Understanding Plastics for Humans, Installment 3: Endocrine Disruption or What Makes Plastic Toxic?

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

When molecules are attached together in a polymer, they generally are not going anywhere and are therefore pretty safe. Some kinds of plastic, like PVC with its Chlorine, can start throwing out nasty stuff if they start degrading. Many studies have been done on substances that may leach from PET in heat or at acidic pH levels, which is a topic that will get its own post at some point. Buoy’s recycled plastic of choice, Polyethylene (#2), and also Polypropylene (#5) are just carbons and hydrogens strung together, as describe in Installment 2, and would not throw off nasties, even if degraded. So in sum, we’re less worried about things locked up in the polymer chain. Where we get into problems is when free chemicals are added to plastic to give them a characteristic that they don’t otherwise have.

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. Manufacturers put dispersions of antimony tin oxide in PET bottles and films to make them flow more smoothly in production equipment. No 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 estrogen receptors, though weakly, and cause other mischief in the endocrine system. It is feared 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 reviewedthe 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 efforts, 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 conservative 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.

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 articlecomparing 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.

I’m sorry if that paragraph read like a despair-inducing scare post. You should know that the very journal article about the substitute additives was commissioned and fundedby 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 very real effects on fish and gastropods in rivers where factories dump buckets of endocrine disrupting chemicals. In these cases, the additives are having well-understood effects on these smaller, less complex animals. I’ll keep my eye on the research and return to it as relevant.

The bottom line I want you to walk away with is that not all polymers have structures that could be endocrine disrupting. HDPE (#2), LDPE (#4) and Polypropylene (#5) are all food safe with no endocrine disrupting potential. They are affordable and #2 is recyclable, 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.

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