Isotopic characterisation of lead in contaminated soils from the vicinity of a non-ferrous metal smelter near Plovdiv, Bulgaria

Soil samples from the vicinity of a non-ferrous metal smelter near Plovdiv, Bulgaria contained very high concentrations of cadmium, lead and zinc (up to 140, 4900 and 5900 mg kg−1, respectively). A roadside soil in a relatively uncontaminated area also contained high concentrations of the same metals (24, 1550 and 1870 mg kg−1, respectively) indicating that the transport of ores could be a source of contamination. Even though the lead isotope ratios in all the samples fell within a very narrow range (for example, 1.186-1.195 for 206Pb/207Pb), the samples could be differentiated into three distinct groups: ores (206Pb/207Pb and 208Pb/207Pb ratios of 1.1874-1.1884 and 2.4755-2.4807, respectively), current deposition (1.1864 and 2.4704-2.4711, respectively) and local background (1.1927-1.1951 and 2.4772-2.4809, respectively). Although most of the current deposition has its origin in the ores used at the smelter, up to 12% could be from other sources such as petrol lead.