Study On Photochemical Degradation Of N-Methylcarbamate Pesticides In Seawater

Marine organic photochemistry (MOP), as one of the important branches of marine chemistry, has close relationship with many marine subjects such as marine biology and marine environment science. The comprehensive study on MOP is of realistic significance for further understanding the removal patterns of ofganic pollutants in the oceans.Based on the research work, the thesis focused on the photochemical degradation reaction of three representative N-Methylcarbamate pesticides in seawater by the simulated method in laboratory.Upon the instrument determination and analysis, we systematically studied the photochemical degradation of methomyl, propoxur and carbofuran and obtained the following results :1. The three pesticides could be degraded remarkably under the irradiation of high pressure mercury lamp and ultraviolet lamp. The reaction shows that the ultimate product of methomyl is (NH₄)₂SO₄ and the transformation products of propoxur and carbofuran are 2-isopropoxyphenol and carbofuranol respectively.2. At the initial stage of exposure, the photo-degradation rates of the three pesticides seem faster and show the first-order reaction kinetic behavior. Under the different experimental conditions, the rate constants (k) of methomyl, propoxur and carbofuran ranged from 0.0855 min^-1 —0.2897 min^-1, 0.1377 min^-1 —0.2166 min ^-1 and 0.0446 min^-1—0.1846 min^-1, respectively.3. Many factors in experiments could influence the photo-degradation of the three pesticides.(1) Lights: The three pesticides were significantly degraded under the radiation of UV. However, no photolysis of methomyl was observed under natural sunlightand int the dark.(2) Aquatic media: The photo-degradations of the three pesticides in seawater were fastest. Compared with synthetic seawater, de-ionized water exhibited somewhat faster photo-reaction rate for the three pesticides.(3) Dissolved oxygen: The experiment results further demonstrated that dissolved oxygen was absolutedly necessary to the photodegradation of methomyl in different aquatic mediates.(4) Heavy metal ions: In all the reactions, different ions in different reaction systems displayed different roles. The results were obtained by changing the concentration of the heavy metal ions in the methomyl solution. The effects of heavy metal ions were resulted maily from the interaction between ions and aquatic media.(5) Photosensitizer: The selected photosensitizer AQ could accelerate the reactions of the three pesticides to changing extent.4. pH detection: The change in the pH of photoreaction solution of methomyl displayed a same trend in de-ionized as in synthetic seawater, but a different trend in seawater: This observation may provide a theoretic base for explaining fastest photoreaction for methomyl in seawater.5. Ultimate products and the TPS: The ultimate product of methomyl is (NH4)2SO4 by IR and the transformation products of propoxur and carbofuran are carbofuranol and 2-isopropoxyphenol respectively by MS.In brief, for the three selected N-Methylcarbamate pesticides in seawater, a series of results have been obtained in the respects of photochemical degaradation, kinetic behavior and the factors influencing them. Based on the experimental results in this thesis, we can have the furher understanding on the photo-degradation situations of the carbamate pesticides in the marine enviroment.