Analytical workflow to trace lead sources in fill-derived soils in Turku, Southwest Finland

We present an analytical workflow scheme to trace the source of lead and to estimate risks to lead contaminated soil and demonstrate the methods with test sites from the city of Turku. This workflow includes lead concentration, sequential extractions, mineralogical characterization, and isotope composition. Lead concentrations higher than 100 mg/kg were found in 16 out of 219 urban topsoil samples in the city of Turku during soil geochemical baseline mapping. Ten samples were selected for detailed geochemical and mineralogical studies. Most of the elevated Pb concentrations were measured from fill-derived soils. Mineralogical investigations using FE-SEM-EDS demonstrated that Pb exists in various types of particles and compounds in the Turku topsoil samples. Most of the particles appear to be of anthropogenic origin. The Pb isotopic compositions measured on individual Pb-bearing particles using laser ablation MC-ICP-MS in Turku soil rule out their origin from Finnish and Swedish bedrock. Thus, Pb in the fill-derived soils must have been imported from other regions. Based on the combined use of traditional geochemical study and advanced micro-analytical techniques, it was found that Pb in urban fill-derived soils is bound to various carrier phases and has several pollution sources. When Pb-containing urban soil is reused in city constructions, care should be taken to prevent direct contact with the Pb-containing soil and dust generation at such sites.