Photolytic Behavior Of Selected Organic Pollutants At Some Interfacial Environment

Persistent organic pollutants (POP) are highly lipophilic and chemically stable. Photodegradation may be one of the dominant abiotic transformations of the chemicals. Therefore, it is of great importance to investigate the photolytic behavior of POP in the environment. Previous studies focus on the photodegradation of POP in aqueous phase and in atmosphere. The photolytic behavior of POP at the interfacial environment is investigated in this study.Spruce (Picea abies (L.) Karst.) needles were exposed exhaust gas containing polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and polycyclic aromatic hydrocarbons (PAH) generated by combustion of polyvinyl chloride (PVC), wood, high-density polyethylene (HOPE), and styrene. Photodegradation of PCDD/F and PAH adsorbed on spruce needles under sunlight irradiation was studied. The factors of sunlight irradiation on the surfaces of spruce needles were taken into consideration when investigating the kinetic parameters.The photodegradation of the 70 PCDD/F and the 18 PAH follows pseudo-first-order reaction kinetics. The photodegradation half-lives range between 20 h and 50 h for PCDD/F and between 15.8 h and 75.3 h for PAH. Thus in the field conditions, photodegradation plays a major role on the fate of PCDD/F and PAH adsorbed on spruce needle surfaces.The photodegradation rates of PCDF congeners are faster than PCDD congeners with the same chlorinated substitutions. Higher chlorinated PCDD/F tend to photolyze slowly. The wax components in spruce needles may act as proton donors and accelerate the photodegradation rate. C-C1 cleavage through the addition of protons to PCDD/F molecules may be an important route for PCDD/F photodegradation. Photooxidation mediated by reactive oxygen species may be an important photodegradation mechanism for PAH on spruce needle surfaces.With the radiation of UV-B part of simulated sunlight, the photodegradation of the 75 PCDD/F absorbed to spruce needle follows pseudo-first-order reaction kinetics for the initial phase (0-48 h) and the second phase (48-528 h), respectively. The photodegradation rate constants for the initial phase are far greater than for the secondIVphase. The degradation rates increase with the age of spruce needles. The photodegradation rate constants of PCDD/F absorbed to 3-year-old spruce needles are greater than that of PCDD/F absorbed to 1 -year-old spruce needles and 2-year-old spruce needles.The photodegradation of PCDD/F on fly ash surfaces follows pseudo first-order kinetics under the irradiation of simulated sunlight with UV-B, whereas inner PCDD/F of fly ash is photostable. The fly ash deposited on spruce needle surfaces can decrease the degradation rates of PCDD/F on spruce needle surfaces. In the field conditions, UV-B radiation plays a major role on the fate of PCDD/F and PAH adsorbed on spruce needle surfaces.The photodegradation of the 16 PAH absorbed to one-year-old spruce needle follows pseudo-first-order reaction kinetics with or without the radiation of UV-B part of simulated sunlight. The photodegradation rates for the PAH with the radiation of UV-B part are greater than for the PAH without the radiation of UV-B part of simulated sunlight.The photodegradation of PAH on fly ash surfaces follows pseudo first-order kinetics under the irradiation of simulated sunlight with UV-B, whereas inner PAH of fly ash is photostable. The transfer of PAH between fly ash surfaces and needle surfaces has little effect on the decrease of PAH on spruce needle surfaces, whereas the transfer of PAH from the exterior to the interior of fly ash can decrease the degradation rates of PAH on spruce needle surfaces.Fourteen sediment samples with different content of Fe2C>3 were collected from lower reach of the Liao River in China. The photodegradation of y-hexachlorocyclohexane (y-HCH) on the sediment surfaces was investigated to observe the effects of Fe2Os and other photoinducable substances, such as TiO2 and organic substances, on photodegradation of y-HCH. The stepwise analysis, fac...