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.