| The combined pollution of heavy metal has always caused much public concern. Rotifer Brachionus calyciflorus is a species of model animal for the study of aquatic ecotoxicology. In this study, the single and combined acute toxicities of Cu, Zn, Cd, Cr, and Mn on B. calyciflorus were evaluated; the chronic effects of the mixtures of Cu, Zn, Cd, Cr, and Mn with different ratio of concentrations on B. calyciflorus were investigated after short and long term exposure; as an example of using Zn and Cd, the influences of temperatures and algal densities on the toxicity of metal combined pollution to B. calyciflorus were estimated. The main results were presented as the following:1. The 24 h single acute toxicity test revealed that the median lethal concentrations (LC50) of Cu, Zn, Cd, Cr, and Mn to the freshwater rotifer B. calyciflorus were 0.00616 mg L-1,12.62 mg L-1,2.89 mg L-1,17.29 mg L-1, and 67.32mg L-1. respectively. The combined toxicity of Cu-Cr was antagonism when the toxicity ratio of the two was 1:1. At the concentration ratio of 1:1, the combined toxicities of Cu-Zn, Cu-Cd, Cu-Cr, and Zn-Cd were also antagonism. The combined toxicities of the other binary mixtures were synergism. Both the combined toxicities of Cu-Cr-Mn and Cu-Cd-Mn were antagonism when combined as the toxicity ratio of 1:1:1 and the concentration ratio of 1:1:1, respectively. The toxicities of the other ternary mixtures were synergism. At the concentration ratio of 1:1:1:1, the combined toxicities of Cu-Zn-Cd-Cr, Cu-Zn-Cd-Mn, and Cu-Zn-Cr-Mn were antagonism. The combined toxicities of the other quaternary mixture were synergism. Regardless of the pattern of combination, the toxicity of the Cu-Zn-Cd-Cr-Mn was synergism. The present results reiterated that the pattern of combination should be fully considered when evaluating the combined acute toxicity of metal mixtures.2. The freshwater rotifer B. calyciflorus was exposed to mixtures of Cu (0.001 and 0.01 mg L-1), Zn (0.01 and 0.1 mg L-1), Cd (0.01 and 0.1 mg L-1), Cr (0.01 and 0.1 mg L-1), and Mn (0.1 and 1 mg L-1), and the life-table demographic parameters including net reproductive rate, generation time, life expectancy at hatching, and intrinsic rate of population increase were calculated. The results showed that the interactions between a given element concentration, except Mn, and the other 4 elements mixture concentration significantly affected the intrinsic rate of population increase. Interactions between Zn concentration, as well as Mn, and the other 4 elements mixture concentration affected the net reproductive rate and the life expectancy at hatching, respectively. The variation of parameters with the rise of the other 4 elements mixture concentrations from 0 to high was mainly attributed to the difference of interaction among the five metals mixture.3. The effects of the mixture of Cu, Zn, Cd, Cr, and Mn with different ratio of concentrations on the population growth and sexual reproduction of the freshwater rotifer B. calyciflorus were investigated. The results showed that interaction between Cu concentration and other 4 elements mixture concentration significantly affected the ratio of mictic females to amictic females and the mictic rate; interaction between Zn concentration and other 4 elements mixture concentration significantly affected the ratio of mictic females to amictic females; the mictic rate, the fertilization rate, the population growth rate, and the 4 days’ resting egg production; interaction between Cd concentration and other 4 elements mixture concentration significantly affected the ratio of mictic females to amictic females, the mictic rate, and the 4 days’ resting egg production; interaction between Cr concentration, as well as Mn concentration, and other 4 elements mixture concentration significantly affected the ratio of mictic females to amictic females and the population growth rate. Overall, a tendency of low-concentration stimulation and high-inhibition was displayed among the endpoint responses.4. The long-term effects of the metal mixture of Cu, Zn, Cd, Cr, and Mn, which were all at environmentally relevant concentrations, on the population growth of the freshwater rotifer B. calyciflorus were studied. The results indicated that interaction between a given element concentration and the other 4 elements mixture concentration all significantly influenced the population growth rate of rotifers. Interaction between Zn concentration and the other 4 elements mixture concentration significantly influenced the maximal population density of rotifers. The population growth rate and the maximal population density of rotifer were inhibited by all mixtures at high level.5. The single and combined effects of Zn (0.315,0.63, and 1.26 mg L-1) and Cd (0.073,0.145, and 0.289 mgL-1) on the population growth rate and the mictic rate of the freshwater rotifer B. calyciflorus were evaluated under three temperatures (15,20, and 25℃) and three algal densities (0.5,1.0, and 2.0×106 cells mL-1 Scenedesmus obliquus). The results showed that Zn concentration, interaction between Zn concentration and temperature, interaction between Zn concentration and algal density, as well as interaction among Zn concentration, temperature, and algal density, significantly affected the population growth rate. Cd concentration, interaction between Cd concentration and temperature, interaction between Cd concentration and algal density, significantly affected the population growth rate. Both Cd concentration and interaction between Cd concentration and temperature significantly affected the mictic rate. Zn-Cd mixture concentration, interaction between Zn-Cd mixture concentration and temperature, interaction between Zn-Cd mixture concentration and algal density, significantly affected the population growth rate. Interaction among Zn-Cd mixture concentration, temperature, and algal density significantly affected the mictic rate. On the whole, with the increase of temperature and decrease of algal density, greater toxixities of Zn, Cd, and Zn-Cd mixture to B. calyciflorus were promoted, and more synergistic effects of Zn and Cd on rotifers were produced. |
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