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Dirty air in urban areas may be having an impact on sperm. Tests on mice showed that those exposed to tiny pollution particles had worse sperm quality and smaller quantities than mice who were not.

Many health problems are linked to pollution emitted by petrol and diesel cars, including respiratory issues, cancer and stunting child development. However, whether the smallest of these air pollutants, PM2.5, could also be contributing to increasing male infertility rates around the world is still .

Elaine Costa at the University of Sao Paulo and her colleagues studied four groups of mice. They exposed three of the groups to PM2.5 for different lengths of time before and after birth, and the fourth was only exposed to filtered air.

They then analysed sperm development when they became adults and the exposed mice showed a deterioration in the tubes in the testes that produce sperm.

The quality of sperm was significantly worse in mice exposed to pollution before and after birth, compared to the control group. Exposure to air pollution after birth appeared to have the most serious impact on sperm. DNA tests also showed changes in the levels of genes related to testicular cell function.

“These findings provide more evidence that governments need to implement public policies to control air pollution in big cities,” said Costa in a press release.

The work, which is not yet peer-reviewed, will be presented at the Endocrine Society conference in New Orleans on Sunday.