A new study finds that young girls developed behavioral problems by the age of three if their mothers ate food stored in containers made with BPA while they were pregnant.

The study, which appears in the journal Pediatrics, found that preschooler girls whose mothers had relatively high urine levels of bisphenol-A during pregnancy were more likely to show signs of hyperactivity, anxiety and depression. Boys' behaviour didn't seem to be affected.

The study draws only a link between in utero BPA exposure and behaviour problems; it's possible that factors other than BPA might explain the results.

The study also failed to find a link between levels of BPA in the urine of the kids themselves and their behaviour.

The researchers note there is considerable debate about the effects of BPA, but they say their findings should prompt additional research.

Canada formally declared BPA to be hazardous to human health in 2010. Its use has been banned in baby bottles sold in Canada and it has been largely phased out of baby bottles sold elsewhere.

But it is still widely used to strengthen the plastic used in hundreds of items, in the lining of food cans, in dental implants, in thermal paper store receipts, and elsewhere.

For the study, researchers from the Harvard School of Public Health in Boston measured BPA in the urine of 244 mothers in the Cincinnati area. They sampled their urine twice during pregnancy and at childbirth.

Nearly all the women had measurable levels of the chemical in their urine -- like most of us do.

The mothers then evaluated their own children at age three using standard behaviour questionnaires. They were asked about how anxious their children were, and whether they showed signs of depression, aggression, trouble controlling their emotions and hyperactivity.

The researchers found that the higher the BPA levels in the mothers' urine during pregnancy, the increasingly worse was the behaviour of their daughters. For every 10-fold increase in mothers' BPA levels, girls scored at least six points worse on the questionnaires.

None of the behaviour problems, though, were considered "clinically abnormal."

That findings held even after researchers took into account other factors known to affect a child's behavior, such as breastfeeding, maternal depression, the mother's marital status and income, and other factors.

Joe Braun, the lead author and a research fellow at Harvard's School of Public Health, said it's possible BPA interferes with fetal brain development.

"Gestational, but not childhood BPA exposures, may impact neurobehavioral function, and girls appear to be more sensitive to BPA than boys," he said in a statement.

As for why boys' behaviour wasn't affected, it isn't clear. But BPA is known to mimic the effects of estrogen, which is a female hormone.

The researchers plan to assess the children's behaviour again at age five and then at age eight.

The authors, who also included scientists from Simon Fraser University in Vancouver, say that more research is needed to fully understand the health effects of BPA exposure.

But they say it's possible to reduce BPA exposure by avoiding canned and packaged foods, polycarbonate bottles with the number 7 recycling symbol, and minimizing contact with thermal paper sales receipts.

The American Chemistry Council, a trade group whose members include companies that use BPA, said the research "has significant shortcomings ... and the conclusions are of unknown relevance to public health."

"The researchers themselves acknowledge that (the study) had statistical deficiencies, including its small sample size and the potential for the results being due to chance alone," Steven G. Hentges of the ACC's polycarbonate/BPA arm said in a statement.