We recently received an ‘Ask the Expert’ question dealing with mercury filling particles in water. Our reader asked, “A dentist drills out a tooth that was previously restored using mercury dental amalgam filling - It’s estimated that 135 mg of mercury by weight enters into an 3.4L of H20 batch solution during this process: How do I calculate the amount of mercury particles in that 3.4L of Water?”
To answer this question, we’ll discuss the following underlying questions:
- What’s a mercury dental amalgam?
- What are the risks associated with mercury when it is used as a dental amalgam?
- What are the legislated limits on mercury in the water supply in the United States?
- How do we measure the concentration of a solution? (We will consider the units ppm, mg/l and number of particles in the solution.)
Mercury Fillings: Dental Amalgam
Mercury fillings, or dental amalgams are materials used by dentists to fill possible cavities present in teeth. Their composition can vary, but generally, mercury (Hg) is the main component – about 50 % weight. The other elements present are silver (Ag), tin (Sn) and copper (Cu).
The amalgam is formed due to the reaction of mercury with the other metals. Hg, being liquid, dissolves into the other solid elements, and chemical bonds form between Hg and the metals.
Mercury is a metal widely used for technological applications, due to its peculiar properties. It is the only metal which is liquid at room temperature; this makes it suitable, for instance, for use in thermometers.
Mercury, however, is also a very toxic element; for this reason, in some applications Hg has been replaced by less toxic elements/compounds. When Hg is employed, stringent legislation is in place to regulate its use, the disposal of Hg-containing wastes and its maximum concentration in the environment.
Considering US legislation, the Environmental Protection Agency (EPA) established a series of limits for Hg concentration values. These apply to water and air concentrations, but also to the maximum amounts which may be emitted from different sources (i.e. industrial processes, combustion of wastes, etc.).
The EPA water concentration limit of mercury is 0.2 ppm.
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