Study On Photochemical Degradation Of Triazophos In Seawater

Triazophos is high-effective, poisoning (percutaneous low toxicity) and broad- spectrum organic phosphorus insecticide and miticide, which was developed in 1970s. It is a kind of phosphorothioate pesticides, with good development prospect. On the other hand, it has inevitably gone into waters (ponds, rivers, lakes and oceans, ect.) since it was used, which causes environmental pollution and ecological effects. Therefore, it is of great practical significance to study behavior of triazophos in the water environment in order to prevent these problems above.The pohotodegradation is an important pathway for the decomposition and transformation of organic pollutants in natural environment. Based on the previous research work, the thesis is focused on the photochemical degradation reaction in seawater by the simulative study in laboratory. Through instrument detection and experimental analysis, we systematically studied the photochemical degradation of triazophos and obtained the following results:1. Kinetic behaviorTriazophos could be significantly degraded under the irradiation of 300 W high pressure mercury lamp, which showed the first-order reaction kinetic behavior. Under the different experimental conditions,the rate constants (k) of triazophos varied from 0.00160 to 0.03028 min-1.2. Factors influencing the photodegradation of triazophos(1) Irradiation light source: Triazophos was photodegraded a little under the irradiation of sunlight while it could be significantly degraded under the irradiation of 300 W high pressure mercury lamp in deionized water (DW), artificial seawater (ASW) and natural seawater (NSW).(2) Light intensity: The photolysis rate of triazophos under 500 W high pressure mercury lamp was faster than that under 300 W high pressure mercury lamp, indicating that triazophos photolysis was controlled mainly by light intensity. (3) Initial concentration: Under the irradiation of high pressure mercury lamp, the photodegradation rate of triazophos decreased with the increasing initial concentration. Under the same initial concentration, triazophos concentration gradually decreased with the irradiation time.(4) Aquatic media: Under the irradiation of 300 W high pressure mercury lamp, the half-life of photochemical degradation of triazophos in distilled water, artificial seawater and natural seawater were 107.97, 109.50 and 85.50 minutes, respectively. The photodegradation rate of triazophos in natural seawater was the fastest among the three media, presumably due to alkalescence of natural seawater and the existence of organic photosensitizer in seawater.(5) Heavy metal ions: The effects of heavy metal ions on photochemical reaction were related to aquatic media. Of all the reactions, different concentration of metal ions in different reaction systems displayed different effects. The results were obtained by changing concentrations of four heavy metal ions (Pb2+, Cd2+, Cu2+, Fe3+, etc.) in triazophos solution. The effects of heavy metal ions were caused mainly by the interactions between ions and aquatic media.(6) Photosensitizer: The selected photosensitizers– acetone and anthraquinone could accelerate the reactions of triazophos. When the concentration of acetone was 0.02 % (V/V), the half-life of photochemical degradation of triazophos in distilled water, artificial seawater and natural seawater shortened more than 79, 80, and 57 minutes, respectively. When the concentration of anthraquinone was 1 mg/L, the half-life of photochemical degradation of triazophos in distilled water, artificial seawater and natural seawater shortened 57, 54, and 41 minutes, respectively.(7) Nitrate and nitrite: Both nitrate and nitrite showed the restraining effects on photochemical degradation of triazophos in the dosage range studied and the restraining degree was enhanced with the increasing concentration of nitrate and nitrite.3. pH: The pH value of solutions showed the decreasing trend in all kinds of systems during the process of photodegradation of triazophos, while the effects were different for the different systems. A series of results have been obtained on the respects of photochemical degradation, kinetic behavior and the factors influencing them, for triazophos in seawater. Based on the experimental results, we can have a further knowledge of the photodegradation process of this pesticide in the marine environment.