Open train cars filled with sand have raised alarm in St. Paul's St. Anthony Park neighborhood, where some residents wonder if the silica that comprises 80 percent of the unprocessed sand is safe.

The cars, which often are parked in a rail yard sandwiched between homes and an industrial zone, are appearing on a more regular basis since an oil boom has increased the demand for the sand for its hydrofracking operations.

BNSF Railway Co., which transports the sand, and Minnesota Commercial Railway representatives said the trains are carrying wet "unprocessed raw sand" -- not pure frac sand -- and that it isn't a health risk. The concern, however, is that nearly all information about silica's health impact are derived from studies in the workplace, where it has been shown to cause cancer, and not of ambient exposure.

"We know it's [silica] not good for you," said Hillary Carpentar, a toxicologist with the Minnesota Department of Health. "It's a classic occupational toxin. I think the concern is that we just don't know" about casual exposure.

Frac sand gold rush

Hydrofracking has grown in recent years, spurring a frac sand gold rush in the Upper Midwest. Southeastern Minnesota and Wisconsin have become ideological and environmental battlegrounds as they become production hubs of the silica, which is as fine as stone-ground flour. The sand, water and chemicals are injected into the earth under high pressure to fracture rock layers to release petroleum.

Though railroad officials insist there is no health hazard, they, along with representatives of the Minnesota Pollution Control Agency will meet with residents Wednesday night.

"We've heard some seemingly contradictory information," said Lauren Fulner-Erickson, the District Council 12 community organizer. "We wanted to get everyone in the same room and make sure the facts are clear."

The controversy hit St. Paul about two months ago when residents of the area started noticing the open train cars and, some said, sand deposits on the Raymond Avenue bridge overlooking the rail yard.

"I'm concerned that they're hauling that stuff through the neighborhood," said Lisa Gunderson, who lives on a street that abuts the rail yard. "I just think that we need to be aware of potential health hazards."

Frac sand comes out of the ground mixed with clay, silt and other rock. It's loaded with moisture and commonly called "unprocessed raw sand" or "industrial silica sand." It has to be processed (washed and sorted for size) before it can be called frac sand.

Silica has been shown to cause cancer and other illnesses when regularly inhaled over long periods.

Dave Christianson, Minnesota Department of Transportation senior planner for rail and freight operations, said his office has received complaints from Winona to the metro area about sand dust blowing off open train cars, and gravel hitting cars. But, he said, they were unsubstantiated and vague.

"We haven't seen any significant dust production from those cars," Christianson said, adding that misinformation and controversy surrounding hydrofracking may be playing into public perception.

Christianson said he has not seen anything unusual at the rail yard in St. Anthony Park. (MnDOT does not have regulatory control of the railways.)

Both unprocessed sand and frac sand are transported across the state, where sand has been mined for multiple uses for more than a hundred years.

Frac sand is always moved in covered cars, said BNSF spokeswoman Amy McBeth, and unprocessed sand is transported wet in open cars.

"It makes any blow-off very unlikely," McBeth said. "Sand in many different shapes and forms have been hauled by the railroad for many years."

Risk of uncertainty

It's little comfort for people such as Jim Tittle, a St. Paul resident who shops in St. Anthony Park.

"The point isn't that we are certain that the dust will make people sick at this level of exposure," said Tittle, an activist who is making a documentary on the industry. "The point is that it has been proven that it can be dangerous, and no one has proven that this level of exposure is safe."

Minnesota Commercial Railway wrote a letter to the District Council saying that independent testing did not show any impact on air quality. McBeth said BNSF had separate tests conducted with similar results. Neither would provide details about how and when they were conducted.

Chao Xiong • 612-270-4708 Twitter: @ChaoStrib