Study On Toxicity Of Copper And Nickel To Eisenia Fetida In Typical Chinese Soils

Soil pollution with heavy metals is aserious problem worldwide, and it has aroused intensive concerns recently among scientists, regulators, and public. Metals are difficult to remove from soil, and may be accumulated by plants and transferred to higher trophic organisms through food chain. Therefore, metal pollution in soil can do harm to both ecosystems and human health. Terrestrial ecotoxicological data are essential for the development of risk-based ecological soil screening levels. Presently, few studies have been involved in the ecotoxicity assessment of metals in Chinese soils, which is incompatible with the increasing requirement of ecological risk assessment at contaminated sites in China. In the present study, acute and chronic toxicities of copper and nickel to the earthworm Eisenia fetida were investigated in eight Chinese soils, including red earth from Hunan, purple soil from Chongqing, cinnamon soil from Henan, black soil from Jilin, paddy soil from Zhejiang, grey desert soil from Xinjiang, fluvo-aquic soil from Beijing and loessal soil from Shaanxi, following standardized methods in ISO and OECD guidelines. Behavioral response of the earthworms to copper contaminated soils, as well as the bioconcentration of nickel in the tissues of the earthworms were alsotested.(1) Results of acute toxicity test showed that both copper and nickel exhibited the highest toxicity in red earthwhereas the lowest toxicity in loessal soil. linear correlationship analysises between copper and nickel LC_50s and soil properties (pH, cation exchange capacity, organic matter content and clay content) were done. The results indicated that soil pH was the major factor that influenced the toxicity of copper and nickel to the earthworm E. fetida. Temperature also had significant effects oncopper toxicity, which showed that toxicity increased with increasing temperature.(2) In the avoidance test, a typical dose-response relationship was found between copper treatment levels and earthworm avoidance rates. This suggested that copper contamination under 50 mg·kg^-1 could result in a limitation of soil function as habitat, and earthworm avoidance test could be used as an early pre-screening test to evaluate copper contaminated soils. (3) Results of chronic toxicity test suggested that the body weight of the earthworms was a less sensitive test-endpoint responding to copper and nickel at low concentrations. However, high levels of copper and nickel could do reduce the earthworm body weight. Cocoon and juvenile production of E. fetida appeared sensitive to copper and nickel contamination, especially the juvenile production was demonstrated the most sensitive endpoint in the present study.(4) The results of bioaccumulation test clearly indicated that a positive correlation existed between nickel concentration in soils and that in the earthworms. It demonstrated that earthworms were able to uptake soil nickel and retained it in their tissues. Bioconcentration could be used as an biological indicator of nickel contaminated soils.