Bisphenol A, known as BPA, is produced in massive quantities around the world for use in consumer products and epoxy resins. Exposure to BPA in humans has been linked to a host of chronic diseases, including diabetes, asthma, and cancer. A ban on the use of BPA in baby bottles was imposed in the EU in 2011. Although as a monomer of polycarbonate plastics BPA is found in products made of polycarbonates, the substance continues to be used widely in other products as well, such as in the linings of food cans or in the thermal paper used to print sales receipts. In response to public concerns, many manufacturers have replaced BPA with a chemical called bisphenol S (BPS), which is often labeled as "BPA-free" and presumed to be safer.
This study is not the first to suggest that the use of BPS may be a cause for concern. A University of Texas study published in 2013 demonstrated that BPS effectively disrupted cell functioning in the same way as BPA. The study, conducted by Dr. Cheryl Watson, examined the effects of low concentrations of BPS - within the ranges humans are normally exposed to - in rats. It showed that even at low levels of exposure, BPS disrupts cellular responses to the hormone estrogen, changing patterns of cell growth and cell death and hormone release.
For the present study, zebrafish embryos were exposed to concentrations of the chemicals at levels found in the Bow and Old Man rivers of Alberta, Canada. The researchers found that this exposure to BPA and BPS changed the timing when neurons were formed in the brains of the zebrafish.
"I was actually very surprised at our results. This was a very, very, very low dose, so I didn't think using a dose this low could have any effect," says Kurrasch, PhD, a researcher in the University of Calgary's Cumming School of Medicine and corresponding author on the paper.
"These findings are important because they support that the prenatal period is a particularly sensitive stage, and reveals previously unexplored avenues of research into how early exposure to chemicals may alter brain development, " says Kinch.
Researchers discovered the number of neurons generated in the developing zebrafish brains increased by 180% compared with unexposed fish. They also learned that BPS increased the number of neurons by 240 per cent in similar experiments. The result was a change in behavior, with the fish demonstrating greater hyperactivity later in life.
"Finding the mechanism linking low doses of BPA to adverse brain development and hyperactivity is almost like finding a smoking gun," says Habibi, a professor of environmental toxicology and comparative endocrinology in the Faculty of Science.
Although further research is needed to explore that link and the potential effect on human brains developing in the womb, Kurrasch says the findings add weight to other studies suggesting pregnant women should try to limit their exposure to items containing bisphenols. The evidence also supports removing all bisphenols and structurally similar chemicals from consumer products, she says.
“The study examines effects of relatively high concentrations of BPA on zebrafish embryos in water, and the authors claim the results are directly relevant to humans, in particular to women during the second trimester of pregnancy. In contrast, humans are exposed to only trace levels of BPA through the diet, and it is well known that humans, including pregnant women, efficiently convert BPA to a substance with no known biological activity and quickly eliminate it from the body.