An assessment of the potentially hazardous element contamination in urban soils of Arica, Chile

Abstract

As a common component of urban ecosystems, urban soils generally have elevated concentrations of potentially hazardous elements originating from both point and diffuse sources of pollution in cities. This study focuses on the port city of Arica in northern Chile, where anthropogenic activities may have led to contamination of the uppermost topsoil layer. The purpose of this study is to (1) establish background content levels of potentially hazardous elements in topsoils of different land uses using different statistical approaches and (2) assess the degree of topsoil pollution and identify the local sources of pollution using multivariate statistical and geostatistical methods. Data from a Chilean Government CONAMA report were analyzed. Geostatistical methods such as kriging were applied to identify the spatial distribution of potential hazards elements. Potentially hazardous elements' background values were determined by median+2MAD, inflection points within cumulative frequency plots and upper whisker of a Tukey's boxplot. Multivariate statistical methods were applied in the identification of trace metal sources (anthropogenic vs natural origin). Soil pollution assessment was performed using the geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (Cf) and integrated pollution index (IPI). The maps obtained show high baseline values for some elements (As, Cu, Pb and Zn), which denote a clear anthropogenic contribution due to the long period of constant human activities in the study area. Therefore, background values are estimated with the median+2×MAD procedure and yielded As (17.4mgkg−1), Ba (23.3mgkg−1), Cr (13.6mgkg−1), Cu (37.4mgkg−1), Ni (8.3mgkg−1), Pb (313mgkg−1), V (101mgkg−1) and Zn (235mgkg−1). The calculated soil pollution indexes Igeo, EF, Cf and IPI revealed significant ecological impacts. Copper and As are the two trace elements with the highest contaminated soil values; however, Cu, Pb and Zn have greater numbers of soil sample sites in the moderately to heavily contaminated range. The IPI showed extremely high pollution index in ten soil sites in Arica. Moreover, significant differences were observed with different land uses, where soils along the railway line and industrial area are the most polluted.