The dental
sector and society in general have long recognized the
benefits of using amalgams to restore and maintain the
dental health of patients. It is therefore understandably
difficult to convey a message of serious environmental
concern for mercury, which has been used with no apparent
negative implications for centuries. However, several
recent studies1 by health and environment
experts have shown that mercury is of great concern when
it enters the biosphere as a contaminant. The governments
of many developed and developing nations are becoming
increasingly aware of the risks to human health and the
environment posed by the inappropriate management of
mercury and mercury-containing wastes.2 In
fact, Canada’s Minister for the Environment, recently
elected president to the United Nations Environment
Program’s Governing Council,3 has strongly
supported the development of a global assessment of
mercury by 2003.
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 Reductions
Recent 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.
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Sept. 15-17, 1999.
Dental
Information 
