Impact of platinum group elements on the soil invertebrate Enchytraeus crypticus

The platinum group elements (PGE) platinum (Pt), palladium (Pd), and rhodium (Rh) are used in automobile catalytic converters, from which they have been emitted into the environment to an increasing degree over the last 20 years. Despite the bioavailability of these metals to plants and animals, studies determining the effects of PGE on organisms are extremely rare. Enchytraeids are ecologically relevant soil organisms, due to their activity in decomposition and bioturbation in many soil types worldwide.

The experiments were carried out as described in the OECD Guideline 220 [CSN EN ISO 16387--Soil quality--Effects of pollutants on Enchytraeidae (Enchytraeus sp.)--Determination of effects on reproduction]. The reproductive effects of platinum (PtCl4), palladium (PdCl2) and rhodium (RhCl3) were examined. The concentrations of PGE tested were as follows: 5, 10, 25, 50 and 100 μmol x L(-1) PdCl2; 50, 100, 150, 200 and 250 μmol x L-1 PtCl4/RhCl3. The EC50 (medium effective concentration) was determined after 28 days of exposure. The inhibition of the reproduction of PGE-exposed enchytraeids was compared against controls.

Values of 28dEC50 of PtCl4, PdCl2 and RhCl3 amounted to 161.9 μmol x L(-1), 70.0 μmol x L(-1) and 246.6 μmol x L(-1), respectively. We can confirm that the relative order of toxicities is Pd (II) >Pt(IV) >>Rh(III).

To the best of our knowledge, this is the first study to use Enchytraeus crypticus as an indicator species to assess the risk of soil contamination by platinum, palladium and rhodium. Results of this study contribute important data on the ecotoxicity of a rarely studied elements.