Osmium isotopes

Studies of sediments from urban areas indicates a relation between elevated Os concentrations (and decreased isotope ratios 187Os/188Os) and anthropogenic Os sources. Catalytic converters containing platinum is one possible anthropogenic source of Os. Os occurs as an impurity in Rh, Pd and Pt. At the high work temperature of a catalytic converter, Os is released as gaseous osmium tetraoxide (OsO4), which is extremely toxic. Catalytic converters may contribute with up to 120 pg Os per year and m2 in urban areas, thus constituting a significant source. The calculations are based on Os analyses in new catalytic converters of different car makes (6-230 ppt). The Os concentration in the reference material IMEP-11 is according to ALS Scandinavia's tests higher (approximately 1000 ppt). Since the release rate of Os is considerably higher for new catalytic converters, the exposure of osmium tetraoxide is expected to be higher near premises where car are made or tested.

Osmium originating from the platinum group elements can be traced by its isotope composition. The 187Os/188Os ratio is higher for environmental samples in general than in Os from the Pt group elements, a result of 187Os originating from radioactive decay of rhenium.

Literature: Env. Sci. Technol. 39 (2005) 4431.