Evaluating natural and anthropogenic inputs on the distribution of potentially toxic elements in urban soil of Valdivia, Chile.

The increasing population in urban areas in the last decades requires an effort to understand the geochemistry of contaminant elements in urban soil. Topsoil plays a crucial role in the exposure of Potentially Toxic Elements (PTEs) to humans through ingestion, dermal contact, and inhalation. In Chile, the last census revealed that 88.6% of people live in cities or towns and only 11.4% in rural areas. This study presents the first systematic geochemical survey of urban soil in the city of Valdivia, in the South of Chile. Topsoil samples (0-10 cm depth) were collected in less disturbed locations within the city at 130 sampling sites using a grid of 0.25 km2 squares covering a total area of approximately 30 km2. The concentrations of Al, Fe, Na, Ca, Mg, K, Ti, Be, V, Cr, Mn, Co, Ni, Cu, Zn, As, Mo, Sn, Cd, Se, Pb and Hg were measured. The results showed that high concentrations of Cu, V, Zn and Pb are located mainly in the city's northern area and exceed international soil quality legislation for agricultural use. Data processing comprised plotting of individual spatial distribution maps and the use of a combination of multivariate statistical methods. Hierarchical cluster analysis and principal component analysis identified three element associations. The two element groups V-Al-Ti-Fe-Cr-Co-Mn-Be-Ni and Ca-Na-K-As-Mg are interpreted as a dominant lithological origin related to the most pristine soil conditions in less populated areas. By contrast, the Sn-Pb-Zn-Mo-(Cu-Hg) association presents a significant correlation with urbanization indicators, including vehicular traffic and industrial activities developed since the end of the nineteenth century in Valdivia.

Hydrogeochemical processes controlling the water composition in a hyperarid environment: New insights from Li, B, and Sr isotopes in the Salar de Atacama.

Northern Chile, NW Argentina, and SW Bolivia, ("the lithium triangle"), represent a world class reservoir of lithium, but this extraordinary enrichment is still controversial, and different processes have been invoked over the years, including, geothermal waters associated with active volcanism, leaching of soluble salts from volcanic rocks and leaching of lithium-rich clays. The Salar de Atacama (SDA) represents one of the richest reservoirs of Li in northern Chile and has been extensively studied during the past years. Most of the studies have been focused in the southern and southeastern portions, where the highest lithium concentrations have been reported. However, a comprehensive model of water recharge at SDA is still imprecise. We used a combination of isotopic methods, including δ7Li, δ11B and 87Sr/86Sr ratios, with their chemical composition of a set of water samples from salt lakes, geothermal manifestations, groundwaters and surficial diluted waters (rivers and streams with low salinity). This study explores the hydrogeochemical processes controlling the water composition and solute distribution of the SDA. Our data confirm that weathering of the ignimbrites constitutes one of the most important processes in relation of solute origin in the region, where deep water-rock interactions would operate at high temperature, enhancing leaching of Li and other solutes. We determine that groundwater flow entering the SDA has undergone pre-enrichment processes (e.g., leak from Altiplano salt lakes; evaporite dissolution, among others) associated with salt inputs in the Western Cordillera. Our results provide a step forward to a comprehensive understanding of the processes that govern brine formation and lithium enrichment in a hyperarid environment, contributing to a sustainable exploration and exploitation of lithium in these environments.