Uranium contamination of groundwaters resulting from U mining activiti
es and the leakage of nuclear waste from storage facilities is a growi
ng concern. In Framvaren Fjord (southern Norway), dissolved U-238 conc
entrations at the bacterial maximum layer (24 m), which is situated a
few meters below the oxic-anoxic (i.e. oxygen-hydrogen sulfide) interf
ace (18 m), are observed to be approximately 60% lower than concentrat
ions above and below this depth. Removal of U occurs well below the de
pth at which Fe and Mn oxyhydroxides are precipitated and under condit
ions inconsistent with abiological reduction of soluble U(VI) to parti
cle-reactive U(IV). Our observations suggest that the microbial popula
tion in the anoxic waters near the O2-H2S interface in the fjord exert
s an effective control on the aquatic biogeochemistry of U in this env
ironment.