Photochemical Reactions Of γ-HCH Under Simulated Sunlight In Ice Phase

Due to the extensive use of organochlorine pesticides in agriculture、non-agricultural areas,its residues have been found in the polar regions，and the pollution phenomenon of the borealecosystems and the snow and ice environment in winter in the temperate ecosystems is also verycommon. Therefore, there is more and more attention of people for the migration andtransformation of organic pollutants on the media of snow and ice. However, the conventionalchemical reactions of organic pollutants and microbial degradation are relatively weak because ofthe low-temperature environment of snow and ice medium, the photochemical process which isless affected by temperature becomes the main way of the transformation of organic pollutants insnow and ice medium automatically. In addition, there have been a large number of studies whichhave shown that the light conversion reactions caused by nitrate, nitrite and hydrogen peroxideplay a very important role in the degradation of organic pollutants.Therefore, based on the above considerations, the paper selected gamma-HCH （typicalorganochlorine pesticides） as the target pollutants, and studied its dynamics and mechanism oflight conversion under simulated sunlight in the snow medium. The specific contents are asfollows.The paper selected80w high pressure mercury lamp as the light source and the glass tube asthe reaction vessel(（filtered off λ<280nm light） and studied the conversion reaction ofgamma-HCH in gamma-HCH system （I）、 gamma-HCH+NO₂^-system （II）、 gamma-HCH+NO₃^-system （III） and gamma-HCH+H₂O₂system （IV） in ice phase under simulated sunlight atlow temperature （-15°C）. We examined the impact of various factors on the light conversion ofgamma-HCH in ice phase and established the light conversion dynamics model. The productswere analyzed with the use of GC-MS to investigate the optical transformation mechanism ofgamma-HCH in ice phase.The results show that: compared with gamma-HCH system, the introduction of NO₂^-,NO₃^-and H₂O₂could improve the light conversion rate of gamma-HCH in ice phase undersimulated sunlight, and the facilitating role was enhanced with the increase of NO₂^-, NO₃^-and H₂O₂. All of the four systems are in line with first-order kinetics model. In the case of the sameconcentration of gamma-HCH and the same reaction conditions, when the concentration of NO₂^-,NO₃^-and H₂O₂are5mmol/L, k-â…¡>kâ…¢>kⅣ≈kâ… ; when the concentration of NO₂^-, NO₃^-and H₂O₂are10mmol/L, kâ…¡>kⅢ≈kâ…£>kâ… . If introduce inorganic ions、change the pH, add hydroxyl inhibitorsinto the four systems, it will have a certain impact on the light conversion of gamma-HCH in icephase. The products of the four systems are different. Specially, the introduction of NO₂^-and H₂O₂can change the light transformation products and mechanism of gamma-HCH, and there areindirect light conversions in system （II）、（III）and （IV） indeed.In addition, the paper studied the light conversion experiments of different systems in icephase in outdoor conditions. And found that after23days, the conversion rate of gamma-HCH ingamma-HCH+NO₂^-system was65%and it also reached nearly20%in gamma-HCH+NO₃^-systemand gamma-HCH+H₂O₂system while it was10%in gamma-HCH system. This also carried outthe actual environmental significance of my paper.