Dentists throughout Wisconsin are being told they must end routine flushing of mercury to sewage treatment plants, where the toxic metal is released to the environment.

Removing silver-colored fillings from patients’ mouths, and placing new silver fillings in, are ongoing and significant sources of mercury to sewers, say federal and state environmental regulators. They are curtailing discharges of the metal as part of a strategy to reduce both contamination of fish in lakes and rivers, and the risk of ill health effects to the people who eat those fish.

Unless there is a large industrial source in a community, about 50% of the mercury in wastewater flowing to sewage treatment plants comes from dental offices using silver amalgam, said Randy Case, community mercury reduction coordinator with the state Department of Natural Resources.

Any Wisconsin sewage treatment plant that cannot meet stringent mercury discharge limits must implement programs in its community to minimize the volume of the metal flushed to sewers, Case said.

The Milwaukee Metropolitan Sewerage District and 25 others in the state are the first group required to test treated wastewater for remaining mercury.

Mandates for dentists

Though treatment plant operators have approached hospitals, medical clinics and schools with voluntary plans to keep mercury out of their drains, MMSD and several other municipal wastewater utilities are mandating use of special mercury collection devices at dental offices.

Silver-colored fillings are formed from an amalgam containing 50% liquid mercury and several other metals: silver, tin, copper and zinc. Mercury has been used in fillings for more than 150 years because it can be easily shaped, is inexpensive and it adheres to a tooth under wet conditions inside a mouth.

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