Single and joint toxicity of cypermethrin and copper on Chinese cabbage (Pakchoi) seeds

The single and joint effects of Cu2+ and cypermethrin (CPM) on the seed germination and the elongation of root and shoot of Pakchoi were investigated. The results showed that in solution low concentrations of Cu2+ could accelerate the germination rate of Pakchoi, whereas high concentrations of Cu2+ could inhibit it. CPM could strongly inhibit the germination of Pakchoi in solution. However, in the joint toxicity effect, CPM reduced the phytotoxicity of Cu2+ on the germination of Pakchoi seeds under solution conditions. In the single-factor experiments and joint effect tests of CPM and copper on the seedling growth, it was found that there were significant liner relationships between concentrations of pollutants and root elongation (P < 0.05). Copper and CPM had synergic effects on root elongation of Pakchoi in solution cultivation test. However, in soil culture test, these synergistic effects were not significant (P < 0.05). Meanwhile, the joint toxicity was more dependent on the effect of copper than that of CPM. The toxicity of the pollutants to seed germination, shoot and root elongation is in the following sequence: root elongation > shoot elongation > germination rate.