Photolysis utilises short wavelength ultraviolet radiation to excite and cleave the carbon-chlorine bond of PCBs, yielding less chlorinated PCBs and ultimately biphenyl which can serve as energy and carbon source of various bacteria. Thus integration of photolysis and biodegradation can be a feasible remediation for PCB contamination. / Polychlorinated biphenyls (PCBs) are ubiquitous environmental pollutants once used as industrial fluids (in hydraulic systems, gas turbines), dielectric fluids (capacitors, transformers), plasticizer (adhesives, textiles, sealants, copy paper), and heat exchangers due to their inertness as well as thermal and electrical insularity. However, they are found to be neurotoxic, immunosuppressive, hepatotoxic, and the USEPA classified PCBs as probable human carcinogens. Although the production of PCBs was banned by the US Congress in 1976, they persist in the environment because of their resistance. Upon entering the marine environment, PCBs will associate with particulates and ultimately with sediment due to their hydrophobic nature and thus sediment become a sink for PCBs. This exerts a threat to marine organisms and human who consume seafood. / The major sink of PCBs in the environment is marine sediment, and the presence of sediment particles as well as other sorbed chemicals may inhibit both photolysis and biodegradation. This study extracts PCBs from sediment and further purify them by various cleanups to prevent the effect of these materials on the efficiency of treatment. / Using 2,4,4'-trichlorobiphenyl (PCB 28), 2,2',5,5'-tetrachlorobiphenyl (PCB 52), 2,2',4,5,5'-pentachlorobiphenyl (PCB 101), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) and 2,2',3,4,4',5,5'-heptachlorobiphenyl (PCB 180) as model compounds, optimal UV intensity, reaction time, as well as reaction solvent were found to be dependent on the congeners used. While PCB 28 was highly reactive and PCB 101, PCB 153 and PCB 180 were comparatively easy to remove, PCB 52 showed high resistance towards photolysis. The photolysis of PCB mixture containing these five congeners with each of them in 1 mg/L was also being optimised. After optimisation, the reaction intermediates and products were identified by gas chromatography coupling mass spectrometry (GC-MS). Less chlorinated congeners and biphenyl were found, indicating stepwise dechlorination of PCB is the major pathway. (Abstract shortened by UMI.) / by Wong Kin Hang. / "August 2005." / Adviser: P. K. Wong. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0159. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 111-140). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

While much is known about the toxicity of polychlorinated biphenyls (PCBs), there are tens of thousands of natural and synthetic chemicals in the environment that can activate the aryl hydrocarbon receptor (AhR) and thus cause toxicity. Since it would be difficult to conduct studies of the toxicity of each and every compound, here is presented a new model based on first-principles taking into account the basic electronic and electron trans- fer characteristics of PCBs, but can be used to predict the toxicities of other AhR-active compounds. The predictive model is based on Density Functional Theory. The model predicts that the energy gap between highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals is the overarching indicator of toxicity of PCBs, but not the only factor. The model explains why chlorination of both para-positions is required for maximum toxic potency. To rank potency of PCBs, the dipole moment in relation to the most chemically active chlorine-sites is critical. The theory is consistent with the accepted toxic equivalency factor (TEF) model for these molecules and is also able to improve on ranking toxic potency of PCBs with similar TEFs. This new model also includes a 13th dioxin-like PCB, PCB 74, not considered in the current TEF model developed by the World Health Organization (WHO). The model was applied to HOMO-LUMO gap mea- surements of a set of PCBs and the measurements are consistent with the model. Values of HOMO-LUMO gap can also be used to predict bio-accumulation of PCBs. The model provides an in silico method to screen a wide range of chemicals to predict their ability to act as an AhR agonist.

by Wong Kin-hang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 99-127). / Text in English; abstracts in English and Chinese. / by Wong Kin-hang. / Acknowledgements --- p.i / Abstracts --- p.ii / Contents --- p.vi / List of Figures --- p.ix / List of Tables --- p.x / Abbreviations --- p.xi / Chemical Equations --- p.xii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Poly chlorinated biphenyls --- p.1 / Chapter 1.1.1 --- Characteristics of polychlorinated biphenyls (PCBs) --- p.1 / Chapter 1.1.2 --- Use of polychlorinated biphenyls --- p.3 / Chapter 1.1.3 --- World-wide production of polychlorinated biphenyls --- p.7 / Chapter 1.1.4 --- Polychlorinated biphenyls in the environment --- p.8 / Chapter 1.1.5 --- Toxicity of polychlorinated biphenyls --- p.12 / Chapter I. --- Mechanism --- p.12 / Chapter II. --- Toxicity towards plant and animals --- p.13 / Chapter III. --- Toxicity towards human --- p.14 / Chapter IV. --- Enzymatic induction by PCBs --- p.14 / Chapter V. --- Carcinogenicity of PCBs --- p.18 / Chapter 1.2 --- Treatments of pollutant --- p.19 / Chapter 1.2.1 --- Physical treatment --- p.19 / Chapter 1.2.2 --- Chemical treatment --- p.20 / Chapter 1.2.3 --- Biological treatment --- p.22 / Chapter 1.2.4 --- Photocatalytic oxidation (PCO) --- p.25 / Chapter Chapter 2 --- Objectives --- p.35 / Chapter Chapter 3 --- Materials and methods --- p.36 / Chapter 3.1 --- Chemical reagents --- p.36 / Chapter 3.2 --- Photocatalytic oxidation reactor --- p.36 / Chapter 3.3 --- Separation and determination of eight PCB congeners --- p.39 / Chapter 3.4 --- Determination of tetra-CB concentration --- p.40 / Chapter 3.5 --- Determination of PCO intermediates and products --- p.41 / Chapter 3.6 --- Optimisation of reaction conditions for UV-PCO in batch system --- p.44 / Chapter 3.6.1 --- Control experiments and effect of initial titanium dioxide concentration --- p.44 / Chapter 3.6.2 --- Effect of initial hydrogen dioxide concentration and UV intensity --- p.44 / Chapter 3.6.3 --- Effect of initial titanium dioxide concentration and initial pH --- p.45 / Chapter 3.7 --- Estimation of tetra-CB degradation pathway by photocatalytic oxidation --- p.45 / Chapter 3.8 --- Evaluation for the toxicity of hydrogen peroxide and toxicity change of tetra-CB during PCO by Microtox® test --- p.45 / Chapter 3.9 --- Determination of H202 concentration after PCO --- p.47 / Chapter Chapter 4 --- Results --- p.50 / Chapter 4.1 --- Separation and determination of eight PCB congeners --- p.50 / Chapter 4.2 --- Photocatalytic oxidation of mono-CB --- p.50 / Chapter 4.3 --- Determination of tetra-CB --- p.55 / Chapter 4.4 --- Optimisation of reaction conditions for UV-PCO in batch system --- p.56 / Chapter 4.4.1 --- Control experiments and effects of initial titanium dioxide concentration --- p.56 / Chapter 4.4.2 --- Effect of initial hydrogen peroxide concentration and UV intensity --- p.56 / Chapter 4.4.3 --- Effect of initial titanium dioxide concentration and initial pH --- p.60 / Chapter 4.5 --- Estimation of tetra-CB degradation pathway by photocatalytic oxidation --- p.71 / Chapter 4.6 --- Evaluation for the toxicity of hydrogen peroxide and toxicity change of tetra-CB by Microtox® test --- p.72 / Chapter 4.7 --- Determination of H202 concentration after PCO --- p.72 / Chapter Chapter 5 --- Discussion --- p.89 / Chapter 5.1 --- Separation and determination of eight PCB congeners --- p.89 / Chapter 5.2 --- Photocatalytic oxidation of mono-CB --- p.89 / Chapter 5.3 --- Determination of tetra-CB --- p.90 / Chapter 5.4 --- Optimisation of reaction conditions for UV-PCO in batch system --- p.90 / Chapter 5.4.1 --- Control experiments and effects of initial titanium dioxide concentration --- p.91 / Chapter 5.4.2 --- Effect of initial hydrogen peroxide concentration and UV intensity --- p.91 / Chapter 5.4.3 --- Effect of initial titanium dioxide concentration and initial pH --- p.93 / Chapter 5.5 --- Estimation of tetra-CB degradation pathway by photocatalytic oxidation --- p.95 / Chapter 5.6 --- Evaluation for the toxicity of hydrogen peroxide and toxicity change of tetra-CB by Microtox® test --- p.96 / Chapter 5.7 --- Determination of H202 concentration after PCO --- p.97 / Chapter Chapter 6 --- Conclusions --- p.98 / Chapter Chapter 7 --- References --- p.99

Graduation date: 1996

The photodebromination of selected bromoarenes has been studied at 300 nm to determine the the possible mechanistic pathways leading to product. Irradiation of 4-bromobiphenyl (BpBr) at this wavelength leads to the product biphenyl. The quantum yield of intersystem crossing (0.98) and quenching studies with cis-1 ,3-pentadiene suggest that the reaction occurs only via the triplet state. The observed increase of quantum yield of reaction with increasing concentration of BpBr suggests formation of a triplet excimer between the triplet state and ground state of BpBr as the key reactive intermediate. The log of the rate constant for excimer formation showed a linear increase with solvent polarity. The correlation of rate constants for excimer formation with linear solvation energy parameters indicates only a weak polarization of the excimer species. In order to understand the extent of radical anion character in the excimer, the regiochemistry of the photo-debromination of 3,4-dibromobiphenyl (3,4-BpBr) was studied. 3,4-BpBr was irradiated with and without an electron donor (triethylamine). 3,4-BpBr was also chemically reduced with lithium biphenylide (LiDBB). The difference in the regiochemistries under these conditions has been interpreted in terms of reaction via a free radical anion in the case of reactions with triethylamine and LiDBB and a weakly polarized excimer in the case of direct irradiation. In order to understand the extent of polarization in the excimers and their conformation, it was decided to study systems where the structure of the molecule would fix the geometry of potential intramolecular charge-transfer complexes. Towards this goal, brominated [2.2]paracyclophanes, 4-bromo[2.2]para-cylophane (CpBr), pseudo-para-dibromo[2.2]cyclophane (ps-p-CpBr) and pseudo-ortho-dibromo[2.2]cyclophane (ps-o-CpBr), were studied. The effect of substitution pattern of the bromines on the efficiency of excimer formation was also investigated. The brominated [2.2]para-cyclophanes showed varying efficiencies of formation of intermolecular excimer and intramolecular charge-transfer. A probable conformation for the excimer from BpBr has been proposed based on these results. / Graduation date: 1991

This study presents the first reconstruction of pollution history of Polychlorinated biphenyls (PCBs) in Taiwan coast. Six sediment cores were collected from Gaoping submarine canyon and its adjacent area to investigate the distribution and source recognition of PCBs. The concentrations of PCBs in the cores from Gaoping canyon ranged 0.155--2.281 ng/g dry wt, whereas the maximum concentrations of PCBs reached 21.0 and 2.93 ng/g dry wt, respectively, in the cores from the northern and sourthern continental shelf of Gaoping canyon. The toxicological effects assessed by sediment quality guidelines (SQGs), show that only 2-10cm in core L27 exceeded the guideline value suggested by Förstner (6 ng/g), which indicated the sediment in this area had been polluted seriously and should not be disturbed. Overall, compared with studies in the world, the sediment PCB concentrations in Kao-Ping coastal areas were relatively low. Hierarchical Cluster Analysis identified the source of PCBs in the study area was a mixture of Aroclor 1016, Aroclor 1242 and Aroclor 1260. Similarity in vertical variations of total concentrations of PCBs among the six cores was observed and the trend is consistent with the history of the PCB usage in Taiwan. The drastic decrease in PCB concentrations around the late 1980s, clearly demonstrates the effectiveness of the ban of PCBs use in 1980 in Taiwan.

Polychlorinated biphenyls (PCBs) are ubiquitious environmental pollutants that cause a number of diverse toxicities. The chemical stability of PCBs is responsible for their persistence in the environment, while their lipid solubility and resistance to biotransformation results in their accumulation in a number of animal species. The rate of PCB elimination is dependent on the ability of each animal species to metabolize a particular PCB congener. The goal of this project was to determine if in vitro liver microsomal metabolism studies could predict in vivo metabolism and to examine the reasons for the species variation in PCB metabolism. Kinetic constants were developed from in vitro metabolism studies using 4,4'-dichlorobiphenyl (4-DCB), 2,2',3,3',6,6'-hexachlorobiphenyl (236-HCB) and 2,2',4,4',5,5'-hexachlorobiphenyl (245-HCB) and liver microsomes from the human, dog, monkey and rat. An excellent correlation between the in vitro Vmax values and the in vivo hepatic clearance values was obtained. Human microsomal PCB metabolism was most similar to the rat. The in vitro human results were consistent with available in vivo data. All species produced the same major metabolites. The major metabolite of 4-DCB was 4,4'-dichloro-3-biphenylol and the two major metabolites of 236-HCB were 2,2',3,3',6,6'-hexachloro-4-biphenylol and 2,2',3,3',6,6'-hexachloro-5-biphenylol. The dog was the only species found to metabolize 245-HCB in vitro. Metabolites of 245-HCB were not identified. Studies of metabolism, covalent binding of PCB-equivalents to microsomal protein and metabolites demonstrated that the dog can metabolize PCBs more readily than other species because the dog has an alternate pathway of PCB metabolism. This pathway is either not found in other species or only found to a limited extent. Furthermore, an arene oxide does not seem to be involved in this alternative pathway. In summary, for certain classes of compounds in vitro to in vivo extrapolation is possible and may prove to be very useful in predicting the appropriate animal model for humans. Secondly, the dog appears to be quite different in its metabolism of PCBs in that it may have an alternate route of metabolism not involving an arene oxide.

The accumulation of polychlorinated biphenyls (PCBs) into humans was described using CoZMoMAN, a mechanistic multimedia fate and transport model coupled to a human food chain model. Model results demonstrated that concentration-age relationships for population cross-sections and individuals over time are not equivalent and that, under steady-state conditions, the lipid-normalized concentration of PCBs in an individual does not monotonically increase with age. By considering the decades-long emission history of PCBs in the model simulations, it was shown that an individual’s concentration mostly depends upon when she/he was born relative to the peak in emissions. Similarly, the two most influential factors controlling the shape of cross-sectional concentration-age trends obtained in human biomonitoring studies are the time lapse between the peak in emissions and sample collection and chemical elimination half-life. As a result, it should be possible to deduce information on these two factors from the shape of cross-sectional concentration-age trend. Reproductive behaviours (parity, age at birth, breastfeeding) were shown to potentially have a significant impact on exposure (and can contribute substantially to the observed variability in biomonitoring studies) though the mother’s reproductive history has a greater influence on the prenatal and postnatal exposures of her children than it does on her own cumulative lifetime exposure. A case study of the influence of dietary transitions in a hypothetical Arctic community demonstrated that dietary transitions are an important factor underlying the variability in PCB body burdens within and between subpopulations in addition to partially explaining the observed temporal trends. Comparison of PCB partitioning to various lipid materials suggested that 1) triolein is a good surrogate for human storage lipids; 2) liposomes are not an appropriate surrogate for human storage tissues; and 3) that partitioning into human MCF-7 cells is dominated by the storage lipids rather than by membrane lipids. Finally, a new bioenergetically-balanced bioaccumulation (3B) fish model is presented. Comparison of results from the 3B model with that of existing models revealed that feeding and growth rates used by previous fish bioaccumulation models were not bioenergetically consistent. Differences in biomagnification factors with fish size and temperature as a result of differing energetic requirements demonstrated the importance of the assumptions regarding growth rate and feeding rate.

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