| Snow and ice have become an important accumulation spaces of persistent organicpollutants because of the effect of global climate and the volatility of organic pollutants, organicpollutants and their secondary pollutants in snow and ice have an important impact on thesnow-covered areas. Snow and ice contain not only organic pollutants, but also plenty ofmicrobial secretions and their apoptosis that can be transformed into natural photosensitizer aftera series of physical and chemical processes. Photosensitization of such substances could impactthe fate of organic pollutants in snow and ice. Gamma-HCH, as a typical organochlorinepesticides, is a priority control pollutant, and still has an important impact on the environmentand human health due to its persistence and biological toxicity.Therefore, this paper selected high pressure mercury lamp (80W) as light source (filteredwavelength <290nm), rose bengal as photosensitizer and gamma-HCH as the target pollutant tostudy photodegradation of gamma-HCH in ice and water phase in order to contrast the similarityand difference. What’s more, we used natural light to make experiments to predict the fate ofgamma-HCH which is persistent organic pollutants in snow or ice.The results showed that:(1)The direct photolysis efficiency and photosensitizationdegradation efficiency of gamma-HCH in the ice phase was faster than that in aqueous phase, itis mainly due to the frozen concentrated effect on photosensitizers and repression on dissolvedoxygen.(2)Rose bengal impacts the degradation of gamma-HCH via three forms:(a) Promotingthe photolysis of gamma-HCH as electron donor;(b) Transferring energy of triplet excited stateof RB to gamma-HCH and enhancing its reactivity (type I mechanism of photooxidation);(c)Promoting its photolysis though removing the secondary products of gamma-HCH by singletoxygen generated by RB (type II mechanism of photooxidation).(3) Gamma-HCH may mainlyexist in the micropockets, grain boundaries and air-ice interface for its less polar, the type andconcentration of ions and temperature can impact photosensitized degradation of gamma-HCHthough affecting the percentage of liquid-like layer and the effect of dissolved oxygen.(4) Theactivity of photosensitized degradation of gamma-HCH in alkaline conditions is stronger thanthat in acidic conditions.(5) The photosensitized products of gamma-HCH mainly involegamma-pentachlorocyclohexene and tetrachlorocyclohexane. Simultaneously, gamma-HCH canbe transformed into alpha-HCH, it is different from the direct photolysis products ofgamma-HCH which contain gamma-pentachlorocyclohexene, tetrachlorocyclohexane, chlorophenol and phenol accumulated in ice.(6) the degradation of gamma-HCH under naturallight is similar with laboratory, indicating that natural photosensitizer such as humic acid andhumic-like substances have major impact on photolysis of organic pollutants in snow and ice. |
PDF Full Text Request