After six years, a study investigating why Minnesota’s Iron Range taconite miners were at higher risks of developing deadly mesothelioma, lung cancer and heart disease unearthed few answers.
Preliminary 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.
Researchers on Monday released the final results of the taconite miners study and said they were unable to determine if the short, needle-like fibers found in the dust of crushed taconite increased the risk or if it stemmed from exposure to the longer, microscopic fibers 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 fiber types,” Mandel said. “All we can say is there is a relationship between fiber-like exposure and the mesothelioma, but we can’t break it down any further than that. If you had exposure to the longer fibers, you also had exposure to the shorter ones.”
The University of Minnesota School of Public Health and the University of Minnesota-Duluth Natural Resources Research Institute launched the Taconite Workers Health Study in 2008.
Mesothelioma is a rare, aggressive cancer caused primarily by exposure to asbestos.
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. Heart disease is much more common than either lung cancer or mesothelioma.
The study, which was not designed to research cardiovascular disease, recommended Iron Range communities and the mining companies increase their efforts to control risk factors like high blood pressure and smoking. The study found that almost two-thirds of all taconite miners were either current or former smokers.
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 fiber-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 fibers 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 minimize disease risk.”