TY - JOUR
T1 - Influence of Fe(III) source, light quality, photon flux and presence of oxygen on photoreduction of Fe(III)-organic complexes – Implications for light-influenced coastal freshwater and marine sediments
AU - Lueder, Ulf
AU - Jørgensen, Bo Barker
AU - Maisch, Markus
AU - Schmidt, Caroline
AU - Kappler, Andreas
N1 - Publisher Copyright:
© 2022 Elsevier B.V.
PY - 2022/3
Y1 - 2022/3
N2 - Iron(III) photoreduction is an important source of Fe(II) in illuminated aquatic and sedimentary environments. Under oxic conditions, the Fe(II) can be re-oxidized by oxygen (O2) forming reactive O-species such as hydrogen peroxide (H2O2) which further react with Fe(II) thus enhancing Fe(II) oxidation rates. However, it is unknown by aquatic sediments how the parameters wavelength of radiation, photon flux, origin of Fe(III) source and presence or absence of O2 influence the extent of Fe(II) and H2O2 turnover. We studied this using batch experiments with different Fe(III)-organic complexes mimicking sedimentary conditions. We found that wavelengths <500 nm are necessary to initiate Fe(III) photoreduction and that the photon flux, wavelength and identity of Fe(III)-complexing organic acids control the kinetics of Fe(III) photoreduction. The formation of photo-susceptible Fe(III)-organic complexes did not depend on whether the Fe(III) source was biogenically produced, poorly-crystalline Fe(III) oxyhydroxides or chemically synthesized ferrihydrite. Oxic conditions caused chemical re-oxidation of Fe(II) and accumulation of H2O2. The photon flux, wavelength and availability of Fe(III)-complexing organic molecules are critical for the balance between concurrent Fe(III) photoreduction and abiotic Fe(II) oxidation and may even lead to a steady-state concentration of Fe(II) in the micromolar range. These results help understand and predict Fe(III) photoreduction dynamics and in-situ formation of Fe(II) in oxic or anoxic, illuminated and organic-rich environments.
AB - Iron(III) photoreduction is an important source of Fe(II) in illuminated aquatic and sedimentary environments. Under oxic conditions, the Fe(II) can be re-oxidized by oxygen (O2) forming reactive O-species such as hydrogen peroxide (H2O2) which further react with Fe(II) thus enhancing Fe(II) oxidation rates. However, it is unknown by aquatic sediments how the parameters wavelength of radiation, photon flux, origin of Fe(III) source and presence or absence of O2 influence the extent of Fe(II) and H2O2 turnover. We studied this using batch experiments with different Fe(III)-organic complexes mimicking sedimentary conditions. We found that wavelengths <500 nm are necessary to initiate Fe(III) photoreduction and that the photon flux, wavelength and identity of Fe(III)-complexing organic acids control the kinetics of Fe(III) photoreduction. The formation of photo-susceptible Fe(III)-organic complexes did not depend on whether the Fe(III) source was biogenically produced, poorly-crystalline Fe(III) oxyhydroxides or chemically synthesized ferrihydrite. Oxic conditions caused chemical re-oxidation of Fe(II) and accumulation of H2O2. The photon flux, wavelength and availability of Fe(III)-complexing organic molecules are critical for the balance between concurrent Fe(III) photoreduction and abiotic Fe(II) oxidation and may even lead to a steady-state concentration of Fe(II) in the micromolar range. These results help understand and predict Fe(III) photoreduction dynamics and in-situ formation of Fe(II) in oxic or anoxic, illuminated and organic-rich environments.
KW - Iron(II) oxidation
KW - Iron(III) photoreduction
KW - Light
KW - Organic complexation
KW - Reactive oxygen species
KW - Redox reactions
UR - http://www.scopus.com/inward/record.url?scp=85122384289&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2021.152767
DO - 10.1016/j.scitotenv.2021.152767
M3 - Journal article
C2 - 34982989
AN - SCOPUS:85122384289
SN - 0048-9697
VL - 814
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 152767
ER -