Lead isotope composition and risk elements distribution in urban soils of historically different cities Ostrava and Prague, the Czech Republic

The impact of intensive industry and other human activities on urban soil pollution and the origin of these pollutants were studied in industrial Ostrava and residential Prague. The concentrations of fourteen risk elements and lead isotopic compositions were assessed in soil samples of urban parks. Prague was characterised by elevated concentrations of As (median 22 mg·kg− 1), Se (0.7 mg·kg− 1), Cu (50 mg·kg− 1), Pb (67 mg·kg− 1) and Ni (27 mg·kg− 1), while Ostrava by Cd (median 0.8 mg·kg− 1), Zn (152 mg·kg− 1), Mn (828 mg·kg− 1) and Cr (43 mg·kg− 1), where Cd reached on average two times higher values compared to Prague parks. Significantly higher concentrations of risk elements were found in both cities in sites under tree crowns compared to open areas. A more considerable trend was observed in Ostrava, a city affected by strong airborne deposition. Differences in Pb isotopic composition between both cities were proven despite their having similar values. Lower 206Pb/207Pb ratios of 1.164–1.206 (median 1.174) were found in Prague, compared to Ostrava with the ratios 1.159–1.198 (median 1.180). The broad range of isotopic ratios in cities corresponds to a combination of different pollution sources and a long term accumulation of pollutants in the soils. One of the lowest ratios (206Pb/207Pb 1.172, mean calculated from all samples of the park — Karlovo náměstí in Prague) was assessed in a park which is significantly influenced by traffic.