This study evaluated the efficiency of a bioretention system installed in Daly City, California, for a large suite of pollutants, including some that have been rarely evaluated in such systems. Water quality improvements (concentration or load reductions) were demonstrated for total Hg, polychlorinated biphenols (PCBs) and dioxins ranging between 18 and 100%, and a suite of more conventional pollutants [sediment, cadmium, copper, nickel, lead, zinc, and polycyclic aromatic hydrocarbons (PAHs)] ranging between 20 and 90%.