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Other experts on mesothelioma and mining said that it is extremely difficult to reconstruct exposures that occur over a lifetime.
“It’s not that taconite is not indictable,’’ said Dr. Michael Harbut, an expert on mining-related mesothelioma at Wayne State University in Detroit. “But it’s so hard to separate out the exposures.”
Nonetheless, the research is an important advance, said Christopher Weis, an expert on asbestos and mesothelioma at the National Institutes of Health.
“Dr. Mandel and his team have now confirmed what many have suspected for decades,” he said. “There is a clear relationship between exposure to taconite dust and mesothelioma in humans.”
Moreover, Weis said their future research could play an important part in exposing the role that other, shorter mineral fibers play in lung diseases, which might show that the risks for mesothelioma come from more than just the long fibers typical of asbestos.
“We’ve long suspected that those fragments contribute significantly to lung disease,” he said.
Risk limited to workers
Other findings in the multipart study suggested that spouses of workers and others in the community don’t face an increased risk of diseases. Researchers also said that occupational exposure to dust in taconite operations is generally within safe limits. Air tests for fibers in Iron Range communities found no excessive dust, and no sign of asbestos particles at all.
One major part of the study reconstructed historic exposure to airborne mineral fibers back to the 1960s. This was necessary because mesothelioma can take 30 or 40 years to develop.
From that, researchers concluded that victims of the rare cancer were more likely to have had higher exposures to longer, needle-like fibers including asbestos and non-asbestos rock fragments such as those produced by crushing ore. But researchers reached no precise conclusions about it.
“It’s not a huge risk, but it is a risk potentially associated with this exposure,” said Bruce Alexander, a professor of environmental health at the university.
The study also found that asbestos-related cancers struck all across the Iron Range, and were not concentrated in some parts as some miners have suspected.
Mandel said additional findings will be presented in one or two future meetings. A report on the current phase is expected to be published in days, with a final report later this year. Researchers also are planning continued research, and have applied for more than $2 million in federal and foundation grants.