Most recently, concentrations of both total mercury and methylmercury in fish and water of lower East Fork Poplar Creek (LEFPC) of Oak Ridge increased although the majority of mercury in the site is mercury sulfide. This drives the US DOE and the Oak Ridge Site to study the long-term bioavailability of mercury and speciation at the site. The stability and bioavailability of mercury sulfide as affected by various biogeochemical conditions –presence of iron and manganese oxides have been studied. We examined the possible mechanisms and pathways of iron and manganese oxides in triggering the most recent increase of mercury solubility, bioavailability and mobility in Oak Ridge site. The kinetics of these processes will be discussed.