the Harvard researchers identified three issues.
First, they point out that the standard comes from an old version of the department’s model, LeadSpread 8. When DTSC recalculated the number with the updated LeadSpread 9, they got 70 mg/kg, but determined that the difference wouldn’t significantly impact IQ.
The Harvard researchers argue DTSC does not have a strong basis for that assumption.
Second, the Harvard scientists warn that the LeadSpread model is disconcertingly dependent on other assumptions. For example, the model determines what percent of lead that enters the body ends up in the blood based on a 1983 study looking at infants who consumed formula contaminated with lead.
It’s a very different situation than soil, the Harvard scientists argue, and even a slight shift of that percentage can give a much stricter result of around 55 mg/kg. The same is true if DTSC were to use a higher estimate for how much dirt, on average, a kid ingests per day.
Finally, the Harvard researchers point out that lead causes harm not just to the nervous system — for which the IQ metric attempts to account — but also to bones, the kidneys and the heart. And not all kids have the same risk. Kids with other health conditions may be more sensitive, as are 2-year-olds compared to 6-year-olds.
“The model sort of happens in a vacuum,” said Lindsey Burghardt, chief science officer at Harvard’s Center on the Developing Child and author of the paper. “But kids … live in the context of their developmental environment where they’re having a number of different exposures and experiences, whether they’re positive or negative.”
DTSC did not immediately respond to a request for comment.
What does it mean for fire survivors hoping to move home?
Many soil and environmental health researchers say the debate shouldn’t concern fire survivors all that much.
Given all the uncertainty in lead modeling — and the wide range of sensitivity different kids may have based on their health conditions and how much they play in the dirt — many researchers say concerned residents should focus on their own risks and think about lead levels as “much lower than the standard,” “close to the standard,” and “much higher than the standard” instead of obsessing over differences in digits.
For example, much higher levels in soil that’s about to get covered with a new concrete foundation might not matter all that much. Levels close to the standard in the yard of a home with no kids may not matter if the residents aren’t avid gardeners and always take their shoes off when entering the house.
On the flip side, even lower levels in the soil in an area where a 2-year-old likes playing in the mud could pose a risk that’s unacceptable for a resident.
Seth John, a professor of earth sciences at USC, pointed out that, while different LeadSpread assumptions could lead to a much lower standard, the opposite is also true.
John also noted that the federal Environmental Protection Agency’s standard is even higher at 200 mg/kg — which is down from 400 mg/kg for play areas and 1,600 mg/kg for other residential areas just a year ago. California didn’t adopt its current standard until 2009.
The Harvard scientists point out this downward trend in the standard has been due to new science showing kids are more sensitive to lead than previously thought. Their 55 mg/kg update, they say, is for the same reason.
USC’s Contaminant Level Evaluation and Analysis for Neighborhoods (CLEAN) project team, which John is working with to test the post-fire soil across L.A. County, said 43% of properties they’ve tested exceed the 80 mg/kg standard, while 57% exceeded 55 mg/kg.
How can fire survivors stay safe?
John also argued the debate over the lead standard distracts from the simple steps residents can take to protect themselves and their kids.
USC CLEAN continues to offer free soil testing for all L.A. County residents — thanks in part to funding from FireAid. The L.A. County Department of Public Health is also offering free soil testing for residents in select areas inside and downwind of the Eaton fire burn scar.
The department also offers free lead blood testing (as do most insurances) through Quest Labs for anyone concerned about their exposure.
Soil researchers say the most effective way to remediate contaminated soil is to have the top layer scraped off and replaced with fresh soil. If residents can’t afford a full scrape, simply adding fresh top soil on the contaminated soil can shield residents from the contamination.
Even without remediation, there are plenty of ways residents can reduce their exposure. The most direct is by limiting contact with soil. For kids, that might mean going to clean parks to play in the dirt. For adults, it could mean always wearing gloves when gardening.
To avoid continued exposure when inside, residents can routinely wash their hands, take their shoes off when entering the house, wipe down pets after they play in the yard, and invest in air purifiers to remove any contaminated dust.
