Abstract: Photodegradation of propargite and fenpyroximate and their photoactivating and photoquenching effects on each other in water were studied.Under the illumination of a 300 W high pressure mercury vapor lamp,the half-life of propargite was 9.06 minutes and that of fenpyroximate 1.48 minutes.The photolytic rates of propargite were in a decreasing order of redistilled water>pond water>river water>well water;and of fenpyroximate in the order of well water>redistilled water>pond water>river water;The photolytic rates of the two pesticides were both in the order of sampled water>filtered (water>)sterilized water.There were significant photoactivating and photoquenching effects on photodegradation of each other and these effects were different in different sorts of water,and under different illuminating lights.It was observed that the photolytic rates of the two pesticides were quicker in pH 5 and pH 9 phosphate buffers than in pH 7 phosphate buffer,and so were the photoquenching effects.In redistilled water under sunlight propargite and fenpyroximate were photoactivator to each other,whereas under a 300 W high pressure mercury vapor lamp they were photoquencher to each other.

Key words: pesticide, photodegradation, propargite, fenpyroximate, photoactivator, photoquencher, water