More than half a century after the official end of discriminatory redlining, 45 million people across the United States—overwhelmingly in communities of color—are exposed to elevated levels of illness-inducing air pollution, a study published Wednesday affirmed.

“This groundbreaking study builds on the solid empirical evidence that systemic racism is killing and making people of color sick.”

A study conducted by researchers at the University of California, Berkeley and the University of Washington and published in the journal Environmental Science and Technology Letters found that Black and Latino people living in formerly redlined zones breathe more polluted air than whites who live in nonredlined areas. Breathing smog and particulate matter emitted by motor vehicles, coal plants, and industrial facilities causes wide-ranging health problems from strokes and heart damage to respiratory illnesses including asthma.

“The consistency we found shows us how many of the pollution problems we have today are tied to patterns that were present in cities more than 80 years ago,” Haley Lane, a graduate student at the Department of Civil and Environmental Engineering at U.C. Berkeley and the study’s lead author, told The Washington Post.

Julian Marshall, a U.W. professor of civil and environmental engineering and study co-author, said that “racism from the 1930s, and racist actions by people who are no longer alive, are still influencing inequality in air pollution exposure today.”

“Redlining” describes the federally sanctioned discriminatory mortgage evaluation practice in which the Home Owners’ Loan Corporation (HOLC) drew maps of neighborhoods in U.S. cities that ranked their desirability for mortgage lending. Loans were denied to people—predominantly people of color and immigrants—residing in neighborhoods deemed “hazardous” for investment. As a result, most Black and Brown Americans were effectively barred from federal mortgages; between 1945 and 1959, less than 2% of federally insured home loans were issued to Black families.

Although redlining officially ended following passage of the Fair Housing Act in 1968, studies have shown the policy persists in practice in scores of metropolitan areas across the nation. Additionally, communities that were redlined remain predominantly minority and low-income today. A 2015 study by the National Community Reinvestment Coalition found that in Baltimore, race–and not economic status—was the most important factor in mortgage lending. Formerly redlined communities also face greater climate-related risks.

As the new study’s researchers have shown, environmental pollution and attendant health problems are some of the most persistent harms of redlining. In neighborhoods the HOLC deemed the most unworthy of mortgages—areas with “infiltration of foreign-born, Negro, or lower grade population”—nitrogen dioxide levels were higher than the citywide average in 80% of the 202 cities analyzed. In contrast, NO2 levels were lower than average in 84% of the cities in the study. Nitrogen dioxide forms smog and other toxic particulate matter that can damage the human respiratory system.

“We’ve known about redlining and its other unequal impacts, but air pollution is one of the most important environmental health issues in the U.S.,” Joshua Apte, an assistant professor at U.C. Berkeley’s School of Public Health and a co-author of the study, told the Post. “If you just look at the number of people that get killed by air pollution, it’s arguably the most important environmental health issue in the country.”

“We’ve known about redlining and its other unequal impacts, but air pollution is one of the most important environmental health issues in the U.S.”

Study co-author and U.C. Berkeley professor of public health and environmental science Rachel Morello-Frosch said the new research goes “a long way toward highlighting the lasting consequences of structural racism on community health.”

“These results can point the way toward targeted approaches for regulating emission sources and reducing exposures, as well as longer-term strategies to address discriminatory land-use decision-making that adversely impacts communities of color,” she added.

Commenting on the new research, author, professor, and White House Environmental Justice Advisory Council member Robert D. Bullard told the Post that it “makes clear the elevated air pollution disparities we see today between Black Americans and white Americans have their roots in systemic racism endorsed, practiced, and legitimated by the federal Home Owners’ Loan Corporation some eight decades ago.”

“This groundbreaking study builds on the solid empirical evidence that systemic racism is killing and making people of color sick,” he added, “it’s just that simple.”