SUITABILITY OF TEST MEDIA CONTAINING EDTA FOR THE EVALUATION OF ACUTEMETAL TOXICITY TO DAPHNIA-MAGNA STRAUS

The acute toxicity of six metals [Hg, Cd, Cu, Zn, Cr(II), and Cr(VI)] to Daphnia magna neonates was evaluated using three different test med ia (Elendt M7, a complex medium containing EDTA; ASTM hard water and E EC, two simple media free of chelators), The EC50 values, at both 24 a nd 48 h, obtained for Zn, Cr(II), and Cr(VI) were similar in all of th e media tested. Hg was more toxic in ASTM than in M7 and in EEC media, The toxicity of Cd and Cu was similar in ASTM and EEC media and highe r when evaluated in M7 medium, Thus, M7 should be used only carefully for the toxicity evaluation of mixtures and effluents containing metal s, It is recommended, however, that it be excluded from use in tests e valuating samples of unknown composition, or those known to contain Cu and Cd, For the metals tested in this study, a factor of five applied to each 48-h EC50 would be sufficient in order to attain the respecti ve acute NOECs for immobility. (C) 1997 Academic Press.