Browsing by Subject "Photolysis"

Now showing 1 - 4 of 4
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    Abiotic transformations of pesticides in prairie potholes
    (2012-08) Zeng, Teng
    The prairie pothole region (PPR) is among the most extensively altered ecosystems on Earth. This region covers approximately 780,000 km2 of central North America, and contains numerous glacially formed wetlands embedded in an agricultural landscape. These wetlands, commonly known as prairie pothole lakes (PPLs), provide essential ecosystem services. Over the last 150 years, agricultural drainage has resulted in severe loss of native prairie wetlands. The remaining PPLs continue to be threatened by nonpoint source pesticide pollution from agriculture. Currently, little is known about the fate and persistence of pesticides in PPLs. In this work, the abiotic transformations of commonly used pesticides in PPL sediment porewaters and surface water were explored. Chloroacetanilide and dinitroaniline pesticides were found to react rapidly with naturally abundant reduced sulfur species (i.e., hydrogen sulfide and polysulfides) in sediment porewaters via nucleophilic substitution and reduction reactions, respectively. Dissolved organic matter (DOM) was also found to play a vital role in the reductive transformation. Next, the photodegradation of a suite of pesticides was investigated in PPL surface water under both simulated and natural sunlight. Enhanced pesticide removal rates pointed to the importance of indirect photolysis pathways involving photochemically produced reactive intermediates such as singlet oxygen and triplet excited-state DOM. Finally, the sedimentary sulfur speciation was examined by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Sulfur species in PPL sediments were found to consist of organic (di)sulfides, sulfonate, sulfate, and the mineral pyrite. Notably, the fractional abundances of reduced and oxidized sulfur species fluctuate on a seasonal basis.
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    The environmental fate of the phytoestrogens genistein and daidzein
    (2013-08) Kelly, Megan
    Genistein and daidzein are two phytoestrogens, compounds that come from plants (especially legumes) and interact with the estrogen receptors present in humans, fish, and other animals. Although they are naturally produced in the environment, they can become concentrated in the effluent of facilities treating the waste of plant-processing industries. They are also detected in run-off from fields where plants such as red clover are found. At environmentally-relevant concentrations, genistein and daidzein have been shown to produce reproductive, behavioral, and immunosuppressive effects in fish. This work develops the chemical and microbiological parameters necessary to predict the concentrations of genistein and daidzein in a body of water receiving a discharge containing the phytoestrogens. The attenuation processes studied include direct and indirect photolysis, sorption to settling particles, and biodegradation. Biodegradation is shown to be an extremely efficient removal process. Work by the Aquatic Toxicology Lab at Saint Cloud State shows that estrogenicity is removed by biodegradation, but some component of the biodegradation product mixture produces an androgenic or anti-estrogenic effect. Therefore, more research is needed to fully understand the exposure of aquatic wildlife to phytoestrogens and their degradates.
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    Neonicotinoid Hydrolysis and Photolysis: Rates and Residual Toxicity
    (2018-05) Todey, Stephen
    Neonicotinoid insecticides are currently the most widely used class of insecticides worldwide, accounting for 25% of total insecticide use. They are registered in 120 countries for use on more than 140 crops. Concern has grown, however, over their widespread detection in global surface waters, soil, finished drinking water, and wastewater, and for their potential role in colony collapse disorder in honey bees. This work set out to examine hydrolysis and photolysis reaction rates of neonicotinoids, as well as to identify reaction products and determine the toxicity of the reaction products on mosquitoes. Hydrolysis rates were tested between pH 4 and pH 10. Reaction rates were pseudo-first order and highly pH dependent. Calculated half-lives ranged from >1000 days to 10 days. Divalent metal ions (Cu2+, Ni2+, Zn2+) and minerals (kaolinite, goethite, TiO2) were found to have little to no effect on neonicotinoid hydrolysis. Experiments from pH 4 to pH 10 revealed a non-elementary rate law for neonicotinoid degradation, with the hydroxide concentration being raised to a power of 0.55 ± 0.09. Nitenpyram, imidacloprid, thiamethoxam, and clothianidin were found to undergo direct photolysis, with quantum yields of 0.025 ± 0.001, 0.0119 ± 0.0001, 0.0167 ± 0.0002, and 0.0133 ± 0.0001, respectively. Acetamiprid degraded very slowly via direct photolysis, but was found to undergo indirect photolysis due to reaction with OH∙ with a bimolecular rate constant of 1.7 ± 0.2×109 M-1 s-1. Reaction products were identified for all reactions, with the urea derivative as the most commonly detected product. Toxicity experiments on mosquitoes indicate no residual toxicity from hydrolysis or photolysis products, which may be expected given the removal of the pharmacophore during reactions. While abiotic reaction products were found to be non-toxic, results from experimental work indicates long environmental half-lives for the tested neonicotinoids, which may help to explain their observed persistence in environmental matrices.
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    Transformation of pharmaceutical and personal care product pollutants by wastewater chlorine disinfection and aqueous photolysis
    (2009-08) Buth, Jeffrey M.
    Concern has grown over the presence of pharmaceutical and personal care products (PPCPs) as pollutants in aquatic systems because these chemicals are specifically designed to elicit biological effects. To fully assess the environmental impact of these pollutants, their transformations by engineered and environmental processes must be considered. The transformation of cimetidine, an antacid drug, and triclosan, an antimicrobial compound, by wastewater chlorine disinfection was studied, as well as the photochemical transformations and environmental occurrence of triclosan, its chlorinated derivatives, and their dioxin photoproducts.Cimetidine was found to react rapidly with free chlorine, indicating that it will likely undergo significant degradation during wastewater chlorination. Four major products were identified, two of which were estimated to have lower predicted no-effect concentrations than cimetidine. Reaction pathways and reaction mechanisms were proposed. The aquatic photochemistry of triclosan and three of its chlorinated derivatives was explored. Reaction kinetics were studied, quantum yields were measured, and photoproducts were identified. Notably, dioxin photoproducts were observed to form at yields of 0.5 to 2.5% from triclosan and its chlorinated derivatives. A method was developed to analyze for triclosan and its chlorinated derivatives throughout the wastewater treatment process. A five-fold increase in the chlorinated derivatives of triclosan was observed in wastewater effluent after the chlorine disinfection step, showing this process to be a significant source or these pre-dioxins. Two sediment cores from Lake Pepin, a wastewater-impacted depositional zone of the Mississippi River, were analyzed for triclosan and the dioxin photoproducts of triclosan and its chlorinated derivatives. These dioxins were detected at levels that trended with levels of triclosan that increased over the last 45 years since its introduction in the mid-1960s, providing strong evidence for the photochemistry of triclosan and its chlorinated derivatives as their source. The triclosan-derived dioxins comprised an increasing percentage of the total mass of all dioxins detected in Lake Pepin, reaching as high as 31% in recent years.