Binding affinities of arsenic to environmental dissolved organic matter: Behavior differences of hydrophilic/phobic...

The As binding properties of environmental water-soluble organic matter (WSOM) fractions from the Chaohu Lake Basin were investigated following their separation and extraction based on polarity. Specifically, the hydrophilic component (HPI-WSOM) constituted 8.7 % to 59.2 %, the transitional component (TPI-WSOM) made up 19.1 % to 74.1 %, and the hydrophobic component (HPO-WSOM) represented 17.2 % to 37.5 % of the bulk WSOM dissolved organic carbon (DOC) content. The experimental approach involved measuring As concentrations both inside and outside a dialysis bag during complexation equilibrium. The equilibrium times and strengths were analyzed, and the findings revealed that WSOM derived from aquatic plants, which had the highest percentage of HPO, required the longest time to reach equilibrium, suggesting a more extended period was necessary to achieve balance. The adsorption efficiency (AE) of As was assessed by examining the influence of the DOC to As concentration ratio (Fc) on As complexation. A strong linear correlation was observed between AE and Fc (with R2 values ranging from 0.85 to 0.99), indicating a reliable prediction of As speciation and, consequently, its bioavailability in natural waters. The binding capacity of As to different environmental WSOM, as well as the hydro-philic/phobic fractions, was quantified using the conditional distribution coefficient (Kd). Sedimentary WSOM exhibited the highest Kd values, while that from farmland soil showed the lowest, with this trend positively correlating with the combined percentage of HPI and TPI DOC concentration percent in the samples. The results also highlighted the key role of TPI fractions in the complexation process.