The study examined death records among the 4,000 workers at the Cottage Grove plant from 1943 to 1997.
Workers who were exposed to a chemical called PFOA at 3M's factory in Cottage Grove died of stroke and prostate cancer at higher rates than other workers at the plant, according to a new industry-funded study.
The study of nearly 4,000 people who worked at the plant from 1943 to 1997 found elevated stroke and prostate cancer death rates among those exposed to the chemical, which was used until 2000 for nonstick coatings and other products.
Workers with the highest exposures were twice as likely to die of prostate cancer and stroke than colleagues with little or no exposure to the chemical, the study found.
The death rates from those diseases among all workers at that plant were similar to those of the general population, leading 3M officials to call the difference a statistical anomaly.
"Nothing in this study changes our conclusion that there are no adverse health effects from PFOA," 3M spokesman Bill Nelson said Wednesday.
3M manufactured PFOA from 1947 to 2000 at its Cottage Grove plant and phased out production by 2002. It was used for nonstick cookware, stain-repellent coatings and dozens of other products.
Starting in the 1970s, scientists became concerned about the tendency of PFOA -- perfluorooctanoic acid -- and other perfluorochemicals to accumulate in people's blood. 3M started monitoring the health of its employees who worked with the chemical, and in 1980 undertook the first occupational mortality study of its workers.
Although PFOA has been shown to cause liver, pancreatic and testicular cancer in laboratory animals, 3M has maintained that studies of its workers show no health problems.
Dated August 2007
The latest study was financed by 3M and conducted by Bruce Alexander, a University of Minnesota epidemiologist. Although dated August 2007, the study wasn't placed in a public file with the Environmental Protection Agency until last month.
Alexander did not respond to several requests for comment, and Nelson said Alexander would not talk about the study publicly because it has not been peer-reviewed by scientists and published in a scientific journal.
The study of Cottage Grove workers included nearly 4,000 people who worked at the plant for at least a year any time from 1943 until the end of 1997. About 12 percent of them had definite exposure to the chemical, which can be absorbed through "inhalation, ingestion, and dermal contact," the study said. The rest were evenly divided between those who probably had some exposure to it, and those who had no exposure.
Researchers studied death certificates for workers through Dec. 31, 2002.
"A high or moderate exposure work history, compared to only working in low exposure jobs, was associated with an increased risk for [stroke] and prostate cancer," it concluded.
Nelson said that differences between the employee groups led to "skewed ratios," and that the important thing is that overall results for employees show no higher cancer risks than for the state's population.
However, the researchers also noted that mortality studies "miss the cases that do not result in death," or that for some reason "may not be listed as contributing causes of death on a death certificate."
They mentioned that the association between prostate cancer and exposure to PFOA was similar to research conducted by others in 1993. That study found that those who worked for 10 years in the chemical division at the Cottage Grove plant had three times more prostate cancer deaths than those who worked for a decade in nonchemical areas there.
Nelson said that the 1993 research was a "flawed study" because it incorrectly characterized some of the exposed workers, and that the research was disproved by a 2002 study. He agreed with the latest study's findings that more analysis is needed, now that the mortality study is done.
"Instead of death rates, we plan to look at the incidence of prostate cancer," Nelson said. "That would be the next step."
Informing the public
John Linc Stine, environmental health division director for the Minnesota Department of Health, said state officials received the latest 3M study of its Cottage Grove workers Wednesday and have not had time to review it.
Stine said it's important that 3M has done the work, and that the public will want to know what it means. PFOA is more than merely a concern for 3M workers: Community wells in Oakdale and private wells in Lake Elmo were contaminated with the chemical, likely from wastes that 3M sent to dumps in those areas decades ago. The company has paid for Oakdale to install a huge water filtration system to remove all perfluorochemicals, and for more than 200 private wells in Lake Elmo to be hooked up to untainted city water.
"It's likely that people exposed to this chemical in drinking water will want to know if they are at elevated levels for heart disease or stroke or cancer," Stine said. "I can't answer those questions now but we will look at the study and try to put it in context for the communities."
Information about the research comes just a week after state health officials relaxed a limit for a different perfluorochemical, PFBA, that has been detected in groundwater beneath much of the east metro area. Water supplies in those communities are no longer considered to be contaminated except for a few private households, which continue to use bottled water or filtering systems.
Tom Meersman • 612-673-7388