| Hexabromocyclododecane, a widely used additive brominated flame retardant (BFR), is mainly employed in resident and industry insulation, electric and electronic appliances and interior textiles.With the increasing demands of HBCD, many environment problems caused by HBCD have appeared and attracted more and more attentions. At present, HBCD had been detected from almost all environment mediums, including surface water, sediments, sludge, soil, atmosphere and so on. Furthermore HBCD in the environment mediums is easy to enter and be accumulated in biota. Although the acute toxicity of HBCD is very low via some toxicological researches, it has detrimental effects on thyroid hormone systems, nervous systems and reproductive systems and may cause cancer through a longterm exposure. Due to its persistence, bioaccumulation, and long-range transport potential, HBCD has been listed tc Annex A of Stockholm Convention on Persistent Organic Pollutants as a new persistent organic pollutant (POPs) in May of 2013. At present, there are very few reports on the behavior, fat< and degradation of HBCD in environment. Especially, the photochemical environmenta behavior and the degradation mechanisms of HBCD are still unclear. Therefore, this work mainly focuses on the photochemical transformation behavior of HBCD in environment; which can provide theoretical basis for the further works on the environmental fate of HBCD and can provide theory evidence for disposing pollutants containing HBCD in natui environment with some practical significance. This thesis includes 4 chapters:(1) A study on establishing the analysis methods for HBCD. The method for quantitative analysis of HBCD was established. By comparing the solubility of HBCD in a mixure soluti of different ratio of ACN and water,40%ACN-water (v/v) was chosen in the following we to ensure 5 mg L"1 HBCD completely dissolved. Furthermore the extraction methods for HBC in soil minerals was established by ultrasonic assisted extraction and using 1:1 methyle chloride-acetone (v/v) solution as the extractant, and the recovery ratio was 75.8%. In additi the concentration method using liquid-liquid extraction for the samples containing HBCD its products were established. And after comparing the qualitative analysis for HBCD and products using liquid chromatography tandem mass spectrometer (LC-MS) and s chromatography tandem mass spectrometer (GC-MS), GC-MS was selected as the anal s method in the following work.(2) A study on the direct photolysis and photooxidation of HBCD in ACN-water solu a using UV-C irradiation as the light source. The photolysis of HBCD followed the pseudo i order kinetics reaction. Mechanism study reveals that HBCD was mianly degradated thn h direct photolysis, while the contribution of HO· on HBCD photooxidation was only 14.3%.The presence of 10 mmol L-1 or 100 mmol L-1 H2O2 inhibited the photolysis of HBCD partly. The second-order reaction constant for the reactions between HBCD and HO· was calculated to be kHBCD, HO= 2.48 (± 0.23) × 108 L mol-1 s-1 by a competitive reaction between HBCD and Rodamine B. The singlet oxygen (102) is unlikely to directly contribute to the photolysis of HBCD, which was confirmed via an experiment using methylene blue as the photosensitizer excited by red LED (λ = 660 nm). However, it indirectly contributed to the degradation of HBCD through an oxidation reaction with the completed debrominated product-Cyclododecatriene (CDT). Afterward, the quantum yields of HBCD at 224,240 and 254 nm were measured as 0.22,0.15 and 0.033 respectively by a momochromator and an iodide-iodate actinometric solution. The identify of photolysis products indicated that the degradation products mainly consisted of some debromination prouducts including Tetrabromocyclododecene (TBCD), Dibromocyclododecadiene (DBCD) and CDT, while some epoxy-debromination products were also found.(3) A study on the photoreduction of HBCD in n-propanol-water solution via aqueous electron generated by UV-C/Fe(CN)64-. Comparing the degradation efficiency in three different systems (Fe(CN)64, UV-C, UV-C/Fe(CN)y64-) found that HBCD can only be degradaded in UV-C/Fe(CN)64- system, and the degradation kinetic fitted well to pseudo first-order kinetics model. Moreover, the degradation efficiency of HBCD can be inhibited completely in the presence of oxygen. The degradation efficiency increased with the incresing of Fe(CN)64- dose. Furthermore, the effect of pH on the degradation efficiency of HBCD was investigated, and the results show the degradation efficiency of HBCD at different pH values were pH 3 (no degradation observed)< pH 5< pH 6.3≈pH 9≈pH 11, and the difference in degradation efficiency was mainly caused by varies of H+ concentrations at different pH. Moreover, the degradation mechanisms were studied through a quenching experiments using N2O, NO3- and CCl4 as the inhibitors, and the results indicated that in this system HBCD is degradated mainly by aqueous electron. The second-order reaction constant for the reaction between HBCD and aqueous electron was determined as kHBCD,eaq = 1.33 (± 0.32) × 1010 L mol-1 s-1 L mol-1 s-1 through a competitive reaction between HBCD and 2-bromophenol. The degradation of HBCD in a UV-C/Fulvic acid system was investigated and the results indicated that no degradation or adsorption occurred in this system.(4) A study on the photochemical transformation of HBCD on the solid surface of soil mineral particles and in the suspension solution. Results revealed that HBCD cannot be degraded on the surface of kaolinite, montmorillonite and goethite under the irradiation of black light lamps (λ= 365 nm), while photolysis of HBCD occurred on the surface of kaolinite using UV-C lamps (λ> 224 nm) as the light source. The pH, relative humidity, the thickness of layer and the initial concentrations of HBCD influence the photolysis of HBCD. Through a quenching experiment using n-hexanol as the scavenger, the indirect photolysis (via HO·) is unlikely to contribute to the photolysis of HBCD. And the photolysis can also occurr on the surface of goethite, activated carbon and silica gel, among which the photolysis of HBCD on the surface of silica gel shows has the highest degradation ratio. In addition, the photolysis of HBCD on the surface of activated carbon followed pseudo first-order kinetics. Furdermore, the degradation of HBCD cannot occur in goethite suspension solultion using a xenon lamp (λ> 290 nm) as the light source, while HBCD could be adsorbed rapidly by activated carbon. Comparing the effects of TiO2, montmorillonite, kaolinite and activated carbon on the adsorption of HBCD, it was found HBCD can be strongly adsorbed on activated carbon. The intra-particle diffusion was found to be the only rate-limiting step of adsorption through the adsorption kinetics. And the adsorption isotherm fitted the Sips model well, while the fitting curve corresponds with the type S adsorption isotherm which indicated there existence of strongly competitive adsorptions on the surface of adsorbent. |
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