Fátima Guerrero grew up in Maywood, a few blocks from where the Exide Technologies battery plant operated for nearly a century in Vernon. She remembers the smell. She remembers the dust. And she remembers being told, years after the plant closed, that the cleanup was working, that the soil crews had come through, that her neighborhood was getting safer.
New research from UC Irvine suggests the reassurances fell short.
A peer-reviewed study published this spring found that more than two-thirds of soil samples collected from properties inside the state’s designated cleanup zone still exceeded California’s own lead threshold, even after remediation. In some cases, by a wide margin.
What the Research Found
The study, led by Jill Johnston, an associate professor of environmental and occupational health at UC Irvine, is the first peer-reviewed examination of how lead contamination from the Exide site extends across the cleanup zone and beyond it. Between October 2021 and September 2024, Johnston’s team worked alongside East Yard Communities for Environmental Justice to collect more than 1,000 soil samples from 373 residential properties in the surrounding area.
California’s Department of Toxic Substances Control uses 80 parts per million as its lead threshold for residential property. More than two-thirds of samples from homes that had already been remediated came back above that level. Nineteen percent of those samples topped 200 ppm.
Outside the state’s defined cleanup zone, the numbers were worse. Nearly 90 percent of sampled homes exceeded acceptable lead levels. Seven in 10 had at least one sample above 200 ppm.
The study raises two possibilities for why remediated homes still show contamination at these levels. Either crews did not fully remove the lead-bearing soil during cleanup, or the soil was recontaminated by other historically present sources of lead, including paint and freeway exhaust particles, which have accumulated in these communities for decades. In many cases, researchers believe it is likely both.
A Century of Contamination
Exide Technologies operated its 15-acre lead-acid battery smelting facility in Vernon from 1922 to 2015. At its peak, the plant processed roughly 11 million auto batteries a year. Over its lifespan, it released an estimated 3,500 tons of lead into the air and soil of surrounding communities, including Maywood, East Los Angeles, Commerce, Bell, and Huntington Park.
These are communities with large working-class Latino populations, limited political capital, and some of the highest industrial pollution burdens in Southern California. The plant operated for decades before regulators moved against it.
Federal authorities shut down Exide in 2015 over hazardous waste violations. California declared the site an environmental disaster. The state set the remediation zone at a 1.7-mile radius around the plant, and cleanup efforts have now cost more than $750 million. As of late March 2026, more than 6,000 properties had been processed by the state’s Department of Toxic Substances Control.
Residents and environmental advocates have challenged the adequacy of that work for years. Prior investigations found excessive lead on properties that had been officially cleared. Contractors reportedly violated state standards for soil removal, and in some cases spread toxic dust during the remediation process itself.
This article draws on reporting from LAist.
The Question of Boundaries
One of the study’s more pointed findings is what happens at the edge of the cleanup zone. The 1.7-mile radius was a regulatory decision, not a scientific one, and Johnston’s data suggests lead contamination does not stop where the state’s map does.
The nearly 90 percent exceedance rate in unmediated homes outside the zone is not a marginal finding. It points toward a remediation boundary that may have been drawn too conservatively, leaving whole blocks of residential properties with no cleanup plan and no timeline.
Lead exposure carries serious health consequences. The metal affects neurological development, reproductive health, and kidney function. The risks fall hardest on children and pregnant people. In communities like Maywood and Huntington Park, where families have lived through decades of industrial pollution and are now raising children in soil that still tests hot, the abstraction of parts-per-million becomes something more immediate.
A Long Fight, Still Going
California’s cleanup of the Exide zone has never been a smooth story. The state’s own contractor oversight drew criticism early on. Environmental justice groups pushed for years to get remediation taken seriously at a scale matching the contamination. And the communities most affected had little margin for error. They couldn’t move. They couldn’t wait out the process in a second home somewhere else.
Johnston’s study, built partly on partnerships with those same community organizations, represents something the remediation effort has largely lacked: independent, peer-reviewed verification of what residents have been saying all along.
More than 6,000 properties have been formally cleaned. The state has spent three-quarters of a billion dollars. And the soil in these neighborhoods still carries lead at levels the state itself defines as unacceptable.
For the people who live there, the gap between those two facts is not an abstraction. It is the backyard where their kids play.