Studies On Photodegradation Of Fipronil In Aqueous Solution

The photochemical degradation of Fipronil irradiated by high pressure mercury Lamp (HPML) and sunLight was investigated in this paper. The effects of different types of water, surfactants, pigments,nitrate and nitrite ,metallic ions on the photodegradation of FiproniL in aqueous solution were studied. The main results were summarized as followings:1.The direct photodegradation rate of Fipronil in aqueous solution or on glass surface by HPML is very quickly, the half-life was only 4.71min in aqueous solution,and 4.14 min on glass surface. And Fipronil in aqueous solution is also degradated under Sunlight with the half-life of 55.58min,which is shorter than that of many other kinds of pesticides.But Fipronil does never degradate under xenon Lamp. And the photolysis of Fipronil follows the first order kinetics.2.The photolytic rates of Fipronil in 4 types of water ranged as: distilled water> Tapped water> CHaoHu Lake water> pond water from shou xian The half-life of FiproniL is 4.71 min in the distiLLed water WhiLe 5.61min in tapped water,7.03 min in the Chaohu Lake water and 7.33 min in the pond water.The effect mechanism was reLated to the physicaL and chemical properties of the water samples.3.The photolytic rates of Fipronil is also affected by its concentration in laqueous solution. the higher concentration is ,the lower photosis rate constant and the longer half-Lives is.In the test,with the increasing concentration of 1.0 mgL^-1 2.0 mgL^-1,5.0mgL^-1,Fipronil has half-life of 4.71min,5.07min,6.26min,respectively.4.Three kind of halogen ions such as , I^- , Br^- and Cl^-, showed great quenching effect,especially for I^- , the effect ranged as: I^-> Br^->Cl^- .and I^- has much greater quenching effect than Br^- and Cl^-. The half-life of I^-, Br^- and Cl^- are 43.32min,7.34min,6.33min respectively with the adding concentration of 10.0 mgL^-15The affect of positive ions on photodegradation of Fipronil is complex, The results is NH₄⁺ can accelerate photochemical degradation of Fipronil in aqueous solution and had photosensitive effects on photochemical degradation of Fipronil.with the role of NH₄⁺ ,the half-life of Fipronil is only 4.57min, 4.27min, 3.15min . but the Cu²⁺ has photoquenching effects on photochemical degradation of Fipronil and with the increasing of Cu ,the photoquenching effects would become more obvious. Mg can accelerate photochemical degradation of Fipronil in aqueous solution in Low concentration, But Mg²⁺ will prolong photochemical degradation of Fipronil in high concentrations. 6.Both nitrate and nitrite showed photoquenching effects on Fipronil in their added dosage range. The photoquenching rate was improved with the increases of nitrate and nitrite concentration.7.H₂O₂ can greatLy promote photodegradation of Fipronil, Under HPML irradiation,with the role of H₂O₂, the photolysis rates of Fipronil were improved about 1.32-2.11 times.But H₂O₂ has a most sutiabLe concentration:50ppm, with the increasing of H₂O₂ dosage, the photosensitive rate will decrease a Litter.8.Three pigments(methyl orange,riboflavin, crystal violet) can slow the photolysis rate of Fipronil in aqueous solution under HPML,the role order of them is ribofLavin> crystaL violet> methyl orange;the photosensitive efficiency of the three pigments is 77.49%,45.86% ,42.04% withthe same adding concentration of 1.0 mgL^-1.9.Under HPML, surfactants(601# , 400#, BY-140,700#) all enhance the photodegradation rate of Fipronil.Of them, 700# , 400# can significantLy reduce the half-Lives of Fipronil and the effect showed the direct proportion with the dosage ratio. BY-140 aLso promote photodegradation of Fipronil,but its effect on Fipronil will be most significant at the adding concentration of 1.0 mgL^-1.if adding concentration is too high,the rate of degradation will decrease.Though 601# can accelerate photochemical degradation of Fipronil in aqueous solution.But with concentration of 601# increasing, the rate of photochemical degradation of Fipronil would decrease. The result showed that the degree of effects of surfactants on the photolysis of Fipronil is affected by properties of surfactants, UV spectra, the additive dosage and so on.10.The outcome of the photolysis of Fipronil is MB46513,it could be detected by GC at the same condition with Fipronil with the retention time of 1.1 minutes.The quantity of it is increasing within 10 mins under HPML during the experiment every time.the quantity of it is increasing followed quadratic function.When aqueous solution contains sudstance which can accelerate potodegradation, the quantity of MB46513 would increase faster,On the contrary, the quantity of MB46513 would increase slower.