Master of Science (MS)
The fungicide 2,6-dichloro-4-nitroaniline (DCNA) is applied to crops grown in areas near both freshwater and saltwater bodies and it can enter the surface waters where it is susceptible to photolysis; limited information is published on the photodegradation of DCNA. It has been shown that the salinity of seawater can influence both the overall rate of degradation of chemicals and impact the distribution and types of photoproducts generated during the photodegradation processes of a pesticide. The photodegradation of DCNA was measured in distilled water, artificial seawater, estuarine water, and phosphate buffer to determine the degree of differences in the degradation rate in various matrices. The brominated analogue 2,6-dibromo-4-nitroaniline (DBNA) was measured identically to determine the impacts of other halogens on the degradation process. Solutions of DCNA and DBNA at a concentration of 1 ppm were prepared and irradiated for 24 hours in an Atlas SUNTEST XXL+ photochamber that mimics the wavelength distribution and intensity of sunlight. Dark controls were run simultaneously. Samples were withdrawn at 0, 2, 4, 6, 12, and 24 hours and analyzed for residual DCNA or DBNA using an Agilent 1260 Infinity High Performance Liquid Chromatograph. The formation of ions such as nitrate, nitrite, bromide, and chloride were measured using a Thermo Dionex ICS-5000+ Ion Chromatograph. The half-life of DCNA in distilled water was calculated to be 7.62 ± 0.094 hours and 7.37 ± 0.279 hours in artificial seawater; statistically there was no significant difference in the degradation rate through the first half-life. Analysis of the quick formation of nitrite and chloride ions, and later formation of nitrate ions, suggests photonucleophilic substitution processes are occurring as the compound is degrading, followed by further degradation of nitrite to nitrate likely also due to photolysis processes. Small aliphatic acids, maleic and fumaric acid, were detected after 12 hours of irradiation by HPLC indicating degradation of the aromatic ring structure. Differences in formation rate and decline for intermediate photoproducts were observed in seawater and distilled water suggesting salinity affects the rate of formation of this photoproduct.
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Vebrosky, Emily Noelle, "The Photodegradation of 2,6-dichloro-4-nitroaniline (DCNA) in Freshwater and Saltwater" (2016). LSU Master's Theses. 352.