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.

No description available.

No description available.

Two strains of Alcaligenes denitrificans, designated BRI 3010 and BRI 6011, were isolated from polychlorinated biphenyl (PCB) contaminated soil using 2,5-dichlorobenzoic acid (2,5-DCBA) and 2,4-DCBA, respectively, as sole carbon and energy sources. Both strains degraded 2-chlorobenzoic acid (2-CBA), 2,3-DCBA, and 2,5-DCBA. BRI 6011 alone degraded 2,4-DCBA. Metabolism of the chlorinated substrates resulted in the stoichiometric release of chloride, and degradation proceeded by intradiol cleavage of the aromatic ring. Growth of both strains on dichlorobenzoic acids induced pyrocatechase activities having catechol (catechol 1,2-dioxygenase) and chlorocatechols (chlorocatechol 1,2-dioxygenase) as substrates. Growth on 2-CBA and benzoic acid induced a pyrocatechase activity (catechol 1,2-dioxygenase) directed against catechol only. / The chlorocatechol 1,2-dioxygenase from BRI 6011 was purified, characterized, and compared with the chlorocatechol 1,2-dioxygenase from Pseudomonas sp. B13 and P. putida, organisms limited with respect to their CBA degradative versatility. These enzymes appear to be very similar based on biochemical and genetic data and possess sufficient broad substrate specificity to accommodate a wide range of chlorinated catechols, hence the increased versatility for chlorobenzoic acid degradation of A. denitrificans cannot be attributed to a more specialized chlorocatechol 1,2-dioxygenase. / Uptake of benzoic acid by BRI 3010 and BRI 6011 was inducible, exhibited saturation kinetics and the substrate was accumulated intracellularly against a concentration gradient by a factor of 8 and 10, respectively, indicative of active transport. Uptake of 2,4-DCBA by BRI 6011 was constitutive and saturation kinetics were not observed, suggesting passive diffusion of 2,4-DCBA and other CBAs into the cell down a concentration gradient. / Based on oxygen uptake experiments with whole cells, benzoic acid dioxygenase and chlorobenzoic acid dioxygenase activity was induced by benzoic acid and ortho-substituted chlorobenzoic acids, respectively. Since 2,4-DCBA diffuses across the membrane and the expected catecholic intermediates of 2,4-DCBA metabolism are metabolizable by BRI 3010, this suggests that the major difference between BRI 3010 and BRI 6011 might be the inability of the chlorobenzoic acid dioxygenase in BRI 3010 to recognize 2,4-DCBA as a substrate.

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.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.