"All Canadians intuitively know diesel exhaust is bad," said Jacqueline Sharp, the report's author. "It's incredibly damaging to human health. We're showing just how dangerous it really is."

People in certain groups are particularly at risk, since they are exposed to higher levels of DPM, the study found.

Diesel bus mechanics, people operating and driving trucks, heavy equipment and tractors, and those in other highly exposed occupations faced an average 33 to 47 percent greater risk of developing lung cancer because of their exposure to DPM at work.

Also, children riding on diesel school buses are exposed to levels of DPM that, over a lifetime, would lead to an excess cancer rate of up to one in 256.

"Children are at greater risk since they breathe proportionately more air than adults, spend more time outside, etc.," said Sharp. "If there's any group who shouldn't be exposed to higher levels of DPM, it's kids at this vulnerable time in their life."

Those living near high-volume highways and warehouse distribution operations also had elevated cancer risks.

Though diesel engines emit many dangerous air contaminants, DPM is the most harmful component of diesel exhaust, explained Sharp. The tiny particles are inhaled deep into the lungs and can cause many negative health impacts in addition to cancer.

The report found exposure to DPM causes an estimated 800 non-cancer premature deaths, tens of thousands of asthma attacks, and hundreds of bronchitis hospital admissions each year in Canada.

Air pollution does cause several thousand premature deaths each year, agreed Dr. Ling Liu, senior evaluator for the Air Health Effects Division of Healthy Environment and Consumer Safety Branch, Health Canada.

"But it's difficult to determine the number of deaths related to DPM," she said. "The science still isn't mature enough to separate the effect of diesel emissions from other air pollutants."

Health Canada conducted a workshop last year to examine research strategies for evaluating diesel exhaust's health effects and is currently analyzing the health impacts of alternative fuels and new formulations of existing fuels. They are also working with the New Brunswick Lung Association to look at ways to reduce children's exposure to diesel exhaust on school buses.

Meanwhile, the Federal government has adopted regulations to help clean the air -- new on-road diesel engines must be cleaned up by 2010, and low-sulfur diesel fuel will be required in Canada by 2006, said Sharp.

"We're proposing mandatory retrofitting of existing diesel vehicles with particulate filters, since these regulations don't do anything for older vehicles," she added. "The DPM regulations also don't apply to off-road diesel vehicles. We should start regulating emissions from these vehicles as strictly as we will be for on-road diesel vehicles."

The report also recommends municipal governments prohibit diesel vehicles from idling when parked and that they restrict access by heavy-duty diesel vehicles into city centers.