Placental black carbon across five decades and associations with traffic-related air pollution and birth outcomes

Abstract

Background: Prenatal exposure to traffic-related air pollution (TRAP) has been associated with adverse health outcomes, yet accurate retrospective assessment of individual exposure remains challenging. Because detailed individual air pollution measurements are often unavailable for earlier decades, retrospective exposure assessment is limited. Recent advances in the detection of placental black carbon (BC) particles in archived placental tissue provide new opportunities to retrospectively characterize prenatal air pollution exposure over time. Over recent decades, traffic-related emissions in Europe have declined following regulatory measures, although it remains unclear whether such temporal changes are reflected in placental BC concentrations.
Objective: This study aimed to retrospectively characterize prenatal exposure to traffic-related air pollution (TRAP) over a five-decade period (1970–2017) using placental black carbon (BC) concentrations measured in archived placental tissue samples, and to examine associations with emission estimates, residential proximity to major roadways, policy measures, and birth outcomes. Methods: In this retrospective cohort study, placental BC concentrations were measured in placental tissue samples from the East Flanders Prospective Twin Survey, a historical twin birth cohort in Belgium. Placental BC was quantified using a label-free white-light detection technique. Temporal trends were analysed using Spearman correlation, the Mann-Kendall trend test, and log-linear regression. Associations between placental BC concentrations, emission data (EDGAR), residential distance to major roadways, policy implementation periods based on EURO emission standards, and birth outcomes were analysed using multivariable and segmented regression models adjusted for temporal, spatial and individual-level covariates.
Results: Placental BC concentrations showed a statistically significant increase over time (approximately 0.6% per year; p = 0.049). No significant associations were observed with traffic-related emission estimates, EURO emission standards, or birth outcomes. Residential distance to major roadways was negatively associated with placental BC concentrations but did not reach statistical significance (ΔBC-4.31% per doubling in distance; p = 0.10).
Conclusion: These findings indicate that placental BC concentrations showed a statistically significant increase over the five-decade study period (1970–2017). Although no clear associations were observed with historical emission estimates, policy measures, or birth outcomes, local spatial exposure factors appeared to be more closely associated with placental BC concentrations than temporal indicators. More detailed individual-level exposure assessment approaches, including local traffic exposure and mobility patterns, are needed to better understand placental BC concentrations and their potential health implications. In line with the precautionary principle, these findings highlight the importance for policymakers to continue addressing local traffic-related exposure, particularly for susceptible populations such as pregnant women and developing fetuses.

Date of Award	17 Jun 2026
Original language	English
Supervisor	Esmée Bijnens (Examiner), Tim S. Nawrot (Co-assessor) & Frank Van Belleghem (Co-assessor)