Effects of organic ligands on toxicity of copper and zinc toCarassius auratus

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Abstract
Effects of EDTA, peat soil extracts (PSE) and humic acid (HA) on toxicity of copper and zinc to goldfish, Carassius auratus were studied in toxicity tests. Data obtained indicated that the toxicity of Zn was effectively reduced in the presence of EDTA because of complexation of Zn to EDTA. Toxicity of Cu in the presence of EDTA, PSE and HA, however, was less predictable on the basis of complexation/speciation theory because at high concentrations of added Cu, mortality of test organisms occurred despite the fact that free Cu2+ was low (pCu < 7) and could not be detected by Cu ion-selective electrode (Cu-ISE). All complexants tested managed to suppress the toxic effects of Cu at the lowest concentration of Cu used (0.25 mg L-1), while higher Cu concentrations tested resulted in mortality indicating that the Cu complexes formed could have been toxic to goldfish. Cu-EDTA complex seem to be the most toxic, followed by Cu-PSE and Cu-HA which were of similar toxicity.

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