Toxicity Evaluation of Copper, Nickel, and Mixture on Daphnia Magna

This study conducted acute (48 hours) and chronic (21 days) toxicity tests of nickel (Ni2+), copper (Cu2+) ions, and a mixture of the Ni2+ - Cu2+ ions on Daphnia magna (D. magna) under M4 medium. The acute test results showed that the toxicity of Cu2+ was about 15 times higher than Ni2+, demonstrated by the 50% effect concentration (EC50) value of 185.2 μg.L-1 and 2706.97 μg.L-1. In addition, the results also illustrated that the mixture of the Cu2+ – Ni2+ ions was more toxic to D. magna than a single metal with an EC50 value of 175.22 μg.L-1. Acute toxicity tests showed that the metal affected the viability of D. Magna, while the organism maturation and reproduction were affected under chronic exposure. Chronic test results showed that the toxicity of Cu2+ was higher than that of Ni2+ with EC50 values of 9.06 μg.L-1 and 162.12 μg.L-1; noticeably, the toxicity of the mixture of the two metals is higher than that of the single metal. In particular, Ni2+ at a concentration of 100 μg.L-1 stimulated the maturation, survival, and reproduction of D. magna. but at higher concentrations (> 100 μgNi.L-1), Ni2+ would bind to Cu2+, which exerted a more substantial effect on the test organism. This study initially evaluated the toxicity of Cu2+ and Ni2+ on microcrustaceans D. magna, which is the premise for further studies on the genotoxicity of heavy metals on microcrustaceans in general and D. magna in particular to ensure the quality of the ecosystem.