WASHINGTON (AP) – new studies reveal a link between the exhaust of diesel engines and the risk of developing lung cancer.

Long is classified as probable carcinogen diesel exhaust. But a study by the National Institute of cancer tracked over 20 years to more than 12,000 workers in potash, lime and other non-metallic mineral mines, where used equipment with diesel fuel.

miners exposed to exhaust gas showed a risk of death by lung cancer three times higher than the less exposed, according to the study published Friday in the journal of the National Cancer Institute.

But even less exposed workers showed a 50% higher, according to the lead author, epidemiologist Debra Silverman risk.

“Our findings are important not only for the miners but also for the 1.4 million U.S. workers and 3 million European workers exposed to diesel exhaust and for worldwide urban populations,” wrote Silverman.

Said that the long-term exposure in cities of high pollution in China, Portugal and Mexico has similar effects to the miners with low exposure.

Dissemination of the findings was delayed by proceedings instituted by mining companies.

An industrial camera that did not participate in the trials said that the study covered companies that used outdated equipment, and pollution caused by today’s diesel engines is much lower.

“Manufacturers of engines and machinery diesel, fuel refiners and emissions control technology manufacturers have invested billions of dollars to develop and implement technologies that reduce emissions of engines now almost to zero to meet increasingly tougher clean air standards in United States and the world”, said Allen Schaeffer, the Agency non-profit Diesel Technology Forum.