Toxicity of Cd2+ and Pb2+ to Chironomus kiiensis larvae, and its effects on three biochemical markers

Author of the article:WANG JianNan；XU LiShan；CAO ChuanWang

Author's Workplace：College of Forestry, Northeast Forestry University, Harbin 150040, China；College of Forestry, Northeast Forestry University, Harbin 150040, China；College of Forestry, Northeast Forestry University, Harbin 150040, China

Key Words：heavy metal; Chironomus kiiensis; acute and joint toxicity; biochemical markers

Abstract：[Objectives]  To investigate the effects of heavy metal exposure on Chironomus kiiensis larvae. [Methods]  The toxicity of Cd²⁺, Pb²⁺ and Cd-Pb ions, to 4th instar C. kiiensis larvae, and on three biochemical markers (CAT, SOD and MT) were measured. [Results]  C. kiiensis larvae developed typical toxic symptoms after exposure to Cd²⁺ and Pb²⁺ and their ions. The LC₅₀ of Cd²⁺ was significantly lower than that of Pb²⁺ after 24 h and 48 h. The joint toxicity of Cd²⁺ and Pb²⁺ varied with ion ratios and exposure time. The joint toxicity of 1︰1 Cd²⁺+Pb²⁺ was partially additive whereas 2︰1 and 1︰2 of Cd²⁺+Pb²⁺ had an antagonistic effect after 24 h. However, the joint toxicity of different ratios of Cd²⁺+Pb²⁺ was partially additive after 48 h. SOD and CAT activity was inhibited to various degrees by Cd²⁺ and Pb²⁺. The MT content of larvae exposed to Cd, Pb and mixed ions of these elements, was significantly higher than that of the control, and MT content increased, then decreased, with duration of exposure. [Conclusion]  Cd²⁺ and Pb²⁺ are both independently, and jointly, toxic to C. kiiensis larvae. The activity of the anti-oxidative enzymes CAT and SOD, and MT content, changed in response to exposure to these heavy metals in a time and dose-dependent manner, which suggests that these could be biochemical markers of water quality.