Mercury > Mercury Measures > Mercury in Biosolids/ Sewage Sludge

Mercury in Biosolids/Sewage Sludge

Sewage sludge, often called “biosolids,” is dried-out sewage. Biosolids are often incinerated or used as a fertilizer. Either of these processes may release mercury into the environment.

The amount of mercury in biosolids represents the amount of mercury entering the sewage-treatment works. Not all mercury is captured as biosolids, and it cannot be treated, so it can enter our waterways as effluent from treatment plants.  Further, biosolids are often incinerated or applied to land as fertilizer. Either of these methods of disposal may allow mercury to enter the environment.

Recent tests of biosolids show mercury levels in decline.  There is an especially marked decline since focused elimination efforts began with dentists. 

Biosolids as an Indicator of the Effectiveness of Mercury Reduction Programs (1995-2007) is an Excel Spreadsheet of the most recent data.

Following are links to information on sampling at three statewide facilities through 2006. 

Mercury in Sewage Sludge/ Biosolids, South Seattle

Mercury in Sewage Sludge/ Biosolids, West Point, Seattle

Mercury in Sewage Sludge/ Biosolids, Spokane

Related information

Mercury in Biosolids is a Beyond Waste performance measures page that explains how mercury reduction is measured through testing sewage sludge.

Manage Dental Waste is an Ecology page that offers technical assistance for Washington state dentists.

Biosolids as an Indicator of the Effectiveness of Mercury Reduction Programs is a pdf of an Ecology presentation

Federal Pretreatment Regulation, 40 CFR part 403, requires that all non-domestic sources of wastewater which represent significant sources of loadings which could harm POTW water systems must obtain a permit and meet local limits. Dentists must generally install and maintain an amalgam separator to meet those limits.