UPDATED — Plenty of studies have outlined the potential adverse effects of bisphenol-A exposure, but a study released this week by University of Calgary researchers says its replacement, bisphenol-S, isn't any better for developing human brains.
BPA, a key component in polycarbonate, can linings and epoxy resins, has been replaced in some applications by BPS since being repeatedly linked in studies to cancer, attention deficit-hyperactivity disorder, diabetes and other problems.
But the Calgary researchers' findings suggest both BPA and BPS can cause problems in brain development, leading to hyperactivity in zebrafish, even at what the scientists consider “very low” doses.
Zebrafish are frequently used by researchers to understand and mimic human embryonic brain development. About 80 percent of the genes found in humans have counterparts in zebrafish, which also have embryonic developmental processes similar to humans.
The new study, published this week in the Proceedings of the National Academy of Sciences, started off by testing a BPA level of 1.5 nanograms per milliliter level in zebrafish — a level that has come up other recent Canadian studies. Even at that low level, researchers saw changes in the fishes' brains with initial BPA testing, “so we decided to dig deeper,” said Hamid Habibi, one of the authors of the study and a professor of environmental toxicology and comparative endocrinology at Calgary.
At the exact same 1.5 nanograms per milliliter concentration of BPS, Habibi said saw changes in the timing of the development of neurons in the zebrafish. The number of neurons generated in the developing zebrafish brains increased by 180 percent in BPA-exposed fish compared with unexposed fish, the study shows. BPS increased the number of neurons by 240 percent in similar experiments. The exposed fish also demonstrated significant hyperactivity in maturity, the study shows.
One of the study's most significant findings is that low doses can be just as harmful as larger doses, he said. The research also suggests that pregnant women particularly should limit their exposure to plastics containing BPA or BPS. Habibi also said that while the study did not include such data, plastics industry workers should “take the appropriate precautions” when working with either, especially until more definitive answers about their effects can be reached.
“We're not here trying to give bad publicity or sensationalize these things,” Habibi said. “We're just reporting our scientific work.”
The U.S. Food and Drug Administration declared in 2012 that BPA could no longer be used in the manufacture of baby bottles and sippy cups, though the ruling came after manufacturers had stopped using it. Since then FDA had repeatedly declared its belief that BPA is safe to use in the lining of cans beverage containers. But in the industry's rush to meet consumer demands to get BPA out of certain plastics products, little time was taken to consider or test alternatives.
“I don't know what the logic was or what the selection went into that,” Habibi said “Here we are spending time and resources testing BPS now.” Industry experts should work with chemists and endocrinologist to come up with a polymer that has less adverse effects but similar properties to BPA-containing plastics, he said.
“Get someone like me to work with them in partnership… It would take about one year and would cost them far less, and not have all this negative publicity and come up with something that is not reactive,” Habibi said. “And then use that to replace these problematic substances.”
Industry experts, including the American Chemistry Council, cautioned that one small study is hardly definitive.
"The relevance of this limited study on zebrafish, as asserted by the authors, is not at all clear, and it would not be scientifically appropriate to draw any conclusions about human health based on this limited experiment," said Steven Hentges, of ACC's Polycarbonate/BPA Global Group.