Dental facilities

Studies have shown that about one third of the mercury discharged to EBMUD's wastewater treatment plant is from dental practices. EBMUD issues permits to dental facilities to reduce the discharge of amalgam waste to the sanitary sewer. The dental facilities are required to install a separator, which removes the amalgam from the process wastewater prior to discharge.

Frequently asked questions

Mercury is one of the 12 toxic pollutants identified by the U.S. EPA that is impairing Central San Francisco Bay, and is listed in Section 303 (d) list of the Clean Water Act. Mercury bioaccumulates and persists in the environment. Currently, fish consumption advisories are issued in 41 States. The San Francisco Bay is included on the fish consumption advisory list.

Studies have shown that approximately one third of the mercury discharged to EBMUD's wastewater treatment plant is from dental practices.

In July 2001, the California Regional Water Quality Control Board, San Francisco Bay Region (Regional Board) issued the National Pollutant Discharge Elimination System permit (Permit) for EBMUD's wastewater treatment plant (Order No. 01-072). The Permit requires compliance with new wastewater discharge limitations for pollutants, including mercury.

The Permit requires the District to comply with not only a monthly average mercury wastewater discharge concentration limit of 87 nanograms/liter, but also a mass-based loading limit of 1.0 kilograms/month. This is the first time the Permit includes a mass-based limit.

The Permit requires the District to develop and implement an aggressive source control and pollution prevention program to comply with the new mercury limits and maximize EBMUD's control over mercury sources impairing the San Francisco Bay.

In addition, U.S. EPA's Section 503 Sludge Regulations and state and local biosolids regulations require the District to meet concentration limits for heavy metals, including mercury. These regulations ensure that biosolids can be safely reused for land application and landfill cover.

Wastewater treatment plants, including EBMUD's, are designed to treat wastewater containing conventional pollutants such as human waste and food waste.

Heavy metals, including mercury, are not removed by the treatment for conventional pollutants. As a result, the fate of mercury is to end up in the wastewater discharged to the San Francisco Bay or in the biosolids, which are used for land application and landfill cover.

Many dentists use amalgam, which contains approximately 49% mercury (Massachusetts Water Resources Authority). Studies have shown that about 54% of the amalgam mixed for placement ends up as waste (Arenholt-Binslev, 1992). With proper management, much of this waste, as well as amalgam waste from filling removals, will be prevented from being discharged to the sanitary sewer.

Studies have shown that an estimated 40-50 grams of mercury per dentist are discharged to the sanitary sewer each year (Bay Area Pollution Prevention Group). This amount is subsequent to screening and filtering of the wastewater within the dental office. It also includes amalgam washed down from the sink areas. The City of Palo Alto's studies show about 47% of its mercury source is from dental offices. EBMUD's data shows about 33% of mercury was from dental offices.

In the United States, dentists are the third largest users of mercury. In 1997, 40 metric tons of mercury was used for dental supplies (11.6% of the 346 metric tons used for all purposes).

The District is investigating all mercury sources, including dental practices, hospitals, medical facilities, and the general public, that discharge to the wastewater treatment plant.

The dental profession is very proactive in the areas of health, safety, and environmental protection. However, a significant percentage of dentists continue to improperly dispose of amalgam waste.

Studies indicate that more than one in four dental practices dispose of scrap amalgam into red bags, garbage, or down the drain to the sanitary sewer.

Currently there is no permit fee. A monthly waste minimization fee is assessed on the water bill for all businesses, including dental practices. The District's Pollution Prevention Program, required by the Regional Board, is funded primarily by this waste minimization fee.

Currently, the District is gathering information regarding the implementation of mercury hygiene best management practices (BMPs). These BMPs were developed by the American Dental Association and are considered "industry standard."

Based on the information provided through its permitting process, EBMUD will evaluate the current state of BMPs employed by dentists in the District's service area and take appropriate steps (which may include specific treatment requirements) to meet EBMUD's Permit discharge limits for mercury.

Red bag waste may require incineration. Incinerated mercury volatilizes and becomes an air pollutant. It also may eventually end up in surface water.

If the amalgam is disposed of with other garbage, the mercury may end up in the landfill leachate, which may eventually contaminate groundwater or surface water.

Contact your local dental association for information on amalgam recycling options.

Not all of the scrap amalgam and particulates are captured by the chair-side traps and vacuum filters. Grinding, drilling, and polishing of amalgam fillings may result in the production of fine particulate matter that passes through the chair-side traps and vacuum filters (Nimmo et al., 1990, Brune et al., 1980). The residual particulates remain in the wastewater discharged to the sanitary sewer.

An additional source of mercury is wastewater from instrument washing, and chair-side trap and vacuum filter cleaning. This wastestream may not be managed by a device designed to capture amalgam.

A practical type of treatment is amalgam separators used to remove amalgam waste and particulates from wastewater prior to discharging to the sanitary sewer (see the Naval Dental Research Institute's website for the American Dental Association's evaluation of available amalgam separators).

Studies (Arenholt-Bindslev and Larsen, 1996, MASCO) have shown that significant amounts of amalgam particulates can accumulate in dental office plumbing lines. When biomass build-up sloughs off the inside of the pipe, mercury ends up in the sanitary wastestream. A study in Sweden found as much as 30 pounds (lbs) of waste amalgam (~15 lbs of mercury) in the plumbing of a large dental office.

Cleaning or replacing the p-trap can be a cost-effective means of removing the build-up of amalgam that may end up in the sanitary sewer system. Even if a dental practice has an up-to-date amalgam management system, mercury may still be present in the building's plumbing from years past.

The Regional Board and local agencies for wastewater treatment plants are collaborating in the development of Total Maximum Daily Loads (TMDL) for pollutants, including mercury, that are impairing the San Francisco Bay. The TMDL is a quantitative assessment of water quality problems, contributing sources, load reductions or control actions needed to restore and protect water-bodies. The TMDL process will include waste load assessments for non-point sources including abandoned mines.