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Scientists hope to prove whether common environmental chemicals, such as those used to make plastics, are to blame for rising testicular cancer rates.

Experts suspect that exposure while in the womb might explain why the rate of this cancer has doubled in 35 years.

The Edinburgh team told Human Reproduction such a study was only now possible because they had made a model to study the disease in development.

They will use mice harbouring human cells to test the theory.

Testicular cancer occurs in young men, but doctors have known for some years that the abnormal changes that lead to testicular cancer happen in the first few months that the foetus is growing.

But because these changes occur during early pregnancy, when there is no means of studying the foetal testes, doctors do not know how and why these changes occur.

Researchers are fairly certain there must be an environmental cause because the rate of the cancer has increased so rapidly.

According to Professor Richard Sharpe, of the Medical Research Council's Human Reproductive Sciences Unit, one theory is that the changes are caused by pregnant women being exposed to environmental chemicals such as phthalates, which are used in many different household items, including plastic furniture and packaging.

But because the cancers only develop 20-40 years after the patient is born, it has been hard for doctors to discover what happened in foetal development to cause this to happen, especially when trying to establish if their mothers were exposed to phthalates or other environmental chemicals to establish a causal relationship.

Now the MRC researchers have developed a model in which early human foetal testis development can be studied and manipulated experimentally to establish once and for all if exposure to environmental chemicals is a likely culprit.

Prof Sharpe's team has grafted testis tissue from aborted foetuses under the skin of mice. The germ cells in the testes are at the critical stage when any faults in their development can result in changes which make them pre-cancerous.

The researchers will expose the mice to phthalates or other environmental chemicals to see if this induces changes in the foetal germ cells that would predispose them to develop into a cancer.

Prof Sharpe said: "We are choosing to study phthalates first for several reasons, because we know that in the test-tube they can affect foetal human germ cells. They are also the most ubiquitous of environmental chemicals. We are all exposed to them."

Phthalates are used to make plastic flexible, and so can be found in carpets, wall boards, car upholstery and fittings and certain cosmetics and pharmaceutical drugs.

However, Prof Sharpe said that there was uncertainty about whether phthalate effects on the foetus in animal models were relevant to humans.

He said: "This is one of the critical unresolved questions as to whether phthalates pose a risk to human health or not.

"It's a huge industry. These compounds are literally part of the fabric of our modern society so they cannot easily be banned or removed without having widespread effects on everyday life. We need to know for sure if these compounds are harmful or not. The hope is that our studies can resolve this one way or another."

The researchers say that if phthalates do cause effects on human foetal germ cells they could know within a year. If the chemicals are not responsible it could take much longer to conclusively disprove any link.