Evaluation of the health risk of platinum group metals emitted from automotive catalytic converters

A health risk assessment of platinum ŽPt. emitted from automotive catalytic converters is presented. Following a stepwise approach, the relevant literature is discussed in order to characterize Pt emissions as well as the toxic potential of Pt and its compounds. In an exposure assessment, ambient Pt concentrations in air are predicted to range from approximately 4 pg m3 Žstreet canyon, typical conditions. up to approximately 112 pg m3 Žexpress motorway, severe conditions.. These values agree well with the few measured concentrations, which are also in the low pg m3 range. Pt is emitted from catalytic converters in very small amounts Žng km range., mainly in the Ž0.-oxidation state Želemental Pt.. The nanocrystalline Pt particles are attached to m-sized aluminum oxide particles. Whether free ultrafine Pt particles may be emitted and result in biological effects has not been studied sufficiently. Hence, risk assessment can only be based on the respiratory sensitizing potential of halogenated Pt salts. The presence of such compounds in automotive Pt emissions cannot definitely be excluded. From recent occupational studies conducted in catalytic converter production, a conservative no-effect level ŽNOEL. of 1.5 ng m3 can be derived for the sensitizing effect of halogenated Pt salts. In a Žreasonable. worst case approach, it is assumed that such compounds comprise 1% Ž0.1%. of the total Pt emissions. Applying a safety factor of 10 to account for interindividual variability, a guidance value of 15 Ž150. ng m3 is derived for catalyst-borne Pt. The exposure to Pt in ambient air as measured or predicted is at least two orders of magnitude below this guidance range. Rhodium is also contained in automotive catalysts, palladium has increasingly substituted Pt, and iridium-based catalysts have recently been introduced. Although the database on these platinum group metals is rather small, there is no evidence that they pose a health risk to the general population