Short-term toxic effects of chlorobenzenes on broadbean (Vicia faba) seedlings

The root growth,changes in superoxide dismutase(SOD,EC 1.15.1.1)activity,malonyldialdehyde(MDA)and total soluble protein level of broadbean(Vicia faba)seedlings were researched at different soil concentrations of chlorobenzene(CB),1,2,4-trichlorobenzene(TCB)and hexachlorobenzene(HCB).The results showed that root growth of seedlings was interrupted after 5d of 50-200μg·g^(-1)TCB treatment.During a 3 d of recovery period,root growth was,however,restored to some extent although there was a delay in returning to the control level.The total soluble protein content in seedlings increased with TCB concentration and duration of exposure.Effect of TCB stress on SOD activity in seedlings displayed a significant dose-effect relationship for 1-5 d of 50-200μg·g^(-1)treatment.When broadbean seedlings were placed in clean tap water for 3 d following exposure to 5 d of TCB stress to clear tap water for 3 d,SOD activity at 50μg·g^(-1)TCB recovered towards control level(P>0.05)while a significant increase in SOD activity was observed at 100 and 200μg·g^(-1)TCB compared to control(P<0.05).The experiments also revealed that a significant increase of MDA level in seedlings occurred after 3 and 5 d of 100 and 200μg·g^(-1)TCB treatment(P<0.05 and P<0.01),and there was a positive correlation between TCB concentration and MDA level.All the above results showed that SOD activity and MDA level of broadbean seedlings might be proposed as the biomarkers for short-term TCB contamination in soil.Compared to TCB,the toxicity of 50-1000μg·g^(-1)CB or HCB in soil to broadbean seedlings was not observed after a 3 d exposure.