Single And Joint Toxic Effect Of Isoproturon And Cadmium On Green Algae(Chlamydomonas Reinhardtii)

Recent years, pollutants in the aquatic environment are seriously increasing and eliciting a variety of toxicity effects to the aquatic organisms and the aquatic environment. Aquatic pesticide contamination is known to be toxic to the aquatic plants, and the accumulation of pesticides by these plants has great danger to human beings. The characteristics of heavy metal pollution are persistent, non-degradable and relatively stable. Heavy metals and their interactions with the pesticides usually occur and have biological toxicity to the organisms exposed to the combinations. Isoproturon (IPU), belonging to the phenylurea family, is widely used to control weeds, but has been prohibited by the European Union for its environmental pollution. Cadmium (Cd) is one of the most dangerous heavy metals for its highly mobile nature and brings damage to the organisms even in low concentrations. A model alga, Chlamydomonas reinhardtii, was selected to evaluate the eco-toxicity of IPU/Cd to the algae, as well as its biological adaptation to single and joint toxicity of IPU/Cd and its bioaccumulation ability.The algae were cultured in four different types in terms of:the IPU treatment (treated with50μg L"1of final concentration); the Cd treatment (treated with20μmol·L-1of final concentration); the IPU+Cd treatment (final concentration with50μg L"1of IPU and20umol L-1of Cd); the control (without IPU or Cd). They were treated for60h. Study on the toxicity of IPU/Cd to C. reinhardtii indicated that that both IPU and Cd restrained chlorophyll content and the action of chlorophyll fluorescence while the combinations showed great significant effect. IPU/Cd were toxic to cell and caused over-production of ROS in membrane, the content of thiobarbituric acid reactive substances (TBARS) was increased and the single IPU increased most, showing the evidence that all the treatments leading to severe oxidative damage by ROS. The membrane permeability of C. reinhardtii under contamination was increased, along with the exudation of intercellular water soluble substance, the relative conductivity was also increased.Single and combined pollution treatments arose excessive accumulation of ROS and induced the change of antioxidant enzyme activities to a certain degree, including the activities of superoxide dismutase (SOD), peroxidase (CAT) and ascorbate peroxidase (APX); also, the glutathione S-transferase (GST) was activated to participate in cell detoxification metabolism; moreover, the activity of polyphenol oxidase (PPO), a sort of plant respiration terminal oxidase, was enhanced due to the injury of tissue structure. The result of RT-PCR further validated the enzymology response of algae under the oxidative stress. The HO-1expression in the cells exposed to IPU-Cd revealed in a up-regulated manner, showing this heme oxygenase plays a certain role in the process against IPU-Cd oxidative stress.C. reinhardtii showed certain bioaccumulation of isoproturon and cadmium. The results indicated that in the setting concentrations, the accumulation capability of isoproturon by algae is relatively low, while the bioaccumulation of Cd is comparatively strong.