Water Journal : Water Journal April 2012
wastewater water APRIL 2012 145 health authorities across the globe, the national representative body for dentists in Australia, the Australian Dental Association Inc (ADA Inc), recently labelled amalgam as a "necessary" option and "the restorative material of choice in many situations" (ADA Inc, 2011). The realities are: amalgam is not only one of the most common replacements for biological tissue in the human body, but also one of the most extensively researched; scientific and health authorities continue to endorse the safety of amalgam; dentists prescribe amalgam in clinical situations, particularly those involving low socioeconomic patients, because they have to; and its removal from the market will pose problems for the delivery of dental services in many nations. There is another inescapable conundrum. While the population load of amalgam is unknown, dentists will remove it from teeth for decades. Clearly, if dentists want to continue to either use amalgam or remove it from teeth, associated mercurial problems in wastewater have to be addressed. International Developments By 2000, both overseas and in Australia, anthropogenic sources of mercury had attracted mounting government and regulatory body attention. Mercury was on the European Union's Dangerous Substances Directive, the US Government's List of Hazardous Substances, the UK Department of Environment's Red List (of dangerous substances) and the WHO List of Industrial Pollutants. Reports almost invariably cited dental surgeries as significant contributors to the mercurial burden in wastewater. In the new millennium, three streams of investigation emerged in the dental literature. They focused on: dentists' contributions to mercurial component of wastewater; need for and efficiency of separators; and institutional responses. At an international level, dental organisations began to openly acknowledge the environmental footprint of amalgam. North American evidence dominated analyses of dentists' contributions to the mercurial component of wastewater. Canadian researchers estimated that Ontario dentists removed 1,880.32kg of amalgam (940.16 kg of mercury) throughout 2002. Compensating for dentists' use of amalgam particle separators, researchers estimated that 861.78kg of amalgam (430.89kg of mercury or 170.72mg per dentist daily) was released throughout 2002. The use of amalgam separators by all dentists could reduce the quantity of amalgam (and mercury) entering wastewater to an estimated 12.41kg (6.21kg of mercury, or 2.46mg per dentist per day). Two earlier studies, with a number of acknowledged limitations, estimated that dentists collectively discharged 686kg and 781kg mercury per annum into wastewater. In California, where some sewage sludge was being incinerated, the annual discharge of mercury, in the form of amalgam from dental facilities, to publicly operated treatment works was estimated at approximately one ton. These statistics not only fuelled concerns regarding collection and management of amalgam waste, but also provided further impetus for solutions. The conclusions were obvious: separators dramatically reduced amalgam and mercury loading in wastewater. Efforts to quantify the transfer of dental practices' mercurial loads to wastewater were not without problems. Many poorly defined variables and confounding factors permeated researchers' methods. For example, the aforesaid influences on pre-1999 separator efficiency influenced mercurial load to outlets. Additionally, some estimates were extrapolations from monitoring of waste in selected practices. Researchers almost invariably investigated small numbers of clinics. Few investigations were blind. Other analyses used models based on purchase statistics of amalgam and generic estimations of waste production. These projections ignored other important variables: the size, type and design of the bur used in amalgam removal, the presence of a spittoon and the work habits of the dentist. Each dentist has a characteristic profile in terms of treatment provided and waste generated. All these variables influence particulate size and efficiency of chairside capture. Another investigation measured urinary and faecal mercurial levels from dentate patients with amalgam restorations and estimated the community contribution to mercurial sewerage loads from this source. The extrapolation ignores the surface area, location, type and age of the restoration: all vary from patient to patient. Nonetheless, while many of the above studies were pilot investigations, and while investigators acknowledged limitations in their methods, the emerging trend in evidence was convincing. Dental surgeries significantly contributed to mercurial burden in wastewater. Some national dental organisations sought solutions. Concurrent research into separators exposed operational issues. Standard 111 43 was subject to patent rights and international ratification by 75% of the members of the worldwide federation of national standard bodies. The standard did not enunciate a specification for measuring the mercury content of effluent water and ignored the mercury content of influent water. Moreover the tiniest particles, which are most likely to avoid harvest in separators involving high levels of fill, have a high surface area to volume ratio. Consequently, they are amenable to accelerated degradation in downstream infrastructure. Installing a separator did not mean automatic compliance with mercurial controls in wastewater legislation. The paucity of authoritative dental research in the clinical setting and "wide disparity in amalgam removal efficiency in the same amalgam separator system" further hampered authoritative responses from national dental organisations. By 2002, and notwithstanding a dearth of independent scrutiny of manufacturers' claims, 12 separators had appeared on the US market. All exceeded the ISO 111 43 requirement of 95% amalgam removal efficiency. However, this laboratory- based trial found significant statistical differences in the efficiencies of the separators. Total mercury concentration and total dissolved mercury concentration in the effluent varied widely for each amalgam separator. The researchers concluded: "Additional research is needed to develop test methods to evaluate the efficiency of amalgam separators in removing small amalgam particles, colloidal amalgam particles and ionic mercury in solution." However, even with all the inherent problems in research method, several findings were clear. Separators worked. Moreover, controlling mercurial waste at chair- side was practical and far preferable to attempts at downstream containment. International scrutiny of all generations of anthropogenic mercury escalated rapidly in the first decade of the new millennium. In November 2003, the Government of Sweden commissioned the Swedish Chemicals Inspectorate to investigate the feasibility of a ban on the handling, import and export of mercury. Within two years, the WHO had published Elemental Mercury and Inorganic Mercury Compounds: Human Health Aspects and the associated policy paper Mercury in Health Care. The latter cites mercury in amalgam as "the greatest source of mercury vapour in non-industrialized settings" (Department of Protection of the Human Environment, 2005). It also alludes to 7.41 tonnes of mercury from dental amalgam discharged into sewers in the United Kingdom.
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