It seems that bisphenol A is not the only junk scrambling our reproductive systems. New evidence from a Health Canada study suggests that elements of air pollution could be causing DNA mutations in the sperm of male mice. In the experiment - conducted in Hamilton, Ontario - two groups of mice were reared in cages kept in sheds near two steel mills and a busy highway. One of the groups breathed ambiential air, while the other breathed only filtered air. The group that was exposed to the outside air had a 60% higher instance of mutated DNA in their sperm cells. These mutations manifested in a number of ways: some DNA strands were broken, others had chemical modifications to their bases.

The chemical modification - known as DNA methylation - is particularly troubling. It occurs when a methyl group chemical attaches to the end of a strand which can cause a gene to remain dormant. In other words, it can potentially disrupt the expression of genes and genetic traits in offspring.

While previous research into the effects of air pollution on reproduction has focused on maternal or infant health, fewer studies explore the possible effects to the paternal contribution. The mouse study is particularly valuable as previous attempts to study this correlation in humans have found a reduction in male fertility, but have been thwarted by a multitude of factors that are difficult to control for, such as lifestyle, genetic background and socio-economic class. However, evidence from similar studies in other species such as wild birds corroborates the results of this mouse study.

The researchers were not able to determine which aspect of air pollution was responsible for the mutations. They initially predicted that polycyclic aromatic hydrocarbons - a known disruptor and carcinogen generated by steel mills - would be responsible, but found no evidence that this was true. The study's lead author and University of Regina biology professor, Christopher Somers instead suggests that simply breathing in metallic particulate matter from the air could cause these mutations. The metal from pollution particles generates chemically reactive forms of oxygen which are breathed in by all living creatures. Perhaps, he suggests, this reactive oxygen is responsible for the changes.

The good news is that the mice who breathed filtered air passed on fewer genetic defects to their children, which means that there is a pretty straightforward and manageable culprit: if we clean up our air, we can eliminate the presence of mutant DNA in our offspring. In the meantime, it may be prudent to buy a home air filtration device.