Although growing evidence suggests that early-life excess manganese (Mn) impairs neurodevelopment, data on the neurodevelopmental effects of mancozeb, a fungicide containing Mn, and its main metabolite ethylenethiourea (ETU) are limited. We examined whether prenatal mancozeb exposure and excess Mn were associated with neurodevelopment in 355 1-y-old infants living near banana plantations with frequent aerial mancozeb spraying in Costa Rica. We measured urinary ETU, hair Mn, and blood Mn concentrations in samples collected 1-3 times during pregnancy from mothers enrolled in the Infants' Environmental Health (ISA) study. We then assessed neurodevelopment in their 1-y-old infants using the Bayley Scales of Infant and Toddler Development, 3rd edition (BSID-III). We estimated exposure-outcome associations using linear regression models adjusted for maternal education, parity, gestational age at birth, child age, Home Observation for Measurement of the Environment score, and location of neurodevelopmental assessment. Median (P25-P75) urinary ETU, hair Mn, and blood Mn measured during pregnancy were 3.3 μg/L (2.4-4.9; specific gravity-corrected), 1.7 μg/g (0.9-4.1), and 24.0 μg/L (20.3-28.0), respectively. Among girls, higher ETU was associated with lower social-emotional scores [β per 10-fold increase=-7.4 points (95% CI: -15.2, 0.4)], whereas higher hair Mn was associated with lower cognitive scores [-3.0 (-6.1, 0.1)]. Among boys, higher hair Mn was associated with lower social-emotional scores [-4.6 (-8.5, -0.8)]. We observed null associations for blood Mn, language, and motor outcomes. Our findings indicate that maternal exposure to mancozeb and excess Mn during pregnancy may have adverse and sex-specific effects on infant neurodevelopment. https://doi.org/10.1289/EHP1955.

Manganese (Mn) is an essential element, but overexposure can have neurotoxic effects. In this article, we review and summarize studies on exposure to Mn and nervous system impairments in children. We identified 12 original articles published between 1977 and 2007. Overexposure to Mn was suspected to occur through diverse sources: infant milk formula, drinking water, industrial pollution, and mining wastes. The most common bioindicator of exposure to Mn was hair Mn content, but some studies measured Mn in blood, urine, or dentin; one study on prenatal exposure measured Mn content in cord blood. Most studies indicate that higher postnatal exposure to Mn is associated with poorer cognitive functions and hyperactive behavior. The limitations of the existing studies are numerous: most were cross-sectional, had a modest sample size, and lacked adjustment for important confounders. Future investigations should be performed on a larger sample size and include a more detailed exposure assessment, addressing multiple sources of exposure such as food, water, and airborne particulates.