Identifying sources of Pb pollution in urban soils by means of MC-ICP-MS and TOF-SIMS

Lead pollution was evaluated in 17 urban soils from parks and gardens in the city of Vigo (NW Spain). The Pb isotope ratios ((207)Pb/(206)Pb, (208)Pb/(204)Pb, (206)Pb/(204)Pb and (208)Pb/(206)Pb) were determined after being measured by MC-ICP-MS. The association of the isotopes ((204)Pb, (206)Pb, (207)Pb and (208)Pb) with the different components of the soil was studied using TOF-SIMS. The isotopic ranges obtained for the samples were between 1.116 and 1.203 ((206)Pb/(207)Pb), 2.044-2.143 ((208)Pb/(206)Pb), 37.206-38.608 ((208)Pb/(204)Pb), 15.5482-15.6569 ((207)Pb/(204)Pb) and 17.357-18.826 ((206)Pb/(204)Pb). The application of the three-end-member model indicates that the Pb derived from petrol is the main source of Pb in the soils (43.51% on average), followed by natural or geogenic Pb (39.12%) and industrial emissions (17.37%). The emissions derived from coal combustion do not appear to influence the content of Pb in the soil. TOF-SIMS images show that the Pb mainly interacts with organic matter. This technique contributes to the understanding of the association of anthropogenic Pb with the components of the soil, as well as the particle size of these associations, thus allowing the possible sources of Pb to be identified.