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Using Nitrogen and Carbon Dioxide Adsorption to Estimate Arsenic(V) Bioaccessibility in Soils

Peter I. Ravikovitch1, Alexander V. Neimark2, Konstantinos C. Makris3, Dibyendu Sarkar3, and Rupali Datta3. (1) ExxonMobil Research and Engineering, 1545 Route 22 East, Annandale, NJ 08801, (2) TRI/Princeton, 601 Prospect Ave, Princeton, NJ 08542, (3) Earth and Environmental Science Dept., University of Texas, San Antonio, 6900 North Loop 1604, San Antonio, TX 78249-0663

We propose a novel As(V) bioaccessibility model, which was tested on 17 model soils. The model includes only two parameters characterizing surface properties of soils that are readily determined from N2 and CO2-based specific surface areas( SSAs), and total organic carbon (OC) content. We found that N2 and CO2 molecules act as As(V) "surrogates", probing easily-accessible, and relatively difficult to access soil porosity, respectively. The objectives of this study were: i) develop and independently validate an As(V) sorption and bioaccessibility empirical model, utilizing soils comprising a wide range in texture, specific surface area and OC contents; and ii) relate the proposed soil physical properties to soil As bioaccessibility measured by an in-vitro stomach phase test. Three interrelated linear models were constructed that were significant (p<0.001) in explaining 50 and 95 % of the variability observed in As(V) sorption and bioaccessibility, respectively. The models successfully predicted bioaccessible As concentrations for 4 out of the five soils, reaching RMSE values of < 10 %. The performance of the proposed simple models is quite remarkable, which suggests that similar models may be effective for estimation of metals bioaccessibility in soils and sediments.