Toxicity and critical body residues of Cd, Cu and Cr in the aquatic oligochaete Tubifex tubifex (Müller) based on lethal and sublethal effects.

The aim of the present study was to estimate critical body residues (CBRs) of three metals [cadmium (Cd), copper (Cu), chromium (Cr)] in the aquatic oligochaete Tubifex tubifex based on lethal (LBR) and sublethal effects (CBR), and to discuss the relevance of the exposure to sediment for deriving CBR. Toxicity parameters (LC50, EC50, LBR50 and CBR50) were estimated for each metal by means of data on survival and on several sublethal variables measured in short-term (4 days), water-only exposures and in long-term, chronic (14 and 28 days) exposures using metal-spiked sediment. Sublethal endpoints included autotomy in short-term exposure, as well as reproduction and growth in chronic bioassays. LBR50 and CBR50 were 3-6 times higher in sediment than in water-only exposure to Cd and about 2-11 times higher for Cu, depending on the measured endpoint; however, for Cr these parameters varied only by a factor of 1.2. Cu and Cr LBR50 and CBR50 values in 96 h water-only exposure were very similar (survival 2.39 μmol Cu g(-1) dw, 2.73 μmol Cr g(-1) dw; autotomy 0.53 μmol Cu g(-1) dw, 0.78 μmol Cr g(-1) dw). However, in metal-spiked sediments, 28 d CBR50 values for autotomy, reproduction and growth ranged 6.76-29.54 μmol g(-1) dw for Cd, 3.88-6.23 μmol g(-1) dw for Cu, 0.65 μmol g(-1) dw for Cr (calculated only on total number of young). Exposure conditions (time and presence/absence of sediment) seem to be influential in deriving metal CBR values of Cd and Cu, while appear to be irrelevant for Cr. Thus, CBR approach for metals is complex and tissue residue-toxicity relationship is not directly applicable so far.