The silica data were released Thursday; particulate data were released previously.
The health implications of silica sand became a major issue a few years ago when a number of silica mines opened in Wisconsin. The area produces some of the world's best sand for hydraulic fracturing or fracking. Oil companies combine the sand with water and chemicals and inject it deep into the ground to free oil and natural gas trapped in rock.
Fracking has drawn criticism from some who say it has a negative impact at drilling sites and contribution to noise, air and water pollution.
But the Winona monitor found virtually no silica. Twice it detected silica at levels of about 0.4 micrograms per cubic meter; the federal limit is 3 micrograms cubic meter.
As a reference, the MPCA also put an air monitor at Stanton, which is between Cannon Falls and Northfield, "because it does not house silica sand-related facilities or transportation, but does have other sources of airborne silica such as unpaved roads and farm fields." That monitor detected silica nine times, with the highest level being about 0.8 micrograms per cubic meter.
"Airborne silica is a fairly ubiquitous pollutant and is not unique to silica sand mining and processing facilities," the MPCA report states.
The federal level is "set to protect against health effects associated with long-term exposure to respirable crystalline silica. This suggests that crystalline silica levels inWinona and Stanton are not contributing to chronic health risks," the report states. But it adds that a full year of data is needed to estimate the health risks.
The fine particulate levels detected by the monitor in Winona were similar to the levels of silica. In eight months of testing, fine particulate levels exceeded federal levels once when weather patterns trapped bad air throughout much of the Upper Midwest.