A comparative study of soil metal concentrations in Chilean urban parks using four pollution indexes

Abstract

Toxic metal enrichment in urban soils from natural and anthropogenic sources is a public health concern that challenges sustainable urban development. Active and legacy mining is likely a major contributor of localized metal pollution in resource-based economies, although other sources associated with industrial and trans- portation activities may also contribute in urban settings. In mining countries, such as Chile, with no soil quality regulation, public policies that seek to protect human health should assess metal distribution and pollution in- dexes to guide interventions, especially in urban green spaces. To assess the role of active and legacy mining waste sites within the urban and peri-urban areas, metal concentrations in the soils of urban parks were measured in this study, and four pollution indexes were calculated for four cities of Chile. Copiapo ? and Andacollo in northern Chile represented the cities with several active and legacy mining waste sites located within the urban and peri-urban areas, while conurbation La Serena-Coquimbo and Gran Santiago represented the cities in mining districts that lacked major mining waste sites within their urban perimeters. A total of 82 (Copiapo ?), 30 (Andacollo), 26 (La Serena-Coquimbo), and 59 (Gran Santiago) composite surface soil samples were collected from the urban parks. Considering Canadian guidelines for residential/parkland soils, the value for Cu (63 mg/ kg) was found to be exceeded in 99%, 50%, 100%, and 97% of samples collected from Copiapo ?, La Serena- Coquimbo, Andacollo, and Gran Santiago, respectively. The guidelines for lead (140 mg/kg) and zinc (250 mg/kg) were exceeded in less than 12% of samples collected from Copiapo ? and Gran Santiago. Arsenic was not mainly quantified (<10% quantification frequency, quantification limit = 36 mg/kg). The calculated modified pollution load, Nemerow, and soil quality indexes indicated that soils in the urban parks were more polluted in cities with urban mine wastes, however, the pollution load index ranked higher metal pollution in Gran Santiago. This study presented the first comparative study of metals in urban parks of Chile, highlighting a large proportion of parks with soil copper concentrations above the international guidelines, while showing higher median values in cities containing urban mine waste disposal sites.