Confounding of ozone's cardiorespiratory health effects by ozone reaction products: Evidence from two panel studies with contrasting exposure conditions

Personal ozone (O3) exposure is often regarded as a more accurate metric of individual-level O3 exposure relevant to health outcomes than outdoor O3 concentration. However, epidemiological studies of personal O3 exposure health effects have been inconsistent, including paradoxical “protective’ effects, suggesting the presence of confounding factors yet to be identified. When O3 enters indoors, it reacts with indoor chemicals to form ozone reaction products (ORPs) that may adversely affect cardiorespiratory health. The correlation between personal ORPs and O3 exposure can vary largely across individuals, which leads us to hypothesize ORPs exposure as a confounder for cardiorespiratory effects of personal O3 exposure. We analyzed two complementary datasets from panel studies in 89 healthy adults and in 43 asthmatic children, each measured four times for cardiorespiratory biomarkers and personal exposures to O3, O3 loss (a proxy for ORPs exposure), and PM2.5, respectively. We found personal O3 and O3 loss exposures were highly correlated in the Adults’ Study but poorly correlated in the Children's Study. In the Adults’ Study, personal O3 exposure was significantly associated with biomarkers of pulmonary oxidative stress, airway inflammation, lung function, systemic oxidative stress, thrombosis, arterial stiffness, and blood pressure. After adjusting for O3 loss, the O3 effects on many of these biomarkers were largely changed in terms of effect sizes and/or statistical significance. However, similar confounding effects were not observed in the Children's Study. These findings may help explain the inconsistencies in the literature regarding the cardiorespiratory effects of personal O3 exposure and highlight the need to account for potential confounding from ORPs in future studies.

Duke Scholars

Author Junfeng Zhang Environmental Natural Science

Author Yinghong Zhang  

Author Michael Howard Bergin Civil and Environmental Engineering