Prenatal exposure to certain environmental hazardous substances may be associated with an increased risk of autism in preschool children. Such toxic substances include metals, pesticides, polychlorinated biphenyls (PCBs), phthalates, and bisphenol-A (BPA).

According to Medical Express, experts analyzed the level of 25 chemicals in blood and urine samples taken from 1,861 Canadian women in the first trimester of pregnancy. They also interviewed 478 people in order to identify autistic behavior in preschool children. The survey results were compared with the Social Awareness Scale.

It turned out that higher concentrations of cadmium, lead and some phthalates in blood or urine samples from the mother were associated with higher scores on the Scale. This association was particularly strong in children with higher rates of autistic behavior. Moreover, the increased concentrations of manganese, trans-nonachlor, many metabolites of organophosphate pesticides, and monoethyl phthalate in the mother were most closely associated with the decreased indices of the scale.