It's a number that thousands of survivors of the Palisades and Eaton fires depend on: 80 milligrams of lead in every kilogram of soil.
Below this concentration, California has historically considered yards safe enough for families to rebuild and move home after a fire. What's more, government scientists say there is a significant risk of children developing neurological problems from the lead they accidentally inhale, absorb through their skin and eat while playing outside.
IN the newspaper will be published on FridayHarvard environmental health researchers say this isn't rigorous enough. Scientists say the state health standard is not based on reliable science and should instead be around 55 milligrams per kilogram of soil (a measure also called “parts per million”).
“We, like every other scientist, get asked these questions every single day… 'Is this safe for my children?' said Joseph Allen, lead author of the paper and a professor at the Harvard T.H. School of Public Health. Fire HEALTH Study in Los Angeles research program. “I can no longer look someone in the eye, knowing what I know about these models, and say yes to them.”
In a statement to The Times, the California Department of Toxic Substances Control stood by its public health standards and the science behind them, saying they remain the strictest in the country.
However, other soil and health researchers say the debate is best limited to technical scientific articles and has little relevance to fire survivors wondering whether their property is safe.
Here's what you should know:
Why a stricter standard?
Lead can cause negative health effects at almost any level of exposure, so DTSC scientists established a health standard for lead in residential soil, starting with the goal that the standard should prevent children from losing one IQ point due to lead exposure.
To answer that question, the department uses a computer model called LeadSpread, which estimates how much lead a child playing in the dirt might absorb, primarily from accidentally eating dirt on their hands.
It then determines how much of the lead ingested actually ends up in the bloodstream.
The DTSC estimates that 1 microgram of lead per deciliter of blood results in a loss of one IQ point.
After reviewing DTSC documents that describe how the 80 mg/kg standard is calculated, Harvard researchers identified three problems.
First, they note that the standard comes from an older version of the department's model, LeadSpread 8. When DTSC recalculated the number using the updated LeadSpread 9, they came up with 70 mg/kg, but determined that the difference would not have a significant impact on IQ.
The Harvard researchers argue that DTSC does not have a strong basis for this assumption.
Second, Harvard scientists warn that LeadSpread's model is confusingly dependent on other assumptions. For example, the model determines what percentage of lead ingested ends up in the bloodstream based on a 1983 study that looked at infants who consumed formula contaminated with lead.
This is a very different situation than in soil, say the Harvard scientists, and even a small change in this percentage can produce a much more stringent result of about 55 mg/kg. The same would be true if the DTSC used a higher estimate of how much dirt the average child ingests per day.
DTSC said the 1983 study remains the best data source available. Conducting such a study today would be unethical, given that scientists now understand that there is no safe level of lead exposure.
Finally, Harvard researchers note that lead harms not only the nervous system, which IQ measures attempt to measure, but also the bones, kidneys, and heart. And not all children are at the same risk. Children with other medical conditions may be more sensitive, as may two-year-olds compared to six-year-olds.
“This model occurs in a vacuum,” said Lindsay Burghardt, chief scientist at the Harvard Center on the Developing Child and an author of the paper. “But children… live within the context of their developmental environment, where they are exposed to many different influences and experiences, both positive and negative.”
What does this mean for fire survivors hoping to return home?
Many soil and environmental researchers say the debate shouldn't focus so much on fire survivors.
Given all the uncertainty in lead modeling—and the wide range of sensitivities that different children may have depending on their health status and how much they play in the dirt—many researchers say concerned residents should focus on their own risks and think of lead levels as “well below standard,” “close to standard,” and “way above standard,” rather than focusing on differences in numbers.
For example, much higher levels in soil that is about to be covered by a new concrete foundation may not make much of a difference. Near-standard levels in the yard of a home without children may not make a difference unless the residents are avid gardeners and always remove their shoes when entering the home.
On the other hand, even lower soil levels in an area where a two-year-old child likes to play in the dirt may pose a risk that is unacceptable to the local resident.
Seth John, a professor of geosciences at the University of Southern California, noted that while LeadSpread's various assumptions may result in a much lower standard, the opposite is also true.
John also noted that the Federal Environmental Protection Agency standard is even higher at 200 mg/kg, down from 400 mg/kg for playgrounds and 1,600 mg/kg for other residential uses just a year ago. California did not adopt its current standard until 2009.
Harvard scientists note that this downward trend in the standard is due to new scientific data that shows that children are more sensitive to lead than previously thought. They say their upgrade to 55 mg/kg is for the same reason.
The USC Neighborhood Contaminant Assessment and Analysis Project team, with whom John is working to test soils following the Los Angeles County fire, reported that 43% of the properties they tested exceeded the 80 mg/kg standard and 57% exceeded 55 mg/kg.
How can fire survivors stay safe?
John also said the debate over the lead standard is distracting residents from simple steps they can take to protect themselves and their children.
OSK CLEANING continues to offer free soil testing for all residents of Los Angeles County – thanks in part to funding from FireAid. The county health department is also offers free soil testing for residents of some areas in and downwind of the Eton fire scar.
The department also offers free blood test for lead (like most insurances) through Quest Labs for anyone concerned about their risk.
Soil scientists say the most effective way to remediate contaminated soil is to scrape off the top layer and replace it with fresh soil. If residents cannot afford a complete cleanup, simply adding fresh topsoil to the contaminated soil can protect residents from contamination.
Even without remediation, there are many ways residents can reduce their exposure. The most direct is limiting contact with the soil. For children, this may mean having to clean up parks and play in the dirt. For adults, this may mean wearing gloves at all times when gardening.
To avoid long-term exposure while inside, residents can wash their hands regularly, remove shoes when entering the home, dry off pets after they play in the yard, and purchase air purifiers to remove contaminated dust.
