Higher levels of certain metals in mothers’ blood during pregnancy—including lead, mercury, and cadmium—were associated with autism-related traits in children, and higher levels of cadmium were associated with higher odds of an ASD diagnosis, according to a study funded by the National Institutes of Health’s Environmental influences on Child Health Outcomes (ECHO) Program.
Lead, mercury, and cadmium are metals that people may be exposed to through sources such as food, air, water, tobacco smoke, and some consumer products. During pregnancy, some metals can cross the placenta and reach the developing fetus. Previous studies have suggested possible links between prenatal metal exposure and ASD, but findings have been mixed, and many studies have examined one exposure at a time rather than the combined effects of multiple metals.
In this study, researchers analyzed data from mother-child pairs enrolled in the ECHO Cohort. They found that higher prenatal blood levels of lead and mercury were associated with higher scores on the Social Responsiveness Scale, Second Edition (SRS‑2), a caregiver-reported measure of social and behavioral traits related to autism. Higher blood cadmium levels were associated with higher odds of an ASD diagnosis.
When researchers looked at the metals together, higher combined levels of arsenic, cadmium, mercury, and lead were also associated with differences in autism-related behaviors, particularly in areas related to social functioning. Most metals measured in urine were not associated with these outcomes after accounting for other factors, although one metal (barium) showed differences by child sex that may warrant further study.
“We found that higher prenatal levels of metals—including lead, mercury, and cadmium—both individually and in combination, were associated with a higher likelihood of autism diagnosis and greater levels of autism-related behaviors, even at concentrations not typically considered elevated,” said Pi-I Debby Lin, ScD, of Harvard Pilgrim Health Care Institute. “These findings underscore the importance of increasing awareness of environmental exposures and strengthening approaches to screening during pregnancy, while continuing to evaluate what levels of exposure may be considered safe during this critical window of development.”
The study included 479 mother-child pairs with prenatal blood metal measurements and 482 pairs with prenatal urine metal measurements. Mothers provided samples during pregnancy, and researchers later compared those measurements with children’s SRS‑2 scores and ASD diagnoses when available. The analyses accounted for factors such as study site, maternal age, income, education, smoking exposure, and child sex.
The study, “Associations of prenatal metal exposures with autism-related outcomes in the ECHO Cohort,” was published in Environmental Epidemiology.
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