Amalgam
Dentistry, Amalgam, and Pollution Prevention
William J. Johnson and Teresa J. Pichay
Copyright 2001 Journal of the California Dental Association.
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California has issued fish consumption advisories because of mercury in lakes, reservoirs, creeks, rivers, and bays. Mercury in these waterways leads to the formation of methylmercury, which is toxic and bioaccumulative. Dental practices and other health care settings contribute a portion of this mercury. Government agencies are implementing programs to reduce mercury pollution. Dentists can reduce their contributions by implementing best management practices. They may also consider using pretreatment technologies as more information becomes available about their use and effectiveness. |
Dentists have used amalgam as a restorative material for almost 200 years, and the use of amalgam has improved human health and quality of life. However, amalgam contains mercury, and mercury is a rising environmental concern. Because the U.S. dental industry uses several tons of mercury each year (estimates include 34 metric tons in 1997 1 and 48 tons in 2001 2), it is being asked, and in some places required, to reduce or eliminate mercury in its waste and wastewater. This article provides information on mercury in the global environment, related links to dental practices, and regulatory issues that are putting pressure on dental offices to change some practices.
A Persistent Environmental Problem
Mercury is a persistent, bioaccumulative toxin. It exists in elemental, inorganic, and organic forms. It does not degrade in the environment, but it can change from one form to another and circulate throughout the environment. Elemental and inorganic mercury can be converted to an organic form, methylmercury, through the biological processes of microorganisms, such as those in wetland sediments. Small fish and other small aquatic organisms absorb methylmercury, allowing it to enter the food web. As mercury rises through the food web, it accumulates in living tissues at ever-increasing concentrations. High levels of methylmercury have been found in large, predatory fish, including the fish humans eat. The concentrations of methylmercury in fish can be 7 million times greater than the concentrations of mercury in the surrounding water.3 The connection between mercury in the water column and methylmercury in fish requires further study, but it is apparent that extremely small mercury discharges into water can result in harmful mercury levels in the environment. In surface waters, such as bays, lakes, and rivers, mercury concentrations less than the parts-per-billion level (i.e., less than one microgram per liter) can be of concern.4
In fish, mercury can impair growth and reproduction, cause behavioral abnormalities, reduce feeding rates, and impair predatory success. Birds and mammals that consume large quantities of fish may also consume large quantities of mercury. As a result of mercury exposure, some birds have exhibited reduced feeding, weight loss, impaired grown and reproduction, lack of coordination, hyperactivity and hypoactivity, and liver and kidney damage. The neurological effects of mercury can be especially harmful to mammals that require speed and agility to obtain food or avoid prey. Mercury ingestion can lead to an early death for fish, birds, mammals, and other wildlife. Mercury exposure to plants can inhibit their growth, reduce their chlorophyll content, and damage their roots and leaves.5
In humans, mercury is a neurotoxin that affects the brain and spinal cord, interfering with nerve function. Mercury poisoning can result from inhalation of vapor, ingestion of soluble compounds, or absorption of mercury through the skin. Symptoms of exposure depend on the form of mercury, the mode of contact, and duration of exposure. Organic mercury compounds are considerably more toxic than elemental mercury. Adults exposed to methylmercury may experience abnormal sensations in their hands and feet, tiredness, or blurred vision. Higher levels of methylmercury exposure can impair vision, hearing, and speech. Long-term exposure can damage the kidneys. Pregnant women and nursing mothers can pass methylmercury to their fetuses and infants through the placenta and breast milk. In children, particularly those younger than 6, methylmercury can decrease brain size, delay physical development, impair mental capabilities, cause abnormal muscle tone, and result in coordination problems.6
Mercury levels in fish have resulted in several human health advisories for fish consumption. In most parts of California, fish have not been evaluated for their safety, but the California Office of Environmental Health Hazard Assessment has issued mercury-related advisories for fish from Clear Lake, Lake Berryessa, Lake Herman, and Lake Nacimiento. In the San Francisco Bay Area, adults are advised to consume no more than two eight-ounce meals per month of sport fish from the bay or delta, including sturgeon and striped bass. Pregnant women, nursing mothers, and children younger than 6 are advised to limit their consumption to one eight-ounce meal per month. No one should consume any fish from Alamitos Creek, Almaden Reservoir, Calero Reservoir, Guadalupe Creek, Guadalupe Reservoir, or the Guadalupe River.7
The Sources of the Problem
Mercury has many useful applications in commercial products. It is also a naturally occurring byproduct of some commodities, such as fuel. Burning fossil fuels, particularly coal, releases naturally occurring mercury into the air. Municipal incineration and medical waste incineration release mercury from wastes. Combustion and incineration are the largest contributors of mercury pollution in the United States.8
In California, mercury occurs naturally in the cinnabar deposits of the Coastal Range. During the Gold Rush, the cinnabar deposits were mined, and mercury was shipped to the Sierra Nevada Range to extract gold from gold-containing ore. The legacy of this era is that many rivers, creeks, lakes, and reservoirs of both eastern and western California contain mercury, and mercury-laden sediments continue to flow downstream into San Francisco Bay. Today, mercury associated with historic mercury mines remains a substantial source of mercury in surface water.9
The San Francisco Bay Regional Water Quality Control Board has identified sources of mercury in San Francisco Bay. They include runoff from historic mines in both the Sierra Nevada and the Coastal Range; remobilization of contaminated sediments within the bay; wastewater treatment plants discharging into the bay; and atmospheric deposition, including storm water runoff. The greatest portion of the mercury (about 45 percent) enters the bay through the Sacramento/San Joaquin River Delta, which drains most of the Central Valley. Sediment remobilization is also a major contributor (about 37 percent). Bay Area wastewater treatment plants account for only about 3 percent of the bay’s mercury (but when wastewater treatment plants outside the Bay Area are considered, their total contribution is greater than 3 percent because the discharges from Central Valley plants are included within the 45 percent estimate for the delta).10
Wastewater treatment plants are not designed to optimize mercury removal from sanitary sewage. They do remove about 99 percent of the mercury that comes to them, however.11 This mercury ends up in sludge that is used as a soil amendment, sent to a landfill, or incinerated. In any case, it is returned to the environment. Incineration, in particular, emits mercury to the atmosphere, where it falls to the ground through deposition and precipitation, potentially entering surface water and the food web. The roughly 1 percent of the mercury not captured by wastewater treatment plants passes directly into surface water.
Wastewater treatment plant operators have investigated the sources of mercury in their systems. Mercury loads are difficult to estimate. The sources of mercury and the percentage of mercury each source discharges to a sanitary system vary considerably among treatment plants. In most cases, however, dental facilities contribute a sizable portion of the mercury at wastewater treatment plants, often exceeding the combined contributions of other industrial wastewater dischargers. Wastewater treatment plant operators have estimated that dental offices contribute from 6 percent to 80 percent of the mercury in wastewater.12,13 The wide variation in these estimations can be attributed to attempts to extrapolate from the "typical" dental waste stream. Differences among the numbers and types of restorative procedures done daily, sizes of restorations, and various plumbing set-ups make it difficult to determine the average amount of mercury in dental office discharges. Most estimates, however, have been less than 25 percent of the total wastewater load.14
In addition to studying dental clinics, treatment plant operators have been looking at hospitals, laboratories, schools, and certain industries as sources of mercury in wastewater. Treatment plant operators are also looking at mercury-containing products, such as fluorescent lamps, thermometers, batteries, and electric switches, which are typically placed in landfills but sometimes release mercury into the environment through different pathways. Mercury in these products can leach into water or, in the case of broken fluorescent lamps, be emitted to the atmosphere.
As shown in Figure 1, in addition to contributing to wastewater discharges, dental offices release mercury to the atmosphere if amalgam is improperly disposed of as trash or medical waste that is subsequently incinerated. Mercury is also released when an individual with amalgam fillings is cremated. Crematories typically do not capture mercury from their air emissions. If they did, most current emissions control technologies would convert these air emissions into wastewater discharges. On average, about 0.6 grams of mercury is released by each cremation.15
Residential discharges into sanitary sewer systems have also been identified as significant sources of mercury. Mercury in food (e.g., fish) is excreted in urine and feces, and it is also excreted when mercury that escapes amalgam fillings is absorbed. The amount of mercury excreted from individuals with amalgam fillings has been shown to be about 17 times greater than the amount of mercury excreted from individuals without fillings,16 although other studies have reported factors of 12 and 46.17,18 The Association of Metropolitan Sewerage Agencies estimates that human waste from individuals with amalgam fillings contributes more than 80 percent of the mercury in domestic wastewater. For most metropolitan wastewater treatment plants, this amount, by itself, is sufficient to exceed levels of concern for water quality.11
Amalgam, Mercury, and Wastewater
Studies have described dental operatory systems and the path of mercury and amalgam wastewater discharges through them. Figure 2 presents diagrams of filter systems typical of many dental facilities. At each chair, there is typically a chairside trap to collect large amalgam particles. As shown in Table 1, if the wastewater generated by a dentist who routinely removes and places dental amalgam contains roughly 2 grams of total mercury per day (total mercury is measured by acidifying samples to release mercury from amalgam particles), about 1.2 grams of this mercury is captured by chairside traps.12,19 Therefore, if the only filter a dentist uses is the chairside trap, he or she could discharge as much as 0.8 grams of mercury to the sewer each day.20 These estimates are very rough and are provided for illustrative purposes.
As shown in Figure 2, liquid-ring vacuum systems are equipped with vacuum filters (dry vacuum systems may or may not have equivalent filters). Vacuum filters are intended to protect vacuum pumps from particles in the wastewater stream, but they also collect amalgam particles. Some dental facilities with dry vacuum systems are equipped with air/water separators, which may also trap some solids prior to discharge to the sewer.20 The amount of mercury in wastewater passing through chairside traps and vacuum filters, if both exist, appears to be about 0.4 grams per day per dentist.21
Attempts to find this much mercury in dental facility discharges have not always been successful. Table 2 lists estimated mercury loads attributed to dentists by different municipalities. These estimates span from about 0.03 grams per day per dentist to about 0.3 grams per day per dentist. In each case, the variation among individual measurements is reported to have been substantial. Mercury loads from the same dental office have varied more than three orders of magnitude for similar activity levels.22 The differences among these estimates account for the differences in estimated wastewater treatment plant loads.
A major factor affecting the measurement of mercury discharges is suspected to be the settling of mercury and amalgam particles, which are both very dense. There are many locations where dense particles that settle can become trapped on their way to a wastewater treatment plant. Many dental office vacuum hoses have flexible accordion folds. The amount of amalgam released from such a hose could have more to do with how the hose is jiggled or moved than with how much mercury enters the hose at any particular time. Disturbing a vacuum line could dislodge particles and result in uneven releases. Particles could also build up in a line until reaching a large enough mass to result in a sudden release. Such uneven releases could explain the wide range of individual sample results reported by investigators.
Plumbing systems also contain low points, ridges, and crevices that can capture small sediments. Particles may not readily dislodge from these areas and may build up over time. Trapped amalgam particles would be expected to continually leach small amounts of mercury as time passes. Mercury has also been found in many p-traps under sink drains. Therefore, wastewater samples collected outside a dental building may actually reflect historical mercury and amalgam use more than current mercury and amalgam use. As dental activities continue, the mercury levels in plumbing systems could approach a steady state, where releases from mercury trapped in the pipes make up almost the entire mercury discharge. A study of 20 Danish dental clinics found no correlation between the number of amalgam surfaces produced or removed at a clinic and the amount of mercury found in its simultaneously collected wastewater.23 The results of this study suggest that mercury discharges potentially relate to several complex factors and do not simply correlate with the day-to-day activities at each operatory.
Compared to the elemental and ionic forms of mercury, mercury bound within amalgam particles may be less available for conversion to ecologically harmful methylmercury. Amalgam particles may also be more readily removed by wastewater treatment plants. Wastewater treatment typically involves sedimentation and filtration. Therefore, the ecological significance of amalgam particles is uncertain. A study commissioned by the American Dental Association simulated a typical wastewater treatment process under both aerobic and anaerobic conditions. The study did not detect mercury of more than one part per billion when amalgam particles were subjected to simulated wastewater treatment procedures.24 However, mercury may be environmentally relevant at levels less than one part per billion. A study to determine whether certain oxidizing disinfectants in the waste stream, such as hypochlorite, could dissolve amalgam particles found that smaller particles may be easier to dissolve than larger ones.25 In wastewater, therefore, the smallest amalgam particles may be more likely to release biologically available mercury into surface water than may the larger ones.
Most amalgam particles flowing to a wastewater treatment plant are trapped in the sludge recovered during the treatment process. In many parts of the United States, this sludge is incinerated, although this practice is less common in California. Sludge incineration, medical waste incineration, refuse incineration, and cremation release mercury from amalgam particles. Therefore, in the environment, these emissions may be more easily converted to methylmercury than may any amalgam particles discharged directly from wastewater treatment plants. The forms of mercury in feces and urine may also be more available for biological uptake than most amalgam particles. The capability of mercury in the environment to enter the food web is an important consideration when developing and prioritizing pollution prevention strategies.
The Regulatory Environment
The mercury-related fish consumption advisories have stimulated enhanced efforts to control mercury discharges in surface water. Government agencies at the federal, state, and municipal levels are addressing the mercury issue; and environmental activists are watching. Because mercury concentrations in many water bodies are far greater than acceptable levels, some regions have decided to simply eliminate all mercury discharges to the extent possible, beginning with the largest sources that are easiest to control. In the Great Lakes area, the United States and Canada have adopted a "virtual elimination" policy to reduce discharges of persistent, bioaccumulative toxic substances, including mercury.26 The United States has agreed that, by 2006, it will reduce its deliberate mercury use and its mercury releases from human activity by 50 percent.27 The Chesapeake Bay and Everglades areas are also addressing significant mercury problems.
In California, the State Water Resources Control Board and the nine Regional Water Quality Control Boards are acting to reduce mercury levels in fish. In accordance with the federal Clean Water Act and California’s Porter-Cologne Water Quality Control Act, these agencies place limits on the amounts of pollutants that municipal wastewater treatment plants may discharge. In turn, the cities and counties that operate these plants require industrial dischargers to comply with restrictive permits. Few municipal agencies require dental facilities to obtain such permits. In the past, when a municipality attempted to control mercury discharges by requiring dentists to obtain these permits, the California Dental Association sued the State Water Resources Control Board, the San Francisco Bay Regional Water Quality Control Board, and the Office of Administrative Law. As a result of a 1998 settlement, these agencies agreed to review mercury regulations and develop a regional regulatory policy that accounts for historic and ongoing mercury sources. The San Francisco Bay Regional Water Quality Control Board, in particular, agreed to review mining, natural background, atmospheric, point, and nonpoint sources, and study the fate and transport of mercury in San Francisco Bay. The agencies agreed to work cooperatively with other agencies with jurisdiction over mercury sources, and not to promulgate any specific regulation of dental amalgam while developing the regional policy.28
Industrial permit requirements have improved water quality throughout California, but they have done little to reduce mercury levels because the targeted industries do not discharge much mercury. Where existing permitting requirements have proven inadequate to ensure that water bodies achieve water quality objectives, the federal Clean Water Act mandates a special regulatory process, known as a total maximum daily load. This process is intended to identify the sources of a pollutant and allocate discharges among the sources to ensure that water quality standards are met.
The San Francisco Bay Regional Water Quality Control Board is undertaking the total maximum daily load process for mercury in San Francisco Bay; other agencies throughout California are addressing other water bodies. Through the process, the San Francisco Bay Regional Water Quality Control Board has completed much of the work called for by the 1998 settlement agreement. The California Dental Association has participated as a stakeholder in the process, and both sides have benefited from the dialogue.
As a result of the total maximum daily load process, the San Francisco Bay Regional Water Quality Control Board and other agencies, such as the U.S. Environmental Protection Agency, are addressing the largest sources of mercury in San Francisco Bay. Strategies to clean up historic contamination are being developed. Eventually, if mercury discharges to San Francisco Bay do not decrease, however, the San Francisco Bay Regional Water Quality Control Board may seek to change the discharge limits it places on wastewater treatment plants. By decreasing these limits, the San Francisco Bay Regional Water Quality Control Board could cause municipal wastewater treatment plant operators to seek new ways to reduce their mercury discharges. In time, municipalities may require dental offices to obtain industrial wastewater permits. Whether and to what extent they pursue this strategy is unknown. They are likely to first pursue voluntary pollution prevention strategies.
Mercury Pollution Prevention in the Dental Office
Individual dentists exhibit varying levels of awareness about environmental issues. Their awareness about mercury in the environment likely affects their waste management practices. Personal anecdotes and surveys conducted by treatment plant operators suggest some dental workers may not clean chairside and vacuum traps appropriately. Some workers may dispose of amalgam with medical waste, which is typically incinerated, releasing mercury into the atmosphere. On the other hand, many dental facilities implement "best management practices," and some have installed state-of-the-art pretreatment devices, such as amalgam separators.
Best management practices are the simplest practices dentists can implement to reduce their mercury discharges, and they encompass a range of "common sense" or "good housekeeping" strategies. As shown in Table 3, the primary best management practices suggested for dental facilities include recycling mercury and scrap amalgam, and keeping mercury and amalgam out of sinks, trash, and medical waste bins. The California Dental Association and local and regional environmental agencies promote best management practices through such means as the "Never the Down Drain" brochure distributed in San Francisco and other materials distributed by the City of Palo Alto and the Los Angeles Bureau of Sanitation.
Best management practices require some training and vigilance, but they are typically cost-effective. From 1996 to 1998, the University of Michigan Department of Occupational Safety and Environmental Health conducted a mercury reduction project for the university’s School of Dentistry wastewater. The implementation of several best management practices, including discontinuing the discharge of suction waste to the sewer and cleaning or replacing sink traps, resulted in mercury concentrations in wastewater near or less than the 0.2 part per billion analytical detection limit for the project.29,30 Although some agencies may desire lower mercury concentrations (lower detection limits are now attainable), the University of Michigan experience offers a definitive success story.
Low-technology pretreatment technologies, such as filtration and settling, can effectively capture significant amounts of amalgam particles passing through chairside traps.31 Removal efficiencies of more than 95 percent can be achieved using technologies currently on the market. Vendors include ADA Technologies, Avprox, Dental Recycling North America, MDS Matrx, Metasys, Nalco, Reber Ecological Systems, and SolmeteX. Their products rely on various combinations of sedimentation, filtration, ion exchange, and adsorption technologies to trap mercury that would otherwise be discharged to the sewer. Those that best address the smallest, most readily soluble amalgam particles (those most likely to bypass treatment and be converted to methylmercury) may most benefit the environment. The ease of maintenance and cost of the equipment varies considerably, however. The original equipment purchase ranges from about $200 to $3,000, and annual maintenance costs range from less than $400 to as much as $2,500, including amalgam disposal costs.14,20,32
Agencies in Seattle; Duluth, Minn.; and Saint Paul, Minn., have investigated some of the separation technologies on the market. The Massachusetts Water Resources Authority has demonstrated that at least one type of separator can reduce mercury discharges from clinics by roughly 95 percent. (The product also reduced silver concentrations; but, surprisingly, it appeared to increase copper and zinc concentrations.)14 The International Organization for Standardization has adopted a standard (ISO 11143) for evaluating the effectiveness of amalgam separation devices. The American Dental Association has pointed out that the standard test does not necessarily represent actual conditions, and no laboratories in the U.S. perform the test. The American Dental Association plans to address the standard, in part, by developing its own testing capabilities.33
Dental offices that consider the use of separators need to account for a few factors:
* The technology should not affect the effectiveness of the existing vacuum system or reduce the amount of suction;
* Space should be available on the vacuum line to install the equipment;
* Maintenance should be simple, and service technicians should be readily available;
* Operational failures should be easy to detect; and
* The equipment should be easy to disengage from the vacuum line if a problem arises.
Because amalgam use has been linked to mercury in the environment, some have proposed the elimination of amalgam as a restorative material. Although insurance data indicate that amalgam use has decreased in recent years while the use of composite restorative material has increased proportionally,34 industry leaders predict the continued use of amalgam while research and development of alternatives continue. An evaluation of the clinical merits of alternative materials and their potential environmental consequences is beyond the scope of this article. However, it bears repeating to those who seek to change dental practices that dentistry’s mission is to improve oral health, and reducing the need for dental restorations has always been at the forefront of the profession.
Conclusion
Concerns regarding mercury in the environment are based on real problems that exist throughout much of California and the United States. Many dental offices can modify their waste management practices to improve pollution prevention efforts. Informed dentists can be relied upon to make reasoned decisions about how to implement best management practices and whether to install pretreatment technologies. Many regulators and environmental activists are sensitive to the concerns of dentists, but they may also seek further action on the mercury issue. Dentists who understand the environmental and regulatory issues that underlie potential pressures to change their practices will be in the best position to suggest solutions that are reasonable, equitable, and effective.
Authors
William J. Johnson is TKTK
Teresa J. Pichay is the coordinator of the California Dental Association’s Council on Dental Research and Developments.
Disclosure
William J. Johnson is employed by the California Regional Water Quality Control Board, San Francisco Bay Region, which is currently undertaking a total maximum daily load process for mercury in San Francisco Bay. As a regulatory agency, the interest of the Regional Board in the subject matter is not financial, although it financially supported his participation in the manuscript’s preparation.
References
1. Stone M, The Environmental Aspects of Mercury in Dental-Unit Wastewater, prepared for the American Association for Dental Research. Naval Dental Research Institute (http://home.xnet.com/~aadr/thetest.htm), undated.
2. Johnson J, The mercury conundrum. Chemical & Engineering News, 79(6):21-4, Feb 5, 2001.
3. US Environmental Protection Agency, Office of Air Quality Planning and Standards and Office of Research and Development, Mercury Study Report to Congress, Volume VI: An Ecological Assessment for Anthropogenic Mercury Emissions in the United States. EPA-452/R-97-003, December 1997, page 6-1.
4. US Environmental Protection Agency, Office of Air Quality Planning and Standards and Office of Research and Development, Mercury Study Report to Congress, Volume VI: An Ecological Assessment for Anthropogenic Mercury Emissions in the United States. EPA-452/R-97-003, December 1997, page 2-29.
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6. California Office of Environmental Health Hazard Assessment, Methylmercury in Sport Fish: Answers to Questions on Health Effects. California Office of Environmental Health Hazard Assessment, May 28, 1997.
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8. US Environmental Protection Agency, Office of Air Quality Planning and Standards and Office of Research and Development, Mercury Study Report to Congress, Volume I: Executive Summary. EPA-452/R-97-003, December 1997, page 3-6.
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10. California Regional Water Quality Control Board, San Francisco Bay Region, Watershed Management of Mercury in the San Francisco Bay Estuary: Total Maximum Daily Load Report to U.S. EPA. California Regional Water Quality Control Board, San Francisco Bay Region, June 30, 2000.
11. Association of Metropolitan Sewerage Agencies, Evaluation of Domestic Sources of Mercury. Association of Metropolitan Sewerage Agencies, August 2000.
12. Water Environment Federation, Controlling Dental Facility Discharges in Wastewater. Water Environment Federation, 1999.
13. EIP Associates, 1998 Mercury Sources, technical memorandum prepared for Palo Alto Regional Water Quality Control Plant. EIP Associates, April 23, 1999.
14. McManus K, MWRA Dental Control Program Review. Massachusetts Water Resources Agency, Yankee Dental Congress, January 25, 2001.
15. Obenauf P and Skavroneck S, Mercury Source Sector Assessment for the Greater Milwaukee Area, prepared for the Pollution Prevention Partnership and Milwaukee Metropolitan Sewerage District, September 1997.
16. Osterblad M, Leistevuo J, et al, Antimicrobial and mercury resistance in aerobic Gram-negative bacilli in fecal flora among persons with and without dental amalgam fillings. Antimicrobial Agents and Chemotherapy, 1995.
17. Bjorkman L, Sandborgh-Englund G, and Ekstrand J, Mercury in saliva and feces after removal of amalgam fillings. Toxicology and Applied Pharmacology, 144:156-62, 1997.
18. Skare I, Mass balance and systemic uptake of mercury released from dental amalgam fillings. Water, Air, and Soil Pollution, 80:59-67, 1995.
19. Drummond J, Cailas M, et al, Dental waste water: quantification of constituent fractions. Acad Dent Materials, Abstract P-22, 1995.
20. EIP Associates, Mercury Amalgam Treatment Technologies for Dental Offices, technical memorandum prepared for Palo Alto Regional Water Quality Control Plant, July 10, 2000.
21. Water Environment Federation, Controlling Dental Facility Discharges in Wastewater. Water Environment Federation, 1999.
22. EIP Associates, Mercury Source Identification Update: Dental Office and Human Waste, technical memorandum prepared for Palo Alto Regional Water Quality Control Plant, March 2, 1999.
23. Arenholt-Bindslev D and Larsen A Mercury levels and discharge in waste water from dental clinics. Water, Air, and Soil Pollution, 86:93-9, 1996.
24. Kunkel P, Cook K, et al, Investigation of the Fate of Mercury in Dental Amalgam in Wastewater Treatment Processes, prepared for the American Dental Association, April 1995.
25. American Dental Association Board of Trustees Report 12, 1994. Dental office wastewater. Supplement to Annual Reports and Resolutions 1994, pp 456-459.
26. EIP Associates, Virtual Elimination Strategies for Mercury, technical memorandum prepared for Palo Alto Regional Water Quality Control Plant, April 6, 1999.
27. Environment Canada and US Environmental Protection Agency, The Great Lakes Binational Toxics Strategy: Canada -- United States Strategy for the Virtual Elimination of Persistent Toxic Substances in the Great Lakes, April 7, 1997.
28. Settlement Agreement and Release, California Dental Association v. State Water Resources Control Board, Regional Water Quality Control Board, San Francisco Bay Region, California Office of Administrative Law, Sacramento County Superior Court No. 95CS03125, Jan 1998.
29. Chock D, Berki A, and Stowe L, Wastewater Pollutant Reduction and Pollution Prevention at University of Michigan, prepared for University of Michigan Occupational Safety & Environmental Health, Abstract No. 376, undated. (www.umich.edu/~oseh/wwprpp.html).
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35. Drummond J, Cailas M, et al, Dental waste water: quantification of constituent fractions. Acad Dent Materials, Abstract P-22, 1995.
36. Palo Alto Regional Water Quality Control Plant, "Set a Shining Example: Don’t Flush Mercury Down the Drain!" poster, September 2000.
To request a printed copy of this article, please contact: William J. Johnson, San Francisco Regional Water Quality Board, 1515 Clay St., Suite 1400, Oakland, CA 94612.
Figure 2. Chairside Traps and Vacuum Filters35
Table 1. Basic Filter Effectiveness12,35
Mercury Load (g/day/dentist) Mercury Load(g/day/chair)
Total mercury generated 2.0 1.3
Amount retained by chairside trap 1.2 0.8
Amount passing chairside trap 0.8 0.5
Amount passing secondary filtera 0.4 0.3
a The load per dentist passing secondary filters is estimated here on the basis of the ratios between the other loads in the table (per dentist and per chair). Actual measurements vary widely.
Estimated Dental Facility Mercury Discharges23
Location Mercury Discharge (grams/day/dentist)
San Francisco 0.035
Cleveland 0.042
Seattle 0.064
Boulder, Colo. 0.10
Boston 0.043 to 0.27
Duluth, Minn. 0.1 to 0.3
Aarhus, Denmark 0.25
Mercury Do’s and Don'ts for Dentists1,14,16
Do Don’t
Use precapsulated amalgam. Use bulk mercury.
Recycle unwanted bulk mercury. Combine mercury and nonmercury waste.
Recycle scrap amalgam. Rinse traps in the sink.
Recycle waste from traps. Put mercury in medical waste containers.
Replace or clean traps regularly. Place mercury waste in the trash.
Toss empty amalgam capsules in the trash (unless incinerated). Use oxidizing line cleaners or disinfectants (e.g., bleach).
