A study investigating why Minnesota’s Iron Range taconite miners were at higher risks of developing mesothelioma and heart disease has revealed new answers.

Initial findings of the $4.9 million study showed a taconite miner’s risk of developing mesothelioma increased by 3 percent every year that miner spent working in an iron ore mine. Their rate of diagnosis also was three times that of the general Minnesota population.

The final results of the taconite miners study and said they were unable to determine if the short, needle-like fibres found in the dust of crushed taconite increased the risk or if it stemmed from exposure to the longer, microscopic fibres from commercial asbestos traditionally used in the taconite mining industry.

Jeffrey Mandel, University of Minnesota associate professor, epidemiologist and lead researcher on the project, explained the complexity of finding the cause to a group of miners, their families, state legislators and others.

“It’s really difficult to separate out the different fibre types,” Mandel said. “All we can say is there is a relationship between fibre-like exposure and the mesothelioma, but we can’t break it down any further than that. If you had exposure to the longer fibres, you also had exposure to the shorter ones.”

Significant higher-than-usual rates of mesothelioma among taconite miners a decade ago in the Iron Range region, located in northeast Minnesota, prompted the study that was commissioned by local lawmakers.

The study found that miners had a 3.3 per 1,000-person rate of mesothelioma by the time they reached age 80. The rate of mesothelioma for the general population of Minnesota was just 1.4 per 1,000, according to the study.

Only in recent years has commercial asbestos been removed from the mining operation. The long latency period (10-50 years) between exposure to asbestos and diagnosis of mesothelioma, made it impossible to determine what was causing the high incidence rates.

Researchers were surprised to also find a 30 percent higher rate of heart disease among miners than the general population in Minnesota, but could not pinpoint the exact cause.

While the number of years spent in the mines was directly correlated with the likelihood of mesothelioma, it was not the cause of elevated rates in lung cancer among miners, according to researchers.

“The lung cancers don’t appear to be related to those exposures [to the fibre-like materials],” Mandel said.

Miners with 21 years or more on the job were 60 percent more likely to have scarring on the pleural lining around the lungs, compared to those with less time in the industry. Pleural scarring is a potential warning sign of future mesothelioma.

The study was originally designed to determine specifically if taconite ore dust — and not asbestos — was causing the mesothelioma, but the findings never determined that. It did link dust from the mining industry to the asbestos-related disease.

The researchers strongly recommended all taconite industry workers wear respirator masks in dusty conditions to filter any possible fibres in the air. The authors also said the masks have been available to workers, but infrequently worn.

“By its nature, it’s a very dusty industry,” said Gurumurthy Ramachandran, professor at the Division of Environmental Health Sciences and one of the study’s authors. “Exposure avoidance is the most effective way to minimise disease risk.”

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