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Environmental Health Division
Crystalline Silica in Air & Water, and Health Effects
Crystalline silica is a substance of concern for human health. Dust sized silica particles, invisible to the naked eye, are generated during a variety of activities and can be breathed into the body where they reach deep into the lungs. Once in the lungs, these particles can be coughed up, or pass from the lungs to other organs in the body through the blood stream, or stay stuck in the lungs. Breathing crystalline silica repeatedly over many years is a well-known cause of health problems.
Silica is a "building block" material that forms rocks, soil, sand, and other parts of the earth. A large amount of the earth is made up of silica. Silica occurs in either a crystalline or an amorphous structure. Over many years, silica in the soil can form into crystalline silica due to natural heat and pressure. Crystalline silica is very commonly found throughout the Midwest, and is more toxic to human health than amorphous silica.
Many industrial and commercial processes require crystalline silica. Some of the more notable uses for crystalline silica include glassmaking, road-building, molds for molten metals poured at foundries, hydraulic fracturing, or "fracking," for oil and gas production, water filtration, and even electronics. Crystalline silica can be released into the air from cutting, grinding, drilling, crushing, sanding, or breaking apart many different materials. Silica is a well-known occupational hazard and has also been recently examined for its environmental concentrations near silica sand mines and transport terminals.
Disease risk is related to both the levels and duration of crystalline silica exposure. The onset of disease may occur long after the exposure has stopped. Silicosis, lung cancer, chronic bronchitis, and several autoimmune diseases have been linked to long term or very high exposures to crystalline silica.
Health effects of crystalline silica have been well studied in workers. Occupational exposures are associated with serious health effects at higher concentrations in the air, and new rules have recently been implemented to better control worker exposures.
We do not currently know what impacts silica has at lower concentrations such as those typically found in air. At this time, there is no evidence that exposure to low-levels of breathable crystalline silica in air has adverse health effects. This continues to be an area of on-going research.
A few years ago, concern mounted surrounding silica sand mining activities and the potential release of large amounts of crystalline silica into the air. In response, MDH developed a health-based guidance value for crystalline silica in the air and the Minnesota Pollution Control Agency (MPCA) received air quality monitoring data from silica sand facilities in Minnesota between 2012 and 2017. For more information, contact the MPCA at 651-296-6300 or 800-657-3864.
Water and Silica Sand Mining
Any mine may create a pathway for chemicals and/or bacteria to more easily reach the groundwater.
- The risks to drinking water depend on:
- How close the mining operations are to the upper surface of the groundwater
- The use of heavy equipment
- Leaks and spills of fuel, engine oil, or other chemicals
- Runoff from contaminant sources
- Waste illegally dumped in the mine
- Some frac sand mines (mines that extract silica sand to be used for hydraulic fracturing) use products called flocculants to remove silt and clay in the sand washing process. These products are generally considered to be environmentally safe; however, they often contain low concentrations of chemicals (acrylamide and DADMAC) that are of potential concern. The Minnesota Pollution Control Agency sets limits in the mine's permit for the amount of flocculants that can be used and MDH recommends monitoring of the groundwater at facilities where the chemicals are used to ensure safe drinking water levels are not exceeded.
- Groundwater near frac sand mines may become slightly more acidic (lower in pH). This may cause minerals (like iron and manganese) to more easily dissolve, which can cause water to have unpleasant taste and odor, and may cause staining. MDH recommends monitoring pH of groundwater near frac sand mining operations.
Mining can remove large volumes of groundwater and has the potential to impact nearby wells. Impacts could include the lowering of water levels, possibly even causing a nearby well to go dry.
- The Minnesota Department of Natural Resources reviews large water removal activities to ensure that groundwater use will not harm wells in the area.
- MDH evaluates whether there are any potential risks to community water supply wells.
- MDH recommends a number of actions to prevent or reduce the potential for pollutants to enter the groundwater and water quality monitoring to protect nearby drinking water wells.
For more information, see: Wellhead Protection Issues Related to Mining Activities (PDF).
In 2013, legislation was passed to update environmental review rules, provide technical assistance, and develop model standards and criteria to support local units of government as they consider permits for silica sand mining, processing, and transportation in Minnesota. For more information, see the Minnesota Environmental Quality Board's website Silica Sand Projects.
MDH was directed to adopt an air quality health-based value for silica sand (See: Chapter 114, Article 4, Section 105 (c)). MDH completed a review of breathable (respirable) crystalline silica and released an air quality chronic health-based value (HBV) of 3 micrograms per cubic meter (µg/m3) in July 2013. MDH developed this guidance because there are no federal or state guidelines or standards for respirable crystalline silica in ambient air.
The focus of MDH's health-based guidance is on crystalline silica that is found in the air, and may be breathed into the lungs. Crystalline silica is toxic to humans when inhaled because of how it damages tissues in the lungs. Crystalline silica in other places in the environment, such as surface water or groundwater, is not a concern for human health because it is not breathed in from these sources.
Guidance values already exist for occupational exposures to breathable silica particles in the workplace. These guidance values are based on workplace silica exposures that took place over many decades. MDH used these studies to determine a level of silica in air that would not be expected to harm human health based on current scientific understanding. The 3 µg/m3 chronic HBV is many times lower than occupational guidelines or standards due to adjustments for continuous exposure and consideration of uncertainty factors to protect sensitive subpopulations in the general population. The HBV protects even the most sensitive people exposed to crystalline silica at any time during their life.
Sufficient data is not available to support development of quantitative health-based guidance for shorter duration exposures (1 - 30 days) to respirable crystalline silica. Extremely high levels of respirable crystalline silica are needed to cause short-term health effects in occupationally-exposed individuals and are far higher than what the general public would be expected to encounter in ambient air. Existing ambient air standards for particulate matter (which includes crystalline silica) provide protection against health effects in these short-term exposure timeframes.
The concentration of breathable crystalline silica in air can vary considerably from day to day. Air monitoring may show that values are greater than 3 µg/m3 on occasion. Daily or weekly values greater than 3 µg/m3 are not cause for concern. The health-based value is a yearly average concentration because long term exposure to crystalline silica is the primary health risk.
For technical information, refer to the Crystalline Silica Toxicological Summary Sheet (PDF)
Addressing Community Concerns: Health Impact Assessment
Community concerns related to general mining activities include increased traffic,noise, and risk of accidents. Health Impact Assessment (HIA) is a process that could lead to a more complete evaluation of all of the risks associated with the frac sand mining process.
Crystalline Silica Toxicological Summary Sheet (PDF)
A summary of health based values for crystalline silica in ambient air.
Wellhead Protection Issues Related to Mining Activities (PDF)
Guidance for revising local government land use comprehensive plans, rules or regulations as they may apply to aggregate mining in drinking water supply management areas in Minnesota.
The Minnesota Environmental Quality Board is a resource for coordinating and connecting state agencies that work on issues related to Silica Sand Mining in Minnesota.
Particulate Matter (PM) Pollution
The US Environmental Protection Agency provides further information about particulate matter—like crystalline silica.
The Minnesota Pollution Control Agency activities related to silica sand mining.
The Minnesota Department of Natural Resources provides addition information about silica sand projects and silica sand mining.