Mercury levels in King County biosolids:

Over the last few years, 95 percent of King County dental offices have taken steps to reduce the amounts of mercury and silver discharged to the sewer system. Most offices have installed amalgam separators and followed the required Best Management Practices (BMPs) for amalgam wastes and spent fixer.

Partially as a result of these activities, mercury levels in King County biosolids have dropped by 50 percent.

The following graph illustrates the reduction in mercury in the county's biosolids:

The condition of our biosolids is the best indicator of the quality of King County wastewater discharges. King County's biosolids contain only very small amounts of metals and organic chemicals, thanks to the cooperation of county businesses and industry. After processing and treatment, the county's biosolids are beneficially recycled used as soil conditioners on farms, forests, lawns and gardens. Efforts to remove mercury from wastewater are ways to keep biosolids clean and safe for recycling.

To help sustain this success, the King County Industrial Waste Program is monitoring how dental offices are practicing the required BMPs by continuing to inspect a portion of these offices each year. And we will continue to track mercury levels in the county's biosolids.

The county is also participating in a national study of mercury concentrations in the treatment plant influent, effluent, and biosolids, under the auspices of the National Association of Clean Water Agencies (external link).