Oxidative stress biomarkers and metallothionein in Folsomia candida--responses to Cu and Cd

Folsomia candida (Collembola) is a standard soil ecotoxicological species; effect assessment includes survival and reproduction as endpoints. In the present study, and for the first time, a range of oxidative stress biomarkers measurement was optimized and validated. The antioxidant capacity was measured by the activities of catalase (CAT), glutathione reductase (GR), glutathione-s-transferase (GST) and content of total glutathione (TG). The oxidative damage in the lipid membranes was estimated by lipid peroxidation (LPO) and metallothionein (MT) levels. The exposure included the essential and non-essential metals Cu and Cd, in LUFA 2.2 natural standard soil, using a series of sampling times along a 10 days period (0, 2, 4, 6 and 10 days). Exposure concentrations were selected based on their reproduction EC50 values, 60 and 1000 mg/kg soil DW, for Cd and Cu respectively. The protocols were optimized and results show that oxidative stress biomarkers can be successfully used in F. candida, this being highly relevant as complementary information to the mechanistic level. The selected sampling times gave a good indication of the markers dynamic and can be reduced/adapted in future testing. Results showed that both metals caused an increase in the MT levels after 6 days but Cd acted as a stronger oxidant agent compared to Cu, i.e. causing higher damage. In sum, Cd mobilized/activated more antioxidant enzymes, but the increased activities were not enough to prevent LPO. This study confirms that the oxidative stress caused by Cd is higher despite the use of same reproduction EC50 indicating that toxicity seems more reversible for Cu than for Cd. Among others, GST and MT would be a good selection of biomarkers for Cd effect.