Trace element content in soil after a sediment-laden flood in northern Chile

Purpose: Arid and hyper-arid zones worldwide are reservoirs of chemical compounds, among them are various trace elements. With climate change, abnormal precipitation is occurring in arid and hyper-arid mountainous zones, which in turn is increasing the displacement of trace elements from mountainous to populated areas. The objective of this study was to evaluate trace element displacement of a sediment-laden flood in the Copiapó River Basin on March 24–25, 2015. Materials and methods: Sixty topsoil samples were taken from 20 agricultural fields. Soil organic matter content, pH, electrical conductivity, and particle size were determined according to accepted procedures in Chile. Samples were acid-digested to determine total Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, and Zn content by flame atomic absorption spectroscopy. Hydride generation AAS was used for As and Se determination, and Hg was quantified by cold vapor AAS. Detection limits were 0.2, 0.05, 0.1, and 5.0 mg kg⁻¹ for Cd, Hg, Se, and Mo, respectively. Correlation and principal component analyses were made, and theoretical distribution functions were fitted to each element. Results and discussion: Metal concentration showed a strong correlation between SOM and particle size, explaining the first component from the principal component analysis. All trace elements correlated well between each other except for Mo and Se. Mo values were consistently below detection levels (<5.0 mg kg⁻¹). Expected values for the elements were (95% of probability): 13–37 g Al kg⁻¹, 10–50 mg As kg⁻¹, <0.2–0.6 mg Cd kg⁻¹, 13–25 mg Cr kg⁻¹, 27–281 mg Cu kg⁻¹, 27–40 g Fe kg⁻¹, <0.05–6.5 mg Hg kg⁻¹, 516–1.080 mg Mn kg⁻¹, 7–24 mg Ni kg⁻¹, 13–50 mg Pb kg⁻¹, 0.2–0.6 mg Se kg⁻¹, and 61–172 mg Zn kg⁻¹. Concentrations of As, Cu, and Hg were consistently above national standards. Conclusions: The authors conclude that the trace element contents in sediments deposited by the event are within expected values based on soil data in Chile.