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Fig. 12.10 Conceptual model showing selected a abiotic and b biotic redox processes that
influence the fate of arsenic in the environment. Abiotic processes include (A) oxidation of As
III
and reduction of As
V
(dissolved or surface-bound) by semiquinones and hydroquinones,
respectively (as present, e.g., in humic substances) and (B) formation of reactive Fe
II/III
mineral
phases (e.g., by microbially produced Fe
2+
) that can lead to As
V
reduction or As
III
oxidation as
illustrated in (C). Biotic processes include (A) microbial oxidation of Fe
II
leading to Fe
III
mineral
formation and sorption or coprecipitation of As
III
or As
V
to/with these Fe
III
minerals (oxidation of
Fe
II
can also occur abiotically), (B) microbial reduction of As-loaded Fe
III
minerals leading to
release of As
III
or As
V
into solution, (C) formation of secondary Fe minerals by reaction of
microbially released Fe
2+
with remaining Fe
III
minerals leading to sorption/coprecipitation of As,
and finally (D) direct microbial oxidation of As
III
or reduction of As
V
for either dissimilation or
detoxification (Borch et al.
2010
). Reprinted with permission from Borch et al. (
2010
). Copyright
2010 American Chemical Society
