When ‘Safer’ isn’t Safe: BPA and BPS

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Two weeks ago on Backyard Talk, I wrote about BPA, a major plastic component that has been linked to number of health impacts, particularly endocrine disruption. The jury is still out on BPA; the European Food Safety Authority has declared that BPA does not pose a health risk at normal exposure levels, while recent studies have emerged showing that BPA affects stem cells and may impact reproductive health later in life. In the face of all this scientific uncertainty, it’s lucky that we have access to BPA-free products. Or is it?

I have a few new water bottles from Christmas sitting in my cabinet, stamped with a leaf design and a guarantee that their plastic is BPA-free. Our eco- and health-conscious readers probably have similar items in their homes. BPA-free products have proliferated since the U.S. Food and Drug Administration banned the sale of baby bottles containing BPA in 2012. Unfortunately, studies over the past few years have shown that even BPA-free products release estrogenic compounds, some of which can even be more potent than those released by BPA-containing products.

One common replacement for BPA, or bisphenol A, is BPS, or bisphenol S, which has been shown to disrupt cell functioning at very tiny concentrations. It’s no surprise that the compounds might have similar effects, because they are close in structure as well as in name. A brief organic chemistry interlude:




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Image from the blog ‘Science Minus Details.




To the right is an image of BPA side-by-side with a particular estrogen, estradiol.

This image highlights the structural similarities between BPA and estradiol, which enable BPA to mimic the hormone and cause disruptions to the endocrine system.

Below is the structure of BPS:




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BPS molecule









Though the two molecules are not identical, BPS contains the essential ring structure, called a ‘phenol’ group, which is highlighted in both BPA and estradiol. Structural similarity between BPA and BPS is what enables them to play a similar role in conferring hardness to plastics. It also enables them to interact with cells in similar ways. According to Scientific American, BPS is thought to be more resistant than BPA to escaping from plastics when they are heated. However, studies have demonstrated that it is prevalent in human urine, and that even small amounts can cause changes to cells.

We are caught between a rock and a hard place when it comes to developing safe, or safer, alternatives to chemicals that have been linked to adverse health or environmental impacts. When replacing chemicals in products, we often first look to chemicals that share properties with the ones we are seeking to eliminate. As in the case of BPA, however, these similarities that preserve the function of a product can also preserve its toxic effects. When health risks are demonstrated for a given compound, is it prudent to bring in a replacement, even if this new player has not been vetted by scientific studies? Should we settle for lesser risk and continue working towards an even safer ideal? What does ‘safe’ mean, anyway? Tune in next time!

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