1 research outputs found
Reducing Conditions Influence U(IV) Accumulation in Sediments during <i>In Situ</i> Bioremediation
This study presents field experiments conducted in a
contaminated
aquifer in Rifle, CO, to determine the speciation and accumulation
of uranium in sediments during in situ bioreduction.
We applied synchrotron-based X-ray spectroscopy and imaging techniques
as well as aqueous chemistry measurements to identify changes in U
speciation in water and sediment in the first days follwing electron
donor amendment. Limited changes in U solid speciation were observed
throughout the duration of this study, and non-crystalline U(IV) was
identified in all samples obtained. However, U accumulation rates
strongly increased during in situ bioreduction, when
the dominant microbial regime transitioned from iron- to sulfate-reducing
conditions. Results suggest that uranium is enzymatically reduced
during Fe reduction, as expected. Mineral grain coatings newly formed
during sulfate reduction act as reduction hotspots, where numerous
reductants can act as electron donors [Fe(II), S(II), and microbial
extracellular polymeric substances] that bind and reduce U. The results
have implications for identifying how changes in the dominant reducing
mechanism, such as Fe versus sulfate reduction, affect trace metal
speciation and accumulation. The outcomes from this study provide
additional insights into uranium accumulation mechanisms in sediments
that could be useful for the refinement of quantitative models describing
redox processes and contaminant dynamics in floodplain aquifers