Brown University researchers found that more than half of women aged 16 to 49 had median or higher levels of at least two of three pollutants that could harm brain development.
Nearly 23 per cent of American women of childbearing age met or exceeded the median blood levels for all three environmental chemical pollutants - lead, mercury, and PCBs - tracked in an analysis of data on thousands of women.
All but 17.3 per cent of the women were at or above the median blood level for one or more of these chemicals, which are passed to foetuses through the placenta and to babies through breast milk.
"The three pollutants are of greatest interest because they are pervasive and persistent in the environment and can harm foetal and infant brain development, albeit in different ways," said study lead author Dr Marcella Thompson.
Scientists don't know much about whether co-exposure to these three chemicals is more harmful than exposure to each chemical alone. Most researchers study the health effects of exposure to an individual chemical, not two or three together.
The new study analysed data collected between 1999 and 2004 from 3,173 women.
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The results showed that most of the childbearing-age women - 55.8 per cent - exceeded the median for two or more of the three pollutants.
The study identified specific risk factors associated with increased odds of having higher blood levels of lead, mercury, and PCBs.
The most prominent risk factor was age. As women grew older, their risk of exceeding the median blood level in two or more of these pollutants grew exponentially to the point where women aged 30 to 39 had 12 times greater risk and women aged 40 to 49 had a risk 30 times greater than those women aged 16 to 19.
Women aged 40 to 49 would be at greatest risk not only because these chemicals accumulate in the body over time, but also because these women were born in the 1950s and 1960s before most environmental protection laws were enacted, Thompson said in a statement.
Fish and heavy alcohol consumption also raised the risk of having higher blood levels. Women who ate fish more than once a week during the prior 30 days had 4.5 times the risk of exceeding the median in two or more of these pollutants.
Women who drank heavily had a milder but still substantially elevated risk.