Oral Presentation SETAC Asia-Pacific Virtual Conference 2022

Insight into the Effect of Natural Organic Matter on the Photooxidation of Arsenite Induced by Colloidal Ferric Hydroxides in Water (#31)

Yi Wu 1 , Xingyun Huang 1 , Jing Xu 2 , Jinjun Li 1 , Gilles Mailhot 3 , Feng Wu 1
  1. Hubei Key Lab of Biomass Resource Chemistry and Environmental Biotechnology, School of Resources and Environmental Science, Wuhan University, Wuhan 430079, China
  2. State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
  3. Universite Clermont Auvergne, CNRS, SIGMA Clermont, Institut de Chimie de Clermont-Ferrand, F-63000, Clermont–Ferrand, France

Surface complexation of arsenite (As(III)) onto colloidal ferric hydroxide (CFH) plays an important role not only in the adsorptive immobilization of As(III) but also in the subsequent oxidation of As(III) to As(V) via light-induced ligand-to-metal charge transfer (LMCT) in water at near-neutral pH. However, the effects of natural organic matters (NOM), especially humic substances (HSs) and low molecular weight carboxylic acid (CAs) have not been sufficiently understood. In this work, the inhibition of photooxidation of As(III) in terms of the apparent rate constants (kobs) by six typical HSs and seven CAs has been observed in water containing 66 μM Fe(III) and 5 μM As(III) at pH 7 under UVA and UVB irradiations. A model for calculating the total inhibition factor (T) was defined as Tcal = S × C, wherein light-screening factor (S) was obtained by the absorbance of NOM, and competitive complexation factor (C) was obtained by fitting modified Langmuir or Freundlich models to the amount of As(III) desorbed from CFH upon the addition of NOM. By comparing Texp (ratio of kobs values with and without NOM) with Tcal, it can be concluded that the model was accurate and the Freundlich model (RMSE for HSs 0.1609 and for CAs 0.1771) was better than the Langmuir model (RMSE for HSs 0.1969 and for CAs 0.2496). A linear equation of Texp versus the product of S and C was obtained as Texp = (0.84 ± 0.04) S × C + (0.02 ± 0.03) (RMSE 0.1700) based on the Freundlich model, which was simple and more accurate for all of the NOM investigated. This work provided an estimation method for the effects of NOM on As(III) photooxidation in the presence of CFH and facilitated a deep understanding of the geochemical cycle and fate of arsenic in sunlit water.

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  3. Huang, X., Peng, Y., Xu, J., Wu, F., Mailhot, G., 2021. Iron(III)-induced photooxidation of arsenite in the presence of carboxylic acids and phenols as model compounds of natural organic matter. Chemosphere. 263.