CHICAGO (CBS) — A disturbing study finds two-thirds of children under the age of 6 are estimated to have been exposed to lead through their drinking water.

The study also found that predominantly Black and Latino populations were disproportionately less likely to be tested for lead but also disproportionately exposed to contaminated drinking water.

The study, published in the journal JAMA Pediatrics, found that 68% of children 6 and under in Chicago – a total of 129,000 –  have been exposed to lead-contaminated drinking water. The study also found that 19% of those children use unfiltered tap water as their primary source of drinking water.

Investigators used a retrospective assessment of lead exposure based on 38,385 household lead tests collected from January 2016 until September 2023. The information was publicly available from Department of Water Management records.

The study said machine learning and microsimulation were used to estimate childhood lead exposure citywide.

The study defined water to be contaminated if most of the tests within a census block had 1 part per billion or more lead concentration on the second draw. This value was chosen because no amount of lead in drinking water at all is considered safe and because one ppb is the limit for detection in lead water tests.

The study warned that increased blood lead levels in children can cause cognitive development deficits and other health hazards.

“The impact of low-level, long-term exposure to lead-contaminated drinking water may not be easily identifiable at the individual level,” the study said. “Instead, it could cause population-level increases in adverse health outcomes, such as lower population-level mean IQ or increased preterm births, underscoring the need for reduced exposure to lead-contaminated drinking water.”

The study also concluded that Black and Latino households disproportionately drink bottled water, while white households disproportionately drink tap water. However, the study emphasized that bottled water is not necessarily less contaminated with lead than tap water – as the U.S. Food and Drug Administration sets the lower limit for lead in bottled water at five ppb. The study also found that using filtered tap water doesn’t necessarily prevent lead exposure either.

“The racial and ethnic disparities present are indicative of the myriad ways environmental racism can manifest. Lower screening rates, lower consumption of tap water, and higher levels of lead exposure among predominantly Black and Hispanic blocks may indicate mistrust toward water sources or lack of community engagement from relevant authorities,” the study said. “Neighborhoods with high-risk estimates as well as low screening rates were largely clustered in the South and West sides of the city, corresponding to the city’s geographic history of segregation and disinvestment.”

Benjamin Huynh, an assistant professor at the Johns Hopkins Bloomberg School of Public Health, is the study’s lead author. He reemphasized that no amount of lead in water is safe.

“The goal is to have zero lead in water at all,” Huynh said, “and we know from the science that even small amounts of lead in the water can impact your child.”

However, Huynh also noted that the study’s findings should not draw comparisons to high-profile water crises of relatively recent years.

“I don’t think we need to be alarmist,” Huynh said. “It’s not as bad as the Flint crisis. Your kid’s not going to be hospitalized from the levels of lead that we’re seeing. But yeah, I think there’s some concern – because even these low levels of lead, these are things that can affect your child without you noticing.”

In addition, exposure to lead-based paint dust remains the overwhelming source of elevated blood levels in children in Chicago. This is why the Chicago Department of Public Health has invested in robust lead-based paint and dust inspection and mitigation, especially in communities most impacted.

In a statement, the Chicago Department of Water Management has said it took issue with the study’s sampling – saying it only indicated whether or not there is a lead service line, not routine exposure.

The city also said lead testing shows the water meets the standards of the U.S. Environmental Protection Agency.

Chicago has 380,000 lead service lines. City officials estimate that replacing all of them will cost up to $9 billion.

On Tuesday, the Department of Water Management reiterated that it has introduced five programs to remove the city’s lead service lines and offers its residents free water testing.

This past November, the Biden administration announced a $336 million low-interest loan for Chicago through the Water Infrastructure Finance and Innovation Act to replace up to 30,000 lead pipes.

Elizabeth Chin of the Johns Hopkins Bloomberg School of Public Health and Mathew Kiang of the Stanford University School of Medicine also authored the study.