EXPOSURE to everyday environmental pollution could be a factor in the rising rates of breast cancer, new research suggests.

A study carried out at Aberdeen University found evidence that subjecting female sheep to a "real-life" cocktail of chemicals triggered abnormalities in the mammary glands, including in some types of proteins associated with breast cancer in humans.

The researchers, who admit they were surprised by the effects shown, say that further work should now be carried out to see whether environmental pollution could be a factor in the steady increase in rates of breast cancer among women in the past few decades.

Breast cancer is the most common cancer among women in the UK, with more than 41,000 new cases being diagnosed each year.

The research, which is being unveiled at the Fertility 2007 conference in York this week, involved grazing sheep for up to five years on a field treated with processed human sewage sludge, used to represent the everyday mix of chemicals present in the environment, such as pesticides and synthetic oestrogen, found in the contraceptive pill.

Dr Paul Fowler, senior lecturer in reproductive physiology at Aberdeen University, said the model of "real-life" exposure was a vital element of the work, instead of using extremely high doses of chemicals which are often used in other toxicology studies.

"A human being would be unlikely to receive those kind of doses unless they had an accident of some kind," he said. "We are really trying to determine the real-life situation."

Fowler said they had not expected to see any changes in the mammary glands of the pregnant ewes - who were compared with sheep grazed on land treated with a standard fertiliser - but cautioned that it still had to be established if these were long-term abnormalities. More work would also be needed, he said, to identify the potential chemicals or mix of chemicals that could be causing the changes.

"It would suggest that we should definitely look at whether there may be similar effects in the human," he added.

Professor Steven Heys, professor of surgical oncology at Aberdeen University and clinical collaborator on the research, said that the incidence of breast cancer was rising by 2% every year. "It is absolutely vital that we carry out research into various things in the environment," he added.

Environmental campaigners pointed out that previous studies had also linked the "chemical cocktail" present in modern lifestyles to diseases such as breast cancer and asthma.

Duncan McLaren, chief executive of Friends of the Earth Scotland, said: "While this latest study should help us to better understand how exposure to chemicals can impact on health, we already know enough to know that we should be taking steps to eliminate or replace the most problematic chemicals."

However, breast cancer charities cautioned that there is no "conclusive evidence" of a link between environmental pollutants and the disease.

Lorraine Dallas, assistant director of Breast Cancer Care Scotland, said more research was needed to determine whether there was link.

And Liz Baker, Cancer Research UK's science information officer, said the strongest risk factor for breast cancer in women is lifestyle changes, such as having fewer children later in life, breast-feeding less and drinking more alcohol.