Individual And Combined Toxicity Of Cadmium And Chromium On The Earthworm Eisenia Fetida

It is estimated that more than 90% of the total burden of pollutants resides in the surface soils. As an importment part of environment, soil is a typical compound polluting system. Heavy metals are frequently found together as contaminants in soils and have attracted much attention in recent decades. To assess the potential ecological risk of Cr and Cd on terrestrial ecosystems, multi-discipline research incorporating traditional earthworm toxicology and molecular toxicology were conducted with earthworm Eisenia fetida as an important soil animal.The aim of this study was to investigate the multi-level ecotoxicological effects of Cr and Cd with attention to the acute toxicity, protein content, stress defense protein content, antioxidant enzymes and biological transport enzymes, which mainly based on individual organism level and molecular level. Metallothionein was choosed on behalf of the stress defense protein; superoxide dismutase(SOD) and catalase(CAT) were choosed on behalf of the antioxidant enzymes; sulfur enzyme(GST) was choosed on behalf of the biological transport enzyme.1. Acute toxicity tests, both filter paper contact method and natural soil method, showed that the toxicity of Cr is slightly stronger than Cd. Filter paper contact tests indicated that median lethal concentration of Cd were 259 mg·L–1(24 h) and 194 mg·L–1(48 h); median lethal concentration of Cr were 213 mg·L–1(24 h) and 135 mg·L–1(48 h). Natural soil tests shows that median lethal concentration of Cd were 1395 mg·kg–1(7 d) and 810 mg·kg–1(14 d); median lethal concentration of Cr were 889 mg·kg–1(7 d) and 582 mg·kg–1(14 d). The toxicities of Cd and Cr in natural soil were medium. The interactive effects of Cd and Cr were antagonistic; Cd was the main contributive factor of toxic effect.2. Earthworm’s avoidance test showed that the avoidance rate under Cd containmination was higher than under Cr containmination when the concentration was the same level.3. Individual and combined toxicity of Cd and Cr on earthworm’s protein test showes that protein content increased when the stimulation of heavy metal is individual. Protein content showed a trend of decline when increased the concentration of heavy metal. Cd concentration was the main contributive factor of individual Cd contamination; time was the main contributive factor of individual Cr contamination. There is no clear toxicological effect in Cd and Cr combined contamination on protein content.4. In individual and combined toxicity of Cd and Cr on earthworm’s MT content, SOD activity, CAT activity and GST activity were studied.The MT content increased under individual Cr or Cd stimulus, and changed significantly over time. Cd concentration was the main contributive factor of Cd and Cr combined contamination in this experiment.SOD activity was increased and then decreased under individual Cr or Cd stimulus. Cr concentration was the main contributive factor of Cd and Cr combined contamination in this experiment.CAT activity was not shown the significant order under individual Cr or Cd stimulus. The effects Cd concentration and Cr concentration did not reach significance level. Time was the main contributive factor of Cd and Cr combined contamination in this experiment.GST activity was increased and then decreased under individual Cr or Cd stimulus. Relationship among Cd concentration, Cr concentration and time is not obvious of Cd and Cr combined contamination in this experiment.