Hypothetical Thresholds for Effects of Platinum Group Elements

The platinum-group elements are rhodium, ruthenium, palladium, osmium, iridium, and platinum. Together with rhenium and gold they form the highly siderophilic (“iron-loving”) elements. These are poorly known with respect to toxicity and ecotoxicity. The mobilization by man of the eight metals is about 100 times to 1 million times the natural mobilization. Mean soil concentrations in Europe may now be more than doubled for gold, rhenium and rhodium. The objective of the current work was to enable a preliminary assessment of the consequences of such high environmental levels. Thresholds for ecological effects found in the literature were divided by the element’s mean soil concentration and plotted against group and period in the periodic system. Thresholds for health effects were correspondingly divided by the mean dietary intake of the element over large population groups. For health effects, an upper limit of intake is commonly used. This was shown to be about 4 times the mean normal intake for most period 4 elements. For other periods, occupational exposure thresholds entail upper limits of intake in µg/day of: Ru 18, Rh 8, Pd 17, Re 60, Os 15, Ir 4, Pt 20 and Au 160. For ecological effects, the no effect thresholds for period 4 were 1-5 times the soil concentrations. Very scarce data suggest higher relative thresholds for periods 5 and 6. The current high contaminations of European soil by Rh and possibly Pd may be of concern. Since the estimates of risks are uncertain, further research is warranted.