Bisphenol-A (BPA), known as the “gender bending” chemical because of its connection to male impotence, has now been shown to decrease sperm mobility and quality.

The findings are likely to increase pressure on governments around the world to follow Canada and ban the substance from our shelves.

BPA is used widely to make plastic harder and watertight tin cans.

It is found in most food and drink cans – including tins of infant formula milk – plastic food containers, and the casings of mobile phones, and other electronic goods.

It is also used in baby bottles though this is slowly being phased out.

BPA has been the subject of intense research as it is a known endocrine disruptor which in large quantities interferes with the release of hormones.

Earlier studies have linked it to low sex drive, impotence and DNA damage in sperm.

Now a new five year study claims to have found a link between levels of BPA in the blood and male fertility.

For their study of 514 workers in factories in China, researchers at Kaiser Permanente, a California-based research centre, found that men with higher urine BPA levels were two to four times more at risk of having poor semen quality, including low sperm concentration, low sperm vitality and mobility.

What is more the amount of the BPA in the blood seemed to be inversely proportional to sperm quality.

Even those with less than the national average BPA levels in America were effected, it was claimed.

“Compared with men without detectable urine BPA, those with detectable urine BPA had more than three times the risk of lowered sperm concentration and lower sperm vitality, more than four times the risk of a lower sperm count, and more than twice the risk of lower sperm motility,” said study lead author Dr De-Kun Li.

He claims the research, published in the journal Fertility and Sterility, was the first human study to report an adverse association between BPA and semen quality.

Previous studies found a negative link between BPA and male reproduction in mice and rats

It was also the third study in a series by Dr Li and his colleagues examining BPA’s effect on humans.

The first study, published in November 2009, found that exposure to high levels of BPA in the workplace increases men’s risk of reduced sexual function.

Increasing BPA levels urine are also associated with worsening male sexual function, according to the second study, published in May 2010.

The latest study, funded by the US National Institute of Occupational Safety and Health, throws further doubt on the safety of BPA.

“The finding of the adverse BPA effect on semen quality illustrates two points: first, exposure to BPA now has been linked to changes in semen quality, an objective physiological measure,” Dr Li said.

“Second, this association shows BPA potential potency: it could lead to pathological changes of the male reproductive system in addition to the changes of sexual function.

“When you see this kind of association with semen you have to wonder what else BPA has an effect on,” said Dr Li.

As a precautionary principle, he said, “Everybody should avoid BPA as much as you can.”

The researchers noted that BPA may also affect female reproductive systems and have adverse effects on ailments such as cancer or metabolic diseases.

BPA has already been banned in Canada and three US states.

Bottles and cans containing the chemical have been linked to breast cancer, heart disease, obesity, hyperactivity and other disorders.

Most manufacturers of baby bottles have stopped putting it in their products but older stock containing the chemical is still on sale.

The US Food and Drug Administration (FDA) supports its removal and has stated concerns regarding the impact of the chemical on babies and young children.

It can affect disorders associated with metabolism, fertility and neural development.