The environmental fate, and ultimately bioavailability, of arsenic compounds depends on their surface interactions with reactive components in soil. These components include minerals and natural organic matter (NOM). In general, molecular-level understanding of surface processes at solid/liquid interfaces demands using simple model systems and integrating spectroscopic, calorimetric, computational chemistry and mathematical modeling tools. In this talk, I will show results on the surface chemistry of arsenate, methylated and aromatic arsenicals, with hematite nanoparticles. Spectroscopic data were collected using attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR) and experimental results were complemented with DFT calculations. Flow calorimetric measurements were also completed to gain insight into surface charge and heats of adsorption. Thermodynamic binding constants were extracted from applying the triple layer surface complexation model to adsorption isotherm and pH-envelope data. The kinetics of arsenicals interaction with hematite nanoparticles pre-exposed to three types of low molecular weight organics will also be discussed. The significance of these results will be discussed in relation to improving modeling tools for accurate quantification of environmental exposure to arsenic.

Arsenic speciation at model soil interfaces is key to quantifying environmental exposure

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