Prenatal ozone exposure and risk of intellectual disability.

Background: Knowledge of relationships between tropospheric ozone and mental and developmental health outcomes is currently inconclusive, with the largest knowledge gaps for children. This gap is important to address as evidence suggests that climate change will worsen ozone pollution.

Objective: We examine the association of average ozone exposure during the preconception period, and first, second and third trimesters of pregnancy on the odds of intellectual disability (ID) in Utah children.

Methods: For the period of 2002-2020, we assembled daily, tract-level ozone concentration data, data on ID case status, and data on cases' full siblings and population controls. We analyzed the data using generalized estimating equations.

Results: Ozone was positively associated with the odds of ID in cases vs. their siblings (in the preconception, first, second and third trimester exposure windows, all p < 0.05, n = 1042) and vs. population controls (only in the second trimester exposure window, p < 0.05, n = 5179). The strength of the association was largest during the second trimester in both analyses. A second trimester average ozone level increase of 10 ppb was associated with a 55.3% increase in the odds of ID relative to full siblings (95% confidence interval [CI]: 1.171-2.058) and a 22.8% increase in the odds of ID relative to population controls (CI: 1.054-1.431). Findings were robust to different subsets of sibling controls as well as several sensitivity analyses.

Significance: Results document that ozone has a measurable relationship with children's cognitive development in Utah.

Impact statement: Evidence suggests that climate change will worsen ozone pollution. The potential amplifying effect of climate change on ozone is more certain than it is for fine particulate matter. This means that ozone and health research will remain relevant into the future. Currently, several systematic reviews and meta-analyses have concluded that knowledge about ozone and cognitive health is insufficient, especially for children. Using two different study designs, we find that prenatal ozone exposure is associated with risk of intellectual disability in children.