Abstract
With the objective of increasing information inorganic pollutants in urban soils in Spain, we studied the presence of Cu, Pb, Zn, Ni, Cr, and As in 55 soils in the city of Santiago de Compostela (northwestern Spain). The soils were developed over diverse parent materials (granites, gneiss, schists, and amphibolites) and present different land uses, urban grasslands, urban forests, urban allotment gardens, and peri-urban agricultural soils. Total trace element concentrations, analyzed by XRF of ground samples, were correlated to physicochemical properties of the soils, and the influence of land use, lithology, and location on the degree of pollution was explored. In most soils, trace element concentrations followed the sequence Zn (55–484 mg kg−1) > Pb (20–566 mg kg−1) > Cr (17–277 mg kg−1) > Cu (17–188 mg kg−1) > As (13–205 mg kg−1) > Ni (11–91 mg kg−1). The concentrations were overall higher than regional backgrounds, but not high enough to class the soils as contaminated according to the Spanish regulation. Accordingly, the geoaccumulation index values indicate that most soils present low to moderate pollution levels. Among the elements studied, Cu, Pb, and Zn were correlated between them, with their highest concentrations happening in soils of the green areas in the city center; Cr and Ni concentrations were related to lithology of the parent material, with the highest concentrations in soils developed over amphibolite; finally, As concentrations are higher in two precise points without a clear connection to a known source of pollution.
Highlights
The intensification of urbanization is a key feature of our current society
With the objective of contributing information about urban soil contamination in Spain, in this work, we have studied the presence of heavy metals and arsenic in the soils of the city of Santiago de Compostela (Spain), for which these analyses have not been performed to date
A significant influence of lithology was not observed, but higher Zn concentrations were observed in agricultural soils (Figure 1, p = 0.004**) and if we look at the spatial distribution (Figure 3), Zn concentrations were clearly higher in the city center
Summary
The intensification of urbanization is a key feature of our current society. The spectacular increase in agricultural productivity during the last century has increased global population and reduced the needs of workforce in agriculture, producing a generalized exodus from rural areas towards cities. For example in Europe, the surface area covered by cities increased by 78% since the 1950s, a trend that is expected to continue globally. This spectacular growth in urban population represents a major challenge for the environment: urban areas are confronted by specific environmental issues (e.g., food dependency, local climate), as they concentrate population, activities and infrastructures. These issues have been recognized by the U.N. in their 2030 Agenda for Sustainable Development, in particular in the Sustainable Development Goal no. These issues have been recognized by the U.N. in their 2030 Agenda for Sustainable Development, in particular in the Sustainable Development Goal no. 11: “Sustainable cities and communities”, whose objective is “to make cities inclusive, safe, resilient and sustainable”
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