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Effect of Natural Organic Matter on the Fate of Cadmium During Microbial Ferrihydrite Reduction
journal contribution
posted on 2020-07-17, 00:13 authored by Zhe Zhou, E. Marie Muehe, Elizabeth J. Tomaszewski, Juan Lezama-Pacheco, Andreas Kappler, James M. ByrneNatural
organic matter (NOM) is known to affect the microbial reduction
and transformation of ferrihydrite, but its implication toward cadmium
(Cd) associated with ferrihydrite is not well-known. Here, we investigated
how Cd is redistributed when ferrihydrite undergoes microbial reduction
in the presence of NOM. Incubation with Geobacter sulfurreducens showed that both the rate and the extent of reduction of Cd-loaded
ferrihydrite were enhanced by increasing concentrations of NOM (i.e.,
C/Fe ratio). Without NOM, only 3–4% of Fe(III) was reduced,
but around 61% of preadsorbed Cd was released into solution due to
ferrihydrite transformation to lepidocrocite. At high C/Fe ratio (1.6),
more than 35% of Fe(III) was reduced, as NOM can facilitate bioreduction
by working as an electron shuttle and decreased aggregate size, but
only a negligible amount of Cd was released into solution, thus decreasing
Cd toxicity and prolonging microbial Fe(III) reduction. No ferrihydrite
transformation was observed at high C/Fe ratios using Mössbauer
spectroscopy and X-ray diffraction, and X-ray absorption spectroscopy
indicated the proportion of Cd-OM bond increased after microbial reduction.
This study shows that the presence of NOM leads to less mobilization
of Cd under reducing condition possibly by inhibiting ferrihydrite
transformation and recapturing Cd through Cd-OM bond.