Particulate matter-bound metals and chlorinated paraffins co-exposure: A population-based study on...

Recent studies have indicated that heavy metals and chlorinated paraffins (CPs) are risk factors for neurodevelopmental disorders. However, evidence regarding their potential combined effects remains limited. To investigate the joint associations of heavy metals and CPs with attention-deficit/hyperactivity disorder (ADHD) symptoms, we recruited 122,965 participants under 18 from the Pearl River Delta in China. We measured concentrations of six heavy metals (Pb, As, Cd, Hg, Mn and Ni) and three types of CPs (SCCPs, MCCPs and LCCPs) in atmospheric particulate matter (PM_2.5) samples. ADHD symptoms was defined according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria. Generalized linear mixed-effects models (GLMMs) were used to evaluate the associations between individual pollutants and ADHD symptoms. We investigated the combined effects using a weighted quantile sum (WQS) regression model and examined potential interactions through both multiplicative and additive models. In single-pollutant models, all metals and CPs demonstrated significant positive associations with ADHD symptoms. Additive interaction analyses revealed significant synergistic effects between heavy metals and CPs, particularly between SCCPs and Mn (RERI = 4.63, 95% CI: 4.38, 4.88) and between SCCPs and Pb (RERI = 4.15, 95% CI: 3.92, 4.39). WQS analysis demonstrated a positive association between mixed exposure and ADHD symptoms, with Mn, Pb, and SCCPs as the main contributors. Boys and children younger than 12 years were more susceptible to these combined effects. These findings suggest that heavy metals and CPs may exert synergistic effects on the odds of ADHD symptoms, highlighting the importance of coordinated regulatory strategies targeting both pollutants.