Distribution, Release Law And Photoconversion Of Typical Phenolic Compounds In Ice

Nowadays, persistent, bioaccumulative and toxic compounds (PBTs) have been detected in remote areas, such as the Arctic, and pollute the ice and snow, which are important components of cold ecosystems as well as of temperate ecosystems in winter. But, the pollution of ice and snow has not cause people's attention and the studies on the translocation and transformation of contaminations in ice and snow are rare, in addition, the research of the effect of contaminations on the cold ecological environment is also bare, at present.Up to now, there is only little research on distribution and release law of phenolic compounds in ice. But research on this aspect will help us to know actual distribution of phenolic compounds in the ice whether well-distributed or not and how phenolic compounds entering into ice during ice formation; also research on the release law of phenolic compounds from ice has actual significance for deducing its influence in ecological environment.Because of the low temperature, the ordinary chemical and biological reactions are prohibited in the ice and the good transparence of ice makes the photochemical reactions possible which is little affected by the temperature. Therefore, the photochemistry of the organic pollutants plays a very important role in the ice or snow in the cold and warm ecosystem.Some reports have recently proposed PBTs can be generated by photochemistry of primary pollutants in natural ice and snow, and subsequently released to the environment, it make a possibility of a secondary-pollutant formation in (on) ice and snow. Therefore, the research of the photochemistry in ice has the same important role as in atmosphere and water. Through the research of the photoconversion of p-chlorophenol (4-CP) in ice will help us to know the photodegradation law and mechanism of 4-CP in ice, and propose whether has secondary-pollutant by determine the photoproducts.In order to know the distribution and release law and the partition ratios (Cice/Cwater) of parachlorophenol, phenol and 3-methylphenol in ice and the kinetics and mechanism of the photoconversion of 4-CP in ice at different conditions, there has done three aspect researches. Firstly, through indoor and outdoor simulating experiments, the distribution and release law of parachlorophenol, phenol and 3-methylphenol in ice and the distributive ratios of these materials between ice and water are studied. The effects of concentration, pH value and water quality on the distribution, release and the distributive ratio between ice and water are also investigated. Secondly, the photochemistry of 4-CP for 4-CP system (â… ), 4-CP+NO₂^- system (â…¡) , 4-CP+NO₃^- system (â…¢) and 4-CP+H₂O₂ system (â…£), respectively, under UV irradiation by using a 125W high-pressure mercury lamp as light source has been research. The experiments are carried out in a photochemical cold chamber reactor at -14～-12℃. Each influence factor of the 4-CP photoconversion in ice is inspected, and the kinetics orderliness is established. In addition, intermediate products are characterized and the possible photoconversion mechanism was proposed accordingly.Thirdly, the photochemistry of 4-CP for 4-CP system (â… ) , 4-CP+NO2- system (â…¡) and 4-CP+H2O2 system (â…¢), respectively, under simulated sunlight (λ>300nm) irradiation has been research. The experiments are carried out in a photochemical cold chamber reactor at -14～-12℃. Each influence factor of the 4-CP photoconversion in ice is inspected, and the kinetics orderliness is established. In addition, intermediate products are characterized and the possible photoconversion mechanism was proposed accordingly.The observation shows that the concentration of phenol, parachlorophenol and 3-methylphenol in ice all increases gradually from exterior to interior and its content in the interior is much higher than that in the exterior. When the three materials release from ice, the release amount of the three phenolic compounds declines rapidly along as time goes by. When concentration is less than 200mg/L, all the partition ratios (Cice/Cwater) of the three phenolic compounds are between 0.14 and 0.20. The initial concentration, pH value and the water quality have different effect on the distribution, the release law and the partition ratio.Under UV irradiation, all the 4-CP photoconversion obeys the first order kinetics model at different conditions, and the photoconversion rate constant of 4-CP for the four different system from higher to lower is as follow:â…£(k=0.0423min-1)>â… (k=0.0380min-1)>â…¢(k=0.0188min-1)>â…¡(k=0.0162min-1). H2O2 can accelerate the photoconversion of 4-CP in ice, but NO2- and NO3- prohibit the photoconversion of 4-CP in ice. The initial concentration of 4-CP, the initial concentration of NO2- (NO3- or H2O2), pH value, light intensity, inorganic ions and the water quality all had significant influence on the photoconversion and can change the photoconversion rate constant of 4-CP. The photoproducts are different for the four systems, it is concluded that there has indirect photolysis in systemâ…¡,â…¢andâ…£, therefore, the mechanism and photoproducts of 4-CP photolysis in ice would be changed due to the presence of NO2-, NO3- and H2O2.Under simulated sunlight irradiation, all the 4-CP photoconversion obeys the first order kinetics model at different conditions, too, and the photoconversion rate constant of 4-CP for the three different system from higher to lower is as follow:â…¢(k=0.0593h-1) >â…¡(k=0.0543h-1) >â… (k=0.0238h-1). All NO2- and H2O2 can accelerate the photoconversion of 4-CP in ice. The initial concentration of 4-CP, the initial concentration of NO2- (H2O2), pH value, light intensity, inorganic ions and the water quality all had significant influence on the photoconversion and can change the photoconversion rate constant of 4-CP. The photoproducts are different for the three systems, it is concluded that there has indirect photolysis in systemâ…¡andâ…¢, therefore, the mechanism and photoproducts of 4-CP photolysis in ice would be changed due to the presence of NO2- and H2O2.Though the results of above, we can know that about 17% of parachlorophenol, phenol and 3-methylphenol will consist in ice when the solutions icing, and they will release from ice rapidly to make the concentration increase in a short time. Moreover, we also can know that 4-CP can photodegrade in ice. This will provide theoretical basis for the predictions of the moving-transiting rule and the potential environmental risk of phenolic compounds in practical environment.