In December 2014, miners, retired miners, union officials, local leaders and industry representatives gathered at the Hibbing Memorial Building to hear the final report on a $5M multi-year study of taconite dust and mesothelioma. (Star Tribune/The Minnesota Star Tribune)

Minnesota health researchers say a rare, deadly cancer has struck 21 additional Iron Range miners, making a total of 101 workers afflicted in the state's iron ore industry.

The victims, most of whom have died, suffered from a cancer called mesothelioma that affects the lining of the lungs and other organs. It is linked to exposure to asbestos, and research has shown that Minnesota taconite workers get the disease at 2.4 times the rate expected under normal circumstances.

The Minnesota Department of Health findings released Tuesday add to the evidence that inhaling mine dust can trigger illness decades after exposure. Mesothelioma takes 30 years or more to develop, and is almost always fatal even with improved treatment.

"We know that mesothelioma is a horrible disease," said Health Commissioner Ed Ehlinger.

But Ehelinger, on a conference call with reporters, said the uptick in cases isn't happening in northern Minnesota's general population. The stricken miners likely inhaled commercial asbestos on the job decades ago before the health threat became clear in the 1960s and early 1970s, he said.

"I don't think there is any reason to panic at this point in time," the commissioner added.

"These are newly identified people whose disease after many years … came to a point where it could be clinically diagnosed."

At least 18 of the newly identified victims have died, as have all 80 of the earlier-identified miners, the department said.

University of Minnesota researchers have linked mining dust exposure to scarring of the lungs and higher rates of mesothelioma. But commercial asbestos, which once was used in the taconite industry, remains a prime suspect. All of the victims are men, and women in the region have lower-than-expected mesothelioma rates, the department said.

Dave Trach, who retired from the LTV mine in Hoyt Lakes in 1996, said he was saddened but not surprised to hear that more miners have died of the rare cancer. He said the tally of mesothelioma cases doesn't count the many miners who got sick or died from other dust-related ailments.

"The science goes way over my head, but there is a problem here," said Trach, 80, who coordinates a United Steelworkers retiree group. "When this comes out that there's 21 more, it is bound to be on everybody's mind that, 'Maybe I will have a problem in later years.' "

Tracking miners since 2003

The Health Department has done periodic analyses of miners with mesothelioma since 2003, using the state's cancer-tracking system. New mesothelioma cases are checked against data on 69,000 miners going back to the 1930s. Nearly 4,000 workers now are employed in Minnesota iron mining.

A weakness of the latest findings is that the employment database, assembled years ago by a university researcher, doesn't list miners hired after 1982. Worries about asbestos and cancer on the Iron Range emerged after 1973, when mineral fibers showed up in Lake Superior from tailings dumped by Reserve Mining Co. A scientific debate erupted over the potential risk of taconite fragments, which are shorter than needlelike fibers in commercial asbestos.

A 2003 study by the Health Department concluded that the first 17 miner mesothelioma cases were most likely caused by exposure to commercial asbestos. The Legislature in 2007 appropriated $5 million for an in-depth study by the University of Minnesota.

Although the university research team linked dust exposure in miners to disease, the study didn't explicitly associate short taconite fibers with mesothelioma. A key problem is that researchers lack data on how much commercial asbestos floated in the air decades ago at eight current and former mining operations.

"The most difficult thing in this whole project has been that commercial asbestos is far and away the most likely culprit for these mesothelioma," Dr. Jeffrey Mandel, a U epidemiologist who headed the six-year study, said in an interview Tuesday. "It is one exposure area where we don't have any measured information. We will never have that. These exposures took place in the 1950s and '60s."

Mandel said the discovery of 21 additional cases among miners doesn't change the U researchers' findings released in December. He said U scientists, led by Prof. Gurumurthy Ramachandran, already had plans to more closely analyze mineral fibers collected at mining operations to see if exposure to shorter taconite fibers is linked to disease.

David Shaffer • 612-673-7090 • @ShafferStrib

A 240-ton capacity production truck drives out of an open pit mine with a load of taconite heading to the Hibbing Taconite Co. pellet manufacturing plant. (Ariana Lindquist/Bloomberg/The Minnesota Star Tribune)