Platinum and rhodium concentrations in airborne particulate matter in Germany from 1988 to 1998

Abstract

Increases in platinum group element (PGE) concentrations in ambient air and dust since the introduction of automotive catalytic converters in 1988 is a cause of concern. Until now, data derived from engine-test bench experiments have provided the basis for the assessment of human health risks associated with PGE exposure. Such experiments have provided valuable information regarding emission data that has been used to estimate ambient exposure concentrations. However, these data are not necessarily representative of typical environmental PGE exposure levels and conditions. Data on measured environmental concentrations is needed to provide a more adequate basis for the assessment of exposure and related risks. Twenty air and airborne-dust samples were provided by the Umweltbundesamt (Federal Environmental Agency, Germany) in the years 1988, 1989, 1992, 1997, and 1998. The samples were collected in Frankfurt/Main and the adjacent city of Offenbach. For this, 11 to 80 m 3 of air were filtered over a 24-72 h period using a vacuum. Glass-fiber filters were used to collect samples. Sample platinum and rhodium concentrations were determined using adsorptive voltammetry. Although the number of samples collected in different years is limited, the results indicate a trend toward continuous increases in ambient concentrations of these metals between 1988 and 1998. Specifically, there were 46- and 27-fold increases in Pt and Rh concentrations, respectively. Despite these observed increases, the Pt concentrations measured (i.e., 147 pg/m 3 on average, with a maximum of 246 pg/m 3 in 1998) fell far below 15000 pg/m 3, which has been suggested as a guidance value (i.e., exposure at this level would be expected to be without appreciable health risk). The results of a particle-size distribution analysis of one sample (8-step impactor) that was collected 150 m away from a street show that approximately 75% of Pt and 95% of Rh occurs in association with large particulate matter of >2 μm, with concentrations reaching a maximum in particles of 4.7 to 5.8 μm. The remaining 25% of Pt and 5% of Rh is present in fine particulate matter of <2 μm. An approximate 10% of Pt and <38% of Rh in airborne particles was found to be soluble in 0.1 molar HCl. Further, the results indicate that most of the emitted PGE particles from automotive catalytic converters, particularly those bound to fine particulate matter, are capable of being airborne. As a result, PGEs are not only present in areas close to emissions (e.g., roads), but can be transported over longer distances.