Neil I. Ward*, Karen Stead, Robert J. Hares (ICP-MS Facility, Department of Chemistry, School of Physics and Chemistry, University of Surrey, Guildford, Surrey, GU2 5XH, UK.)

The A34 through Newbury, Berkshire is a main north-south route for many vehicles, having typical daily traffic densities of ~30,000. Roadside dust and soil samples collected from five areas were analysed by acid digestion (total elemental content) and sequential extraction (elemental concentration according to geochemical fraction). Analysis was performed using a Finnigan MAT SOLA ICP-MS instrument for Cd and Pb, with on-line internal standardisation. Total Pb values along the A34 are typically 8 fold higher than non-motorway sites. Higher levels are found in dust samples. Traffic density patterns correlate well with heavy metal levels, especially for Pb. However, traffic movement patterns also have a dramatic influence on Cd deposition. The different sources of these two heavy metals will be discussed, especially in terms of environmental toxicity. Comparison will also be made with data from the London Orbital M25 motorway (daily traffic densities of 120,000) which have much higher heavy metal levels but different distribution patterns. Sequential extraction analysis showed Pb to be associated with the Fe-Mn oxide fraction, and Cd within the carbonate and Fe-Mn oxide fractions. Thus both Pb and Cd are bound more strongly within the soil compared with the exchangeable and water soluble geochemical fractions (greater leachability within the soil environment). Analytical problems with using sequential extraction procedures in terms of Neb(Quad)-ICP-MS and the need for quality control validation will be discussed. In particular, the choice of solvent mixtures used for the various sequential extraction steps has a direct effect on plasma interferences (spectral and matrix-related) and thereby the accuracy and precision of the measurements.