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Mercury in Biosolids

This indicator tracks the amount of mercury detected in  biosolids, or treated sewage sludge, at six facilities in Washington:  the Spokane Advanced Wastewater Treatment Plant, the South Wastewater Treatment Plant (Renton), the West Point Wastewater Treatment Plant (Seattle), Tacoma Central Plant, the LOTT Regional Wastewater Treatment Plant (Olympia and surrounding area), and the Burlington Wastewater Treatment Plant.

Mercury is a heavy liquid metal in its elemental form. Mercury occurs naturally in certain hard-rock and metallic ores, and can enter the environment from both natural emissions and human activities. It reacts with other substances to form organic and inorganic compounds, as well as amalgams with other metals. All forms of mercury can be toxic to humans and other animals, depending on the route and amount of exposure. Currently, about 3,800 to 5,000 pounds of mercury are released into Washington's environment each year from human sources within the state, such as coal-burning power plants, wastewaters from dental offices, and other businesses, homes, and schools.

What are Biosolids?

Biosolids are a semi-solid by-product of wastewater treatment at sewage treatment facilities.  Typically biosolids are treated to meet high standards that allow them to be applied to the land for beneficial use. 

View data: Biosolids data

The amount of mercury measured in biosolids has significantly decreased since 2000. The second largest reduction occurred in 2003 - 2004, after mercury-reduction efforts began. These efforts include the introduction and use of amalgam separators in dental offices, as an alternative to sending the material down the drain.  The average concentration of mercury in biosolids has decreased by 50 to 70 percent since measurements began. This trend is also apparent at the other facilities being tracked.

Why should we be concerned about how much mercury is in biosolids?

Biosolids are used as an indicator to measure the success of mercury abatement programs.  Biosolids are not the original nor the primary source of the up to 5,000 pounds of mercury released in Washington every year.  Mercury collects from many sources upstream of the wastewater treatment plant. Dental use represents a large percentage of mercury in use. Reducing this source has significant effects on the overall amount of mercury in our environment.

The amount of mercury in biosolids represents the amount of mercury entering the sewage system from dental offices and other sources. Biosolids are often incinerated or applied to land as soil amendments. Either of these methods of management may allow mercury to enter the environment, so less mercury in biosolids means less mercury entering the environment.

What are the benefits of reducing the amount of mercury in biosolids?

• Keeps mercury out of the environment.
• Prevents mercury poisoning in humans and animals.

What are some Beyond Waste actions being taken to decrease mercury in Washington?

• Ecology entered into a Memorandum of Understanding with the Washington State Dental Association in 2003 to eliminate mercury released into publicly owned treatment plants through the installation of amalgam separators. In 2005, the use of these separators became mandated by law.
• The Mercury Education and Reduction Act banned the sale of many mercury-containing products in Washington State.
• Through the Mercury Chemical Action Plan (CAP), many local governments have established mercury-thermometer, auto switch, and thermostat take-back programs, as well as school lab cleanups.
• Ecology supports the collection and recycling of fluorescent and other lamps that contain mercury, and is working on implementing the new mercury light products stewardship law.

Want more information on mercury in Washington?

• Mercury Web site
• Biosolids Web site
• Mercury Chemical Action Plan
• Mercury Education and Reduction Act