Placental microplastics contamination and its impact on thyroid function in newborns

Microplastics (MPs), which have been identified in human tissues such as the placenta, may pose potential risks to newborn health by interfering with thyroid function, a critical regulator of growth and development. This study investigates the association between placental microplastic levels and thyroid hormone profiles in newborns. We investigated the effect of placental microplastic exposure on fetal thyroid hormone levels in a cohort of 1250 mother-child pairs enrolled between 2022 and 2024. Umbilical cord blood thyroid hormone concentrations (free thyroxine T4, free triiodothyronine T3, and thyroid-stimulating hormone TSH) were measured, and placental microplastics (PVC, PP, and PBS) were quantified. Multivariable regression models (MLR), quantile g-computation (g-comp) and Bayesian Kernel Machine Regression (BKMR) were used to assess the effects of microplastics on thyroid hormone levels, adjusted for relevant covariates. Adjusted MLR models confirmed that individual microplastic types, including PVC, PP, and PBS, were significantly associated with reductions in T4 levels (β = -1.40, -0.74, and -0.85, respectively) and TSH levels (β = -1.27, -2.87, and -1.94, respectively), as well as decreases in the T4/T3 ratio (β = -5.60, and -2.68 for PVC and PP, respectively). PP exposure was the only microplastic type associated with an increase in T3 levels (β = 0.05; 95 % CI: 0.01, 0.10; p = 0.03). G-comp analysis showed that each quartile increases in exposure corresponded to significant decreases in T4 (β = -1.78; 95 % CI: -2.38, -1.18), TSH (β = -3.72; 95 % CI: -4.71, -2.72), and the T4/T3 ratio (β = -6.24; 95 % CI: -8.53, -3.94; p < 0.01 for all). BKMR analysis further revealed a dose-response relationship, with higher microplastic exposure linked to decreasing T4 levels and a lower T4/T3 ratio, while T3 and TSH exhibited only minimal changes across exposure quantiles. This study reveals that placental microplastic exposure is linked to reductions in newborn thyroid hormone levels, particularly T4 and the T4/T3 ratio, with dose-response effects observed across exposure quantiles.