Despite how often mercury is commercially employed throughout the U.S., the primary source of mercury pollution in our water supply comes not from heavy industry but rather from a far more dreaded source: your dentist. And the EPA is finally about to do something about it.

According to a scathing report published on September 25, too much of the metal, which is used for amalgamate dental fillings, is being washed down the drain as excess amalgamate from new fillings. Per the EPA filing:

According to the 2002 Mercury Source Control and Pollution Prevention Program Final Report prepared for the National Association of Clean Water Agencies (NACWA), dental clinics are the main source of mercury discharges to POTWs. A study funded by the American Dental Association (ADA) estimated in 2003 that 50 percent of mercury entering POTWs was contributed by dental offices.

EPA estimates that dentists discharge approximately 4.4 tons of mercury each year to POTWs. EPA estimates there are approximately 160,000 dentists working in over 120,000 dental offices who use or remove amalgam in the United States – almost all of whom discharge their wastewater exclusively to POTWs.

To combat this source of pollution, the EPA has proposed a set of new guidelines that would instigate dental practices to install in-office water filters capable of sieving out microscopic mercury particles from drainage water, known as amalgam separators, or at least comply with existing ADA mercury limitation practices. Should the rules be adopted (which could happen as soon as next September) the EPA expects to prevent nearly 9 tons of mercury from entering the nation's water supply every year.

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We've also reached out to the EPA as to why it's using decade-old data for this policy shift and will update when they respond.

UPDATE: per Robert Daguillard of the EPA's Office of Media Relations:

For this rulemaking EPA used a number of studies including 2002 and 2003 data on mercury discharges to POTWs. EPA's Health Services Study dated 2008 includes numerous citations to the data and information available to EPA at that time:

http://water.epa.gov/scitech/wastet….

In addition, based on available data and studies, in 2011, EPA modeled estimates of mercury discharges from dental offices that reach POTWs and continued to refine those modeled estimates up to 2014. Descriptions of the modeling EPA used, the data used to construct the models and the resulting calculations are included the technical development document and the environmental assessment for the proposed rule. Those documents will be available in the rulemaking docket at http://www.regs.gov when the proposed rule is published in the Federal Register, which we expect will be in the next 2-3 weeks.

EPA currently lacks a central database on reported discharges from dental offices/clinics. Often, EPA looks to information in the Toxics Release Inventory (TRI) and Discharge Monitoring Report (DMR) databases to gather information on industrial discharges. However, no dental offices/clinics (NAICS Code 621210) are required to report releases to TRI. EPA identified only five dental offices that have National Pollutant Discharge Elimination System (NPDES) permit information. All dental offices were classified as minor dischargers. EPA has not found any DMR data indicating that any significant number of dental offices discharge directly to waters of the U.S.

[EPA - National Journal via Mashable]

Image: Szasz-Fabian Jozsef