Biological effect of cadmium in Daphnia magna: Influence of nitrogen and phosphorus

Aquatic organisms are usually exposed to both metal pollution and eutrophication. The effects of phosphorus levels and nitrogen species on the accumulation and biotoxicity of Cd in freshwater zooplankton Daphnia magna were investigated. Results showed that P in water could increase Cd body burden, and inhibit metallothionein (MT) induction in D. magna after Cd exposure. The ratio of Cd body burden/MT increased markedly with increasing P levels, accounting for phosphorus in water could intensify Cd biotoxicity to D. magna. Different nitrogen species in water had different effects on Cd accumulation in D. magna, with the order NH₄⁺-N > NO₃-N > NO ₂-N. NH₄⁺-N and NO₃^--N in waters, which could disturb MT induction in D. magna, reinforcing Cd biotoxicity to D. magna. NO₂^--N could not affect Cd biotoxicity to D. magna, whereas NO₂^--N itself could produce toxic effects on D. magna inducing MT synthesis. The ratio of metal body burden/MT was more suitable to predict metal toxicity to D. magna than metal body burden or MT alone.