The researchers conclude in this study, "Results of this semiecologic study suggest that living in areas with higher ambient levels of HAPs, particularly heavy metals [i.e. mercury]...during pregnancy or early childhood, may be associated with a moderately increased risk of autism."

This epidemiological study, whose researchers are from the Division of Environmental and Occupational Disease Control, California Department of Health Services and Kaiser Permanente Medical Care Program, Division of Research, evaluated 284 children with autism spectrum disorder (ASD) and 657 controls, born in 1994 in the San Francisco Bay area. They assigned exposure level by census tract of birth residence for 19 chemicals identified as potential neurotoxicants, developmental toxicants, and/or endocrine disruptors from the 1996 HAPs database. They calculated ASD risk in the upper quartiles of these group scores or individual chemical concentrations compared with below the median, adjusting for demographic factors.

These researchers found mercury exposure, among the individual compounds examined, was the most statistically significantly associated with ASD (adjusted relative risk = 1.92, 95% CI = 1.35-2.71).