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A pedestrian walks across a bridge above a main road on a day with high air pollution in Beijing, June 6, 2012.DAVID GRAY/Reuters

Diesel engine exhaust causes lung cancer in humans, international cancer experts declared Tuesday, meaning exposure could have serious health risks for the entire population.

The International Agency for Research on Cancer, an arm of the World Health Organization, assembled a panel of experts for a week-long meeting in Lyon, France, at the conclusion of which it was unanimously decided that diesel exhaust causes lung cancer.

"The scientific evidence was reviewed thoroughly," Christopher Portier, chairman of the IARC working group and director of the Agency for Toxic Substances and Disease Registry at the U.S. Department of Health and Human Services said in a conference call with reporters. "Diesel exhaust is a cause of lung cancer in human beings."

Diesel engine exhaust will be placed on IARC's "Group 1" list of known carcinogens, which includes asbestos, tobacco smoke, ultraviolet radiation and formaldehyde.

The panel also ruled that diesel exhaust possibly causes bladder cancer, while gasoline will continue to be listed in Group 2b, meaning it is possibly carcinogenic to humans.

Although most of the research has focused on the occupational risks of diesel exposure by miners, truckers or railway workers, toll booth operators and other workers, the panel concluded the evidence clearly shows the risks extend to anyone exposed to diesel exhaust.

"Large populations are exposed to diesel exhaust in everyday life, whether through their occupation or through the ambient air," the panel said in its decision, citing exposure from vehicles, diesel trains, ships and power generators.

Governments "have a valuable evidence-base on which to consider environmental standards for diesel exhaust emissions," the IARC panel said.

It has long been suspected that diesel exhaust was linked to an increased risk of cancer. Studies have suggested that workers with occupational exposure to diesel exhaust experience an increased rate of certain types of cancer. For instance, a 2010 study published in the American Journal of Respiratory and Critical Care Medicine found miners, railway workers and others with occupational exposure to high levels of diesel exhaust have a 31 per cent higher chance of developing lung cancer than those without regular exposure.

The IARC panel examined numerous studies that examined the link between diesel exhaust and cancer, with most of the research focusing on occupational sources of exposure.

But there is also limited evidence that exposure could lead to increased health risks in infants and children, such as cancer or asthma. Dr. Portier said some laboratory studies in animals have found an increased vulnerability to the hazards of diesel exhaust in the early stages of life.

The IARC panel acknowledged that it's unclear at what level exposure to diesel exhaust becomes dangerous.

Diesel exhaust contains a large number of small particles made up of many substances, including carbon and polycyclic aromatic hydrocarbons.

When people breathe in these particles, they may become lodged in the throat and lungs, which the IARC says can lead to an increased risk for lung cancer.

Diesel Technology Forum, a Washington, D.C.-based industry association, said major strides in recent years to dramatically reduce emissions and develop cleaner technology have greatly reduced any potential health threats from diesel exhaust.

"We're very confident where we are today, with the path of technology," said Allen Schaeffer, executive director of the group.

Canada has also introduced new measures in recent years to help reduce emissions from diesel fuel.

But the IARC's declaration that diesel exhaust is carcinogenic could increase pressure for further restrictions.

Gillian Bromfield, director of cancer control policy at the Canadian Cancer Society, said in a statement the IARC decision helps clarify the risks of diesel exhaust to certain workers, as well as to the population in general.

"It will be important to consider these findings in light of emission reduction programs, and for setting standards for workplace exposure levels in order to reduce, if not eliminate, exposure," the statement said.