BPA-free plastics appear to disrupt the development of sperm and eggs in mice

Kridtanat Boonyasthian / EyeEm

By Andy Coghlan

Many plastic bottles are sold as "BPA free", which means they do not contain bisphenol A, an ingredient known to disrupt reproduction in mice. But now, it seems that the additives used in place of BPA are potentially as harmful.

The finding could mean that replacements, such as bisphenol S (BPS), could potentially affect people if they leach into food or drink.

There is no evidence that this is happening. But the new results obtained on mice suggest that if there is a risk, it could correspond to that of BPA itself. "Many of these bisphenols induce germline changes similar to those reported previously for BPA," says Patricia Hunt of Washington State University, Pullman, who drew attention to the problem of BPA 20 years ago.

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Hunt's latest discovery emerged in the same way as his discoveries on BPA. As before, she noticed that mice kept in some plastic cages were starting to experience reproductive problems, such as abnormal eggs and low sperm counts. As with BPA, she found that the internal surfaces to which the mice were exposed were contaminated, this time with BPS that had been removed from the plastic.

Screening cells

Hunt has studied the problem in more detail by exposing fetuses of female mice to small amounts of a selection of BPA substitutes to the point where their eggs develop. She also exposed male mice to chemicals just after birth, when they started to develop sperm.

When the exposed mice were older, Hunt screened the cells to become sperm or eggs for the abnormalities. She counted the number of points in the DNA – called the MLH1 foci – where the chromosomes had been reworked. The amount of brewing corresponds to the degree of anomaly, with higher and lower brewing levels, each being worse in different ways.

Exposed females had an unusually high number of MLH1 foci compared to controls – suggesting that they would produce more abnormal eggs. The opposite has been found in men, possibly causing cell death before they mature in sperm – implying that men would have a lower sperm count. "Our previous studies on BPA have shown that these subtle changes increase the frequency of abnormal chromosomal ovules ovulated by adult females and increase cell death during sperm creation in adult males," Hunt explains.

Oliver Jones, from RMIT University in Melbourne, Australia, warns that it's too early for people to worry about the results. "The number of animals used in the work is very small and the animals themselves were very consanguineous," he says. "You also have to remember that mice are not mini-humans. Some chemicals that are problematic do not affect us all.

The anomalies were transmitted for three generations, but then disappeared. Hunt pointed out that more work is needed to determine whether certain replacements for BPA could be safer than others, noting that dozens of products are currently being used.

Journal reference: Current Biology, DOI: 10.1016 / j.cub.2018.06.070