Studies On The Photochemical Degradation Of Two Organophosphorus Pesticides In Water And Vegetables

The photolytic kinetics of acephate and dichlorvos in aqueous solution,filter paper and vegetables(cabbage,spinage) irradiated by excimer ultraviolet light(EUL) and sunlight had been studied.The removal and influence factor of two organophosphorus pesticides in water and vegetables by EUL had also been discussing.The main results were summarized as following:1.Recoveryes of acephate and dichlorvos in water,filter paper and vegetable(cabbage, spinage)were standard,the results showed that:the recoveries of two organophosphorus pesticides in water matrix were 71.33%～113.47%,and RSD were less than 15%;the recoveries of two organophosphorus pesticides in filter paper and vegetable matrix were respectively 76.62.%～102.61%and 73.95%～118.76%,and RSD were all less than 15%.2.Under EUL,sunlight and room light,the photolysis of acephate and dichlorvos in water all followed the first-order kinetics,the half-life of acephate in water was respectively 47.8s,17.16h and 27.84d;the half-life of dichlorvos in water was respectively 35.73s,15.54h and 20.58d.3.The influence of the pH of solution on acephate and dichlorvos in water was studied.The results showed that acephate and dichlorvos was stable in pure water and acidic solution.The results showed the photolysis rates increased with the increase of pH value.Under EUL,the half-life of acephate was respectively 69.31s,34.31s,27.62s;the half-life of dichlorvos was respectively 40.53s,32.09s and 24.75s.Under the sun's rays,the half-life of acephate was respectively 17.68h,16.95h,11.29h;the half-life of dichlorvos was respectively 15.23h,12.14h,4.4h.Under darkness,the pH value has significant effect on the hydrolyzation of acephate and dichlorvos,the half-life of acephate were respectively 128.36d,30.94d,10.68d;the half-life of dichlorvos were respectively 50.59d,12.10d, 11.49h.4.Under EUL,sunlight,the photolysis of acephate and dichlorvos in filter paper was studied.The result showed the photolysis of acephate and dichlorvos in dry filter paper and wettish filter paper followed the first-order kinetics.In dry filter paper,under the sun's rays, the half-life of acephate and dichlorvos were 49.16h,32.85h;under EUL,the half-life of acephate and dichlorvos were 130.78s,88.87s.In wettish filter paper,under the sun's rays, the half-life of acephate and dichlorvos were 30.14h,23.1h;under EUL,the half-life of acephate and dichlorvos were 91.2s,56.35s.From the result,the influence of water on photolysis velocity was very strong.5.Under the same two kinds of lamp-house,the photolysis of acephate and dichlorvos in cabbage and spinage was studied.The result showed the photolysis of acephate and dichlorvos in cabbage and spinage both followed the first-order kinetics.In cabbage,under the sun's rays,the half-life of acephate and dichlorvos were 25.39h,20.6h;under EUL,the half-life of acephate and dichlorvos were 150.7s,117.49s.In spinage,under the sun's rays, the half-life of acephate and dichlorvos were 21.2h,18.1h;under EUL,the half-life of acephate and dichlorvos were 138.64s,115.53s.From the result,the photolysis velocity of two organophosphorus pesticides of the same concentration in different vegetables was different.This may be related with the pigment of vegetables,chlorophyl accelerated the photodegradation of acephate and dichlorvos.Removal of acephate and dichlorvos in vegetables by EUL could efficiently occur in a few minutes.