Partnership with Minnesota Dental Association reaps benefits

Mercury coming into big wastewater plant cut in half

The amount of mercury pollution coming into the region’s largest wastewater treatment plant has been cut in half over the last four years. The next time you visit your family dentist, say “thank you.”

Dr. Scott Lingle, past president of the Minnesota Dental Association, was instrumental in getting the voluntary program to remove mercury from dental office wastewater established. He’s pictured here with the amalgam separator installed in his downtown St. Paul dental clinic.

Why? Because your dentist is likely pitching in to keep mercury out of wastewater. More than 700 clinics in the Twin Cities metropolitan area participate in a voluntary program to separate mercury-containing amalgam particles from their wastewater before it goes down the drain.

“This has been a major effort for both our staff and the Minnesota Dental Association,” said Bill Moore, general manager of Metropolitan Council Environmental Services (MCES). “It’s been very satisfying that a voluntary initiative like this has paid off with significant reductions in mercury loadings to our system.”

Meanwhile, 97% of the mercury coming into the plant is removed by wastewater treatment and air scrubbing technologies.

Reducing pollution at the source

Amalgam is a composite material used to fill cavities in teeth. It contains about 50% mercury with the rest made up of silver, tin and copper. Small particles can get rinsed away at the dentist chair as fillings are placed or removed.

MCES, the Council division responsible for wastewater collection and treatment, and the Minnesota Dental Association (MDA) in 1998 began researching how to reduce this type of pollution at its source. Their studies found that amalgam separators installed within dental clinic vacuum systems could remove 99% of the amalgam particles and significantly reduce the amount of mercury getting into the sanitary sewer system.

In 2003, MCES and the MDA launched a program to identify metro-area dental clinics that dealt with amalgam and encourage them to install the separators. To date, more than 99% of the clinics eligible for the program have installed the special equipment. They report to MCES annually whether the equipment is being operated and maintained properly.

Good results for the region

In the four years since this program began, the amount of mercury entering the Metropolitan Wastewater Treatment Plant in St. Paul has dropped by just over 50%.

From the early 1990s to 2003, there were approximately 250 grams of mercury entering the Metro Plant daily (a gram equals .035 ounces, so that’s a little over half a pound). By midway through 2007, that number had dropped to 113 grams.

Treatment processes remove the vast majority of the mercury. Since a new wastewater solids incinerator with advanced pollution control equipment went into use in 2004, mercury in the solids is absorbed by carbon and is bound up in the incinerator ash. The sand-like ash is covered up in a landfill so the mercury cannot be released into the environment, Moore said.

MCES is studying whether the ash can be reused in things such as road-base material without the mercury being released. The new solids management equipment has delivered a drastic improvement over the old incinerators, which emitted approximately 200 pounds of mercury per year.

Mercury is an element that is found in everyday uses in addition to dental amalgam, such as button-type batteries, older thermometers, thermostats and fluorescent lights. (Some counties offer programs to exchange some of these items for mercury-free versions.) When released to the environment, mercury can accumulate in fish and cause neurological damage in humans and animals eating the fish.