Photo catalytic degradation of chlorophenols in aqueous solution by ZnO nanoparticles under sunlight was investigated. The toxicity of chlorophenols was evaluated by agar plates technique with paper discs in the presence of Escherichia coli. The relative toxicity data of chlorophenols, before and after degradation, was used in comparing between them. The degree of toxicity was estimated by clear zone around each paper disc of chlorophenols. Results show toxicity of chlorophenols as PCP>TeCP>2,4,6-TCP>2,4-DCP>2-CP before photocatalytic degradation. After degradation, no more toxicity was observed by clear zone around each paper disc. The toxicity test indicates that higher degradation of chlorophenols occurred by ZnO nanoparticles under sunlight as alternative method for treatment.

Key words: Chlorophenoles, degradation, toxicity, zinc oxide (ZnO) nanoparticles.