Arsenic, cadmium, lead, and mercury (As, Cd, Pb, Hg), are toxic elements with no known biological functions. Long-term exposure to these elements is possible through the food chain, water contamination, and air pollution depending on local conditions. Arsenic appears to impair neurocognitive performance but not behavioural outcomes (Tolins et al, 2014), and the impacts on language or motor development are less clear. There have been few studies to date of cadmium and neurodevelopment (Rodriguez-Barranco et al, 2013), although previous work within ALSPAC found no association with motor skills (Taylor et al, 2018). Mercury at high-doses is known to delay neurodevelopment (Grandjean & Herz, 2011), but the evidence for an effect at more realistic low-levels is unclear. The strongest evidence of harm during childhood from heavy metals is exposure to lead which has been reliably linked to impaired cognitive, behavioural, and motor development (Sanders et al, 2009). For each of these elements there is a potential to strengthen the evidence base through the use of genetic methods unbiased from confounding factors, and to examine less-studied neurodevelopmental outcomes.