Mercury Dental Amalgam Risks
Due to the health risks associated with mercury, scientists have performed several investigations to establish whether the use of mercury fillings are dangerous for the patients. According to an EPA report, and various studies, no connection has been established between the use of mercury-based amalgams and health problems.
The use of these amalgams, however, can still pose a threat to the environment, if they are not dealt with and disposed of properly.
Generally, the release of amalgam wastes into the environment must be avoided; mercury-containing wastes, coming for instance from dental surgery, should be separated from the other waste, using appropriate separator devices. Subsequently, they should be collected as a special medical waste.
Scales to Measure Concentration: Parts per Million (ppm)
The concentration of a certain substance in solution can be described using different scales. For diluted solutions, we often use the term, parts per million (ppm).
This scale indicates a unit of weight, for instance grams, divided by a million of the same unit – in this case a million grams.
For example, a solution with Hg concentration of 2 ppm means that 2 grams of mercury are present in 1 million (1,000,000) grams of the solution. As 1 million grams is equivalent to 1000 kg (= 1 tonne), 2 ppm concentration is equivalent to 2 g in 1000 kg (or 2 g per tonne), or 2 mg in 1 kg.
Scales to Measure Concentration: Milligrams per Liter (mg/l)
Another way to express the concentration is considering how many milligrams of a certain substance are dissolved in a liter of solution (mg/l).
The concentration expressed in this scale can be converted to ppm and vice versa. To convert ppm into mg/l, usually an assumption is made: the density of the solution is considered equal to 1 g/ml, as if it were pure distilled water. For diluted solutions, this is an acceptable assumption to make, as their effective density does not differ substantially from that of distilled water.
Based on that, a weight of 1000 g is equivalent to 1000 ml (1 liter) of solution.
Therefore, considering the example above, a concentration of 2 ppm corresponds to 2 mg in 1 liter (2 mg/l).
Calculating the Concentration of Mercury in Water
To answer the question, if 135 mg are present in 3.4 liters, this gives a concentration of 39.71 mg/l. This value corresponds to 39.71 ppm, which is well above the EPA limit of 0.2 ppm.
This solution should be, therefore, properly treated and disposed, as mentioned above.
If the mercury is present in the form of small particles, the number of particles in solution will vary, depending on the sizes of the particles.
For instance, if we assume that all particles have a spherical shape, with a diameter of 10 mm, then each particle will have a volume of 5.2×10-7 cm3. As the density of Hg is 13.53 g/cm3, a weight of 135 mg of mercury corresponds to a volume of about 0.01 cm3. Therefore, the number of particles will be:
0.01/(5.2×10-7) = 1.9×10+4
This means approximately 20000 particles.
Similar calculations can be performed considering particles of different dimensions and/or shapes.
Watson, G., et al. Prenatal exposure to dental amalgam: Evidence from the Seychelles Child Development Study main cohort. (2011). Journal of the American Dental Association. Accessed May 15, 2012.
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