Dental amalgam, commonly known as a silver filling, is a durable material composed of a mixture of metals, with liquid mercury making up approximately 50% of its weight. Because of the mercury content, the disposal of amalgam waste is a significant environmental and public health concern. Improperly managed dental waste, such as flushing amalgam down a drain, is a leading nonindustrial source of mercury discharge into publicly owned treatment works (POTWs), or municipal wastewater treatment plants. Mercury that enters the sewer system eventually finds its way into waterways, where it is converted into the highly toxic form of methylmercury, which then bioaccumulates in the food chain.
Categorizing Amalgam Waste
Effective management of amalgam waste begins with meticulous segregation of the different forms it takes in a dental practice. Each category requires dedicated handling to ensure mercury does not enter the standard waste stream or the wastewater system.
Scrap or non-contact amalgam is the unused material left over after a procedure, such as excess mix or drops of fresh amalgam that have never been placed into the patient’s mouth. This material must be collected separately from other waste types.
Contact amalgam includes any material that has been in contact with the patient. This includes pieces removed during drilling, leftover amalgam collected in chairside traps, and extracted teeth containing restorations. Spent amalgam capsules and the solids collected in the dental vacuum pump filters also fall under the mandatory recycling stream.
Required Amalgam Separation Technology
The primary method for compliant management of amalgam-containing wastewater is the use of an amalgam separator. This specialized filtration device is plumbed into the dental suction system before the wastewater enters the sewer line. The separator works by employing a physical process, such as sedimentation, filtration, or centrifugation, to capture solid amalgam particles.
To be compliant, amalgam separators must meet the international standard ISO 11143, which mandates a minimum removal efficiency of 95% of amalgam particles by mass. This technology physically separates the solid amalgam waste from the liquid effluent, allowing the cleaned water to proceed to the POTW.
Proper function depends on routine maintenance and adherence to the manufacturer’s instructions. Maintenance involves the regular inspection and replacement of the collection canister, cartridge, or filter media according to a defined schedule. Many separators include a visual indicator or volume limit to signal when the canister needs to be exchanged for recycling. Failure to maintain the unit can lead to reduced efficiency, allowing mercury to pass into the wastewater system.
Storage and Collection Protocols
Once segregated, amalgam must be stored in specific, designated containers provided by a specialized waste recycler. Non-contact and contact amalgam waste streams are typically stored in separate, sealed, wide-mouthed plastic containers clearly labeled “Amalgam for Recycling.” These specialized containers often contain a mercury-vapor-suppressing solution to minimize the release of mercury gas into the office environment.
Extracted teeth containing amalgam must first be disinfected, such as with a bleach solution, and then placed in a separate, sealed container for recycling, not the biohazard waste bin. Amalgam waste, including chairside traps and vacuum filters, must not be placed into regulated medical waste (“red bag” waste) or standard office trash. The collected containers must be stored in a cool, dry place away from heat sources to prevent mercury vaporization.
When the containers are full, a licensed waste recycling service collects the amalgam waste for proper reclamation. Using these specialized services ensures the mercury-containing material is processed in a facility capable of safely recovering the elemental mercury and other metals. This diverts the hazardous material from landfills or incinerators, preventing mercury release into the environment.
Regulatory Framework and Documentation
The requirements for managing and disposing of dental amalgam are codified by the Environmental Protection Agency (EPA) under the Dental Amalgam Rule (40 CFR Part 441). This federal regulation mandates that dental facilities discharging to a POTW must install and maintain an amalgam separator that meets the 95% removal efficiency requirement. The rule’s objective is to significantly reduce the five tons of mercury annually discharged from dental offices into the nation’s municipal wastewater systems.
Dental offices must adhere to specific administrative duties to demonstrate compliance. A mandatory one-time compliance report must be submitted to the local Control Authority detailing the practice’s amalgam separator model, installation date, and management practices.
Practices must keep records for a minimum of three years. Required documentation includes the amalgam separator’s maintenance logs, disposal manifests from the licensed recycler, and the separator unit’s operating manual. These records prove the facility is actively managing its amalgam waste and is not using oxidizing or acidic drain cleaners that can dissolve mercury and cause it to bypass the separator.