Tin can lining may harm male embryos

A mass-produced chemical which lines the inside of tin cans can harm male babies as they develop in the womb, an embryologist told a conference yesterday.

The chemical, called bisphenol A, is one of 60 known "gender-bender" substances - chemicals which can mimic naturally-occurring hormones and which a growing number of scientists believe are affecting wildlife and humans, causing illness and putting fertility at risk.

Professor Frederick vom Saal, of the University of Missouri, said his studies on mice and on human cells kept alive in test tubes had convinced him the intake of bisphenol A that people received in a normal western diet could harm developing male embryos.

He found that when very low concentrations were given to pregnant mice, their male young had a permanently enlarged prostate gland and a 20 per cent drop in sperm counts when they matured. His laboratory and three others had also demonstrated that the chemical caused a hormonal response in cultured human breast tissue cells.

In the foetus, the great majority of naturally-occurring oestrogen molecules circulating in the blood are attached to proteins and as such are unable to enter cells. But, said Professor vom Saal, "We found that bisphenol can bypass this barrier system."

He pointed out that the prostate gland sighted just beyond the bladder, was "the most diseased organ in the human body" with most elderly men experiencing some problems. Anything affecting the embryo which enlarged the developing prostate more then normal should be avoided, he said.

"We now have an animal study which shows that at the level found in our food, bisphenol A will have an impact on the male foetus ... it has to be perceived as a potential risk, especially to pregnant and breast feeding women and their babies," he said.

As well as being used in can linings, the chemical is a building block in a common plastic, polycarbonate, found in compact discs. It is also used as a sealant in dentistry. Professor vom Saal attacked some chemicals and manufacturing companies for refusing to tell health researchers what chemicals they use in their plastics. "Tupperware told me we do not release this information to the public."

He was one of several scientists talking to a conference organised by the Global Legislators' Organisation for a Balanced Environment and the Worldwide Fund For Nature. It was attended by MEPs and parliamentarians from several continents but no British MPs.

Many environmentalists see synthetic chemicals which interfere with hormone systems during the embryonic development of humans and animal species as a major green issue which will come to rival global warming in importance.

They believe the substances are to blame for rising rates of testicular cancer, falling sperm counts and an increase of cases of malformed, under-sized penises and undescended testicles.

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