Working in a "toxic soup" of chemicals linked to certain occupations can double a woman's risk of developing breast cancer, research suggests.

High-risk jobs include those in agriculture, plastics, food packaging, metal manufacture and the bar and gambling industry, according to the findings.

Women employed for 10 years in some of these sectors had more than twice the normal chance of being diagnosed with breast cancer. For younger pre-menopausal women, working in factories producing plastic components for cars or tin cans increased the risk five-fold.

All these occupations involve exposure to potential carcinogens or "endocrine disrupter" chemicals that interfere with the body's natural hormone systems.

There is increasing evidence that even low-level exposure to endocrine disrupters over long periods of time can lead to changes that trigger cancer.

The study prompted a demand from the charity Breast Cancer UK for the Government to tighten chemical regulation.

Clare Dimmer, who chairs the charity, said: "This research reveals yet more evidence that our daily exposure to a cocktail of chemicals increases our vulnerability to diseases, such as breast cancer.

"This research has implications for everyone, not just those working in the industrial sector. We are all exposed to these cancer causing chemicals on a daily basis due to their use in a whole range of everyday products like food and drink packaging."

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Each year around 46,000 women in the UK develop breast cancer and more than 12,000 die from the disease.
British-led researchers conducting the international study looked at 1,006 women with breast cancer in Southern Ontario, Canada. They were compared with 1,147 randomly selected and matched women from the local community.

Information about participants' occupational and reproductive histories was collected through interviews and surveys.
The scientists assessed the impact on cancer risk of spending 10 years in different occupations, taking account of a five-year time lag between exposure and diagnosis.

Working in agriculture increased the risk by 34% overall, and as much as 74%. Being employed in the metal industry was associated with a 73% increase in risk. Jobs in plastics - especially in the automotive industry - bars and canning more than doubled the chances of developing breast cancer.

Commenting on the findings, published in the journal Environmental Health, senior author Professor Andrew Watterson, from the University of Stirling in Scotland, said: "What we do know about these industries is that they all use chemicals that are either category one or category two carcinogens (definitely or probably carcinogenic), and we also know there's a whole group of endocrine disrupters involved.

"Our line is that we need to be precautionary, because we're looking at a toxic soup in terms of exposure. There's a whole range of lifestyle factors and chemicals and other materials that can be interacting."

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Laboratory studies have come up with plausible mechanisms to explain how endocrine disrupters might contribute to cancer, he said.

"The literature is indicating that relatively low levels of these substances could be having an effect," Prof Watterson added.

Exposure to tobacco smoke may be one reason why bar staff and women working in the gambling industry are more likely to develop breast cancer, said the researchers.

Shift work and working at night, both of which are associated with raised breast cancer risk, may also be involved, said Prof Watterson.

See also: Living With Breast Cancer At 30: Laura Price's Diary

Ms Dimmer said Breast Cancer UK had long called for a ban on the use of one notorious endocrine disrupting chemical, bisphenol A (BPA), which is used to harden plastic and line tin cans.

The charity is asking members of the public to sign a petition calling on the Government to outlaw the use of BPA in the food and drink industry.

"It's time the UK Government stopped sweeping the evidence under the carpet and took positive steps to reduce our exposure to cancer causing chemicals, and to stop the rise in breast cancer, which has now reached near epidemic proportions," said Ms Dimmer.

Another breast cancer charity urged caution. Sally Greenbrook, senior policy officer at Breakthrough Breast Cancer, said: "No solid conclusions can be drawn from this research and there is little evidence to suggest that exposure to occupational chemicals increases breast cancer risk.

"This is a small study with some serious limitations, including making the assumption that women will recall specific details about their exposure to chemicals. We urge women who work in these industries not to worry.

"What we do know is that women can reduce their risk of breast cancer by limiting their alcohol intake, maintaining a healthy weight and increasing their physical activity."