Perinatal Lead Exposure and Risk of ASD: a County-level Natural Experiment in 10 US States

Prevalence of autism spectrum disorder (ASD) is continuing to rise unabated worldwide; however, the origins of this epidemic and the drivers of its sustained momentum remain elusive. While exposure to air pollution and abnormal metal levels in children with ASD have been identified as environmental risk factors of ASD, these studies have failed to explain the emergence of the epidemic. Paramount to protecting against future cases of this neurodevelopmental disorder is a better understanding of its etiology. Here, in part two of a series of natural experiments, we demonstrate at the county level in ten US states that perinatal lead (Pb) exposure is negatively associated with ASD and is likely a potent inhibitor of the disorder. This paper adds to the prior study we conducted at the US state level. These results contrast with how lead is typically perceived, namely, as detrimental to normal neurodevelopment. Lead’s disuse in the last several decades, while benefiting the physiological health of children in many ways, has likely prompted the current epidemic by leaving infants more exposed to other metal toxicants.