TORONTO — To most of us, the idea of handing over our toenail clippings in the cause of science might seem, well, a little weird.

But for researchers trying to figure out why Nova Scotians have the highest overall incidence of cancer in the country - including among the highest rates of bladder and kidney cancer - toenails are serious business.

That's because the nails can tell scientists whether residents have been exposed to arsenic, a naturally occurring metallic element found in rocks throughout the province that can find its way into drinking water.

Exposure to elevated levels of arsenic is known to cause a number of malignancies, chief among them kidney and bladder cancer, said Dr. Louise Parker of Dalhousie University, who has received a $575,000 grant from the Canadian Cancer Society to study the "body burden" of arsenic in 5,000 Nova Scotians.

Parker, a professor of community health and epidemiology, said the three-year study will analyze arsenic levels in toenail clippings from men and women aged 35 to 69 and in samples of tap water from their homes.

That data will be correlated with information on water quality and the underlying geology of the province's different areas.

"What that will tell us is the extent to which the very high rates of cancer observed in Nova Scotia, especially for bladder cancer and kidney cancer, how much of that high rate is due to the fact that people are being exposed to arsenic in the water that they drink."

When the colourless, tasteless substance enters the body through drinking water, most of it ends up getting filtered by the kidneys and bladder and eliminated through the urine. But some settles in the hair and nails, leaving behind a record of exposure, Parker said.

"Toenails and hair both have the advantage that they're with our bodies for quite a long time," she said Tuesday from Halifax. "And toenails, as with hair, gives us a window back in time, so that we can look back to see what the exposure to arsenic has been in maybe the last six to nine months."

Toenail clippings are preferred to either hair or fingernail samples because they have usually had less exposure to other environmental factors, she added.

The study, which has already recruited about 1,000 participants, is designed to examine the potential link between cancer and low to moderate amounts of arsenic in the body and drinking water.

The researchers plan to focus on arsenic concentrations five to six times the acceptable limit as laid out under national guidelines.

Health Canada says arsenic levels in drinking water should not exceed 10 micrograms per litre, yet tests have shown that some Nova Scotia wells contain 70 times that amount.

"We know very high levels of arsenic cause cancer and cause a very high increased risk," Parker said. "The relationship between arsenic and cancer at lower levels is less well understood and that's where our study's going to be making that contribution."

Dr. Prithwish De, an epidemiologist with the Canadian Cancer Society, said Nova Scotia's incidence rates for bladder and kidney cancer are well above the national averages.

The national average for bladder cancer in men is 27 cases per 100,000, but 37 per 100,000 in Nova Scotia. For kidney cancer, the national rate is 14 per 100,000, a rate that jumps to 21 in the province.

For women, the national rate per 100,000 is seven for bladder cancer and eight for kidney cancer, compared with nine and 11 respectively in Nova Scotia.

"Overall, if we take all cancers combined, the rates are highest in Nova Scotia compared to other provinces," De said.

"We don't know exactly what the causes might be. There could be differing causes and there could be overlapping causes as well," he explained. "And that's one of the reasons we're doing this study with arsenic exposure in Nova Scotia, to find out how much of that actually contributes to the bladder cancer and kidney cancer rates."

Depending on the results, the study could have an impact on how drinking water is treated in the province - 45 per cent comes from wells - and whether changes will be needed to guidelines governing acceptable arsenic levels.

De said the study not only applies to Nova Scotia, but also to other areas of the country with a similar environmental or geological status.

The arsenic research is part of the much larger Atlantic Partnership for Tomorrow's Health (Atlantic PATH) study, which will follow 30,000 men and women in the four East Coast provinces for 30 years to determine why some people develop cancer and others don't.

Parker said her study is aimed at better understanding how excess arsenic in drinking water can lead to increased cancer cases, so steps can be taken by the public, government and public health and environmental agencies to reduce arsenic in drinking water supplies.

"Cancer is a big problem," she said. "We want to find out more about what causes it so that we can reduce the burden of cancer in Atlantic Canada."