Mercury

One possible environmental impact from the practice of dentistry results from the unwanted release of mercury in amalgam. Dental amalgam is a solid stable restorative material consisting of a 1:1 mixture of metallic mercury and an alloy powder of silver, tin, and copper, and possibly other metals. Dentists worldwide consume 3 to 4 percent of all the mercury produced. The mercury chemically binds the alloy compounds to form a stable restorative material. Ideally, a filling material that does not contain mercury or silver would provide an adequate substitute filling material. At present, however, amalgam remains the best and least expensive material for some types of restorations.

Effect of Mercury on the Environment

The mercury in amalgam can be released to the environment through various media (air, water, solid waste). Mercury is a persistent and deadly contaminant in the water environment. Metallic mercury such as that used in amalgam is relatively non-toxic. However, when mercury is released to the environment, some portion may be converted by bacteria to methyl mercury, a potent neurotoxin. Methyl mercury biomagnifies in the food chain such that levels of methyl mercury are created that are tens of thousands of times higher in some predatory fish, such as bass and bowfin, than in the surrounding waters. The North Carolina water quality standard for mercury is 0.000012 milligrams per liter (mg/L). The Federal Food and Drug Administration has determined that any level of methyl mercury in fish above 1 mg/L is unsafe. Despite recent reductions of mercury discharges, several fish consumption advisories have been issued throughout North Carolina to protect human health. The combined area covered by these advisories represents almost 10 percent of the state's total land area.

Sources of Mercury

Most mercury (83 percent) generated by humans and released into the environment results from the combustion of fossil fuels and incineration of municipal and medical waste.¹ Evidence of mercury contamination in the environment has created growing pressure for the reduction of mercury waste discharges. Dentists remain one of the last direct contributors of mercury-containing wastes.

¹National Emission Inventory of Mercury and Mercury Compounds. Interim Final Report. EPA/453/R-93-048. December 1993.

Mercury in Incinerated Medical Waste

Incineration of medical waste is responsible for 20 percent or 65 tons of mercury released into the air annually.² When dental wastes that contain amalgam are incinerated, some of the mercury in the fillings of removed teeth or scraps of amalgam on the waste materials are released into the air.

²National Emission Inventory of Mercury and Mercury Compounds. Interim Final Report. EPA/453/R-93-048. December 1993.

Regulation of Medical Waste

Some dental wastes are generated during dental procedures as various materials come into contact with a patient's blood and/or other body fluids. At least two government agencies under two different sets of regulations regulate these waste materials in order to control infectious disease. These wastes must be packaged and handled under certain procedures, as explained below.

I. Disposal of Dental Wastes

The Solid Waste Section of the NC Division of Waste Management regulates the disposal of certain medical wastes. Regulated Medical Waste is defined by North Carolina Administrative Code (15 NCAC 13B .1201) as blood and body fluids in individual containers in volumes greater than 20 mL, microbiological waste, and pathological waste. "Pathological waste" includes human tissues, organs, and body parts but does not include human teeth. Most dental facilities would not have any wastes that would be classified as "Regulated Medical Waste" under these regulations.

In most areas, blood can be disposed in the sewer. The local wastewater authority should be contacted for local requirements. The Solid Waste Section at (919) 733-0692 can provide a copy of Look Here First - A Guide to the North Carolina Medical Waste Management Rules, which contains a full discussion of medical waste and disposal options

II. Worker Protection

The Division of Occupational Safety and Health of the NC Department of Labor regulates waste for worker protection from the spread of bloodborne pathogens. Waste that does not meet the NC Solid Waste Section's definition for regulated waste could still meet the Occupational Safety and Health Act (OSHA) definition (29 CFR 1910.1030). OSHA's definition of regulated medical waste generally includes any materials containing human body fluids that are evident when the materials are squeezed (e.g., blood-soaked gauze). This waste must be labeled, stored, and handled to protect workers in both the dental office and the waste disposal industry. This waste can be disposed as general solid waste in some areas. The local solid waste authority can provide information about requirements.

• Labeling Requirements. Containers of OSHA-Regulated Medical Waste must be colored red, or they must be labeled. The label must be visible when waste is picked up for disposal. The labels should be sturdy, e.g., tie-on tags or stickers, must have an orange or orange-red background, and must have the word "Biohazardous" and the biohazard symbol printed on them in a contrasting color. Waste that is regulated by the OSHA standard and does not meet the Solid Waste Section's definition of Regulated Medical Waste can be disposed as general solid waste unless prohibited locally. Management of some wastes that meet the OSHA definition is discussed below.
  
• Handling Requirements - Sharps. Used sharps such as needles, slides and cover slips, and scalpel blades must be packaged in a rigid, leak-proof, puncture-resistant container; glass bottles are unsuitable. The container must be red or labeled as described above. The sharps containers can be disposed as general solid waste unless prohibited locally. It should be noted that even when properly handled, containers of sharps present potential hazards and liability.
  
• Handling Requirements - Other Waste Materials. Other biohazardous waste materials (e.g. gloves, gauze) that are not Regulated Medical Waste under Solid Waste Management rules, but may be regulated under OSHA and should be stored in a container or bag that is red or properly labeled.

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