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

A health risk assessment of platinum (Pt) emitted from automotive catalytic converters is presented. Following a stepwise approach, the relevant liter ature is discussed in order to characterize Pt emissions as well as the tox ic potential of Pt and its compounds. In an exposure assessment, ambient Pt concentrations in air are predicted to range from approximately 4 pg/m(3) (street canyon, typical conditions) up to approximately 112 pg/m(3) (expres s motorway, severe conditions). These values agree well with the few measur ed concentrations, which are also in the low pg/m3 range. Pt is emitted fro m catalytic converters in very small amounts (ng/km range), mainly in the ( 0)-oxidation state (elemental Pt). The nanocrystalline Pt particles are att ached to mum-sized aluminum oxide particles. Whether free ultrafine Pt part icles may be emitted and result in biological effects has not been studied sufficiently. Hence, risk assessment can only be based on the respiratory s ensitizing potential of halogenated Pt salts. The presence of such compound s in automotive Pt emissions cannot definitely be excluded. From recent occ upational studies conducted in catalytic converter production, a conservati ve no-effect level (NOEL) of 1.5 ng/m(3) can be derived for the sensitizing effect of halogenated Pt salts. In a (reasonable) worst case approach, it is assumed that such compounds comprise 1% (0.1%) of the total Pt emissions . Applying a safety factor of 10 to account for interindividual variability , a guidance value of 15 (150) ng/m(3) is derived for catalyst-borne Pt. Th e exposure to Pt in ambient air as measured or predicted is at least two or ders of magnitude below this guidance range. Rhodium is also contained in a utomotive catalysts, palladium has increasingly substituted Pt, and iridium -based catalysts have recently been introduced. Although the database on th ese platinum group metals is rather small, there is no evidence that they p ose a health risk to the general population. (C) 2001 Elsevier Science B.V. All rights reserved.