# Essential and non-essential metals in children’s intellectual functioning: A multi-media biomarker approach from a Mexico City birth cohort

## TL;DR

The study examines how exposure to various metals during pregnancy and early childhood affects children's cognitive development in Mexico City.

## Contribution

The study introduces a multi-media biomarker approach to evaluate the combined effects of multiple metals on children's intellectual functioning.

## Key findings

- MMB-cadmium and MMB-arsenic showed significant negative effects on children's intellectual functioning.
- MMB-manganese, MMB-selenium, and MMB-molybdenum had the highest positive effects on cognitive function.
- Results from single and multi-pollutant models varied, highlighting the issue of multipollutant confounding.

## Abstract

Metal exposures impact children’s intellectual functioning from pregnancy through early childhood and beyond, being historically evaluated with single-pollutant models which might create errors estimating individual metal impacts beyond other correlated metals which arise from the same shared sources.

We evaluated the effect of exposure to non-essential and essential metals on the cognitive function of Mexican children at 48 months of age.

We included persons from the Programming Research in Obesity, Growth, Environment, and Social Stressors (PROGRESS) longitudinal birth cohort in Mexico City with biomarker data on 13 non-essential (lead, cadmium, mercury, arsenic, strontium, barium, and cesium) and essential (manganese, copper, selenium, molybdenum, magnesium, and zinc) metals during pregnancy and early childhood. We assessed the child’s intellectual functioning with McCarthy Scales of Children’s Abilities. We created a multi-media biomarker (MMB) index utilizing the Weighted Quantile Sum Regression (WQS) method. We utilized generalized linear models to estimate the change in the General Cognitive Index (GCI) per interquartile increase in the MMB index(β) and corresponding 95 % confidence intervals(CIs) in single and multipollutant models.

After adjusting for confounders in multipollutant models, MMB-cadmium (β: −1.52, 95 %CI: −3.03 −0.01) and MMB-arsenic (β: −1.53; 95 %CI: −3.02, −0.03) showed significant negative effects on intellectual functioning. In contrast, MMB-manganese (β: 2.28; 95 %CI: 0.77, 3.77), MMB-selenium (β:2.07, 95 %CI: 0.69, 3.43), and MMB-molybdenum (β: 1.76; 95 %CI: 0.21, 3.31) were the metals with the highest positive effects. We did find variations comparing results from single and multi-pollutant models, indicating the presence of multipollutant confounding.

Our study adds to the current body of literature about the co-pollutant confounding problem of evaluating metals and children’s intellectual functioning, as well as the effect of understudied toxic metals of public health interest, such as barium and cesium as candidates that warrant further investigation for a possible role in children’s intellectual functioning.