Photochemical Generation Of Halogenated Phenolic Pollutants In Aqueous Environment

Halogenated organic pollutants have received extensive attention due to their complex damage effects on the human health and the ecological environment. Their sources were once considered to be predominantly anthropogenic due to their large scale production, widespread use and improper handling. However, many uncertainties exist regarding the origination of halogenated organic pollutants in environment. Photochemical process is one of the most important transformation pathways for organic compounds in natural environment, and many components of natural water could impact the phototransformation pathway of the organic pollutants. Investigation of the photochemical formation of the halogenated organic compounds from the non-halogenated compounds in saline water, and the subsequent formation of the more toxic and persistent pollutants will be more helpful for better understanding the natural sources of halogenated organic compounds in environment. In this dissertation, the following works have been done:(1) The photochemical formation of chlorinated organic compounds was investigated in saline water, using bisphenol A (BPA) (C0, BPA=87.7μM) as a model molecule. The chlorinated derivatives 2-(3-chloro-4-hydroxyphenyl)-2-(4-hydroxyphenyl) propane (3-ClBPA) (328 nM) and 2,2-bis(3-chloro-4- hydroxyphenyl) propane (3,3'-diClBPA) (1.1 nM) were determined during the phototransformation of BPA in saline solution with Fe(III) at pH3.0 under Hg lamp irradiation (λ>290 nm). The amounts of 3-ClBPA and 3,3'-diClBPA increased with the increase of Fe(Ⅲ) concentration, but decreased with the increase of pH. Laser flash photolysis (LFP) and electron paramagnetic resonance (EPR) results indicated that the chlorination of BPA was most likely due to the formation of Cl2·- radical as a consequence of Fe(Ⅲ) irradiation, yielding Cl·and·OH radical species and finally forming Cl2·- radical upon further reaction with chloride. Moreover, the amount of Cl2·- and·OH decreased with the increase of pH, thereby weakened the photochlorination reaction.(2) The effects of Fe(Ⅲ) and fulvic acid (FA) on the photochlorination of BPA were investigated under Xe lamp irradiation(λ>290 nm). Formation of Fe(Ⅲ)-FA complex promoted the BPA chlorination through producing more Cl2·- radical. FA presented two opposite effects:BPA chlorination was enhanced with the increase of FA concentration ([FA]) when [FA]<3.2mg/L; the amount of 3-ClBPA was as high as 16.7 nM when [FA]=3.2 mg/L; however, it reduced to 5 nM when [FA]=10 mg/L. Phototransformation of 87.7μM BPA in the natural seawater resulted in～2 nM 3-ClBPA.(3) Phototransformation of BPA in saline solution with Fe(Ⅲ) under acidic conditions (pH=2.5～3.5) resulted in the formation of BPA dimers and trimers. Photopolymerization of phenol,2-chlorophenol and 2,4-dichlorophenol resulted the structures of (chlorinated) hydroxydiphenyl ether and (chlorinated) hydroxydiphenyl in the coexistence of Fe(Ⅲ) and chloride at pH3.0. Phototransformation of pentachlorophenol resulted in larger amount of octachloro-dibenzodioxin (OCDD) in acidic saline solution (pH=3.0) than in fresh water.(4) Phototransformation of phenol in water containing bromide resulted in bromophenols, and the photopolymerization of bromophenols led to the production of hydroxylated polybrominated diphenyl ethers (OH-PBDEs). Phototranformation of phenol in the bromide solution resulted in 2-bromophenol and 4-bromophenol, and chloride promoted the bomination reaction. When 2,4-dibromophenol was irradiated in aquatic solutions under Xe lamp irradiation (λ>290 nm), significant amounts of 2'-hydroxy-2,3',4,5'-tetrabromodipheyl ether (2'-OH-BDE68) were rapidly formed as the dimeric product of 2,4-diBP. The formation of 2'-OH-BDE68 intensified with the increase of light intensity and with the initial concentration increase of 2,4-diBP, whereas it weakened with an increase in pH. Moreover, Fe(Ⅲ) and fulvic acid played important roles in the formation of 2'-OH-BDE68. The amount of 2'-OH-BDE68 from the phototransformation of 2,4-diBP was determined in the simulated seawater and natural seawater, respectively. Fe(Ⅲ) significantly promoted the formation of 2'-OH-BDE68 in the simulated seawater at pH=8.0 under light ofλ>370 nm. Phototransformation of 2,4-diBP (C0, diBP=10～100μg/L) in natural seawater resulted in 1.38～28.6 ng/L 2'-OH-BDE68, and phototransformation of 2,4-diBP (C0,diBP=100μg/L) and phenol (C0,P=37.5,124μg/L) in natural seawater resulted in 0.16-0.88 ng/L 2'-OH-BDE7.The results of the experiments in this dissertation demonstrated that phototransformation of phenolic compounds in the saline water could result in halogenated phenols. Moreover, phototransformation of these halogenated phenols could lead to some more toxic pollutants, such as, OH-PBDEs and dioxins. These findings provide an important insight into the possible source of halogenated organic pollutants in natural aquatic systems through photochemical approaches, and are significant for better understanding the natural sources of halogenated compounds in the environment.