STUDIES ON THE ANALYSIS AND THE FATE OF ORGANIC POLLUTANTS IN THE ENVIRONMENT
This thesis deals with the analysis and the fate of pesticides in the environment. In the first part of the thesis, new techniques such as solid-phase extraction, solid-phase microextraction, and electrochemical detection, were studied and applied to the analysis of pesticides and their degradation products in environmental samples. Statistical optimizations were used to develop reliable methods for pesticide residue analysis and to improve the efficiency in the method development. In the second part, the fate of organophosphorus pesticides in aquatic environment was investigated. A small-scale multiresidue method for analysis of organochlorine and pyrethroid pesticides in vegetables was developed and was used to survey the pesticide residue levels in vegetables from the Singapore local market. By using miniaturized liquid-liquid extraction and minicolumn cleanup, the solvent consumption was considerably reduced. A carbon-fibre micro-electrode was applied to the determination of phenolic products from the hydrolysis of some organophosphorus pesticides. The electrochemical detection method can serve as an alternative for conventional UV detection in liquid chromatographic analysis of phenolic compounds. Orthogonal array designs were applied to the optimization of gas chromatographic analysis of water-containing samples and liquid chromatographic separation of over 30 pesticides. The experimental design method was also used to systematically examine the factors affecting the recovery of solid-phase extraction of these pesticides. Based on the studies, a method for analyzing pesticides in the golf course waters was established. Ten water samples collected from nine golf courses in Singapore were analyzed by this method. The possibility of using pencil lead as a sorbent for solid-phase microextraction of organic pollutants in water was investigated. The results of the study indicate that pencil lead can be used as a new and convenient source of sorbent for solid-phase microextraction. The photolysis rates and the photodegradation quantum yields of 16 organophosphorus esters were determined at the wavelength of 254 nm and 313 nm. The effects of molecular structure on the photolysis rates of the organophosphorus pesticides were investigated by using a series of compounds with slight differences in the chemical structure. Based on the photodegradation quantum yields, the absorbance of the compounds to UV light, and the spectrum distribution of sunlight, the relative photolysis rates of the organophosphorus pesticides under natural conditions were predicted. In order to gain better understanding as to the effects of chemical structure on the photolysis rates, three pesticides which have similar structure but very different quantum yields were further examined for their product distribution in the primary stages of photolysis. The effects of mercury (II) ion on the stability of some organophosphorus pesticides were studied. It was found that mercury (II) ion can considerably promote hydrolysis of organothiophosphates. The reaction mechanism was abo studied.
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