Lead contamination has been found in children growing up in the southeast Los Angeles County communities surrounding the now-shuttered Exide battery plant, a new USC study has found.

Fifty baby teeth collected from 43 children within a 1.7-mile radius of the Exide Technologies plant in Vernon all tested positive for lead, according to the results published Monday in the journal Environmental Science & Technology.

The research area covered Boyle Heights, Maywood, East L.A., Commerce and Huntington Park.

The results show lead entered while babies were still developing inside their mother’s womb. Communities with the highest level of soil contamination — Boyle Heights and East L.A. — were also where children had the highest lead levels in their teeth, the researchers said.

Lead is a neurotoxin, and there is no level that is considered safe in humans. Lead poisoning can impact children’s growth, learning and behavior, and there are no obvious symptoms or signs.

The results are alarming even though state data has already confirmed elevated levels of lead exposure in the area, said Mark Lopez, executive director of East Yard Communities for Environmental Justice.

“The shocking part was really that the third trimester was when there was a spike in exposure,” he told KTLA. “That was really alarming for us. The primary impacts are brain development, and unfortunately, the impacts are irreversible.”

The researchers used children’s teeth because — unlike with blood testing, which shows only recent exposure — they were able to analyze different layers of teeth and asses past exposures.

“Higher lead in teeth means higher lead in the brain, kidney and bones,” lead author Jill Johnston with USC’s Keck School of Medicine said in a statement. “Testing women for lead during pregnancy, or even earlier, as they enter child-bearing age, may be needed to decrease lead exposure to their future offspring.”

Exide recycled 11 million auto batteries at the site every year, releasing 3,500 tons of lead into the atmosphere in the process.

The plant closed in March 2015 as part of a legal settlement for hazardous waste violations.

As of last Friday, The state Department of Toxic Substances Control (DTSC) has cleaned up 788 properties out of 2,500 it has been given funding for. The agency now has 32 crews in the field, said Barbara Zumwalt, a public information officer.

Experts believe as many as 10,000 properties in the area could have poisonous lead in their soil.

Zumwalt added that the cleanup effort is the largest of its kind undertaken in California.

Boyle Heights resident Cristina Cano said her family was living in a contaminated environment for years, and the state only cleaned soil and replaced grass on their lot a few months ago.

“The problem start three years ago,” she said. “Now, two months ago, they clean my property. We have kids, and my mother get cancer.”

Miguel Santiago, who represents the area in the state Assembly, released a statement on the USC study.

“After Exide carelessly spewed tons and tons of lead into air, 250,000 residents now face chronic illnesses long-term negative health impacts,” he wrote. “We won’t stop fighting against pollution in our communities until our children are healthy and safe.”

In a written statement sent to KTLA, Exide said the company will “continue to be a constructive participant in evaluating and addressing the need for cleanup of industrial and residential properties to the extent they were impacted by the facility’s former operations.”

“There are many significant historical sources for contaminants in urban soils in Southeast Los Angeles County communities, including lead-based paint chips from the predominantly older homes, decades of concentrated vehicle leaded gasoline exhaust from numerous freeways and thoroughfares, and many other industrial sources in the area,” the statement read.

The most significant predictor of high blood lead levels in the area was age of housing, Exide said, citing an April 2016 study by the California Department of Public Health. The company also asserted that the impact from the Vernon facility was confined to surrounding industrial areas and did not reach residences.

“Exide remains fully committed to working with the State and the DTSC on continued review of this matter, as well as our continued implementation of the Vernon facility closure along with funding of ongoing blood testing in the area,” the company’s statement said.

Anyone who lives within the 1.7-mile radius of the Exide plant can contact DTSC to have soil testing conducted at 844-225-3887. More information can be found on Assemblymember Santiago’s website.

Area residents may also obtain free blood tests to determine lead contamination. Contact the county’s Department of Public Health at 844-888-2290.

Correction: A previous version of this story provided an incorrect first name for East Yard Communities for Environmental Justice’s executive director. This story has been updated.