Effects of Mixture of Different Heavy Metal Ions on Population of Freshwater Rotifer Brachionus calyciflorus

To explore effects of combined heavy metal pollution on aquatic organisms, an experiment was carried out using fresh water rotifers, Brachionus calyciflorus, which are among the most important groups of zooplankton in terms of biomass, ecological importance and bio-diversity, and are recognized as ideal bioassay animals for toxicity tests because of their small size, short generation time and rapid reproduction rate. However, few reports are available in the literature on impacts of combined heavy metal pollution on rotifers. This experiment was designed to use solutions of heavy metal mixture, containing Cu²⁺ (0.001 and 0.01 mg·L^-1), Zn²⁺ (0.01 and 0.1 mg·L^-1), Cd²⁺ (0.01 and 0.1 mg·L^-1), Cr⁶⁺ (0.01 and 0.1 mg·L^-1), Mn²⁺ (0.1 and 1 mg·L^-1) and 18 d old freshwater rotifers in the cumulative culture test. Population growth rate and maximal population density of the rotifers were monitored. Results show that concentrations of the metals in the solution was the major factor affecting toxicity of the solution to the rotifers. Population growth rate and maximal population density of the rotifers were significantly lowered by solutions high in heavy metal concentration. Interactions of any given element with the other 4 in concentration in the solution all significantly influenced population growth rate of the rotifers, while interactions of Zn²⁺ with the other 4 in concentration in the solution significantly influenced maximal population density of the rotifers. The rotifers were more sensitive to interactions between the elements in the solution in population growth rate than in maximal population density. So they can be used as bio-indicator to monitor combined heavy metals pollution of water bodies.