DNR Releases Study on Silica Emissions

The DNR has released a study describing what is currently known about the sources, emissions, and health effects from exposure to crystalline and amorphous forms of silica. Interest in this substance has grown as mining for sand in western Wisconsin, one source of silica dust, has increased.

The report’s major findings regarding sources, health effects, monitoring, and regulation of ambient silica air emissions are listed below.

Sources

• Sources of crystalline silica are ubiquitous and include paved and unpaved roads, wind blown soil and agricultural activities (e.g., tilling and harvesting).
• Industrial sources of crystalline silica include construction, foundries, glass manufacturing, abrasive blasting or any industrial or commercial use of sand and quartz, and mining and rock crushing operations.

Health Effects

• Crystalline forms of silica (such as quartz) meet the definition of a known carcinogenic hazardous air pollutant (HAP)1 as defined in Wisconsin’s Air Toxics Rule, Ch. NR 445, Wis. Adm. Code. Wisconsin statutes have specific criteria which must be met in order for a hazardous air pollutant standard to be established.
• Amorphous forms of silica do not currently meet the decision rules for defining amorphous silica as a HAP because they have been delisted by the American Conference of Governmental Industrial Hygienists (ACGIH).
• Studies generally do not indicate the existence of any wide-spread significant concern about airborne crystalline silica exposures to individuals not living near an identified source of crystalline silica emissions. In circumstances where people live near a source of crystalline silica, data from other air pollution control agencies shows that silica ambient air concentrations could be above a level of concern. However, the data also suggests that other non-industrial sources contribute to the ambient levels.

Monitoring

• The size of crystalline silica particles of most concern are those that are smaller than four microns (millionths of a meter), also called particulate matter 4 (PM4). There are no generally accepted methods for monitoring PM4 in ambient air.
• Currently, WDNR has no crystalline silica monitoring data. Additional financial and staff resources would be needed to conduct crystalline silica monitoring. Monitoring to specifically analyze for crystalline silica is difficult, there are no federal standards and there is no standard reference method for monitoring crystalline silica in ambient air.

Regulation

• No federal air quality standards for silica currently exist. Federal standards for particulate matter (PM), a component of which is silica, are in effect for PM 10 and PM2.5.

• Controls for crystalline silica are the same controls typically used for particulate matter (PM). The extent of reduction from existing particulate matter (PM) controls is not currently known and will vary from source to source. The types and costs for these controls need to be evaluated on a facility-by-facility basis.

• Wisconsin Department of Natural Resources (WDNR) has extensive experience applying PM controls to many types of air pollution sources. For example, many permits for industrial sources require dust management plans and other controls to reduce PM emissions, which also help minimize crystalline silica emissions.
• Of the states surveyed, six (Texas, California, Vermont, New York, New Jersey and Michigan) address emissions of crystalline silica. However, these states have not shown impacts from these sources on health. Some states use what may be considered a technology-based approach, focusing on control measures or specific management practices, while others establish an acceptable ambient air concentration of crystalline silica.
• The draft report was released to the public on January 4, 2011 and the WDNR received comments. Comments received requested additional WDNR actions including listing crystalline silica as a HAP, establishing acceptable ambient air concentrations and controls on sources and monitoring for crystalline silica. Other comments state that the WDNR does not have the authority to regulate silica, that only occupational exposures have been associated with silicosis and cancer risk and no public health risk exists from the lower level of exposure in ambient air.

This post was authored by GLLF staff attorney Emily Kelchen.