Determination of traffic-related palladium in tunnel dust and roadside soil

Roadside dust and soil samples were collected at different sites in the area of Ulm and Munich in Germany. Road dust samples were collected in tunnels where the traffic-related dust is less influenced by atmospheric conditions. Soil samples were taken with a drill bar at varying distances to motorways, district and regional roads with different traffic densities. The soil cylinders of 30cm length were divided into four sections in order to obtain depth profiles for palladium (Pd) distribution. Determination of Pd in total digests of the samples was performed by ligand-assisted selective separation and preconcentration of Pd(II) using solid phase extraction followed by high-resolution continuum source graphite furnace spectrometry. The analytical procedure was successfully validated using the certified reference material BCR-723 Road Tunnel Dust and by recovery experiments in spiked soil samples. The average Pd concentration found in the road dusts was 311μgkg^-1, the maximum Pd concentration in the topsoil layer was 193μgkg^-1. Pd depth profiles reveal transportation of Pd into deeper soil layers, where even at a depth of 25 to 30cm a Pd concentration of 19μgkg^-1 was found, proving the high mobility of Pd. Different factors like traffic density and age of the soils are discussed in the context of the found Pd depth profiles.