Study On The Photodegradation Of Selected Brominated Flame Retardants

Brominated flame retardants as a class of emerging persistent organic pollutants (POPs) are detected constantly in the environment. Different kinds of organic pollutants have been widely concerned due to their bioaccumulation and damage to the environment as well as human health. It is difficult to degrade brominated flame retardants quickly by conventional treatment. Therefore, chemical method, electrochemical method and biological method are focused on. Among them, photodegradation is the major degradation pathway. Therefore, photodegradation kinetics, products and pathways of4-bromodiphenyl ether and hexabromocyclododecane were investigated in this paper. In addition, the effects of various aqueous environmental factors on the photodegradation were elucidated to provide theoretical consultation for further environmental migration and photodegradation.Quantitative and qualitative analysis methods of brominated flame retardant in organic phase, water phase and environmental water were established by liquid-liquid extraction, solid phase extraction and gas chromatography. Photodegradation kinetics of4-bromodiphenyl ether and hexabromocyclododecane were investigated under UV irradiation. The effects of light intensity, initial concentration of4-bromodiphenyl ether and hexabromocyclododecane as well as solvent media on the photochemical degradation rate were discussed. Results showed that rate constants of hexabromocyclododecane and4-bromodiphenyl ether in different solvents were remarkably different during the degradation. The rate of the photodegradation of4-bromodiphenyl ether and hexabromocyclododecane become larger as the intensity of light source increases. Considering the effects of the photon competition between the product molecules and the parent molecule, the photon competition between the parent molecules, and the matrix concentration, etc., the influences of initial concentration on the photodegradation reaction of4-bromodiphenyl ether were inconsistent with hexabromocyclododecane. The photodegradation mechanisms of4-bromobiphenyl ether and hexabromocyclododecane were both debromination.4-bromobiphenyl ether in hexane lost a bromine atom during the process of the photodegradation and formed diphenyl ether while hexabromocyclododecane in hexane lost bromine atom in order and formed TBCD (C12H18Br4), DBCDD(C12H18Br2) and CDT (C12H18).Compared with the photodegradation of4-bromodiphenyl ether in pure water, the rate constant of the photodegradation of4-bromodiphenyl ether in environmental water was smaller. Therefore, suspended solids, pH, ions, photosensitizer, surfactants and humic acid were chosen to examine the effects of the different factors in environmental water on the photodegradation of4-bromodiphenyl ether. Experimental results showed that Ca2+, Fe3+, Al3+, NO3-,SO42-, Brij35, SDBS, CTMAB and suspended substances inhibited the photodegradation of4-bromobiphenyl ether while Mn2+, Mg2+, Cl-,CO32-, Tween-80and four photosensitizer promoted the photodegradation of4-bromodiphenyl ether. The photoproduct of4-bromodiphenyl ether in water was the same with4-Bromodiphenyl ether in hexane. To further investigate the photochemical behavior of brominated flame retardants, effects of the position of bromine substitution on the photodegradation were also studied. It is found that the position of bromine substitution influenced the rate of photodegradation strongly. The rates of the three isomers were as followed:4-bromodiphenyl ether>3-bromodiphenyl ether>2-bromodiphenyl ether.