Environmentally persistent free radicals in household dust: the seasonal and longitudinal trends

Objective Epidemiological links between air pollution and adverse health outcomes are strong, but the mechanism(s) remain obscure. A newly recognised combustion by-product, environmentally persistent free radicals (EPFRs), may be the missing link. EPFRs persist for extended periods of time in the environment, however very little is known about the presence of EPFRs inside homes where prolonged exposure is likely to occur. The objective of this study is to explore the presence of EPFRs in household dust and ascertain if EPFR concentration is stable across time and season. Material and methods The ORChID/ELLF cohort is a longitudinal birth cohort (n=82) with dust samples collected from the family vacuum cleaner at multiple time points. EPFR characteristics were assessed with electron paramagnetic resonance. Our team developed an algorithm to estimate oxygen-weighted concentration and impact score for risk of adverse health outcomes. Kruskal-Wallis rank sum test and Fisher’s exact tests were used to assess seasonal differences. A simple mixed-effects linear regression, with random intercepts on participant ID, was employed for longitudinal analysis of EPFR concentration in households that did not move. Results 83 participants returned 238 dust samples. EPFRs were measured in virtually all samples. EPFR concentration was stable across visits, when controlling for season and ambient air pollution (p=0.05), Oxygen-weighted EPFRs were also stable. There was a seasonal trend, with concentration (p=<0.01), oxygen weighted concentration (p=<0.01) and g factor (p=0.05) all significantly lower in summer months. Conclusion Our results indicate that the concentration of EPFRs in household dust are stable across time in households that did not move, but the oxygen-centred radicals are more sensitive to changes. These findings suggest that exposure to EPFRs occurs in the home and may be a significant place for exposure to highly biologically reactive EPFRs.