Isotope dilution ICP–MS analysis of platinum in road dusts from west central Scotland

In response to the increased use of catalytic convertors in motor vehicle exhausts systems, recent studies, employing GF–AAS or ICP–MS analysis of platinum group elements (PGEs), have identified a significant increase of Pt and Pd concentrations in road dust and roadside soils leading to concern over potential effects on human health. After deposition, the PGEs are subject to various physical and chemical transformations, potentially resulting in migration into other environmental compartments i.e. soils, the aquatic system and biota. However, the processes involved are poorly understood and the reactivity, bioavailability, and speciation of the PGEs are ill defined. In contrast to environmental studies, in geochemical research, Isotope Dilution ICP–MS (ID ICP–MS) has primarily been used for the quantification of Pt, providing a significant improvement in accuracy by allowing removal from the analyte solution of elements which could potentially give isobaric interference in the mass spectra. In the present work, an ID ICP–MS analytical technique with a detection limit of 0.1 μg kg−1 has been used for determination of concentrations of Pt in road dust samples from west central Scotland. The study highlights potential interference problems that may occur in analysis of Pt in environmental matrices using ICP–MS. Initial application of ID ICP–MS in a study of roadside environments in west central Scotland has revealed significantly enhanced concentrations of Pt, within the range 13–335 μg kg−1, in road dust samples from a trunk road and motorway, representing a significant increase relative to surface soils in this area that are remote from roads, which have Pt concentrations of less than 1.0 μg kg−1. In contrast, lower levels of contamination of 1.8–11.8 μg kg−1 were observed for dust samples from residential areas, in the town of East Kilbride.