Understanding Plastics for Humans, Installment 3: The Idea of Endocrine Disruption

There’s an often repeated stat about microplastics that says we consume a credit card’s worth of plastic every week. You read other articles saying that plastic is toxic. Both of these things can’t be true at the same time or we’d be dead. But there is some basis in the claims about the endocrine effects of specific plastic additives. Knowing which plastics are potentially problematic and why is key to being a responsible consumer and environmental advocate, so here goes.

Depending on the use case of the polymer, a variety of additives are used to make it perform better in production or in its service life. Few additives are put into food grade HDPE, which is why Buoy uses that exclusively to make our containers. This article gives a good roundup of the various additives used in plastics if you are in the mood for a deep dive.

Bisphenol A or some Phthalate is added to PVC to make it soft, so if you want to make PVC into a pair of vinyl pants or polycarbonate into a baby bottle, you add BPA. This last use is no longer common for food-grade containers in the US as it is the focus of a banning campaign. But what is worrisome about Bisphenol A in the first place? To answer that question, let’s examine Estradiol, which is an Estrogen or female hormone.

Look at each end of Bisphenol A. Do you see that six-carbon ring with the OH group? That is called a phenol. Now look at the bottom left corner of the estrogen molecule. It’s also a phenol, and it’s observed in studies here and here that Bisphenol A can bind to or block estrogen receptors, though weakly, and cause other mischief in the endocrine system. The fear is that the estrogenicity could contribute to daughters menstruating early, sons growing breasts and breast cancers growing faster, which is why pissed-off moms, who do a great deal to drive good things in the world, took collective action and to this day continue to petition the FDA to ban it. The FDA has taken these petitions very seriously and has extensively reviewed the current data. They still cannot find in the research a straight line between the weak estrogen receptor activation by BPA and a negative outcome in humans, so they continue to categorize BPA as safe for food contact. Having failed to move the FDA to action, activists have effectively banned BPA in the form of a grass-roots consumer boycott, driving manufacturers of food contact products to find alternate solutions. 

As a result of consumer concerns over whether they are buying endocrine-disrupting baby bottles, many sites recommending baby products exclusively advise readers to get stainless steel or glass bottles with silicone nipples. These products are safe, no doubt, but the stainless steel bottles are not recycled and none of them are within economic reach of a mother on a budget. It breaks my heart to think of a mom of limited means thinking that she’s hurting her child because she can’t afford a silicone-encapsulated glass baby bottle. Baby bottles or any food-contact product made from #2, #4 or #5 are also safe and #2 is actively recycled, making it a better ecological choice than either glass or stainless.

Just like the recent controversy around Titanium Dioxide in Skittles, it is not well understood how low-level exposure to these additives affect human health. The European authorities, in their ongoing chemical banning practice, have put Titanium Dioxide on their list not because any harm has been proven, but because they could not numerically establish a safe level for human consumption. Similarly, European authorities, unlike the FDA, have restricted the use of BPA in food contact plastics. Our regulatory bodies in this country take a less precautionary approach by requiring that studies establish that the harm is happening before they take action. US and European scientists are looking at the same data. It’s just a different framework. Europe adheres to the precautionary principle. To a lot of people, the very phrase precautionary principle sounds laudatory, but the precautionary principle kept two generations of women from getting the benefits of hormone therapy at menopause. This is well summarized here. 

If you are wondering how the BPA ban is going… Manufacturers proudly list their non-use of BPA, but to maintain the softening or other effect they need to sell their product, they’ve switched to using Bisphenol B, Z and everything in between. (This sounds like sarcasm, but it’s not. Here’s a journal article comparing six common additives used in place of BPA.) Some of these substitutes bind more strongly to estrogen receptors than BPA, some less, but net-net, there’s a question mark about what has been gained from the ban. 

Complicating further the scare story about BPA is that fact that isoflavones, a naturally occurring chemical in soy and many other foods, have a structure that also has a dangling phenol that also weakly binds to estrogen receptors, a good workup here. 

You might remember the scare a while back about not feeding soy to babies. This was vigorously debunked by vegetarian groups and the research seemed to parallel the research about BPA showing that it was a weak interaction and failing to find health effects. But in the case of soy isoflavones, the non-conclusive nature of the research was interpreted as exculpatory whereas in the case of BPA, the same basic results were interpreted as sinister. This is most likely a case of the naturalist fallacy where we see anything natural as good and anything artificial as bad. 

The above referenced journal article about the substitute additives was commissioned and funded by the EPA, a different government agency from the FDA with a different group of scientists. The EPA folks are pushing for the government to evaluate supposedly better substitutes before they are put into service to make sure they are actually better, which is a great idea. All of the scientists in the EPA and FDA are doing their jobs and actively tracking the research.

If it looks like the EPA is doing a “better” job at protecting us, it may be because their scope is different from the FDA. The FDA is only wanting to be sure that the tiny amounts of the additives that humans get from food contact containers are not harming us. The EPA’s scope is much wider. They are looking at environmental effects on fish and gastropods in rivers where factories dump waste streams containing endocrine disrupting chemicals. In these cases, the additives are effects on these smaller, less complex animals. I’ll keep my eye on the research and return to it as relevant. 

PET (#1) is confusing because it has the word Phthalate in its name. Polyester Terephthalate. The Phthalate is not a free-floating additive, but rather tied up in the polymer, so not bioavailable. The additive in PET that gets attention is Antimony, which is part of the catalyst used to make PET and therefore exists in trace quantities in the polymer. It does leach into water and juice, but never to quantities that exceed recommended thresholds. Antimony can be endocrine disruptive at high concentrations, but it's difficult because antimony also exists naturally in water and food because it is an element in the world. Humans evolved alongside this element, so it seems unlikely that it poses an outsized threat at normal concentrations or we would have died like a billion years ago. Heating PET increases the antimony migration, so that's why you get advice to not store bottled water in the trunk (boot) of your car during summer. Here is a good roundup of the results. Tap water has lower regulated levels that bottled water, so if you are worried about antimony, drink tap water. 

The bottom line I want you to walk away with is that not all polymers have additives that could be endocrine disrupting. HDPE (#2), LDPE (#4) and Polypropylene (#5) are all food safe with no endocrine disrupting potential. PET has antimony, but the leaching is at levels too low to influence our health. They are affordable and #2 is commonly recycled, which is why we have chosen it as the source material for Buoy products. In addition, our supply chain partners do extensive testing on our source plastic and we have sent a container sample from our first production run to NSF for more chemical testing. Needless to say, our container passed NSF chemical testing for food safety, so there’s nothing in there to leach out and hurt you. 

The EPA has a program to track endocrine disrupting chemicals that you can learn about here. 

Thanks for hanging in for this three-part series. It was pretty technical, but hopefully understandable. In the next couple of installments, I’ll lighten up on the chemistry lesson and talk about other aspects of the world of green that we Buoy founders find ourselves immersed in.

© Buoy, 2023

Edited in December 2025 to add better information about PET and Antimony and do some general edits.