Could bisphenol S be more harmful than bisphenol A?

Bisphenol S (BPS), which is often used to replace bisphenol A (BPA) in consumer plastics, may in fact be more harmful than BPA itself, new research suggests.

When exposed to BPS at levels lower than those which humans would encounter, zebrafish experience an increase in neuron growth in the hypothalamus by 240%. In comparison, when exposed to BPA at similar levels, the neuron growth in the fish’s brains was recorded at 180%. Both BPA and BPS exposure have been associated with hyperactive behaviours in zebrafish larvae.

“The two important findings of this research are, firstly, that exposure to very low concentrations of BPA, similar to environmental concentrations, produce more change in zebrafish development than exposure to higher concentrations. Secondly, that the BPA-analogue, BPS, produces similar effects,” said Professor Ian Rae, an Honorary Professorial Fellow at the University of Melbourne.

“The apparent non-linear response merits further clinical work but is unlikely to change the minds of regulators, most of whom have judged that humans’ exposure to BPA is generally below levels of concern. It’s a popular field of research, however, and we can expect to see more publications like this that are scientifically interesting but without impact on regulators. Such results will sell well in some quarters and thus increase pressure on manufacturers to seek alternatives to BPA.

“The molecules of BPA and BPS are similar in shape and polarity and so likely to bind to the same receptor and, unsurprisingly, produce similar effects. So while BPS seems to be the alternative of the day, its effects have not been widely investigated and it could come under pressure, too.”

“The effects in this study were seen at low doses of bisphenol A/S exposure (matching the concentrations of bisphenol A seen in a local river) but not at a higher concentration. This is important as many endocrine-disrupting chemicals do not follow linear dose response curves (ie, effects seen at low concentrations may differ from those seen at higher concentrations) and this means that extra caution needs to be taken by regulatory authorities when they determine the tolerable level of exposure for chemicals such as bisphenol A. Also, the fact that similar effects were observed following exposure to the bisphenol A replacement, bisphenol S, is concerning and warrants further research,” said Dr Anna Callan, a lecturer in the School of Medical Sciences at Edith Cowan University.

But not all experts agree that the findings are significant.

“This study is not applicable to human environmental exposures. The concentrations of BPA, while low, are still much higher than humans would be exposed to,” said Dr Ian Musgrave, a senior lecturer in the Faculty of Medicine at the University of Adelaide.

“The concentrations of BPA the zebrafish embryos were exposed to that resulted in hyperactivity were roughly 1000 times higher than found in the blood of children with high exposure to BPA. Furthermore, the zebrafish embryos were directly exposed to the BPA at times when the major degradation pathway of BPA has not yet developed.

“Human embryos at a similar developmental stage are protected by the placental barrier and the mother’s enzymes that remove BPA from the circulation. Human embryos would never be exposed to the kinds of BPA levels in this experiment. While a very interesting paper, it is not cause for alarm.”

The study, Low-dose exposure to bisphenol A and replacement bisphenol S induces precocious hypothalamic neurogenesis in embryonic zebrafish, was published in the journal PNAS.