Analysis and fate of pharmaceuticals and quantum dots as emerging contaminants in the aquatic environment
Celiz, Mary Dawn
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Environmental contaminants such as pharmaceutical residues and nanomaterials are an ecological concern as they pose potential undesirable effects on the biota. Pharmaceutical compounds and their metabolites are detected in surface waters, wastewater effluent, and agricultural areas impacted with biosolids. The occurrence of these compounds in the environment shows inefficient elimination from wastewater treatment plants. Quantum dots (QD) are one of the nanomaterials that have increasing biological and electronic applications. Although its occurrence in the environment has not been determined, its release into the aquatic and terrestrial system is inevitable. There are several studies that have demonstrated toxicity of quantum dots to different organisms. The work presented in this dissertation focuses on the comparison of the two wastewater treatment plant technologies in removing a group of pharmaceuticals, identification of iopromide metabolites from activated sludge, evaluation of molecularly imprinted polymer (MIP) as solid phase extraction material for enrichment of 17β-estradiol, and investigations of the interactions of QDs with humic substances. Conventional activated sludge (CAS) and membrane bioreactor (MBR) technologies were compared in the removal of five pharmaceuticals, namely aceclofenac, carbamazepine, diclofenac, enalapril, and trimethoprim, from wastewater. Diclofenac showed resistance to degradation in the CAS but is amenable to degradation in the MBR. Trimethoprim and enalapril were only slightly eliminated in the CAS but were reduced by more than 95% in the MBR. Carbamazepine removal was negligible, while aceclofenac was only 50% reduced in CAS and MBR. In general, these results indicated that MBR has a higher efficiency in removing some polar pharmaceuticals from wastewater. Iopromide was amenable to biodegradation in activated sludge from a wastewater treatment plant forming three metabolites. Chemical derivatization and the fragmentation pattern of the derivatized metabolites obtained from tandem mass spectrometry served as a supplement in confirming the formation of carboxylated metabolites. The selective preconcentration of 17β-estradiol was explored using the recognition ability of a MIP in the solid phase extraction format. Binding studies of these polymeric particles towards 17β-estradiol showed selectivity over non-imprinted polymers, using acetonitrile as solvent. The imprinted polymer showed a recovery of 88% for 17β-estradiol in deionized water and 81% in surface water. The selectivity of the MIP over the non-imprinted polymer was relatively low, only 10% higher recovery in surface water. The results indicate that the MIP imprinted with 17β-estradiol does not appear to provide a viable approach to be used in a sample clean-up or enrichment step for the determination of 17β-estradiol in aqueous systems. The fluorescence of carboxylic or amine polyethylene glycol (PEG) functionalized CdSe/ZnS QDs behavior in the presence of two aquatic humic substances (HS), Suwannee River humic acid and fulvic acid were investigated using capillary electrophoresis. There was enhancement in the fluorescence of QDs at the onset of the interaction with HS. Quenching of the fluorescence of QDs was observed at longer exposure with HS within 30 minutes. The enhancement and quenching behavior were further corroborated using fluorescence spectroscopy which also showed no shifting in the wavelength of emission in the presence of HS. Dialysis of the samples containing QD and Suwannee River humic acid in 50 kD membrane, to separate any free cadmium from the mixture, did not indicate degradation of QD.