Big science news out of the University of Calgary: researchers have found that BPS impacts brain behaviour in zebrafish! You may have seen it in the new this week: it made it on CBC, the Toronto Star, the National Post and many other news sites. Some contained alarming headlines like “Attention pregnant shoppers: study says those cash register receipts could harm your unborn child. (National Post)” But really, is that what the study said? The title, published in Proceedings of the National Academy of Sciences, reads “Low-dose exposure to bisphenol A and replacement bisphenol S induces precocious hypothalamic neurogenesis in embryonic zebrafish” Seems a bit of a reach to say that you may be harming your unborn child, doesn’t it? And here lies some of the challenges in science communication: making the study accessible to the public, without oversimplifying or over reaching the conclusions. It is a tough balance. This study helps highlight those challenges and it also gives an opportunity to explain how these studies are really important to communicate; how they impact our understanding of our human health and development; and the impact that we have on the world around us.
This study, led by Dr. Deborah Kurrasch at the University of Calgary, is pretty interesting science. What’s more, is that her and her team said they were surprised by the results. So let’s have a look at what Dr. Kurrasch’s team discovered.
The story begins with the compound bisphenol A, abbreviated as BPA. It wasn’t long ago that BPA was making the headlines: it was dangerous and has since been banned from baby bottles. Many of us are now purchasing BPA-free water bottles, baby bottles, plastic packing etc. So what is BPA anyway? It is the compound here on the right. It is used in making plastics, most commonly polycarbonate plastics, but also used in epoxy resins. These are just various types of plastics that have all kinds of uses. Soon it became apparent that we were finding BPA EVERYWHERE. In all kinds of places it shouldn’t be. As someone who studied polymers, I can say what surprised me about this compound is that, unlike some other additives to plastics, it is chemically bonded right into the polymer. The fact that it was leaching out was a bit of a surprise. But what is worse is that BPA behaves as an endocrine disruptor. Endocrine disruptors are a group of compounds that behave similarly to hormones in your body. In this case, BPA behaves similarly to thyroid hormones.
The endocrine system is one of the systems in your body that is responsible for communication and regulation of body functions such as growth, reproduction, metabolism, and behaviour. Hormones are the chemicals produced by your endocrine cells and secreted and transported throughout the body as the chemical communicators. Chemicals that are structurally similar to hormones can bond to hormone receptors in your body and therefore disrupt the communications, which can cause problems with your body’s development.
Now knowing that BPA is an endrocrine disruptor, it became apparent that it should be removed from materials. The trick is to find something else that can function in place of BPA, but won’t pose the same problem. Manufacturers started using bisphenol S, or BPS, in place of BPA. (BPS is shown here on the right.) This compound is used in place of BPA, meaning that BPA-free products may contain BPS in its place.
So we know that both of these compounds are present in the environment, we know that there are found in organisms, that they bioaccumulate, and that they are endrocrine disruptors. Great, so how does this actually impact you? Well…we don’t exactly know. Enter: Dr. Kurrasch and her team.
The study uses zebrafish (Figure 3) as a model organism (Model organisms are other living things that are used in experiments because it would be unethical to test on human subjects.) Zebrafish actually have a spinal cord and a brain, but also reproduce rapidly, making them good models for neural development. (The rapid reproduction allows you to get enough subjects so your results actually mean something without waiting a hundred years.)
Using VERY low doses of bisphenol a and bisphenol s (1000 times less than typical human daily exposure), the team treated the zebrafish embryos and found that they were producing more neurons (brain cells) during development, which resulted in hyperactivity in the zebrafish babies.
The studies on human development are still emerging, meaning that we don’t yet know the long term impacts on human health, or the exact mechanism of how these chemicals work. These studies from the University of Calgary help give in sight into those mechanism and also suggest that it isn’t just BPA that is a problem, but chemicals that are the same class. It also suggests that very minute amounts of these compounds can have an impact on brain development.
Take home messages of this study:
-BPA and its relative BPS both impact the brain development of zebrafish embryos
-Only minute quantities are required to see an observable difference in brain development of zebrafish
-It may be important consider removing all bisphenol compounds from consumer materials
-The impact on human health is still unknown
-These results do give in sight on potential mechanisms on human brain development