Urinary heavy metals and psychosocial behavior of preschool children: a mixed exposure analysis

BACKGROUND AND AIM: The neurotoxic effects of certain heavy metals are well established, but only a few studies have investigated the joint effect of concurrent exposure to multiple ones. The study aims to evaluate the association between mixed exposure to neurotoxic metals and the psychosocial behavior of preschool children. METHOD: Using a stratified sampling strategy, we recruited participants from 105 kindergartens in 41 townships of Taiwan and excluded those with blood lead levels ≥3.5 µg/L. The first-morning void urines were collected and analyzed for cadmium, magnesium, arsenic, chromium, lead, and nickel concentrations using ICP-MS. We applied the parentally reported Strengths and Difficulties Questionnaire (SQD) and Swanson, Nolan, and Pelham IV (SNAP-IV) scales to evaluate the psychosocial behaviors. Multiple linear regressions were utilized to evaluate the associations between each heavy metal and the outcomes, while the mixed effect of concurrent exposure was estimated by using a Quantile g-computation approach. RESULTS: A total of 977 preschool children were included in the study, and the mean (SD) age was 5.7 (0.7) years old. In single pollutant models, we observed adverse effects of urinary magnesium, nickel, arsenic, and lead on the specific subsets of SDQ. Furthermore, the combined effect of the six heavy metals significantly affected the hyperactivity/inattention symptoms (beta = 0.46, 95% CI: 0.13~0.78, with all metals increased by one quartile), and chromium and lead were the two major effect contributors. Similar detrimental effects of the urinary cadmium and lead were also observed in the SNAP-IV subsets, although the joint effect analysis was not significant. CONCLUSIONS: The study provided evidence that concurrent exposure to multiple heavy metals may exert increased risks of hyperactivity/inattention in children compared to single pollutant exposure. Further studies are needed to verify our findings regarding mixed exposure to multiple neurotoxic metals.