Resumen del producto

Potentially toxic element (PTE) geochemical mobility for the sediments of ephemerous arroyo downstream along the San Juan de los Planes drainage basin, affected by heavily polluted tailings and smelting solid wastes of past activities of the San Antonio gold mining district, was assessed to know the PTE bioavailability and related environmental risk in this coastal environment. Due to the desertic semi-arid climate, the fluvial PTEs migration downstream to La Ventana Bay occurs only during episodic rains of tropical cyclones or hydrometeoroligal fronts events. To assess the concentrations of total, reactive and highly reactive PTEs the fine-grained (<63 µm) arroyo sediments were treated by three leaching solutions: a ) concentrated HNO₃; b) 1M HCl and c) ascorbic citrate solution. Arsenic and Cd concentrations in a leachates were determined by electrothermal atomic absorption spectrometry (AAS), whereas Cu, Fe, Mn Pb and Zn were measured by flameless AAS. Total arsenic concentrations in the fine fraction of the sediments remained fairly constant (230-270 mg kg^-1) along the section, while its mobile reactive phase increases downstream from low values of 2.3 mg kg^-1 (0.99 % relative contribution) at the initial point of the arroyo in the mountainous area near Au smelter ruins and reaching 191-220 mg kg^-1 (75-89 % relative abundance) in the sediments of the La Bocana mouth near the sea. Such drastic increase in the mobility might be a result of As (+3) oxidation from insoluble sulphides of the sediments to more reactive As (+5) probably coprecipitated with Fe oxyhydroxides. The mobile phase of a rest of studied PTEs in arroyo sediments remained relatively small part from their total concentration, revealing low reactivity. The high mobility of As represents an potential risk for the drainage basin, especially due to the use of the soils for agriculture. Additionally, mobile As after the rains could reach the aquifer and transported from it through the subterranean estuary to the Ventana Bay, as it occurs with episodical surface fluvial input after the rains.

Palabras clave: Movilidad; Arsénico; sedimentos finos; arroyo San Antonio

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