Is ozone pollution harming unborn children?

Prenatal exposure to ozone pollution could be harming the cognitive development of unborn children, according to new interdisciplinary research from the University of Utah.

The peer-reviewed study found a strong link between pregnant mothers’ ozone exposures and increases in the chances the baby develops an intellectual disability.

“The body of evidence suggests that it is important that we never take our foot off the gas in terms of working to reduce the levels of air pollution that Utahns are breathing,” said research leader Sara Grineski, a professor of sociology. “We don’t want to neglect these issues related to ozone and cognitive health moving forward. Our findings here for Utah suggest a troubling association. This is just one study in a sea of papers documenting the harmful effects of air pollution on health.”

The study, published last month in the Journal of Exposure Science & Environmental Epidemiology, is a collaboration between the College of Social & Behavioral Science and the School of Medicine. It is based on an analysis of public health and air quality data generated on the Wasatch Front, Utah’s largest metropolitan area which has long struggled with episodes high ozone in summer and high particulate in winter.

The findings offer fresh insights into how environmental pollutants can influence neurodevelopmental outcomes during pregnancy.

“This research emphasizes that ozone exposure during pregnancy is a clear risk factor for intellectual disability,” Grineski said. “We were particularly struck by the consistency of the findings across all trimesters and the strength of the sibling-based analysis.”

Her team’s research utilized the Utah Population Database, a rich source of in-depth information maintained by the U’s Huntsman Cancer Institute to support research on genetics, epidemiology, demography and public health, as well as raw ozone data from the U.S. Environmental Protection Agency that enabled researchers to look at daily estimates of ozone concentrations for the nation’s counties.

The study focused on ozone exposure during pregnancy, using exposure data linked to children with intellectual disabilities born from 2003 to 2014, their siblings and population controls. The researchers were able to examine the dates in each child’s trimesters to calculate ozone exposure metrics specific to each child, based on when they were born, length of gestation, and where the mother lived at the time of birth.

 “The study is unique in its use of both population controls and the sibling design, which is a really nice complimentary design to use. Because this is an epidemiological study, it uses observational data, secondary data,” said co-author Amanda Bakian, a research associate professor of psychiatry with the U’s Huntsman Mental Health Institute. “Sibling designs allow us to control for some of these population factors that just would be really challenging to do. It just gives another layer of robustness of rigor to this study, and that would have very challenging on a population level to do without the Utah Population Database and their access to genealogical data.”

Ground-level ozone, a highly reactive oxygen molecule, is a growing summer-time pollution hazard in Utah, particularly as the climate warms. It is not directly emitted, but rather forms in the atmosphere when fossil-fuel emissions interact in the presence of sunlight. Ozone’s negative impact on pulmonary function and other health outcomes has already been well documented.

The federal health standard for ambient ozone concentrations is 70 parts per billion (ppb), a threshold that is frequently breached on summer afternoons on the Wasatch Front and in the winter in the Uinta Basin.

What the Utah researchers discovered

• The second trimester of pregnancy is the most critical period for ozone exposure, with a 10-ppb increase in average ozone levels associated with a 55.3% higher likelihood of intellectual disability compared to full siblings and a 22.8% increase compared to population controls.
• Although the second trimester showed the strongest associations, exposures in all pregnancy stages correlated with elevated risk of intellectual disabilities.
• Findings from sibling-comparison analyses demonstrated the validity of the results even when controlling for genetic and familial factors.

The research community has noted that current knowledge about ozone pollution’s impact on cognitive health is insufficient and that gaps with respect to ozone and cognition are perhaps the widest for children. During the second trimester, the fetal brain undergoes rapid growth, with neurons developing at a rate of 250,000 per minute. Ozone’s potential interference with these processes, along with its impact on placental health, provides plausible mechanisms for the observed associations.

Utah’s Wasatch Front, which often experiences elevated ozone levels in summer, provided an ideal backdrop for the study. The findings underscore the potential impact of environmental pollutants on children’s health, especially given predictions that climate change will exacerbate ozone pollution.

“When it comes to intellectual disability, we have a prevalence estimate of about 1.3% or so, and that has been pretty consistent over time,” Bakian said. “That’s 1.3% of the kids that are born in any one year, and we still don’t have a great understanding of all the risk factors that are involved. What are the underlying mechanisms that drive this risk? Having intellectual disability has lifelong implications.”

Salt Lake and Davis counties as well as portions of Weber, Tooele, Utah, Uintah and Duchesne counties are often out of compliance with federal ozone standards, according to Grineski.

“Salt Lake City ranks 10th for the most polluted cities in the U.S. in terms of ozone, and 2023 ozone levels were higher than 2022 levels,” she added. The study’s authors stress the importance of reducing ozone levels to protect vulnerable populations, particularly pregnant women and their unborn children. Public health measures such as implementing clean car standards, transitioning to electric vehicles, and updating manufacturing and agricultural processes are among the recommended strategies.

This study highlights the need for further research into ozone exposure and neurodevelopmental outcomes. Grineski and her team hope their findings will encourage policymakers, public health officials and the public to prioritize air quality improvements.

The study was published online on Nov. 18 under the title, “Prenatal ozone exposure and risk of intellectual disability,” in the Journal of Exposure Science & Environmental Epidemiology. The interdisciplinary team of co-authors includes Roger Renteria and Camden J. Alexander of the Department of Sociology; Deborah Bilder of the Department of Psychiatry; Timothy W. Collins of the School of Environment, Society & Sustainability; and James VanDerslice of the Department of Family & Preventative Medicine. Funding was provided by the National Institute of Environmental Health Sciences, with collaborative support from the University of Utah, Intermountain Healthcare, Utah Registry of Autism and Developmental Disabilities, Utah Department of Health and Human Services and the Utah Population Database.