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.