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In the latest study to suggest an association between the plastics chemical bisphenol A (BPA) and adverse effects on humans, researchers report that BPA may affect the behaviour of little girls.
Girls exposed to higher levels of BPA displayed more "externalising" behaviours, such as aggression and hyperactivity, according to the study, which is published in the Environmental Health Perspectives.
"We found almost all of the women [in the study] had detectable levels of bisphenol A in at least one of the tests, and elevated concentrations were associated with externalising behaviours in female children," said study author Joe Braun, a graduate student and research assistant in epidemiology at the Gillings School of Global Public Health at the University of North Carolina at Chapel Hill.
No cause-effect results
Not everyone agreed with the study's conclusions, however.
"This type of study has no capability to establish cause and effect, only associations. At the end of the study, the authors even point out that the results 'should be viewed cautiously,'" noted Steven Hentges, executive director of the polycarbonate/BPA global group at the American Chemistry Council, which represents the chemicals industry.
BPA is a commonly used chemical that's found in hard plastics and epoxy resins. The chemical is used in water bottles, food containers, infant bottles and medical devices. BPA may also be found in the lining of canned foods. Most human exposure comes through diet when the chemical leaches into food and beverages from the containers, according to the US National Institute of Environmental Health Sciences.
Effects on foetuses
Animal studies of the chemical have found an association between BPA and adverse neurodevelopmental effects on foetuses and newborns, according to background information in the study.
The current study included 249 pregnant women from Cincinnati, Ohio, who were part of another study that was evaluating interventions to reduce lead levels. Urine samples were collected when the mothers were 16 and 26 weeks pregnant, as well as within 24 hours of birth.
As many as 99% of the women had at least one urine sample with detectable levels of BPA, according to the study.
The children's behaviour was reported by the parents using a standardised questionnaire when the children were 2 years old.
After controlling the data to account for numerous possible confounding factors, such as maternal age, race, education and income levels, the researchers didn't find an association between BPA and externalising behaviours. However, when they split the data by sex, they noted an association between higher BPA levels and more externalising behaviours in girls.
Don't understand difference in sex
Braun said that the researchers don't know why there was a difference in the findings by sex, nor did they know what the potential biological mechanism might be that could cause an increase in aggressive behaviors after BPA exposure.
The researchers did not adjust the data in this study to account for lead exposure, diet or after-birth exposure to BPA. Braun said that the researchers did test additional statistical models to account for lead exposure that weren't included in the paper, and he said that when this was done lead levels didn't change their findings.
However, "once you consider the limitations of the study, as the authors carefully do, there's significant potential for false positives," contended Hentges.
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