Platinum, palladium, and rhodium deposition to the Prunus laurus cerasus leaf surface as an indicator of the vehicular traffic pollution in the city of Varese area

The widespread use of some platinum group elements as catalysts to minimize emission of pollutants from combustion engines produced a constantly growing increase of the concentration of these elements in the environment; their potential toxicological properties explain the increasing interest in routine easy monitoring. We have found that leaves of Prunus laurus cerasus are efficient collectors of particulate with a dimension < 60-80 mu m, and a simple and reliable procedure was developed to reveal traces of platinum, palladium, and rhodium released from automotive catalysts. The analysis of the dust deposited on the foliage is a direct indicator of traffic pollution. Leaves of P. laurus cerasus were washed by sonication in a mixture of water and 2-propanol and the washings, to be discarded, were separated by centrifugation to yield typically 0.05-1.2 g of dust that, after mineralization, was directly submitted for atomic absorption analysis. Comparison of the 2007 and 2004-2005 results showed a dramatic reduction of the platinum levels and revealed that palladium is now the main component of this traffic-related pollution. The results are consistent with the increasing diffusion of cars with a diesel engine whose catalysts are made up of Pt and/or Pd alone, and gives a significant insight into the recent evolution in catalyst design that replaces platinum for palladium. The proposed analytical procedure is simple, with short preparation times, and greatly reduces matrix effects so that atomic absorption spectroscopy can easily detect the three noble metals at the ng/g level in the dust. The results clearly show that Pd concentrations have increased over time, and must be cause for concern.