Dentists are sources of environmental mercury

In the U.S., dentistry is the 5th largest consumer of mercury. According to the American Dental Association (ADA), about 100 million fillings are placed every year. Every filling is composed of 50% mercury, about 1 gram for the typical filling. In Canada, 1300 kg of mercury in new filling material is placed each year.

For those dentists that use gold or composite materials instead of mercury amalgam, they still are removing old mercury laden "silver" fillings as a routine part of their practice. A typical dentist removes between 700 and 800 fillings per year.

The average dental office produces between one and two pounds of mercury each year. Overall, Environment Canada has estimated that more than two metric tonnes (2000 kilograms) of mercury enters our environment every year from dental amalgams. This is roughly equal to the amount of mercury emitted into the atmosphere each year by Canadian fossil fuel-based electricity generators.

About 60-70% by mass of this waste is made up of coarse particles. These are collected in chair-side traps and filters and are generally either recycled, dumped in the garbage, or rinsed into sewage systems. If disposed of in the regular solid waste stream, the mercury ends up in landfills. Landfilling produces mercury emissions at the working face of the landfill, as trucks dump the garbage and it is compacted and covered. Mercury amalgam that is disposed of in biowaste containers ends up at medical waste incinerators which release the mercury as air pollution.

About 25-35% of the waste by mass is made up of fine particles. These particles pass right through the chair-side traps and filters and flow directly into sewage systems. More than 1/3 of the mercury loadings to sewage systems in Canada comes from dental practices. At the sewage treatment plant, these fine particles settle out into the sewage sludge. Environment Canada estimates that two-thirds of the mercury found in sewage sludge comes from dental amalgam. The City of Toronto found that dentists' offices generate as much as 80% of the mercury that ends up in their sewage sludge. In most municipalities, this sludge is either incinerated (which releases the mercury into the air), landfilled (which, as mentioned above, releases the mercury into the air or groundwater), or applied to agricultural land as fertilizer (which causes the mercury to be taken up by plants and animals or to contaminate ground or surface waters).

About 5% of the mercury-bearing amalgam waste by mass ends up as extremely fine particles or dissolved mercury in wastewater. This mercury passes right through the chair-side traps and filters and through the municipal sewage treatment plant and is discharged directly to the aquatic environment.

So just how much mercury do dentists' discharge to the sewer system?

• A 1996 study of 20 Danish dental clinics reported in the journal Water Air Soil Pollution (86, 1-4; pg. 93-99) found that clinics without amalgam separators released 0.27 g (mean value) of mercury per dentist per day into municipal sewers, while clinics equipped with amalgam separators emitted 0.035 g per dentist per day (mean value).
• Studies by the Western Lake Superior Sanitary District in the U.S. revealed an average mercury contribution to wastewater of 0.1 to 0.3 g per dentist per day.
• The American Dental Association estimates that the average dental office discharges through dental wastewater are about 0.035 g of mercury per day.

Disposal down the chair-side sink is not the only source of mercury contamination to the environment from dentists' offices. Other sources include:

• accidental spills
• disposable amalgam capsules
• amalgam condensation
• mechanical amalgamators
• hot-air sterilization of amalgam-contaminated instruments
• improper changing or cleaning of mercury-laden coarse filters
• mercury-contaminated urine and saliva from people with mercury fillings
• contamination from cremation or burial of bodies with mercury fillings in their teeth
• mercury remaining in sewage pipes between the dentists' chair and the main trunk sewers from past decades of mercury use