Dental clinics are the largest point source of mercury to the waste-water. Part of this mercury enters directly the surface waters, where it may get methylated to methyl mercury, enters the fish and hampers the mental development of the fetus of pregnant women eating mercury contaminated fish. Another part of the mercury will remain in the sludge, thereby prohibiting its use as a fertilizer. A third reason is that toxic heavy metals such as mercury and silver may disturb the biologic step in the waste-water treatment plant.
Amalgam separators are used to physically remove dental amalgam from waste water in dental clinics. They are thereby supposed to reduce mercury (Hg) emissions to the municipal waste water system to acceptable levels.
We here present results from a comparative study in situ of three amalgam separators available on the market, all with a claimed efficiency of 99% according to Danish and ISO protocols, and using sedimentation as the principle of separation. We also present corresponding data for an investigational prototype of an improved separator.
The obtained efficiency of the three commercial separators is far below what is stated by the manufacturer and by authorities assumed to be the efficiency in clinical conditions. They reduced Hg emissions by 79 – 91%, leaving an average Hg content in
outgoing waste water of 1.5 mg L_1. However, the prototype separator participating in this study retained 99.9% of the waste water Hg emissions, leaving an average Hg content in outgoing waste water of 0.004 mg L_1. Physical restrictions prohibit
sedimentary type separators to recover the Hg fractions causing the largest damages in wastewater treatment plants. This fraction is not considered in the ISO protocol for testing amalgam separators, which therefore needs to be revised.
Abolishing the use of dental amalgam and cleaning the tubing systems is the most efficient long-term solution to reduce Hg emissions from dental clinics. Until then, Hg emissions originating from placing, polishing or removing existing amalgam fillings, should be counteracted by the use of low-emission amalgam separators, already on the market or presently being developed for use alone or together with sedimentary type amalgam separators.