URANIUM BEHAVIOR IN A PERMANENTLY ANOXIC FJORD - MICROBIAL CONTROL

Uranium contamination of groundwaters resulting from U mining activities and the leakage of nuclear waste from storage facilities is a growing concern. In Framvaren Fjord (southern Norway), dissolved U-238 concentrations at the bacterial maximum layer (24 m), which is situated a few meters below the oxic-anoxic (i.e. oxygen-hydrogen sulfide) interface (18 m), are observed to be approximately 60% lower than concentrations above and below this depth. Removal of U occurs well below the depth at which Fe and Mn oxyhydroxides are precipitated and under conditions inconsistent with abiological reduction of soluble U(VI) to particle-reactive U(IV). Our observations suggest that the microbial population in the anoxic waters near the O2-H2S interface in the fjord exerts an effective control on the aquatic biogeochemistry of U in this environment.