Plastic products that bokken if & # 39; BPA-free & # 39; are not necessarily safer for us, suggests a new mouse study to be published Thursday in Current Biology. The chemicals that are used to replace BPA in these plastics can still leak and affect the semen and eggs of both male and female mice. And these same effects can occur in humans.
Bisphenol A, or BPA, is a chemical commonly used to make polycarbonate plastics and epoxy resins. These clear white plastics are used in food and beverage packaging, as well as consumer products and medical devices, while resins are used to coat metal products such as canned food. When these products are broken down or otherwise damaged (for example by being repeatedly heated in a microwave oven, they can leach and expose BPA.) As a result, it is estimated that 93 percent of Americans have a certain level of BPA in their system.
This is worrying, because there is more and more research that shows that exposure to BPA can have subtle but real effects on our health. It is one of many chemicals thought to interfere with our endocrine system, which regulates how hormones affect everything from our fertility to the development of the brain. Especially BPA has been implicated as a possible cause of genital malformations in men, early puberty in women and developmental problems in very young children; it can also contribute to metabolic disorders such as obesity and certain cancers.
In the wake of this bad publicity, companies have started to move away from the use of BPA-containing plastics, especially in products that are geared to the very youngest, such as baby bottles and the packaging of baby food.
The researchers behind this current study were some of the first scientists to note BPA's potential dangers, although their discovery was an accident. Twenty years earlier, when they studied mouse genetics, they discovered that the female mice they had used as controls produced more unhealthy eggs than normal. Later they discovered that these mice had been stored in damaged plastic boxes and were drinking from damaged plastic water bottles, both of which leaked BPA into their environment.
Unbelievably, it seems that something similar has happened, on a smaller scale. While working on another project, the authors began to develop some, but not all, their control mice, both male and female, with reproductive problems. Although the mice had been kept in cages made of polysulfone, and not of polycarbonate, the researchers noticed a whitish residue in some cages, indicating that they were damaged and were leaching chemicals.
"There was definitely a sense of" Oh no, not again ", senior author Patricia Hunt, a researcher at the Center for Reproductive Biology at Washington State University, told Gizmodo.
When Hunt and her team analyzed the chemical signature of the damaged cages, they found both BPA and BPS, a bisphenol that replaces BPA on a large scale. The cases were polysulphone-plastic, which is partly made of BPA, but it is advertised that it is more heat and chemical resistant than polycarbonate and therefore has less chance of breaking down. Polysulphone is not thought to degrade to BPS, but Hunt's team discovered that if certain chemical bonds in the plastic were broken correctly, BPS could form.
Following their original experiments with BPA, Hunt's team exposed more mice to low-dose BPS, and compared their reproductive health with mice exposed to BPA and mice that were raised in new, new cages, probably free of only BPA / BPS contamination. The BPS mice had more defects in their egg and sperm than the control mice, but the level of damage was similar to that seen in mice that exposed BPA at the same dose alone.
"These replacements behaved almost exactly as BPA did," Hunt said.
Although manufacturers have been deterred from making explicit claims that BPA replacements are safer, Hunt noted that customers have been confident that they are safer. But while the study is only the last to suggest that there is no real difference between these chemicals in their potential harmfulness, demonstrating that this effect is real is a different problem for people.
"We almost never can show cause and effect in humans," Hunt said, noting that even the well-known link between smoking and cancer is largely based on indirect evidence. "But how confident would you feel if I told you that we have seen this effect in mice, nematodes and rhesus monkeys?" I would say that it is a good guess that we would also see it in humans if we had the same kind of experiments. could perform. "
If that is not bad enough, other studies have suggested that the effects of BPA can be inherited. And when Hunt's team bred some of the original male mice exposed to BPS with healthy females, that was exactly what they found: the second generation of mice continued to have more reproductive problems than normal. It was only through the third and fourth generation that these mice resembled healthy mice.
Regulatory authorities, such as the Food and Drug Administration, still maintain that the current levels of exposure to BPA in food are not a concern to human health, suggesting that research shows that people metabolise BPA faster than mice and eliminate any toxic effects . But according to Hunt, this assumption is based on traditional toxicological methods, which may miss the more subtle effects caused by low doses of BPA and similar chemicals.
"You would expect a linear response – the more you give, the worse it is, but this type of chemicals does not behave like that: they behave like hormones or some drugs we take, where a little bit of a powerful effect can be exercised, but stopping the dose could alleviate that effect or generate a new effect, "Hunt said. "And yet the FDA does not want to believe that there is a low-dose effect, although there is some evidence in their data."
Hurt refers to an upcoming government report on BPA, known as CLARITY-BPA. In response to criticism from researchers such as Hunt, the report is aimed at combining data from more traditional toxicological studies and newer methods.
The final results of the first half of the report, based on the earlier type of research, will be announced shortly. The study is expected to confirm the conclusion of the FDA that exposure to BPA from our food is not necessarily a health risk. But scientists elsewhere have criticized the FDA's conclusions based on this investigation as incomplete and possibly marred. The final report, which incorporates the newer methods, will only be published next year.
Because of the ubiquity these chemicals have in our lives, it is possible that no meaningful action is possible in the near future, even if the FDA wanted to do something. The ease with which similar chemical analogs can be developed surpasses the ability of health authorities to effectively study and regulate them, Hunt said.
And because BPA tends to stay in the environment, it can take decades before the consequences have completely disappeared. These long-term effects, as some researchers speculated, might even be an explanation for the declining collective fertility of Western men.
That is all pretty bleak. But Hunt still believes that there is a way that the public can at least better protect himself.
"People need to think differently about plastics, because at the moment we think they are things that last a long time," she said. "But if you see signs of damage, you just have to get rid of it, and I also recommend that people never put plastic in the dishwasher or microwave, because heat is just an invitation to let these chemicals migrate out."
"If it is damaged, it starts to leak chemicals and you do not want to be there," she added.[Current Biology]