The development of vehicle technology during the last decade has led to an increasing use of catalytic converters in automobiles. These converters contain Platinum Group Elements (PGE) such as Platinum, Rhodium and Palladium that are emitted into the environment.
A number of transects at selected sites along country roads, highways and in cities were sampled in three depth sections (0-2 cm; 2-5 cm; 5-10 cm). After separation and preconcentration with Nickel Sulfide fire assay the Noble Metals were analysed by ICP-MS.
The results show that PGE contents in road-dusts and soils by far exceed natural concentrations which are below 0.8 ppb.
The highest values are found in urban road-dusts with concentrations up to one ppm Platinum. These samples reveal a significant correlation of Platinum and Rhodium that results in a characteristic ratio of about 6:1. Palladium contents of 1 to 146 ppb were found. Though it is obvious that samples with high contents of Platinum and Rhodium are Palladium-rich as well, no correlation or distinct element ratio could be determined for Pd.
The Pt/Rh-ratio of 6:1 reflects the application of these elements in the converters in Germany. It is a result of the early pure-Platinum converters and the ratio of 5:1 in the most commonly used Pt-Rh-converters. The recent use of Palladium in converters of new cars as an alternative catalytic material results in varying amounts at the sample sites without yet fixed element ratios.
Platinum contents in upper soils (0-2 cm depth) next to traffic lanes vary from several hundred ppb to a minimum of 30 ppb in the least contaminated of the examined sites. Maximum Palladium and Rhodium contents were found to be about 10 and 30 ppb respectively. The Pt/Rh-ratio is also 6:1 and tends to increase with approach to natural values.
Decrease of PGE with distance to the traffic lane is similar to other automobile emitted elements such as Lead, Zinc and Chromium. Values only a little higher than the geochemical background of each site are mostly reached at a distance less than 20 meters.
Vertical profiles reveal that the highest concentrations of Noble Metals in soils are found in the uppermost sequence of the sample profile (0-2 cm depth). Other traffic-related elements (Lead, Zinc and Chromium) show maximum contents in the second profile section (2-5 cm) and are still abundant in 10 cm depth. I the sequence of 2-5 cm elevated PGE-concentrations were found whereas in the depth-range of 5-10 cm most values reflect local background. Within the section of 2-5 cm the PGE-contents decrease with the distance to the lane similar to the upper section.
A comparison of the different sample sites indicates that the transport distances of the PGE depend on local parameters such as morphology or direction and speed of the wind and others. Though PGE-immissions are related to the density of traffic, there is evidence that other aspects such
as the frequency of traffic-jams or working conditions of
the engines have a big influence on emissions of catalytic material.
These investigations were made in cooperation with the Landesanstalt für Umweltschutz (LfU) Baden-Württemberg with financial support by the Projekt Wasser-Abfall-Boden (PWAB).