That is the finding of a recent study published in the journal Environmental Pollution, which analysed semen samples from more than 1,300 men in China.
The study, led by researchers from China’s Third Military University, compared the quality of sperm from men living in Chongqing City, an industrial city in China’s south-west, to that of men from surrounding rural areas.
The researchers found that city-dwelling men had higher levels of abnormally shaped sperm than their rural counterparts. Their sperm also swam more slowly.
Both sperm shape and motility are important factors in determining male fertility.
The scientists attributed the poorer quality of sperm in urban areas to high levels of air pollution, with concentrations of particulate matter, sulphur dioxide and nitrous dioxide in Chongqing City exceeding World Health Organisation guidelines.
Concentrations of particulate matter were more than eight times guideline values.
Dr Ahmad Hammoud, an Assistant Professor at the University of Utah and Medical Director for the Utah Center for Reproductive Medicine, was not involved in the study, but is an expert in reproductive health.”Particulate matter carries with it polycyclic aromatic hydrocarbons, or PAHs,” he said “These PAHs can have hormone-like activity…so they can possibly affect the hormonal balance in the body.”
Air-borne particulate matter may also contain many other industrial pollutants, such as lead, cadmium and mercury, which can also be toxic to sperm.
Hammoud said it can take up to three months from being exposed to pollution until effects on the sperm are seen.
“Sperm have a 72 day life-cycle. So exposure of the sperm right now in the testicles to those hormone-altering pollutants, you will see results in two to three months when the sperm are ejaculated.”
While the Chongqing study is not the first to make a link between declining sperm quality and air pollution, Hammoud cautions that this does not necessarily mean it is the smoking gun.
“Correlation does not mean causality…It is possible that people who live in areas that are polluted are also eating unhealthy diets or they are just living an unhealthy lifestyle,” he said.
“We have not yet been able to design the perfect study that answers the question once and for all.”
There has been considerable debate in the scientific community concerning reports of a global decline in sperm quality and male fertility.
In Australia, one in six couples has trouble conceiving naturally and half of the cases are related to male infertility. For Jo Immig from the National Toxics Network, the issue extends beyond impacts on male fertility.
“It strikes at the very heart of who we are as a species if we are actually starting to say that the things that we are doing to the environment are stopping us from reproducing,” she said.
“But this sits in a much more complex picture of what pollutants are actually doing overall to our health. It is not just at the reproductive level that they are affecting us, it is also the immune system, neurological problems in children, cancers…it is the full spectrum of disorders.”