Application of spectral gamma and magnetic susceptibility in an As-bearing loessic aquifer, Argentina

Processes that control the dissolution of loess sediments and contribution of arsenic release in the Chaco-Pampean plain, Argentina

“…Two loess samples (TN7 and CN66) were selected from a 70 m deep core drilled in a multilayer loess aquifer in the Claromecó Creek basin near the town of Tres Arroyos (in the southeast of the Province of Buenos Aires): TN7 from a depth of 6-7 m and CN66 from a depth of 65-66 m (Sierra et al, 2018). Both samples were dried at room temperature.…”

“…The hydrogeochemical processes responsible for the elevated As concentrations in shallow groundwaters result from the interaction between the loess sediments and water, which leads to groundwaters usually of the Na-Ca-HCO3 type with pH between 6.7 and 9.2 (Blanco et al, 2006;Nicolli et al, 2010). Under these conditions, the main processes are dissolution of the constituents of the loess sediments (volcanic glass, feldspars, pyroxenes, amphiboles and rock fragments), desorption of As from the surfaces of Fe, Al and Mn oxides and (hydr)oxides, dissolution of fluorapatite coatings (Blanco et al, 2006;Nicolli et al, 2010;García et al, 2014;Sosa et al, 2019;Vital et al, 2019) and dissolution of the arsenate-rich calcite present in the abundant banks of calcrete in the Pampean sediments (Dietrich et al, 2016;Sierra et al, 2018;Vital et al 2019). Thus, it follows that the As concentration in the groundwater depends on (1) the distribution of the phases that make up the loess sediments, (2) the As content in these phases, and on (3) the kinetics of the dissolution and desorption reactions.…”