Dental amalgam is a common filling material composed of an alloy of silver, tin, copper, and up to 50% elemental mercury. Although the mixture creates a stable, durable restoration, the mercury content necessitates strict management protocols for scrap material. Proper disposal is a legal requirement mandated by federal and state regulations to prevent mercury from entering public waterways. This regulated substance requires specialized recycling.
Classification as Hazardous Waste
Scrap dental amalgam is categorized under federal law as a hazardous waste due to its toxicity characteristic. This designation falls under the Resource Conservation and Recovery Act (RCRA), which regulates waste from generation to final disposal. Although not a listed hazardous waste, amalgam exhibits the hazardous characteristic of toxicity. This classification means dental practices generating amalgam are considered hazardous waste generators, subject to specific regulatory requirements.
Some states simplify the process by classifying scrap amalgam as “universal waste,” a subset of hazardous waste that allows for streamlined collection and transport rules. Regardless of the classification, specialized recycling and proper handling remain mandatory. This applies to both contact amalgam (material removed from a patient’s mouth) and non-contact amalgam (unused scrap).
The Role of Mercury in Waste Designation
The classification of amalgam as hazardous waste stems directly from its mercury content and its potential to leach into the environment. Mercury is a potent neurotoxin that bioaccumulates in the food chain. While mercury in set amalgam is chemically bound, scrap material can release toxic forms of the metal if improperly disposed of in a landfill.
The federal standard used to determine this hazard potential is the Toxicity Characteristic Leaching Procedure (TCLP), which simulates leaching in a landfill environment. This standardized test (Method 1311) exposes the waste sample to an acidic solution for 18 hours. If the resulting liquid extract contains mercury above the regulatory threshold of 0.2 milligrams per liter (mg/L), the waste is assigned the hazardous waste code D009. Scrap amalgam almost always exceeds this threshold, confirming its status as regulated waste.
In-Office Requirements for Scrap Amalgam Storage
The day-to-day management of amalgam waste begins with strict segregation and storage within the dental office. All contact and non-contact scrap amalgam must be collected and stored separately in designated, tightly sealed containers provided by the recycler. These containers must be sturdy, non-leaking plastic and clearly labeled to indicate the hazardous contents. Non-contact amalgam includes unused scrap, excess material from capsules, and used capsules.
A crucial handling requirement is the prohibition of heat sterilization, such as autoclaving, for any amalgam-containing waste. Heating the material causes the elemental mercury to vaporize, releasing toxic fumes that create a health hazard and violate environmental regulations. Scrap amalgam must never be placed into the regular trash, biohazard bags, or sharps containers. Any amalgam-containing sludge collected from chair-side traps or vacuum filters must also be stored for recycling, not discarded down the drain.
Regulations Governing Final Disposal and Manifesting
The final disposal of dental amalgam is tightly controlled by the Environmental Protection Agency (EPA) to ensure it is recycled and kept out of the wastewater system. The EPA Dental Amalgam Rule (40 CFR Part 441) mandates that dental offices discharging to a Publicly Owned Treatment Works (POTW) must install and maintain an amalgam separator. This device captures fine amalgam particles from the wastewater stream before they enter the sewer system and must meet the ISO 11143 standard for efficiency.
The rule also enforces Best Management Practices (BMPs) for all dental practices that use or remove amalgam. Specifically, the use of certain line cleaners is prohibited, including oxidizing or acidic agents like bleach, chlorine, or peroxide, if their pH is outside the 6 to 8 range. These cleaners can dissolve solid mercury, causing it to bypass the separator. All collected amalgam, including material captured by the separator, must be sent to a permitted recycler via a licensed hazardous waste transporter. The dental practice, as the waste generator, is responsible for completing a Uniform Hazardous Waste Manifest or similar tracking documentation, which provides a “cradle-to-grave” trail of the waste.