In April, Missoula dentists, the Missoula County Water Quality District, the Missoula Wastewater Treatment Plant (WWTP) and Women’s Voices for the Earth (WVE), a non-profit environmental health group, met to discuss the issue of how to properly manage mercury in the wastewater from dental offices in Missoula.  The Missoula WWTP provided an overview of how the treatment plant works and why mercury in the water is a problem. WVE presented the results of a survey they conducted of Missoula dental offices with the WWTP last year.  The first meeting presented an opportunity for all parties to understand a variety of issues involving the management of mercury waste from dental offices, and the following meetings have resulted in an action plan.

Wastewater Treatment Plant Needs Help to Control Mercury

The Missoula Wastewater Treatment Plant (WWTP) is mandated to test influent (the water coming into the plant), the effluent (the water leaving the plant) and sludge for metals such as mercury. The Missoula WWTP is unable to filter out mercury amalgam particles in the waste stream for proper disposal.

Some mercury amalgam particles are big enough end up in what is called the bio-solids; and some of these bio-solids are used for Eko-compost, a composting company in Missoula.  Because of this, it is important to keep bio-solids as free of toxins as possible. The amalgam particles that are too small to get captured in the bio-solids are sent out in the effluent, which in Missoula’s case is the Clark Fork River.

To date, the treatment plant has not exceeded mercury limits set in their permit. However, they are in the process of reevaluating their local limits for heavy metals such as mercury, and since the last three years has shown four significant mercury “hits” in their testing, they want to be proactive about reducing the amount of mercury coming into the plant.

Sherri Kenyon is the pre-treatment coordinator at the Missoula treatment plant.  “The Waste Water Treatment Plant effluent is required to meet surface water quality standards after mixing with a portion of the river, or the mixing zone,” says Kenyon.  “Each plant has a unique mixing zone based on the receiving stream they discharge to.  Missoula’s plant permit was renewed in November of 2006 and this new permit decreased our mixing zone volume by 75%, which has a significant impact on our allowable effluent concentrations of the 11 heavy metals.”  Kenyon says that the WWTP limits for the removal of metals to the bio solids has not changed; therefore, influent concentrations of heavy metals must be decreased if effluent concentrations must be decreased.

Mercury in the Surface Water is a Health Issue

When mercury reaches an aquatic environment, it can be transformed into methylmercury, an extremely toxic element that dissolves easily in water and bioaccumulates, or builds up, in the food chain.  This poses a serious threat to human health, and in particular, to pregnant women and children who are especially vulnerable to adverse health impacts from mercury.  More than 600,000 babies are born each year in the U.S. at risk for neurological damage due to their mothers eating fish contaminated with mercury.  In addition, this poses a threat to wildlife.  Montana has more than 400,000 acres of lakes and 1,000 miles of streams that are impaired due to mercury contamination. High levels of mercury have forced the state to issue fish advisories for certain Montana water bodies.  The best way to curb this is to prevent unnecessary pollution.

What are the Sources of Mercury Pollution?  Coal-fired power plants, cement kilns, gold mining, mercury-containing products (thermostats, thermometers, etc.), electrical lighting and dental preparations are all sources that emit mercury into the environment.  Nationwide, the EPA estimates that coal plants emit 48 tons of mercury to the air each year.  At the same time, the EPA estimates that mercury-containing products emit 22-29 tons of mercury to the air each year.  The largest source of mercury emissions directly to the water is dental preparations.  The EPA estimates that nationwide this source is responsible for 7.4 tons of mercury to the wastewater.  Other sources of water releases include sewage treatment and sludge incineration which account for 5.5 tons of mercury released per year.