May 2007, Volume 3, Issue 5
Published by AEGIS Communications
Amalgam Separation in the Dental Office—The What and Wherefore
Congress declared it to be the national policy of the United States that pollution should be prevented or reduced at the source whenever feasible; pollution that cannot be prevented should be recycled in an environmentally safe manner whenever feasible; pollution that cannot be prevented or recycled should be treated in an environmentally safe manner whenever feasible; and disposal or other release into the environment should be employed only as a last resort and should be conducted in an environmentally safe manner.1
As National Pollution Discharge Elimination System (NPDES) mandates strive to reduce mercury and other contaminants to low levels to protect beneficial users, the dental profession finds itself under increasing fire as one of the chief sources of mercury pollutants. As this article is being written, eight states have statewide regulations regarding mercury pollution from dental practices2 (see Sidebar), and more are sure to follow, yet there seems to be a marked resistance to installing amalgam separation units that would effectively reduce mercury pollution at its source.
The question is not so much one of willful negligence, but a lack of accurate information. In this author’s experience, dentists are largely unaware of the Best Management Practices (BMPs) prescribed by the American Dental Association (ADA) regarding mercury disposal—or of the fact that these BMPs still fall short of the impending stringent restrictions issued by the Environmental Protection Agency (EPA) and its state subsidiaries. When these restrictions are enforced, hefty fines will likely be the penalty for noncompliance. Clearly, the time for dentists to mobilize to reduce mercury discharges—for the health of their practices as well as the health of the environment—is now.
Mercury in Dentistry
Let’s start with the basics. Mercury is a well-known neurotoxin. Once mercury is discharged to the environment, it converts to methylmercury, a very toxic form, and bioaccumulates in fish. Fish consumption is the number one exposure to mercury for humans and wildlife. The EPA has designated mercury as its number one hazardous waste.3 As a part of the EPA’s strategy, sewage treatment plants are required to meet lower discharge limits for mercury in their liquid effluent discharge and in their sludge content. Sewage treatment plants receive discharge whether a facility is connected to a sewer or not; septic tanks are pumped regularly and the contents are discharged at sewage treatment plants.
The most common use of mercury in dental operations is dental amalgam. Amalgam is made up of approximately 40% to 50% mercury, 25% silver, and a 25% to 35% mixture of copper, zinc, and tin. The total amount of mercury per amalgam can range from 327 mg to 982 mg depending on the size of the amalgam.4
Amalgam particles enter the wastewater from dental offices when dentists remove old amalgam fillings or place new fillings. What most in the dental community do not understand is what actually happens to the amalgam/mercury they discharge, which ends up in the sludge at the sewage treatment plant. Any amalgam/mercury (or other hazardous waste) received at the sewage treatment plant is either incinerated, land-filled, or made into fertilizer pellets, which are land-applied on lawns and gardens and sold to farmers for their crops. In every case of disposal, the mercury in the amalgam will be discharged to the environment.
Estimates of the contribution of mercury in wastewater from dentists to publicly owned treatment works (POTWs) range from 11% of the total mercury load in San Francisco to 14% in King County, Washington, to 76% to 80% in Minneapolis.5 In a recent survey of seven major wastewater treatment plants in California, Minnesota, Ohio, and Maine, dentists were identified as the greatest con-tributor of mercury.4 The Central Contra Costa Sanitary District estimates that approximately 50% of the mercury in its wastewater comes from dental offices6 and a report released in 2002 by the National Association of Clean Water Agencies (NACWA) indicated that dental clinics are the largest single source of mercury in wastewater.7 In addition, there are more than 20 studies from Europe, Canada, and the US which identify the dental industry as the number one source of mercury to the sewer system.4
According to the ADA, the dental industry uses approximately 35 tons of amalgam annually.6 It is estimated that 29.7 tons of mercury in the form of amalgam are discharged to the internal wastewater systems of dental facilities annually during amalgam placement and removal—and it should be noted that a “mercury-free dentist” (that is, one who places only non-amalgam fillings) is not truly mercury-free if he or she removes amalgam fillings and allows that mercury to be dis-charged down the drain. The ADA report suggests the average life of a removed filling is 8 to 9 years. So the question is not what is being used today, but what amount of mercury was being used 8 to 9 years ago. Dental offices have traditionally captured this amalgam waste by chair-side traps and vacuum filters; the ADA estimates that 6.5 tons of mercury annually bypasses these filters and is discharged to POTWs.7 This annual mercury bypass assumes that 100% of the dentists practice ADA’s recommended BMPs.
When and if a dental office is tested for mercury discharge, a sample is collected either at the discharge point in the office or at the sewer connection down the manhole. Before that sample is analyzed it is digested in acid to dissolve the solid particles, in this case amalgam particles, and solubilize the mercury contained in the sample, which is then tested for ‘total mercury’. At SolmeteX (Northborough, MA), we have tested more than 2,000 samples of dental waste water. Not one dental facility we tested would meet the mercury discharge requirements for the City of Boston. The EPA is currently issuing NPDES permits to POTWs around the country to govern mercury and other metals discharge from the treatment facilities. Most, if not all, of the limits for mercury are being set below the limit of one part per billion established by Boston’s POTW. In the Great Lakes region, these mercury limits are almost 1,000 fold more stringent than Boston’s limit.
The National Association of Clean Water Agencies (NACWA), which represents larger POTWs, released a “White Paper” in January 2006 to highlight three options its members can take to limit the amount of mercury effluent from dental offices, in order of degree of intervention and effectiveness. Options include educating dentist on the ADA’s BMPs to limit the release into the sewer systems, implementation of numeric wastewater limits for dental clinics, and requirements or recommendations for amalgam separators.
The white paper points to recommendations for BMPs outlined last year by the ADA on how to handle the dental amalgam, such as stocking it and storing it before shipping it to a certified recycling operation. According to NACWA, however, the dental amalgam is sometimes collected in chairside traps or filters and washed out in sinks, directly discharging the contents into the sewer systems. The ADA itself notes that “(a)lthough chair-side traps and vacuum filters remove some particles from the wastewater stream, particles that remain in the wastewater can settle along the waste pipe or be discharged into the sewer” 8
The next option is to apply a local limit for mercury, either at the “end of pipe” or on a dental facility’s total discharge. The NACWA study indicates that this approach may be complicated due to sewer line access and expensive due to sampling required to characterize the dental office discharge.
The third recommendation is installation of amalgam separators that capture the mercury and other wastes before they enter the sewer system. The White Paper notes that a study is underway to “provide additional insight into whether the installation of amalgam separators at the dental clinics in a particular POTW’s service area may enable the POTW to meet the NPDES limits. Still, amalgam separators may be the best option some communities have to control mercury discharge.”8
Amalgam separators are “solids collectors” installed on the vacuum lines of dental offices. Amalgam separators need to be certified under an International Organization for Standardization (ISO) classification to greater than 95% removal of solids by weight. Most amalgam separators on the market in the US are certified to greater than 98% ISO, providing dentists with a range of certified treatment options to purchase. Because 95% or more of amalgam is captured by the separators before it reaches the sewers, POTW reductions have been dramatic. Toronto recorded a 58% decrease in the amount of mercury in its sludge six months after the required installation of amalgam separators in dental offices.9 Wichita recorded a 74% reduction,10 Seattle 50%,11 and Victoria, BC, a 70% reduction.12 Reports from Europe demonstrate up to 95% reductions in mercury loadings13 over the course of the last 10 years since amalgam separator regulations have been in place.
The three leading amalgam separators on the US market represent approximately 85% of the devices sold. They have an average capital purchase cost of $846.00. Installation costs are approximately $250.00 and in some cases rolled into the cost of the separator. Operational costs of these three separators average $528.00 per year. In comparison to BMPs recommended by ADA, where vacuum pump filters are changed regularly, the annual operational costs of amalgam separators is actually less than the purchase and recycling of the vacuum pump filters.14
Another benefit of amalgam separators is the recycling of mercury. In 2006, SolmeteX reported recycling approximately 5,300 canisters from its installed base of dentists. This resulted in 1,325 pounds of mercury recycled to industry. In addition, vacuum pumps would have a longer life as the material which typically would damage the pump would now be removed before it was able to get to the pump.
The effectiveness of amalgam separators has been recognized and regulations have been implemented in eight states. These states all have statewide requirements for separators in dental offices. Montana, New Jersey, New Mexico, and Pennsylvania are also evaluating statewide requirements. In addition to state regulations, POTWs from Wichita, Seattle, San Francisco, and Milwaukee along with many other communities have required dentists to install amalgam separators.
The amalgam separator has been demonstrated to be a cost effective solution for the removal of 50% or greater of the mercury loads to POTWs. Separation usage has been facilitated in a number of ways; statewide regulation, at the county or municipal level and by the local POTW individually. Amalgam separator usage also facilitates the recycling of mercury that is fulfilling the full intent of the Pollution Prevention Act of 1990.
What is clear regardless of the specific data is that the use of amalgam separators in dental offices is something that will be required in every state in the US at some point in the future. For the practitioner with the foresight to look down the road, perhaps the future is now.
STATES WITH AMALGAM SEPARATION REGULATIONS AND THEIR WEB SITES
New Hampshire (Statewide)
New York (Statewide)
Rhode Island (Statewide)
Washington State (State Wide Memorandum Ended August 2005)
1 Pollution Prevention Act of 1990. Public Law 101-508.
2 Controlling Dental Facility Discharges in Wastewater: How to Develop and Administer a Source Control Program. Water Environment Federation. 1999
3 Mercury Study: Report to Congress. U.S. Environmental Protection Agency Volume I, Executive Summary. 1997.
4 Dental Offices and Mercury Pollution Prevention. Best Management Practices Central Contra Costa Sanitary District 5039-04/06
5 Mercury Source Control & Pollution Prevention Evaluation. NACWA 2006
6 Vandeven JA, Meginnis SK. An Assessment of Mercury in the Form of Amalgam in Dental Wastewater in the United States. Water Air and Soil Pollution. 2005;164:349-366.
7 Fan PL, Batchu H, Chou HN, et al. Laboratory Evaluation of Amalgam Separators. J Am Dent Assoc. 2002;133(5):623-625.
8 Controlling Mercury in Wastewater Discharges from Dental Clinics: White Paper. National Association of Clean Water Agencies. 2006.
9 Stone M. Implementation of Amalgam Separators at Navy Dental Clinics. Naval Institute for Dental and Biomedical Research, PowerPoint Presentation. December 2003
10 www.wichita.gov/cityOffices/WaterAndSewer/SewageTreatment/SilverMercury.htm. Accessed March 22, 2007.
11 Dental Office Waste Stream Characterization Study. Municipality of Seattle. September 1991.
12 Metals in Sewage Significantly Reduced. Times Colonists. Thursday May 5, 2005.
13 OSPAR Commission. Assessment of Implementation Reports in Connection with PARCOM Recommendations 93/2 on Further Restrictions on the Discharge of Mercury from Dentistry. OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic.
14 Dube A. Important issues surrounding mercury reduction: do amalgam separators work? Poster presentation. Mercury 2006 Conference. Madison, WI.
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