Ambient air pollution exposure during the late gestational period is linked with lower placental iodine load in a Belgian birth cohort

Kristof Y Neven; Congrong Wang; Bram G Janssen; Harry A Roels; Charlotte Vanpoucke; Ann Ruttens; Tim S Nawrot

doi:10.1016/j.envint.2020.106334

Ambient air pollution exposure during the late gestational period is linked with lower placental iodine load in a Belgian birth cohort

Environ Int. 2021 Feb:147:106334. doi: 10.1016/j.envint.2020.106334. Epub 2020 Dec 24.

Authors

Kristof Y Neven¹, Congrong Wang¹, Bram G Janssen¹, Harry A Roels², Charlotte Vanpoucke³, Ann Ruttens⁴, Tim S Nawrot⁵

Affiliations

¹ Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium.
² Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium; Louvain Centre for Toxicology and Applied Pharmacology, Université catholique de Louvain, Brussels, Belgium.
³ Belgian Interregional Environment Agency, IRCEL-CELINE, Brussels, Belgium.
⁴ SD, Chemical, and Physical Health Risks, Sciensano, Tervuren, Belgium.
⁵ Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium; Department of Public Health and Primary Care, Leuven University, Leuven, Belgium. Electronic address: tim.nawrot@uhasselt.be.

Abstract

Background: Adequate intake of iodine is required for the production of thyroid hormones and contributes in pregnant women to a healthy brain development and growth in their offspring. To date, some evidence exists that fine particulate air pollution is linked with the fetal thyroid hormone homeostasis. However, possible effects of air pollutants on the placental iodine storage have not been investigated so far.

Objectives: We investigated the association between air pollution exposure to particulate matter with a diameter less than 2.5 µm (PM_2.5), NO₂, and black carbon and the placental iodine load.

Methods: The current study is part of the ENVIRONAGE birth cohort and included 470 mother-newborn pairs. Iodine concentrations were measured in placental tissue. A high-resolution air pollution model was used to estimate the daily exposure to PM_2.5, NO₂, and black carbon over the entire pregnancy based on the maternal residential addresses. Distributed lag nonlinear models (DLNMs) were used to estimate gestational week-specific associations between placental iodine concentrations and the air pollutants to understand the impact of specific exposure windows.

Results: PM_2.5 showed a positive association with placental iodine concentration between the 16^th and 22^nd week of gestation. In contrast, a significant inverse association between PM_2.5 and placental iodine concentration was observed in gestational weeks 29-35. The effect estimate, for a 5 µg/m³ increment in PM_2.5 concentration, was the strongest at week 32 (β -0.11 µg/kg; 95%CI: -0.18 to -0.03). No associations were observed between placental iodine concentrations and NO₂ or black carbon. Assuming causality, we estimated that placental iodine mediated 26% (-0.33 pmol/L; 95%CI: -0.70 to 0.04 pmol/L) of the estimated effect of a 5 µg/m³ increment in PM_2.5 exposure on cord blood free thyroxine (FT₄) concentrations.

Conclusion: In utero exposure to particulate matter during the third trimester of pregnancy is linked with a lower placental iodine load. Furthermore, the effect of air pollution on cord blood FT₄ levels was partially mediated by the placental iodine load.

Keywords: Air pollution; Dlnm; Iodine; Particulate matter; Placenta; Thyroxine.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Air Pollutants* / adverse effects
Air Pollutants* / analysis
Air Pollution* / adverse effects
Air Pollution* / analysis
Belgium
Female
Humans
Infant, Newborn
Iodine*
Maternal Exposure / adverse effects
Particulate Matter / adverse effects
Particulate Matter / analysis
Pregnancy

Substances

Air Pollutants
Particulate Matter
Iodine