Toxicity And Sub-lethal Effects Of Five Pesticides Used In Rice Field On Brachydanio Rerio

The toxicity of five pesticides to Brachydanio rerio was investigated using standardized laboratory procedure; the grade was compartmentalized according to toxicity scope and the safety evaluation was conducted for these pesticides. The results indicated the 96h-LC₅₀ of fipronil and chlorpyrifos was between 0.1-1.0mg·L^-1(belong to high toxicity grade); the 96h-LC₅₀ of triazophos was between 1-10mg·L^-1(belong to moderate toxicity grade); the 96h-LC₅₀ of monosultap and fenobucarb was higher than 10 mg·L^-1(belong to slight toxicity grade).The joint toxicity of six mixtures of pesticide to Brachydanio rerio was evaluated according to the method of additional index based on acute toxicity test of single pesticide. Results showed the toxicity of fenobucarb mixed with fipronil and chlorpyrifos respectively to Brachydanio rerio was synergistic, and the toxicity of monosultap mixed with fipronil and chlorpyrifos respectively to Brachydanio rerio was antagonistic in the early time but synergistic in the later time, but the toxicity of triazophos mixed with fipronil and chlorpyrifos respectively to Brachydanio rerio was antagonistic.The effects of five single pesticides and six mixtures on Brachydanio rerio AChE, EROD and GST were studied from three different sublethal concentration during 96h exposure durations, and changes of these biomarkers were also detected in different concentration and durations for the practical use of these biomarkers in monitoring pesticides. Results obtained from the study showed Brachydanio rerio AChE can be used as a good biomarker for monitoring expsure of chlorpyrifos, triazophos and fenobucarb. EROD could also be a good biomarker for test pesticides, however, the response of GST to the test pesticide was not good as AChE and EROD. Changes of GST activities in all exposure concentration of fipronil were not obviouse. Significant induction of GST activitis was observed only in high concentration of chlorpyrifos and triazophos. Changes of GST activities in monosultap were complicate following concentration and exposure time. Inhibition of GST activity was observerd in high concentration of fenobucarb.