The study led by Jyotsna Jagai, an environmental health researcher at the University of Illinois, Chicago, has found that counties across the US with poor environmental quality had on average 39 more cases of cancer per 100,000 people than counties with high environmental quality.

Counties with the poorest environmental quality - measured through air, water and land - had on average the highest numbers of new cancers per year, according to the study published today in the research journal Cancer. "Our study is the first we are aware of to address the impact of cumulative environmental exposures on cancer incidence," Jagai, a research assistant professor at the university, said in a release.

"Most research has focused on single factors such as air pollution or toxins in water. But these single factors don't paint the full picture of what (people are) exposed to in (their) environment - and may not be as helpful in predicting cancer risk, which is (influenced) by multiple factors including the air you breathe, the water you drink, the neighbourhood you live in and your exposure to myriad toxins, chemicals and pollutants."

For their study, Jagai and her colleagues used the US Environmental Protection Agency's environmental quality index and the US National Cancer Institute's data on cancers available for 85 per cent of America's 3,142 counties.

They found that high levels of air pollution and poor quality of built environment such as the presence of major highways were most strongly associated with the incidence of cancer, but water quality and land pollution had no measurable effects.

Breast and prostate cancers showed the strongest association with the environmental quality. Research studies in the past have shown that a person's genetic makeup can only account for about half of cancers and exposure to environmental toxins and lifestyle factors also play a role in triggering various cancers.

Earlier studies have hinted that air pollution might influence the risk of breast cancer. Scientists at McGill University in Canada had seven years ago used air pollution maps of nitrogen dioxide - a byproduct of vehicular traffic - to detect a link to postmenopausal breast cancer. Their studies confined to the city of Montreal found that the risk of postmenopausal breast cancer increased 25 per cent with every five parts per billion increase in nitrogen dioxide.

Oncologists say Indian research institutions should launch similar studies. "We've suspected for long that prolonged exposure to chemical carcinogens may contribute to some cancers," said Pramod Jhulka, a senior consultant oncologist formerly with AIIMS, New Delhi. Such studies, he said, will help identify people at risk and allow individuals and government departments to take steps to reduce exposure to pollutants.