Meet-in-metabonomics: Insights into associations between hair heavy metal and adverse child growth in e-waste recycling area

Heavy metal pollution from informal e-waste recycling may adversely affect child growth. However, the potential toxic mechanisms from a population perspective remain unknown. Herein, 18 hair heavy metals, urinary metabolomics, and three child growth indices [i.e., weight-for-age Z-score (WAZ), height-for-age Z-score (HAZ), and BMI Z-score (BMIZ)] were measured in children from e-waste recycling (ER, N = 426) and control areas (CR, N = 247). We examined longitudinal changes in heavy metal exposure and child growth after e-waste control to further elucidate causal relationships. Results showed that children in regulated ER site were still exposed to higher levels of several heavy metals and experienced poorer growth compared to those in control areas. Elevated exposure to heavy metals like tin, antimony, lead, cadmium, and cobalt correlated with poor child growth, particularly affecting girls and younger children. Tin, rather than traditionally concerning heavy metals, exhibited the most crucial role in driving the adverse effects of metal mixtures on child growth. Reducing heavy metal exposure through e-waste control could notably improve child growth, confirming the causal relationship between heavy metal exposure and poor child growth and underscoring the health benefits of e-waste regulation. Our research identified the roles of steroid biosynthesis, folate biosynthesis, amino acid metabolism, and purine metabolism in mediating the effects of metal exposure on child growth. Testosterone glucuronide, riboflavin, folic acid, xanthosine, and xanthine emerged as key mediators, potentially serving as metabolic signatures of heavy metal exposure. These findings illuminate the toxic mechanisms underlying poor child growth resulted from heavy metal exposure, offering important insights from a population-based perspective. In addition to lead and cadmium, monitoring and regulating tin and antimony are crucial to mitigate their negative impact on child growth in e-waste recycling areas.