On the Environmental Relevance of Platinum Group Elements

It has recently been demonstrated that platinum group elements (PGE) are released from automobile catalysts into the environment, raising concern over ecological and human health risks. However, there is still a lack of knowledge regarding the dispersion and transformation of PGE in the environment and it is therefore difficult to assess potential risks. The research presented here focuses on the development and use of analytical procedures to investigate the environmental relevance of PGE. While PGE occur at low concentrations, increasingly sensitive analytical techniques allow their determination at environmentally relevant levels. Inductively coupled plasma-mass spectrometry (ICP-MS) is the method of choice for the determination of PGE in environmental samples, although interference is a severe obstacle when trace concentrations have to be determined. Several approaches to ICP-MS were assessed, including quadrupole ICP-MS with mathematical correction, sector field ICP-MS and sample introduction by laser ablation. Besides quantification, the coupling of a laser microprobe to ICP-MS allowed the investigation of PGE emission mechanisms and provided definitive fingerprints for tracking PGE containing particles in the environment. Palladium, platinum and rhodium were determined in exhaust fumes from representative catalysts and the impact of ageing on emissions was assessed for distances up to 80000 km. As a result of emission PGE were found in airborne particles, road sediments and river sediments. Further, bioaccumulation by the freshwater isopod Asellus aquaticus was investigated. Although PGE were previously believed to be relatively inert, this study shows the presence of bioavailable PGE species in the environment, with Pd presenting a higher bioavailability. Results show that PGE concentrations are low and might not present a direct human health risk. However, the occurrence of bioavailable PGE species raises concern about potential ecological risks. The present study provides information on PGE dispersion and evidence of their transformation into bioavailable species, although further studies are still needed to fully understand their environmental behaviour