Experts comment on airborne crystalline silica

By Molly Moser

There was standing room only at the April 28 meeting of the frac sand mining impact study group, where special guests Dr. Patrick O’Shaughnessy and David Osterberg of the University of Iowa presented findings on the effects of silica sand on air quality. Many Guttenberg residents attended the meeting, held in Elkader, alongside landowners and neighbors of the potential future underground mines.

After an introduction by Osterberg, whose work as a clinical professor in the Department of Occupational and Environmental Health encompasses public policy in the fields of both environmental health and environmental quality, O’Shaughnessy shed light on the terminology and research surrounding airborne silica sand.

O’Shaughnessy spent eight years as a construction worker before furthering his education in civil and environmental engineering. He’s now a professor in the University of Iowa College of Public Health Department of Occupational and Environmental Health and directs the UI Heartland Center for Occupational Health and Safety. 

“There are going to be emissions out of mining sand. The wind blows, it kicks up the sand, that’s inevitable,” O’Shaughnessy began. “We’re concerned about our health and trying to decide whether this is going to be an issue or not.” The professor explained that size determines whether a particle is inhalable, and if it is, where it ends up in the lungs. 

“Little particles get in, and some get breathed back out again – you’re doing that right now,” he said, using sand at the beach as an example of a particle too large to be inhaled. O’Shaughnessy used the width of a human hair to describe a particle size 100 microns (a micron is one-millionth of a meter), which is the largest particle diameter that can even enter the airway via mouth or nose. A particle of 50 microns is small enough to actually enter human lungs, and particles of 10 microns (invisible to the naked eye) are respirable, or small enough to reach the very bottom of the lungs and cause pulmonary problems. Crystalline silica particles can cause silicosis, fibrosis, or lung cancer. 

While there are no EPA standards for silica sand in ambient air, the EPA does regulate particulate matter in the air to 10 microns in size. This standard assumes that every person, whether young, old, sick, or pregnant, can handle 150 micrograms per cubic meter of 10 micron sized particles or smaller day in and day out. Minnesota and California have a standard for silica in the air, set at three micrograms per cubic meter, to protect the most at-risk individuals. “Figures for people in the workplace are typically 100 to 1000 times higher than they are for the ambient air, because workers are only in there for eight hours a day and are assumed to be among the fittest individuals in our country,” said O’Shaughnessy. “Worker exposure is controlled and well documented. Community exposure is less clear.”

To decipher the risk of community exposure to crystalline silica, O’Shaughnessy referenced several studies: One on the composition of sand with the same geology as in Clayton County, and others on silica found in the air near two different frac sand mines.

In the first study, both unprocessed sand from a mine and processed frac sand (called proppant) were brought to a laboratory and tested for particle size and composition. “Proppant sand is cleaned and sieved of large and small particles, so it shouldn’t be much of a hazard in terms of getting small particles. It’s the raw sand from the mine that tends to be a concern,” said O’Shaughnessy.

The proppant contains silicon dioxide, which is the cause of silicosis; however unprocessed sand is more likely small enough to be respirable. That’s the stuff that may be blowing around in the wind. Rock samples from this particular mine showed that quarried sand is 10-14 percent respirable crystalline silica while proppant is 17-25 percent respirable silica. “If I’m worried about respirable particles out of this mine, they have to come from some sort of process that takes a rock and turns it into powder so fine it’ll end up deep in my lungs,” said the professor.

An EPA model of particulate dispersion on a mine about six kilometers from New Auburn, Wis., kept track of meteorological data each hour for five years to determine the highest possible concentration of wind-blown particulate in areas such as haul roads, open mines, and at property lines. “Haul roads have a really high impact and showed up as higher concentrations,” explained O’Shaughnessy. Even so, the average daily particulate was 40-50 in comparison with the 150 EPA standard. “A smaller part near the property line was starting to get close to the standard. So bottom line, according to this assessment, this mine was not contributing to particulate matter in the area with relation to the standard,” he told the committee.

O’Shaughnessy did note that the daily averaging of the measurement could lower those figures. At six sites less than a half mile from an active open pit mine, scientists found values spiking as high as 480 – but the average over 24 hours in the same sites could be as low as four. “If silica makes up 10 percent of that we’re down to 48 micrograms per meter cubed, which is way higher than the 4-micron California level over the short-term spike,” said the professor. 

“If you’re the person with your house in the plume that might be getting some of this, then I can understand the concern. As a scientist, with the evidence we know of (that is not absolutely specific to this case,) primarily the risk seems to be low,” said O’Shaughnessy.

The Wisconsin DNR is conducting 24-hour measurements in the west-central part of the state, home to 18 of the largest sand mines in the state. “They have taken over 2000 measurements to date, and 99% have been 50 micrograms or lower,” he explained, again comparing to the 150 EPA standard. 

O’Shaughnessy concluded that alarm is not necessary over air quality for those living near frac sand mines. He suggested judiciously placed ventilation shafts with appropriate setbacks from frequently used areas, purposeful modeling ahead of time and careful monitoring as mining progresses. “In Wisconsin, they force mines to hire a consultant firm that does this at their own expense,” said O’Shaughnessy. “That would be something to consider.”

“Every situation is different. I’ve dealt with enough industries in my business to know that there are good apples and bad apples in every industry, and it behooves all of you to know who you’re dealing with,” the professor finished. “Is this someone with flagrant violations constantly or someone typically with a good sense of safety for their workers, environmental consciousness, and who wants to be a good neighbor?”