Abstract: In order to assess the safety of pesticides used in paddy field to aquatic organisms, the acute toxicity of acetamiprid, profenofos, diazinon and malathion were studied using Scenedesmus obliquus, Daphnia magna Straus and Brachydanio rerio as test organisms by static test, static test and semi\|static test respectively. Safety evaluation had also been conducted. The results showed that acetamiprid, profenofos, diazinon and malathion had low toxicity (55.3 mg·L-1, 72h-EC50), high toxicity (0.00509 mg·L-1, 72h-EC50), high toxicity (0.249 mg·L-1, 72h-EC50), and moderate toxicity (1.69 mg·L, 72 h-EC50) to Scenedesmus obliquus, respectively. It could be seen that acetamiprid, profenofos, diazinon and malathion had low toxicity (49.2 mg·L-1, 48h-EC50), extremely high toxicity (0.00392 mg·L-1, 48h-EC50), extremely high toxicity (0.0308 mg·L-1, 48h-EC50), and extremely high toxicity (0.00165 mg·L-1, 48h-EC50) to Daphnia magna Straus, respectively. As for Brachydanio rerio, acetamiprid, profenofos, diazinon and malathion had low toxicity (49.8 mg·L-1, 96h-LC50), high toxicity (0.706 mg·L-1, 96h-LC50), modreate toxicity (5.12 mg·L-1, 96h-LC50) and low toxicity (10.9 mg a.i.·L-1, 96 h-LC50) , respectively．

Key words: acetamiprid, profenofos, diazinon, malathion, aquatic organisms, acute toxicity, safety evaluation