Plastic products that boast of being “BPA-free” aren’t necessarily any safer for us, suggests a new mouse study published Thursday in Current Biology. The chemicals used to replace BPA in these plastics can still leak out and affect the sperm and eggs of both male and female mice, it found. And these same effects could be happening in people.
Bisphenol A, or BPA, is a chemical commonly used to create polycarbonate plastics and epoxy resins. These clear white plastics are themselves used in food and drink packaging, as well as consumer products and medical devices, while resins are used to coat metal products like canned foods. When these products degrade or are otherwise damaged (from being repeatedly heated in a microwave, for example), they can leach out BPA, exposing us to it.
That’s troubling, because there’s growing research showing BPA exposure can have subtle but real effects on our health. It’s one of many chemicals thought to interfere with our endocrine system, which regulates how hormones affect everything from our fertility to brain development. BPA in particular has been implicated as a possible cause of genital deformities in men, early puberty in women, and developmental problems in the very young; it might also contribute to metabolic disorders like obesity as well as certain cancers.
In the wake of this bad publicity, companies have started to steer away from using BPA-containing plastics, especially in products geared to the very young, such as baby bottles and the packaging of baby formulas.
The researchers behind this current study were some of the first scientists to notice BPA’s potential dangers — though their discovery was something of an accident. Twenty years earlier, while studying mice genetics, they found that the female mice they had been using as controls were producing more unhealthy eggs than usual. They later found these mice had been kept in damaged plastic cases and drank from damaged plastic water bottles, both of which leached BPA into their environment.
Incredibly, it seems something similar happened again, if on a smaller scale. While working on another project, the authors began seeing some but not all of their control mice, both male and female, develop reproductive problems. Though the mice had kept in cages made of polysulfone, not polycarbonate, the researchers noticed a whitish residue in some of the cages, indicating they had been damaged and were leaching chemicals.
“There was definitely this sense of ‘Oh no, not again,’” senior author Patricia Hunt, a researcher at the Centre for Reproductive Biology at Washington State University, told Gizmodo.
When Hunt and her team analysed the chemical signature of the damaged cages, they found both BPA and BPS, a bisphenol that is widely replacing BPA. The cases were polysulfone plastic, which is partly made from BPA, but it’s advertised to be more heat and chemical resistant than polycarbonate and thus less likely to break down. Polysulfone isn’t thought to degrade into BPS, but Hunt’s team found that if certain chemical bonds in the plastic were broken in the right way, BPS could form.
Following in the vein of their original experiments with BPA, Hunt’s team exposed more mice to low doses of BPS, and compared their reproductive health to mice exposed to BPA and mice raised in fresh new cages, presumably free of any BPA/BPS contamination. The BPS mice had more defects in their egg and sperm cells than did the control mice, but the level of damage was similar to that seen in mice they exposed to the same dose of BPA alone.
“These replacements were behaving pretty much exactly like BPA did,” said Hunt.
Though manufacturers have shied away from making explicit claims about BPA replacements being safer, Hunt noted, customers have certainly assumed that they are safer. But while the study is only the latest to suggest that there’s no real difference between these chemicals in their potential harmfulness, proving this effect is real in humans is another problem.
“We can almost never demonstrate a cause-and-effect in humans,” Hunt said, pointing out that even the well-established link between tobacco smoking and cancer relies largely on indirect evidence. “But how confident would you feel if I told you that we’ve seen this effect in mice, in nematodes, and in rhesus monkeys? I’d say it’s a pretty good bet that we would see it in humans, too, if we could run the same kind of experiments.”
If that’s not bad enough, other studies have suggested that the effects of BPA could be inherited. And when Hunt’s team bred some of the original male mice exposed to BPS with healthy females, that’s exactly what they found: The second generation of mice continued to have more genetic issues than normal. It was only by the third and fourth generation that these mice resembled healthy mice completely.
Regulatory agencies such as the Food and Drug Administration still maintain that current levels of BPA exposure in food are not a concern to human health, pointing to research showing that people metabolise BPA faster than mice, dulling any possible toxic effects. But Hunt says this assumption has largely relied on traditional methods of toxicology, which might miss the subtler effects caused by low doses of BPA and similar chemicals.
“You might expect a linear response — the more you give, the worse it is. But these types of chemicals don’t behave that way; they behave like hormones or some drugs we take, where a tiny bit can exert a powerful effect, but bumping the dose up might abolish that effect or induce a new one,” said Hunt. “And yet the FDA doesn’t want to believe there’s a low-dose effect, even though there’s some evidence of that in their data.”
Hurt is referencing an upcoming government report on BPA, known as the CLARITY-BPA. The report, in response to criticisms by researchers like Hunt, aims to combine data from more traditional toxicology studies as well as from newer methods.
The final results from the first half of the report, based on the former type of research, are set to be announced sometime today. The study is expected to reaffirm the FDA’s conclusion that BPA exposure from our food is not necessarily a health concern. But the final report, incorporating these newer methods, will not be published until next year.
Because of how ubiquitous these chemicals are in our lives, it’s possible that no meaningful action could get rid of them in the near future, even if the FDA did want to do something. The ease with which similar chemical analogues can be developed far outpaces the ability for health agencies to effectively study and regulate them, Hunt said.
And because BPA tends to linger in the environment, it might very well take decades before its impact disappeared completely. These long-lasting effects, some researchers have speculated, might even help account for the declining collective fertility of Western men.
That’s all plenty bleak. But Hunt still believes there’s a way for the public to at least better protect themselves.
“People need to think about plastics differently. Because right now, we tend to think of them as things that will last for a very long time,” she said. “But if you see any signs of damage, you should just get rid of it. I also recommend that people never put plastics into the dishwasher or microwave because heat is just an invitation for these chemicals to migrate out.”
“If it’s damaged, it’s starting to leak chemicals and you don’t want to be around that,” she added. [Current Biology]
Featured Photo: Drew McNew (Getty Images)