Studies On The Toxicity Of Heavy Metal Cd～(2+) And Pb～(2+) Pollution To The Four Aquatic Organisms

The single and combined effects of heavy metal ions Cd²⁺ and Pb²⁺ on the mortality of four species of aquatic organisms (Hydra pseudoligactis, Paramecium caudatum, Dugesia japonica and Cipangopaludia cathayensis) and the ultrastructural morphology of H. pseudoligactis were studied by means of acute and chronic toxicity test as well as the scanning electron microscopy technique. The main research contents and results obtained were presented as follows:1. The acute and chronic toxicity of Cd²⁺and Pb²⁺ to H. pseudoligactis were studied in this paper. The result of acute toxicity experiment showed that the 96h lethal concentration (LC₅₀) of Cd²⁺ was 1.81mg/L, and the 96h LC50 of Pb²⁺ was 10.13 mg/L. Cd²⁺ and Pb²⁺ were both poisonous to this animal and the former's toxicity was more severe than the latter's. The result of chronic toxicity experiment showed that the generation time was obviously prolonged when the generation number increased in the cultivating liquids containing the two ions. Moreover, the generation time of this coelenterate animal was much shorter than the white control group's when the concentration of Cd²⁺ was 0.0025 mg/L, or the concentration of Pb²⁺ is 0.015625 mg/L and 0.0625 mg/L, suggesting the two ions in lower concentrations may promote the growth and reproduction of H. pseudoligactis.2. The single and combined toxicity effects on P. caudatum, D. japonica and C. cathayensis exposed at special period of times (12, 24, 48 and 72 h) in different Pb²⁺ and Cd²⁺ concentrations were studied by using toxical experiment techniques. Results of the single toxicity of Pb²⁺ and Cd²⁺ showed: Cd²⁺ is more harmful than Pb²⁺ to P. caudatum, D. japonica and C.cathayensis; among this three kinds of aquatic organisms the P. caudatum is more sensitive than the other two, of which the edurance ability of the C.cathayensi is more prominent than the D. japonica. The statistics indicated that the single and combined toxicity effects are both increasing with the range of the disposed time, especially for the combined toxicity; the toxic effects is more pronounced than the single toxicity (P<0.05), showing obvious time-effect relationship; in addition, the single toxic effects is promoted prominently as the concentration of Pb²⁺ or Cd²⁺ increases (P<0.05). However, the toxicity on these three kinds of the aquatic organism are affected by the proportion of the two pollutants distinctly (P<0.01) for the binary analyses; it was indicated that the patterns of interaction (synergistic or antagonistic action) of the two pollutants are correlated with the proportion of the two pollutants in some degree, showing a marked concentration-effect relatedness in the single and combined toxicity effect experiments. Furthermore, the results of this study showed that there were interaction between the proportion of the pollutants and the exposed time effected on the toxicity of the three kinds of aquatic orginisms obviously too(P<0.01),and there existed little correlation between the toxicity effect with the concentration of pollutant for the C. cathayensis.3. Surface ultrastructural changes of H. pseudoligactis from the Pb²⁺ and Cd²⁺ dispositions were investigated using the scanning electron microscopy technique. The results showed: on the grounds of the same appropriate ion concentrations (Cd²⁺≥0.04 mg·L-1; Pb²⁺≥0.25 mg·L-1), the surface ultrastructural damage was continuous and irreversible as the disposed time increased: the epidermis were gradually erosed, collapsed and eventually disintegrated; the epitheliomuscular cells, interstitial cells and cnidoblasts were mostly deformed and decreased in number, especially for the cnidoblasts which were continuously cracked with the nematocysts exposed. The results also indicated that in the condition of this study, the ultrastuctural change of H. pseudoligactis disposed with Cd²⁺ was greater than that disposed with Pb²⁺ at the same generation number.