Effluent Guidelines

Detailed Studies

Dental Amalgam

December 2008

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Across the United States, many states and municipal wastewater treatment plants (publicly owned treatment works (POTWs)) are working toward the goal of reducing discharges of mercury to POTWs.

Mercury is a concern to human health because it is a persistent bioaccumulative toxic chemical. Many studies have been conducted in an attempt to identify the sources of mercury entering these POTWs. 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 3.7 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.

Mercury-containing amalgam wastes may find their way into the environment when new fillings are placed or old mercury-containing fillings are drilled out and waste amalgam materials that are flushed into chair-side drains enter the solid waste stream. Some of the waste amalgam particles that reach the sewer system settle out in the sewers, and some are carried to POTWs. The physical processes used in POTWs remove about 90% of the mercury received in wastewater. The mercury removed from wastewater then resides in the biosolids or sewage sludge generated during primary and secondary treatment processes.

Dental facilities may employ a variety of controls and management practices to reduce the discharge of mercury amalgam in wastewater. Management practices include the use of amalgam separators, precapsulated alloys, proper disposal and recycle of captured amalgam, and avoiding the use of oxidizing cleaning agents and heat disinfection for amalgam containing materials. Amalgam separators remove particulate mercury amalgam and in combination with traps and vacuum pump filters achieve better than 95 percent removal.

ADA, NACWA, EPA Sign Memorandum of Understanding for the Voluntary Dental Amalgam Discharge Reduction Program

On December 29 2008, the Office of Water signed a Memorandum of Understanding (MOU) with the American Dental Association (ADA) and the National Association of Clean Water Agencies (NACWA) to establish and monitor the effectiveness of a Voluntary Dental Amalgam Discharge Reduction Program.

This agreement will help prevent toxic pollution and track environmental progress. EPA will use this agreement and the cooperation of dental professionals and wastewater utilities to reduce mercury discharges into sewers and watersheds. EPA will also continue progress with other partners and co-regulators, as well, on the many aspects and challenges of mercury pollution.

The purpose of this MOU is to have dental offices install and properly maintain amalgam separators, and recycle the collected amalgam waste. The program will also establish performance goals, and track the percentage of dental offices that install and use amalgam separators. There has been progress to reduce the discharge of mercury into Publicly Owned Treatment Works from dental offices, but much more can be done through collaboration, innovation, and technology. This collaborative effort among EPA, ADA and NACWA will help build awareness and stress the importance of prevention at the local, state, tribal, and national levels.

Resource Documents

The following documents provide a resource to pretreatment programs and dentists that are looking to reduce the discharge of mercury amalgam in wastewater.

ADA, NACWA, & EPA Voluntary Dental Amalgam Discharge Reduction Program Memorandum of Understanding (PDF) (17 pp., 892 K)
Health Services Industry Detailed Study: Dental Amalgam (PDF) (76 pp., 1.0 MB; EPA 821-R-08-014)

Additional Information/Contacts

For additional information regarding dental amalgam, please contact our Dental Amalgam subject matter expert.

316(b) | Analytical Methods | NPDES