Low level prenatal exposure to a mixture of Sr, Se and Mn and neurocognitive development of 2-year-old children.

The excess or deficiency of trace metals can cause adverse neurocognitive development. Evidence of health effect of trace metal mixtures on neurocognitive development is limited in children. We evaluated associations of prenatal exposure to trace metals and metal mixtures with neurocognitive development of 2-year-old children. A total of 544 mother-child pairs were included in the study. The concentrations of 10 trace metals in maternal urine were monitored before delivery. Neurocognitive development indexes, including mental development index (MDI) and psychomotor development index (PDI), were assessed using the Bayley Scales of Infant Development. Linear regression analysis was performed to explore the effects of single-metal and multi-metal exposures. Bayesian Kernel Machine regression (BKMR) was used to investigate overall effect of exposure to metal mixtures and potential interactions among mixture components. We found positive associations of urinary strontium (Sr) and Selenium (Se) levels with MDI scores among all children in the single-metal model. Sr was positively related to MDI, while Manganese (Mn) was negatively associated with PDI in the multi-metal model. The results from BKMR model in girls revealed that MDI scores were improved with the increasing concentrations of Sr, Se and Mn mixture until the concentrations reached their 30th percentiles (Sr: 149.49 μg/g creatinine, Se:18.38 μg/g creatinine, Mn:1.96 μg/g creatinine), with no effect after that threshold level. Sr played a positive role in mental development among mixture components, which was consistent with the results of Sr in the multi-metal models. No signification association of mixture with MDI/PDI was found in boys. The study suggested potential sex-specific association of Sr, Se and Mn mixture levels (at or below their 30th percentiles) with improved mental development, and beneficial role of Sr.