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DETERMINING ARSENIC MOBILITY AND SPECIATION: AN ANALYSIS OF SOIL CONTAMINATED BY WATER FILTRATION TECHNIQUES IN COSTA RICA Danira Garcia Gutierrez a , Amanda Jo Zimmerman b , Matthew G. Siebecker c Introduction o Access to clean water is a fundamental aspect of survival. In areas with contaminated water, filtration systems are used to provide local communities with access to clean potable water. o In Costa Rica, local water filtration plants remove contaminants, such as arsenic, out of drinking water sources. The filters are composed of anatase (TiO 2 ). o The arsenic-enriched filter waste is then partially deposited on soil surfaces and affected by runoff. o The implications of the arsenic contaminated soil with respect to toxicity and transport are still unknown. o Understanding the physical properties of the arsenic, such as speciation and mobility, are the first steps to determining the risk to nearby communities and the environment. Objectives o To determine the physicochemical properties of the contaminated soils and drinking water filter waste containing arsenic. o Physiochemical properties such as mobility, speciation, and mineralogy will be determined. Materials and Methods o The hydrometer method for particle size analysis was conducted to find the distribution percentages of sand, silt and clay in the sediment samples. o X-Ray Diffraction (XRD) measured diffraction values of samples when hit with X-rays to determine the identity of crystalline structures in the sediments. Instrument: Rigaku Ultima III XRD, TTU Department of Chemistry o X-ray absorption spectroscopy of sediment samples were prepared and sent to the synchrotron light source in France, where arsenic speciation and elemental trends in the samples were measured. Instrument: Samba Beamline, Soleil Synchrotron, France o Portable X-ray fluorescence (XRF) detected the elemental concentrations in the sediments. Instrument: Vanta series PXRF analyzer (Olympus) o Scanning Electron Microscope (SEM) images visualized the surface morphology of the sediments. Instrument: Hitachi S-4300 E/N (FESEM), TTU Department of Experimental Sciences Results Discussion Conclusion and Future Work Acknowledgments I would like to thank the Honors College Undergraduate Research Scholars Program supported by the CH and Helen Jones Foundations. I would also like to thank the TTU Office of International Affairs Travel Grant, Department of Plant and Soil Science, Dr. Bo Zhao (CASM, TTU), and Dr. Daniel Unruh (Chemistry and Biochemistry, TTU). References Figure 1: Map of Costa Rica Sampling Sites Figure 4: SEM image of Worm Accretion sample from Don Miguel Site shows suspected TiO 2 on sand grain Figure 5: SEM Image of clay fraction of sample from Montenegro site showing TiO 2 particles As ppm Ti ppm Al ppm Fe ppm V ppm Don Wt Cast 318 225777 8156 8972 397 Don M 161 445 339711 2163 8085 518 Don Surf 262 221435 12856 24735 342 San M. 161 106101 25175 19984 254 Mont #1 517 328629 8682 6775 636 Mont 328 404 270117 7728 6895 446 Mont 413 339 239352 10218 8868 420 Bebe Drive 212 251584 8490 24624 366 Bebe 200 157 252357 9146 22049 393 Figure 3: Ti K alpha versus the As K alpha emission spectra. This figure shows correlation between amount of Titanium and Arsenic. This suggests the As is binding to the Ti particles. Table 1: PXRF values taken at sediment collection site. The values are listed in ppm or part per million. Figure 6: Photograph taken during sediment sample collection in Costa Rica near water filtration plant Figure 2: X-ray absorption near edge spectra (XANES) of As(III)vs. As(V) a Department of Chemistry and Biochemistry, b Department of Plant and Soil Sciences As V As III Table 2: Particle Size Distribution values obtained via Hydrometer Method and soil texture according to USDA. Sand 0.05-2 mm, Silt 0.002- 0.05 mm, Clay <0.002 mm in diameter o The PXRF data revealed the sediments contain 157-517 ppm of As and 106101-339711 ppm of Ti. Titanium (Ti) is the most prominent element in each of the samples because the filters are composed of TiO 2 particles. o X-Ray Absorption Data from the synchrotron helped speciate the arsenic to be As V. The data shows the arsenic in the sediments aligns with the arsenic V standard peak but not with the arsenic III standard peak. o The particle size data analysis shows the sediments are loam texture with high silt values up to 48%. The high percentage of small particles enriched with arsenic increases the mobility of the contaminant through the air, which increases the inhalation risk of nearby residents. o XRD analysis data indicate the sediments are primarily composed of anatase (TiO 2 ) o Arsenic is most likely bound to anatase, a compound containing Ti. The sediments are predominantly Ti with up to about 34% Ti. o The arsenic was successfully speciated using the X-ray absorption spectroscopy and found to be Arsenic V (pentavalent). o The particle sizes of the samples, which is predominantly silt, suggests the soil is susceptible to wind and dust formation. The high percentage of small particles increases the mobility of the contaminant through the air, which increases the inhalation risk of nearby residents. o Additionally, the small particle size increases the mobility of the arsenic-enriched particles due to enhanced transport during water erosion and moves them towards potential sources of groundwater and irrigation water. o Future work will explore the risk of contaminant on the environment and the people in local communities. Sand Silt Clay Result Don Wt Cast 37 59 4 Silt Loam Don M 161 56 32 12 Sandy Loam Don Surf 38 57 5 Silt Loam San M. 45 40 15 Loam Mont #1 29 58 12 Silt Loam Mont 328 28 58 14 Silt Loam Mont 413 27 57 16 Silt Loam Bebe Drive 36 48 16 Loam Bebe 2000 38 36 26 Loam 1.Clancy, T.M., Hayes, K.F., Raskin, L., 2013, Arsenic Waste Management: A Critical Review of Testing and Disposal of Arsenic-Bearing Solid Wastes Generated during Arsenic Removal from Drinking Water, Environ. Sci. Technol., 47, 19, 10799-10812 2. Hu, S., Shi, Q., Jing, C., 2015, Groundwater Arsenic Adsorption on Granular TiO2: Integrating Atomic Structure, Filtration, and Health Impact Environ. Sci. Technol., 49, 16, 9707-9713 3. Jensen, J.L., Schjønning, P., Watts, C.W., Christensen, B.T., 2017, Soil Texture Analysis Revisited: Removal of Organic Matter Matters More than Ever PLoS ONE 4.USDA, Natural Resources Conservation Service, Soil Texture.
