Study On Photochemical Degradation Of Pesticides In Seawater

Marine organic photochemistry (MOP), as one of the important branches of marine chemistry, has a close relationship with many marine subjects such as marine biology and marine environmental science. The comprehensive study on MOP is of realistic significance for further understanding the removal patterns of organic pollutants in ocean. Based on the research work, the thesis focused on the photochemical degradation reaction of two representative pesticides in seawater by the simulated method in laboratory.Upon the instrument determination and analysis, we systematically studied the photochemical degradation of carbendazim and trichlorfor and obtained the following results:1. Photochemical degradation of carbendazim(1) Carbendazim could be degraded remarkably under the irradiation of 300W high pressure mercury lamp and showed the first-order reaction kinetic behavior. Under the different experimental conditions,the rate constants (k) of carbendazim varied from 0.0052 to 0.0403min-1.(2) Many factors in the experiments would influence the photodegradation:a. Lights: Carbendazim was significantly degraded under the irradiation of 300W high pressure mercury lamp. However, no photolysis of carbendazim was observed under natural sunlight and in the dark.b. Aquatic media: The photodegradation of carbendazim in deionized water was fastest. Compared with seawater, synthetic seawater exhibited somewhat faster photo-reaction rate for the carbendazim. c. Dissolved oxygen: The experiment results demonstrated that dissolved oxygen was absolutely necessary to the photodegradation of carbendazim in different aquatic media.d. Heavy metal ions: In all the reactions, Cu²⁺,Zn²⁺,Pb²⁺,Cd²⁺ in different reaction systems displayed different roles. The results were obtained by changing the concentration of heavy metal ions in carbendazim solution. The effects of heavy metal ions were resulted mainly from the interaction between ions and aquatic media. Cu²⁺ was subjected to the weaker influence, so it could restrain the reaction in all the solutions examined.e. Photosensitizer: The selected photosensitizer Anthro-quinone(AQ) and acetone could accelerate the reactions of carbendazim.f. pH detection: The change in the pH of photoreaction solution of carbendazim displayed a same trend in deionized as in synthetic seawater, but a different trend in seawater: This observation may provide a theoretic base for explaining fastest photoreaction for carbendazim in seawater.2. Photochemical degradation of trichlorfor Trichlorfor was hardly degraded under the irradiation of 300W high pressure mercury lamp within 60 min, but was quickly degraded as H2O2 was added into the solution as catalyst. The factors which would influence the photodegradation were:a. Aquatic media: The reaction in seawater was fastest while it seemed a bit faster in synthetic seawater than that in deionized water.b. Amount of H2O2: The optimum was 2.2g/L.c. Heavy metal ions: In deionized water, four metal ions such as Cu²⁺,Zn²⁺,Pb²⁺,Cd²⁺ displayed different roles. Cu²⁺,Pb²⁺ restrained the reaction in all the solutions examined.d. Dissolved oxygen: Nitrogen was added into reaction systems to decrease the concentration of dissolved oxygen, which could accelerate the reaction of trichlorfor.In brief, for the two pesticides in seawater, a series of results have been obtained in the respects of photochemical degaradation, photocatalytic degradation, kinetic behavior and the factors influencing them. Based on the experimental results in this thesis, we can have a further understanding of the photodegradation situations of these two kinds of pesticides in the marine enviroment.