Persistent Organic Pollutants and the Environment : A Chemometric Approach to the Study of Halogenated Aromatics
Abstract: Concern is growing about the environmental and health effects of persistent organic pollutants (POPs), many of which are halogenated aromatic compunds. The research reported in this thesis focuses on factors determining their behaviour and release into the environment. The aims have been to relate molecular features with physical and chemical properties and to interpret casual relationships, with the common methodological approach of chemometrics.Quantitative structure-property relationships (QSPR) were investigated for polychlorinated biphenyls (PCB), polychlorinated diphenyl ethers (PCDE) and polybrominated diphenyl ethers (PBDE). QSPR models were developed from computationally derived descriptors using partial least squares regression (PLSR). The results show that it is possible to model and predict properties such as vapour pressure almost to the limit of the experimental error. The models obtained could be applied both to validate available experimental data and extend the current database of experimental determinations.The distribution and levels of brominated flame retardants (BFRs) in sewage sludge were investigated using exploratory data analysis (EDA), analysis of variance (ANOVA) and principal component analysis (PCA). The levels of polybrominated diphenyl ethers (PBDE) and biphenyls (PBB) agreed well with another investigation reported recently, but for tetrabromobisphenol A (TBBPA) there was a divergence, possible due to the analytical methodology. The variation among wastewater treatment plants was statistically significant, and three distinct types of technical products were shown to contribute.The formation and release of chlorinated aromatics was investigated in an industrial afterburner with a series of statistically design experiments. Th effect of temperature was studied with some detail and the results indicate different decomposition pathways for hydrocarbons and chlorinated aromatics. Additional factors were studied in a multifactor experiment, with a full factorial design in two blocks. Catalytic lowtemperature formation and chlorine input were both statistically highly significant factors. Polychlorinated dioxins (PCDD) and dibenzofurans (PCDF) showed a statistically significant correlation to chlorinated benzenes, and the results could thus be described and interpreted within a simple conceptual model. The efficiency of the final oxidation, the chlorine input and the presence of a catalyst (e.g. copper) control the thermal formation of the different groups of chlorinated aromatics.The reported investigations show that empirical 'soft' models can provide insight and understanding of complex chemical properties and reactions. Latent variable models and Taylor polynomials were able to approximate the behaviour of these systems within the investigated boundaries. The chemometric models and methods are thus likely to find use also in other areas of environmental science where theoretical understanding is still limited.
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