University of Minnesota researcher Bruce Alexander studied 3M employees who worked at the company's Cottage Grove plant in the years from 1943 to 1997. Nearly 4,000 employees were included in his study.
3M manufactured stain resistant products, like Scotchgard, for decades at the plant. PFOA was a part of the process. The company phased out those operations in 2002.
Alexander divided the workers into three groups -- those with definite exposure to PFOA, those with probable exposure to the chemical and those who weren't exposed.
He found that the group with the highest exposure to the compound had twice as many deaths from prostate cancer and stroke than employees who weren't exposed to PFOA.
“We spent a lot of time trying to figure out if we'd missed something, done something wrong. The results were there, and they're not that clear.”Researcher Bruce Alexander
That difference would seem to imply that PFOA exposure contributes to those diseases. But it's not that simple.
Alexander says his data could be skewed by the fact that the non-exposed workers had extremely low rates of both conditions compared to the statewide average. He says that factor alone makes his results very difficult to interpret.
"We spent a lot of time trying to figure out if we'd missed something, done something wrong. It was just very confusing results," Alexander said. "And in the end the results were there, and they're not that clear. And so we just have to move forward and think of better ways to look at it."
3M funded the U of M study. The company doesn't question Alexander's findings, spokesman Bill Nelson says. In fact, the company believes the findings prove that PFOA doesn't cause any harmful health effects in humans, because overall the 3M death rates were no different than the rest of the state's death rates.
As for the differences found within the company workers, Nelson attributes it to the extremely small number of deaths that were analyzed.
"There's a statistical anomaly here that was driven by the unusually low number of prostate cancer deaths among people who never worked in the chemical production area," Nelson said.
3M intends to continue working with Alexander to learn more about employees exposed to PFOA, Nelson says.
The company thinks it would be more useful to look at current disease rates rather than death rates, since death certificates don't contain important information about employee lifestyles and family disease history, he says.
The Minnesota Department of Health is reviewing the 3M worker study. Department spokesman Doug Schultz says despite the study's limitations, it is helpful to agency scientists.
"We look at studies in workers as useful for identifying potential areas of concern, because workers are more likely to be vastly more exposed to hazardous substances, whatever it might be. So if you're going to see health impacts, you're going to see them show up in worker populations."
But Schultz agrees the study inspires more questions than answers. He also says the findings probably have very little meaning for east metro residents who have been exposed to PFOA in their drinking water.
Residents' exposure to the chemical is dramatically lower than 3M workers in the study. It wouldn't be appropriate to draw any parallels between the study's findings and health risks in the community, Schultz says.