Inorganic pollution in urban topsoils of Latin American cities: A systematic review and future research direction

Pollution in urban environments has a direct impact on urban topsoils, which act as sinks and sources of trace elements. This article reviewed the contamination by trace elements (As, Cd, Cu, Pb, Cr, Ni and Zn) in studies of 31 cities in Latin America, including the countries of Argentina, Brazil, Colombia, Chile, Cuba, and Mexico, between 2011 and 2020. The sample collection, analytical tools, references guidelines, range levels of trace elements and their related sources in urban topsoils are presented and were widely compared and discussed in this study. The results showed a great variation in methodologies approach related to sample collection and analytical tools. The type of occupation in urban areas, land use, local geological setting, historical development of anthropogenic actives and the distance of the sources were the most important factors that explain the levels of contamination found. The elements As, Cd, Cu, Pb, and Zn, were the most frequently pointed trace elements, with Cd, Cu, Pb and Zn in high concentrations, related to anthropogenic sources (vehicular traffic, industrial emissions, and combustion of fossil fuels). On the other hand, Ni and Co were related to mixed sources (anthropogenic and natural). Among the studies, the highest concentrations of trace elements associated with industrial sources occur in Mexican cities. Vehicular traffic is pointed out as one of the main sources of contamination in Brazilian cities. Moreover, we discussed literature gaps and propose suggestions for future related studies.