Dental amalgam is a mixture of two nearly equal parts of liquid mercury (D009) and a powder containing silver (D011), tin, copper, zinc and other metals.13 When amalgam restorations are placed in or removed from teeth, or during chewing, a small amount of mercury vapor is released. Although the vapor may be absorbed by inhalation or ingestion, the FDA considers amalgam restorations safe for adults and children over the age of six.
However, amalgam waste not captured or removed at the dental office is discharged into a sanitary sewer system. From the sewers the amalgam waste is transferred to publicly-owned treatment works (POTWs), i.e., sewage treatment plants. POTWs remove about 95 percent of the amalgam waste, which then becomes part of the POTWs sewage sludge. The sludge may then be disposed of in landfalls, incinerated, or applied to agricultural land as fertilizer.
If the sludge is sent to a landfill, the mercury component may be released into ground water or the air; if it is incinerated, mercury may be emitted into the air; and if the sludge is used as fertilizer, evaporating mercury may become airborne. Airborne mercury is eventually deposited onto surface water, land and vegetation. Mercury is a persistent and bio-accumulative pollutant in the environment with well-documented neurotoxic effects on humans.
On June 14, 2017, the EPA finalized specific regulatory guidance to require dental practices to comply with requirements for controlling the discharge of mercury and other metals in dental amalgam into POTWs based on the best available technology.14 Most dental offices already use some type of basic filtration system (chairside traps, vacuum pump filters); in addition, some states and local governments have enacted regulations requiring dental offices to install amalgam separators.8
Amalgam separators are devices designed to remove amalgam particles from dental office wastewater through sedimentation, filtration, centrifugation, chemical removal by ion exchange or a combination of these technologies. Amalgam separators that meet the International Organization for Standardization (ISO) standard (ISO 11143) can capture over 95 percent of the amalgam waste discharged by dental offices into sanitary sewer systems.15,16
The ADA encourages dentists to implement best management practices (BMPs) to help reduce the environmental effects of amalgam waste (Box C).15 BMP is a method or technique available to oral healthcare facilities that has been generally accepted as the best because it produces results that are superior to those achieved by other means or because it has become the standard way of doing things, i.e., the standard way of complying with legal or ethical requirements.