BPA-free plastics harm eggs and sperm in mice

Plastics that do not contain bisphenol A (BPA) – a compound known to harm reproductive health – may not necessarily be any safer than those that do, experiments in mice have shown. 

The findings, published in Current Biology, come from the same team that first uncovered the effects of BPA some 20 years ago. The research suggests that exposure to chemicals used as alternatives to BPA have similar DNA-altering effects. 

'Several of these bisphenols induce changes in the germline similar to those we reported previously for BPA,' said Dr Patricia Hunt at Washington State University in Pullman, one of the authors of the study.

The findings came about by chance. The researchers noticed that mice housed in damaged plastic cages had increased numbers of abnormal eggs and lower sperm counts. The effects appeared to be a result of exposure to compounds such as bisphenol S (BPS), a common plastic additive to replace BPA.

To investigate further, the researchers exposed the mice to BPS at critical points of early development. They counted the number of 'MLH1 foci' in the DNA of sperm and eggs – these are alterations of that indicate abnormalities in the chromosomes. 

Females exposed to BPS had unusually high numbers of MLH1 foci compared with controls. The authors predict that these changes will lead to increased numbers of chromosomally-abnormal eggs. In contrast, males exposed to BPS experienced fewer MLH1 foci compared with the controls. This too has harmful consequences for reproductive health, such as reducing sperm count. 

The team found that the effects were inherited down the generations. When Dr Hunt's team bred the male mice that had been exposed to BPS with unexposed females, they found that the second generation had altered numbers of MLH1 foci. The effects progressively wore off in the third and fourth generations.

Despite a lack of evidence in humans, the results add to a body of studies from other species including zebrafish, worms and rats that have found that replacements for BPA may be no less harmful. 

'It suggests these replacement bisphenols are not safe,' Dr Patrick Allard, a molecular biologist at the University of California, Los Angeles, who was not involved with the study, told Science magazine.

However, other researchers have cautioned that it is too early to conclude that BPA replacements are harmful in humans. 

'The number of animals used in the work is very low and the animals themselves were very inbred,' said Dr Oliver Jones at the RMIT University in Melbourne, Australia, who was not involved in the study. 'It should also be remembered that mice are not mini-humans. Some chemicals that cause problems for them don't affect us as all.'