Photoconversation Of γ-Hexachlorocyclohexane With The Presence Of Humic Acid In Ice And Snow

Photochemical reaction is an important way of organic pollutant’s migration and transformation. Humic acid (HA), as natural photosensitizer, can promote indirect photoconversion reaction of the organic pollutant. HA has significant impaction on the migration, transformation and fate of organic pollutant. Simultaneously, ice and snow have become an important sink of persistent organic pollutants (POPs) under the effect of global climate action. The POPs and their secondary reaction products in ice and snow have an important influence on local environment. Hence, the study about photochemical reaction of organic pollutants in snow and ice with the presence of HA is crucially important.Typical organochlorine pesticide gamma Hexachlorocyclohexane (y-HCH) was chose as target pollutant,80 W high pressure mercury lamp as light source (λ<280 nm) and studied the photoconversion regularity of organic pollutants in snow and ice with presence of HA. The migration and transformation mechanism of organic pollutants in natural ice and snow were further investigated through these studies. What’s more, these studies provided theoretical basis for the establishment of pollution control countermeasures in temperate zone and frigid zone area.The results showed that the sequence of photoconversion efficiency of y-HCH in water, ice and snow was:snow> ice> water. The freeze-concentration effect and the weaken inhibition of dissolved oxygen to y-HCH during frozen made the photoconversion efficiency of y-HCH in ice was greater than that in the water. The photoconversion efficiency of y-HCH in snow, which was greatest, was due to the larger specific surface area and the LLL. We studied the influence factors of the photoconversion efficiency of y-HCH in ice, including the initial concentration of y-HCH and HA, salt concentration, pH, Fe3+, NO2- and NO3-, specific surface area. The photoconversion efficiency of y-HCH was promoted at the low initial concentration of y-HCH and HA, but inhibited at high concentration. Salt ion concentration, pH, Fe3+, NO2- and NO3-, specific surface area all promoted the photoconversion efficiency of y-HCH. The influence factors, which were salt concentration, pH and Fe3+, were also been studied in snow. Compared with the photoconversion efficiency of y-HCH in ice, the salt ion concentration had less effect, because the LLL in snow is thick enough for y-HCH to enter in, the photoconversion efficiency of y-HCH didn’t change again; the influence of pH on the photoconversion efficiency of y-HCH was similar to the results in ice; inhibition phenomenon occured at low concentration of Fe3+, due to the faster photoconversion of y-HCH in snow, making more sensitive to inhibitory response of Fe3+. What’s more, HA accelerated the photoconvers ion of y-HCH by producing singlet oxygen (1O2), hydroxyl free radical (·OH) and triple excited state (HA*),In addition, Outdoor experiment was done. Under the natural light, the photoconversion efficiency of γ-HCH in ice was similar with the laboratory simulation experiment, while the photoconversion efficiency of γ-HCH in snow was lower. Finally, photoproducts of γ-HCH with the presence of HA are mainly pentachloro-cyclohexene, p-dichlorobenzene and o-dichlorobenzene,1-chlorobenzene, and 1O2 indirectly accelerated the photoconversion of γ-HCH by consuming the intermediate products.