Lessons learned from studies with the freshwater mussel Dreissena polymorpha exposed to platinum, palladium and rhodium.

The platinum group elements (PGE) platinum, palladium and rhodium gain increasing (eco-)toxicological interest due to their cumulative introduction into ecosystems. So far, most PGE exposure studies investigating biological availability, uptake and bioaccumulation of PGE as well as their effects on different toxicological endpoints were performed under non-standardized conditions which occasionally make an interpretation and comparison of the results difficult. Here we compare the results of different PGE exposure studies with zebra mussels (Dreissena polymorpha) showing influences due to the PGE source, the exposure medium, the exposure concentration and period as well as the test system. Problems associated to the performance and evaluation of these studies were identified and recommendations as well as needs for future studies are given. As nominal exposure concentrations often did not reflect real exposure conditions the reference for exposure concentration has to be chosen with caution, i.e. nominal versus quantified aqueous concentrations. The determination of bioaccumulation factors can be problematic when PGE concentrations in the exposure medium and in the test organism did not reach steady state even after several weeks of exposure. For future studies it would be advantageous to regularly correlating PGE bioaccumulation and biomarker responses to increase the knowledge on potential adverse effects of these metals, preferably using environmentally relevant PGE concentration scenarios. Many aspects discussed in the present study for zebra mussels and PGE can be transferred to other aquatic animals and other metals, respectively.