Trace metals concentrations in schoolyard and playground soils in Coronel city, Chile

An urban world population of 0.75 billion in 1950 and expected 6 billion in 2050 shows the tremendous potential growth of urban areas. The urban soil fulfills the role of the reactor for the physical, chemical and biological transformations of matter but also covers such functions as reduction of air pollution, regulation of climate elements in cities, source of biodiversity and formation of areas for ornamental and recreation purposes. As a usual part of urban ecosystems, urban soils in general have high concentrations of trace elements derive from human activities. The objectives of this work were (1) to quantify the concentrations and establish background levels of Ba, Co, Cr, Cu, Mn, Pb, Ni, V and Zn in soils of Coronel city; (2) to assess the degree of pollution and identify local sources of pollution and (3) to assess the health risks of TE in soils of Coronel city. From Coronel city were collected 129 samples from 43 sites located in schoolyards and playground areas. At each sampling point were taken three samples: topsoil sample (TS) (0-10 cm), subsoil sample (SS) (10-20 cm) and deep soil sample (DS) (150 cm). Multivariate statistical analysis and depth ratios were used to distinguish the source. Ecological indices were implemented to evaluate the degree of contamination. The median and (range) of the trace elements (TE) in TS were Ba 38 mg kg^-1 (12-147 mg kg^-1), 38 mg kg^-1; Co 4-40 mg kg^-1; 15 mg kg^-1; Cr 10-35 mg kg^-1, 18 mg kg^-1; Cu 12-70 mg kg^-1, 22 mg kg^-1; Mn 167-950 mg kg^-1, 536 mg kg^-1; Ni 11-115 mg kg^-1, 35.5 mg kg^-1; Pb 1.5-115 mg kg^-1, 6 mg kg^-1; V 52-528 mg kg^-1, 94 mg kg^-1; Zn 42-373 mg kg^-1, 65 mg kg^-1. Depth ratios and multivariate statistical analysis suggested that Co, Ni and Mn have principal contribution of geogenic sources and Ba, Cr, Cu, Pb, V and Zn anthropogenic sources. The upper limit of background values estimated with median absolute deviation (MAD) method and DS samples were Ba 30 mg kg^-1,  Co 24 mg kg^-1,  Cr 22 mg kg^-1,  Cu 24 mg kg^-1,  Mn 662 mg kg^-1,  Ni 66 mg kg^-1,  Pb 1.5 mg kg^-1,  V 108 mg kg^-1,  and Zn 52 mg kg^-1. Contamination factor showed that some soil sample were categorized as considerable contamination to very high contamination for Pb, Zn and V. Both Hazard index and cancer risk indicated no adverse health effects.

Keywords: Heavy metals, urban soils, ecological indices, health risk assessment