MERCURY DISTRIBUTION IN POPLAR CREEK, OAK-RIDGE, TENNESSEE, USA

As a result of the lithium-isotope separation process used in the prod uction of thermonuclear fusion weapons during the mid-1950s and early 1960s, 150 t of mercury were released into Poplar Creek (via East Fork Poplar Creek) in Oak Ridge, Tennessee, USA. This project was performe d as part of a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) remedial investigation to define the nature an d extent of mercury contamination in Poplar Creek. Ultraclean sampling techniques and ultrasensitive analytical methods were used to determi ne methylmercury and inorganic mercury concentrations in surface water , sediment, and pore water from Poplar Creek. Total methylmercury and inorganic mercury concentrations (0.08-0.7 ng/L and 0.4-560 ng/L, resp ectively) in surface water from reaches downstream from the East Fork Poplar Creek confluence were significantly higher (p < 0.05) than the upstream reference reach (0.05-0.3 ng/L and 0.1-27 ng/L, respectively) . Concentrations in surface water increased with distance downstream f rom the source (East Fork Poplar Creek), which was opposite of expecte d results. Sediment methylmercury and inorganic mercury concentrations also increased with the distance downstream from the source and were highest near the mouth of Poplar Creek (1.0-12 ng/g and 630-140,000 ng /g, respectively). High concentrations in surface water and sediment n ear the mouth of Poplar Creek appear to be a result of sediment deposi tion and resuspension, apparently caused by the stronger Clinch River current acting as a barrier and its backflow into Poplar Creek as a re sult of hydropower operations.