University of Minnesota researchers on Friday release findings of their study into possible links between asbestos exposure in taconite mines on the Iron Range and a deadly disease called mesothelioma. Eighty former Minnesota miners have died from the rare cancer, which attacks the lining of the lungs.
The goal of the five-year study is to determine whether exposure to dust in the mines and processing plants makes workers more vulnerable to mesothelioma, and to other respiratory diseases.
The suspicion of such a link has been around for decades. Here is a timeline of developments in the investigation of mesothelioma and its relationship to taconite mining.
1973: "Asbestos-like fibers" are found in waste rock dumped by Reserve Mining Co. into Lake Superior at Silver Bay. As a result, many Duluth residents drink bottled water until a new filtration plant is built. A landmark court case forces Reserve to dump waste rock on land.
1985: A radiologist in Virginia, Minn., reports an excess of lung abnormalities on patients' x-rays.
1997: The Minnesota Department of Health (MDH) finds a 70 percent excess of mesothelioma in men in northeastern Minnesota, which is 39 cases. Some are attributed to occupational exposures at a Carlton County ceiling tile manufacturing facility.
1998: The Minnesota Legislature funds a new Occupational Respiratory Disease Information Center, to study mesothelioma and other respiratory diseases. The project is stripped of funding in 2002.
2003: An MDH study says the "most likely cause" for high levels of mesothelioma among taconite workers is exposure to commercial asbestos, rather than to fibers in the rock itself.
June 2007: MDH has determined a higher number of mesothelioma deaths -- 58 -- but it does not release the information for a year while it designs followup studies. The apparent secrecy leads to outrage among residents of the Iron Range, and legislators direct the University of Minnesota to take over the research.
August 2007: The University of Minnesota announces it will launch a new study to determine whether there is a link between taconite mining and mesothelioma.
October 2007: MDH Commissioner Dianne Mandernach resigns after being criticized for months over her handling of the mesothelioma data.
October 2011: The death toll from mesothelioma in Minnesota rises to 82, as MDH officials check records in other states for former Iron Range residents who moved out of Minnesota.
March, 2012: The mesothelioma death toll is revised downward to 80, as some cases reported earlier were duplicates.
April, 2013: The University of Minnesota reports its study results.