The ballpark, one of two in this town of about 700 people, is covered with crushed gravel containing erionite, a mineral found in the chalky white rock mined from the nearby Killdeer Mountains.
The rock, used for decades on everything from gravel roads to flower beds, contains fibers that can collect in the lungs of people who breathe it, health officials say.
Steve Way, a federal Environmental Protection Agency coordinator, said studies have shown that erionite causes cancer in lab rats, though the mineral is not regulated by his agency.
Erionite is found in at least a dozen states in the West, but Way said he did not know of another area in the U.S. that uses it "at the same magnitude" as Dunn County.
The mineral also has been found in gravel mines in Stark and Slope counties, in southwestern North Dakota. Officials there also have been asked not to use the gravel.
"We definitely should be looking at this for health concerns," Way told a group of about 60 residents at a meeting Tuesday night in Killdeer.
Killdeer Mayor Dan Dolechek said the ballpark was shuttered as a precaution, and the county voluntarily quit using gravel from the Killdeer Mountains until studies are completed. But many residents are more worried about road maintenance than the risk of cancer from the gravel.
State Rep. Shirley Meyer told federal and state officials at the meeting that Dunn County now will have to look outside its borders for gravel, a potentially costly change.
"It seems to me like you're making a mountain out of a molehill with what little data you have," Meyer told EPA and state officials. "The taxpayers in this county are having a tough time trying to swallow this."
Federal and state officials have been testing rocks and airborne samples from Dunn County over the past two years. But they say more tests, including tests on humans, are needed.
The EPA said it wants to test local residents who have had long-term exposure to erionite, and is looking for volunteers. Way said testing would continue through the spring, with results of the study completed in about 18 months.
"I'm 80 years old and it hasn't killed me yet," said Milton Johnson, who ranches in the Killdeer Mountains. "They can test my lungs if they want
- I've been breathing it all my life."
Gary Jepson, another rancher in the area, called the worries over erionite "one of those sky-is-falling kind of deals."
