Intrauterine and early postnatal exposures to submicron particulate matter and childhood allergic rhinitis: A multicity cross-sectional study in China

Abstract

Background: Airborne particulate matter pollution has been linked to occurrence of childhood allergic rhinitis (AR). However, the relationships between exposure to particulate matter with an aerodynamic diameter ≤1 μm (PM₁) during early life (in utero and first year of life) and the onset of childhood AR remain largely unknown. This study aims to investigate potential associations of in utero and first-year exposures to size-segregated PMs, including PM₁, PM_1-2.5, PM_2.5, PM_2.5-10, and PM₁₀, with childhood AR.

Methods: We investigated 29286 preschool children aged 3-6 years in 7 Chinese major cities during 2019-2020 as the Phase II of the China Children, Families, Health Study. Machine learning-based space-time models were utilized to estimate early-life residential exposure to PM₁, PM_2.5, and PM₁₀ at 1 × 1-km resolutions. The concentrations of PM_1-2.5 and PM_2.5-10 were calculated by subtracting PM₁ from PM_2.5 and PM_2.5 from PM₁₀, respectively. Multiple mixed-effects logistic models were used to assess the odds ratios (ORs) and 95% confidence intervals (CIs) of childhood AR associated with per 10-μg/m³ increase in exposure to particulate air pollution during in utero period and the first year of life.

Results: Among the 29286 children surveyed (mean ± standard deviation, 4.9 ± 0.9 years), 3652 (12.5%) were reported to be diagnosed with AR. Average PM₁ concentrations during in utero period and the first year since birth were 36.3 ± 8.6 μg/m³ and 33.1 ± 6.9 μg/m³, respectively. Exposure to PM₁ and PM_2.5 during pregnancy and the first year of life was associated with an increased risk of AR in children, and the OR estimates were higher for each 10-μg/m³ increase in PM₁ than for PM_2.5 (e.g., 1.132 [95% CI: 1.022-1.254] vs. 1.079 [95% CI: 1.014-1.149] in pregnancy; 1.151 [95% CI: 1.014-1.306] vs. 1.095 [95% CI: 1.008-1.189] in the first year of life). No associations were observed between AR and both pre- and post-natal exposure to PM_1-2.5, indicating that PM₁ rather than PM_1-2.5 contributed to the association between PM_2.5 and childhood AR. In trimester-stratified analysis, childhood AR was only found to be associated with exposure to PM₁ (OR = 1.077, 95% CI: 1.027-1.128), PM_2.5 (OR = 1.048, 95% CI: 1.018-1.078), and PM₁₀ (OR = 1.032, 95% CI: 1.007-1.058) during the third trimester of pregnancy. Subgroup analysis suggested stronger PM-AR associations among younger (<5 years old) and winter-born children.

Conclusions: Prenatal and postnatal exposures to ambient PM₁ and PM_2.5 were associated with an increased risk of childhood AR, and PM_2.5-related hazards could be predominantly attributed to PM₁. These findings highlighted public health significance of formulating air quality guideline for ambient PM₁ in mitigating children's AR burden caused by particulate air pollution.

Keywords: Allergic rhinitis; CCHH; Children; Early life; PM(1).