Fourth and fifth graders in El Paso, Texas, are more likely to have lower grade point averages if heavily exposed to contaminated air at home, according to a new study.

The study is the first to look at kids’ exposure to air toxics at home and its impact on their school performance. It bolsters a growing body of evidence that air pollution can impair success in school.

“This is an interesting paper that deals with a serious problem affecting millions of children around the world,” said Dr. Lilian Calderón-Garcidueñas, a researcher who studies air pollution and health effects at the University of Montana in an email.

“These exposures start in utero, so the detrimental effects upon the developing brain are affecting the embryo and the fetus and continue once the child is exposed to the outside environment,” said Calderón-Garcidueñas, who was not involved in the study.

University of Texas at El Paso researchers analyzed the grade point averages of 1,895 children and, using their home location, estimated their exposure to air toxics—such as benzene, arsenic, lead, mercury, hydrochloric acid, toluene, vinyl bromide, xylenes, and diesel particulate matter—using federal data.

They found that for all types of air pollution sources, more exposure corresponded with lower grade point averages. Only one type of pollution—point sources such as factories—was not significantly linked to lower grade point averages.

“A lot of other studies have been school based,” said Frederica Perera, a professor at Columbia University and director of the Columbia Center for Children's Environmental Health who as not involved in the study. “But kids spend more time at residences.”

In the study, published this month in the journal Population and Environment, the authors said that air toxics may not cause dramatic drops in school performance but, nonetheless, the results were “disturbing.”

“Effects appear to be insidious, since they are mild, unlikely to be perceived, and, hence, unlikely to be addressed in any way … seemingly trivial effects on children’s development may translate into substantial impacts throughout the life course in terms of physical and mental health and personal success,” the authors wrote.

The researchers did control for some other things that can affect children’s grades such as poverty, mother’s age, education and ability to speak English, and the child’s race and sex.

Still, the study doesn’t prove that dirty air makes kids do worse in school. It does, however, suggest children’s developing bodies are more susceptible to air pollution, which can harm their respiratory systems and brain.

Air pollution might hamper kids’ grades via two primary ways: Illnesses, mostly respiratory, that would make them miss school, and developmental problems resulting from long-term exposure, said Sara Grineski, an associate professor of sociology at The University of Texas at El Paso and co-author of the new study.

Others have found similar links between air pollution and academic performance.

Three months ago Columbia University's Perera and colleagues reported that New York City children born to mothers in poverty and exposed to certain air toxics during pregnancy had lower IQs. Perera, tracking the mothers and children since before birth, said the pollution exposure prior to birth is more strongly linked to learning and behavioral problems.

In the current study it’s unclear if the children were exposed in their mothers’ womb—an exposure window that is critical to brain development, Perera said.

It’s “certainly not implausible that exposure over the childhood years could continue to influence a child’s academic performance,” she said. “Although the prenatal window is when extremely rapid development of brain happens, the process continues through first few years of life.”

Other studies support this—in February Calderón-Garcidueñas and colleagues reported Mexico City smog was linked to impaired short-term memory and IQ in children.

Timothy Collins, a University of Texas at El Paso geography professor and co-author of the study, said the El Paso findings suggest an environmental justice issue in El Paso.

The city is more than 80 percent Hispanic. "There’s a long history, more than a century, of air pollution,” Collins said. “It’s hard for us to not look at environmental justice implications.”

Previous studies have shown that El Paso’s minorities are disproportionately impacted by toxics, Grineski said.

The city of 675,000 is one of the worst when it comes to particulate matter—a mix of substances emitted by combustion sources, including cars, trucks, industrial plants and wood burning—especially coarse particulates, PM10, those between 2.5 and 10 micrometers (from about 25 to 100 times thinner than a human hair, according to the EPA).

El Paso’s 24-hour PM10 average is about 233 micrograms per cubic meter of air, according to the latest EPA data from 2013, which was eighth highest among more than 500 U.S. cities. El Paso, along with Laredo, has the highest carbon monoxide levels in Texas.

Major contributors to El Paso’s air fouling are the many trucks along the U.S.-Mexico border, the El Paso International Airport, an expanisve system of railways and Fort Bliss, the country’s second largest military base with an expansive missile and artillery airspace.

The city is poorer and more poverty stricken than the rest of Texas: El Paso’s median household income is 22 percent lower than the rest of the state, and has a 23 percent poverty rate compared to Texas’ 17 percent, according to the U.S. Census 2014 estimates.

Grineski said they have a follow-up study to more accurately pin down why air pollution seems to hamper El Paso kids.

The preliminary results hint that “there’s something else going on that’s not fully explained by poor health,” she said.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.

For questions or feedback about this piece, contact Brian Bienkowski at bbienkowski@ehn.org.