Each year, about 26 pounds of mercury arrive at the Union Sanitary District Wastewater Treatment Plant. Sources of mercury discharge to wastewater include laboratories, hospitals, dental offices, human waste, food waste, household products, and storm water inflow. Since 1999, the Union Sanitary District has quantified the relative importance of mercury sources using local sampling information in conjunction with data from other wastewater treatment plants and the scientific literature. The source identification study was updated in October 2001, leading to the pie chart presented here.