• Luke Trip, B.Sc. Chem. •
MeSH Key Words: dental amalgam/adverse effects; environmental pollutants/prevention and control
© J Can Dent Assoc 2001; 67:270-3
MeSH Key Words: dental amalgam/adverse effects; environmental pollutants/prevention and control
© J Can Dent Assoc 2001; 67:270-3
Mercury in the environment contaminates the food chain, particularly the fish and traditional foods consumed by Northern Canadians.4 The nutritional benefits of eating fish and traditional foods are so important that a rational approach to pollution prevention actions is mandatory. Although mercury is a naturally occurring element in the global environment, most scientists throughout North America and the world are in agreement that the volume of emissions from naturally occurring mercury and the volume of emissions resulting from human activities — that is, from anthropogenic sources — are about equal.5
Levels of mercury in the environment have been increasing since the beginning of the industrial age (about 1800-1850 ad).6 The impacts of this increase are felt around the globe, because mercury vapours are carried by air currents in a phenomenon known as long-range atmospheric transport. This same phenomenon is responsible for acid rain and its resulting problems, as described by the Canadian government in the early 1980s.7 We now know that mercury is similarly carried from various sources of emissions to distant receiving environments.
This article explains the relationship between mercury, particularly dental amalgam waste, and the environment. It also describes a significant new pollution prevention initiative intended to ensure that the dental community becomes part of the solution to this serious environmental health problem.
The Paradox of “Liquid Silver” The chemical symbol for mercury is Hg, derived from the Latin word hydrargyrum, or liquid silver. The apparent paradox of mercury being both beneficial and noxious typifies the unique physical and chemical properties of this element. It is a liquid at room temperature, yet it is also a metal, with all of a metal’s electrical properties. It has the unique ability to dissolve or soften many other metals at room temperature — the basis for its use as a dental amalgam. In some societies, elemental mercury is an icon of health and good fortune.8
Despite the fact that it is very dense, the elemental form of mercury is volatile. It can evaporate and travel throughout the atmosphere on air currents and thus affect ecosystems extremely remote from the source of emission. This atmospheric source is consequently captured by rainfall and other precipitation events and adds to the burden of mercury contamination entering lakes and rivers from various land-based sources such as sewage treatment effluent and sewage sludge applied to land.
Mercury Contamination In both Canada and the United States, the greatest environmental health impact of mercury is manifest in the thousands of fish consumption advisories issued as a result of elevated mercury levels in fish tissue.9 These advisories are either for specific varieties of fish or for specific water bodies — or even for entire provinces such as New Brunswick or Nova Scotia.
In the natural environment, the mercury that enters water bodies, including the amalgam wastes from dental practices, can be transformed by bacteria in the water column and sediments of lakes and rivers into a class of organometallic chemical compounds collectively referred to as methylmercury. Methylmercury is persistent in the environment. It bioaccumulates in living tissues and organs and is extremely toxic. Canada, the United States and many other countries have extensive programs in place to reduce the presence of methylmercury and other persistent, bioaccumulative and toxic substances (PBTs).
Although all affected ecosystems are of concern, the most significant environmental impacts of mercury are in water and air. The contribution to water leads to the direct bioaccumulation of methylmercury in fish, and the contribution to air emissions leads to water contamination through both wet and dry atmospheric deposition.
Canada’s major industrial source of mercury contamination in the 1970s was the chlorine-producing sector. The industrial production of chlorine for the pulp and paper industry involved a mercury cell process that left a legacy of mercury pollution in many of Canada’s freshwater ecosystems.10 As a consequence, the Canadian Environmental Protection Act11 designates mercury and mercury compounds as toxic substances under Schedule 1 and thus subject to the requirements under that Act. Mercury is also regulated under the Fisheries Act and the Hazardous Products Act and is subject to the guidelines of the Canadian Food Inspection Agency. Provinces and municipalities also have legislation and bylaws that restrict discharges of mercury or mercury-contaminated wastes to the environment.
Keeping Track of Mercury The Canadian government maintains an inventory of mercury emissions to the environment through the National Pollutant Release Inventory (NPRI). This regulated requirement to report releases of pollutants is mandated under the Canadian Environmental Protection Act, 1999. Reporting requirements for mercury have recently been amended to include any person or enterprise that manufactures, produces or otherwise uses 5 kg or more annually.12 Dentists are exempted from this reporting requirement to minimize the paperwork burden of establishing that most clinics generate less than the minimum reporting quantity. This fact was confirmed with the dental community during the consultative discussions leading to the NPRI amendment in December of 1999.
The NPRI shows that the primary generators of mercury emissions are the mining and smelting sector, the coal-fired electric power generating sector and waste incineration facilities. In 1995, about 12 tonnes of mercury were emitted directly to the atmosphere by Canadian industry and enterprises. Despite the exemption noted above, dental offices did add significantly to the total emissions, as a Health Canada report indicates: “The main contributors to anthropogenic releases are coal-burning power stations and municipal and medical waste incinerators, followed by a host of minor sources. The release of mercury from dental offices due to the widespread use of mercury amalgam tooth fillings has now been recognized as an important source in municipal sewers.”13 The cities of Toronto, Victoria and Montreal have recently focused bylaws on restricting the discharges of amalgam wastes from dental offices to sewer systems.14,15
Overall, the dental sector contributed about 2 tonnes of mercury in total to the environment and about 0.5 tonnes through atmospheric emissions (Fig. 1). By comparison, the Canadian electrical power generating sector emits about 2 metric tonnes of mercury to the atmosphere, due almost entirely to fossil fuel combustion. Mercury emissions from dental waste management practices to all environmental media are calculated and shown in Table 1.
Regulating the Problem In Canada, the management of mercury pollution crosses many jurisdictional boundaries, with different responsibilities residing among various government agencies. To effectively and efficiently manage expectations and to avoid duplication, the responsible jurisdictions are working together under the auspices of the Canadian Council of Ministers of the Environment (CCME) to develop a made-in-Canada mercury management program.
The CCME is a unique intergovernmental council comprised of the 14 ministers of the Environment for the federal, provincial and territorial governments in Canada. Under its auspices, the Canada-wide Accord on Environmental Harmonization is the framework agreement establishing the common vision, objectives and principles that govern the partnership between jurisdictions and the development and implementation of sub-agreements.16
To date, mercury management options under the CCME process are proposed or under consideration for the base metal smelting sector, the waste incineration sector, the electric power generation sector (including lighting products) and the dentistry sector. For the last, the specific program is called the Canada-wide standard (CWS) for mercury in dental amalgams.17
During the initial development of the CWS for mercury in dental amalgams, it became clear that there would be questions raised about environmental regulators propos ing initiatives that would have a direct impact on the health care of dental patients. Consequently, the CWS focuses specifically on the waste management aspects of dental amalgam use and pollution prevention as mandated by the CCME partners.
At a products workshop held in Winnipeg in March 2000, members of the CWS development committee met with stakeholders, including representatives of the Canadian and Ontario Dental Associations, to ensure that there was consensus on the path forward. Regulators are keenly aware of the extensive and expert knowledge of dental practitioners and have no interest in directing the dental profession on the best way to treat its patients. Nationally, the policy on the use of dental amalgam and the various other dental products for restorative work falls under the auspices of Health Canada.18
The CWS for mercury in dental amalgams proposes to adopt a national reduction target based on best management practices to achieve a 95% national reduction in mercury releases from dental amalgam waste by 2005, from a base year of 2000.
To ensure that all dentists are aware of and will have the opportunity to participate in implementing the CWS for dental amalgams, Environment Canada and the Canadian Dental Association (CDA) are developing a Memorandum of Understanding (MOU). The MOU will focus on issues surrounding the management of amalgam waste in dental practices and will assist in implementing the associated CWS. The aims of the MOU are to achieve the voluntary implementation of the CWS, to provide regular progress reports in an open and transparent manner and to advocate and recognize supportive action by provincial and territorial governments and dental regulatory authorities. The text of the MOU is expected to be approved by CDA and Environment Canada in the spring of 2001 and will be available on the Greenlane Web site ( www.ec.gc.ca ) and on CDA’s Web site ( www.cda-adc.ca ).
Achieving Significant ReductionsRecent certification tests have shown that the installation of ISO-11143-certified amalgam separators can attain an efficiency of at least 95% removal of amalgam based on mass fraction (see Table 2, ISO-Certified Amalgam Separators). The anticipated benefits to be achieved by this CWS are shown in Fig. 2, showing mercury reductions in sewage after high-efficiency separators have been installed in a typical town in Denmark.20
One of the areas still requiring investigation is the amount of mercury remaining in waste discharge lines and facility sewage pipes between the dentist’s chair and the main trunk sewers of a municipality. Environment Canada has undertaken such a study and results are expected by June 2001. It is anticipated that careful cleaning of this residual source of mercury and incorporating the new CWS in the practitioner’s clinics will have an impact even more dramatic than the 63% reduction shown in Fig. 2.
The scientific community and regulatory jurisdictions across Canada recognize that mercury is a toxic substance of concern because of its impact on the environment, particularly in marine and freshwater ecosystems. The Canadian dental sector, along with other commercial and industrial sectors, can play a significant role in preventing mercury releases to the environment.
Mr. Trip is manager, National Mercury Programs, National Office of Pollution Prevention, Environment Canada, Hull, Quebec.
Correspondence to: Mr. Luke Trip, National Office of Pollution Prevention, Environment Canada, Place Vincent Massey, 20th Floor, 351 St. Joseph Blvd.; Hull, QC K1A 0H3. E-mail: LukeTrip@ec.gc.ca
The views expressed are those of the author and do not necessarily reflect the opinions or official policies of the Canadian Dental Association.
References 1. The 5th International Conference, “Mercury as a global pollutant”, book of abstracts, May 23-28, 1999. Pub, CETEM-Center for Mineral Technology, Rua 04, Quadra,D-Cidade Universitária - Ilha do Fundão, 21949.590 - Rio de Janeiro, Brazil.
2. Aarhus Protocol, Protocol to the 1979 Convention on Long-Range Transboundary Air Pollution on Heavy Metals, UNECE, 1998.
3. 21st Session of the UNEP governing council, Nairobi, KENYA, 5-9 February 2001.
4. Methylmercury in Canada, exposure of First Nations and Inuit residents to methylmercury in the environment, Health Canada, volume 3, 1999.
5. Trip L, Chevalier P, Smith J, editors. The status of mercury in Canada, report #2. A background report to the Commission for Environmental Cooperation. May 2000. p. 10.
6. Lockhart WL, Wilkinson P, and others. Current and historical inputs of mercury to high altitude lakes in Canada and to Hudson Bay. Water Air Soil Pollution 1995; 80:603-10.
7. Still waters, the chilling reality of acid rain, report of the Sub-committee on Acid Rain of the Standing Committee on Fisheries and Forestry, 1981, Minister of Supply and Services, Canada, Catalogue # XC 29-321/2-01E.
8. Mercury use in the Hispanic community of Chicago, Chicago Department of Public Health, August 1997.
9. Listing of fish and wildlife advisories, August 1999. USEPA, Office of Science and Technology. Available from: URL: http://fish.rti.org/.
10. Trip L, Allan RJ. Sources, trends, implications and remediation of mercury contamination of lakes in remote areas of Canada. Water Science Technology 2000; 42(7-8):171-4.
11. Canadian Environmental Protection Act, 1999, c. 32. [Assented to 14th September, 1999].
12. Extract, Canada Gazette, Part I, December 25, 1999, Department of the Environment, notice with respect to substances in the national pollutant release inventory.
13. Methylmercury in Canada, exposure of First Nations and Inuit residents to methylmercury in the environment, Health Canada, Volume 3, 1999, p. 28.
14. City of Toronto, by-law No. 457-2000, To regulate the discharge of sewage and land drainage, enacted by Council, July 6, 2000.
15. Communauté urbaine de Montréal, by-law 87-4, by-law amending by-law 87 respecting waste water disposal in sewer systems and waterways, enacted by Council, August 16, 2000.
16. Canadian Council of Ministers of the Environment. Available from: URL: http://www.mbnet.mb.ca/ccme/1e_about/1e.html.
17. Canadian Council of Ministers of the Environment. Available from: URL: http://www.mbnet.mb.ca/ccme/3e_priorities/3ea_harmonization/ 3ea2_cws/3ea2.html.
18. Health Canada. The safety of dental amalgam. August, 1996. Minister of Supply and Services Canada, catalogue # H49-105/1996E.
19. O’Connor Associates Environmental Inc. Mass balance of dental-related mercury wastes in Canada. Prepared for Office of Transboundary Air Issues and National Office of Pollution Prevention, Environment Canada, Hull, Quebec K1A 0H3.
20. Arenholt-Bindslev D. Environmental aspects of dental restorative materials. A review of the Danish situation. Publication in: AWMA (Air and Water Management Association) International Specialty Conference on Mercury in the Environment. Minneapolis, Sept. 15-17, 1999.