Lack of data makes dental mercury risk assessment ‘not possible’

European scientists say there is insufficient information to quantify environmental health risks posed by the use of mercury in dental fillings.1 Meanwhile, a UN-based working group has heard that dental use is often a front for international trade in the metal destined for use in hazardous and dispersive applications.2

The European Commission had asked its Scientific Committee on Health and Environmental Risks (SCHER) to evaluate the environmental and indirect health risks posed by the use of mercury in dental amalgam. Now the committee has found there is inadequate data to come to a conclusion.1

The background to the request was the EU’s mercury strategy, which was finalised in January 2005. Its aim is to reduce environmental levels of the toxic element and human exposure to it (ENDS Report 350, p 56 ).

The chlor-alkali industry is the major market in the EU, using mercury cells for the electrolysis of brine. The technology is due to be phased out, leaving dental emissions - including surgeries and crematoria - as the major source.

The chief risk from mercury in the environment is from the methylated form that may be produced by bacteria from inorganic mercury in the environment. Methyl mercury is more toxic and bioaccumulative than inorganic mercury and humans are particularly exposed through eating fish.

But SCHER found that the potential for methylation of mercury emissions in the environment was too variable to predict. Environmental quality standards for methyl mercury in the water framework Directive have generally been set only by reference to levels in fish or wildlife (ENDS Report 379, p 48 ).

The committee also found it was not possible to compare the environmental risks posed by amalgam fillings with those from alternatives such as resin polymers.

The uncertainties about global mercury pollution sources seem considerable. SCHER said key data needed includes:

  • data on the contribution of dental sources to the environmental pool of mercury
  • more specific data on mercury releases from dentistry in many member states
  • an evaluation of atmospheric mercury emissions and deposition
  • a review of methylation of mercury under EU environmental conditions
  • International efforts to control mercury releases took a step forward in November with the meeting of the UN Open-ended Working Group (OEWG) in Bangkok. The group was formed in February 2007 by the UN Environment Programme to assess the options for measures to control industrial emissions and to reduce the demand and supply of the metal.2 The Bangkok meeting was chaired by John Roberts, head of chemicals and nanotechnologies at the Environment Department (DEFRA), who reported on the meeting at the Chemicals Stakeholder Forum on 22 January.

    The OEWG has set in train work on global funding mechanisms for developing countries, sustainable technology transfer, legally binding measures, data gathering on mercury-containing products and substitutes, and an assessment of whether appropriate demand for the metal could be met if primary mining was phased out. The group will meet again in November before reporting back to the UN governing council in 2009.

    One issue highlighted at the forum was the difficulty in controlling international trade in mercury to restrict its use in small-scale gold mining. Such processes are a significant source of water pollution in areas such as South America and China.

    The trade in mercury for dental purposes allows the metal to be diverted for mining, David Santillo of Greenpeace told the meeting. Dr Roberts said that use in small-scale mining was not illegal in some countries but there were moves to introduce more sustainable processing methods. Packaging dental mercury in a form that would make other uses impossible and monitoring of mercury exports are also under consideration.

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