FORMATION, ADSORPTION, AND DEGRADATION OF N-NITROSOATRAZINE IN WATER AND SOIL

Authors

Hsin-Ro Wei, University of Nebraska – LincolnFollow

Date of this Version

4-2011

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Natural Resource Sciences, Under the Supervision of Professor Patrick J. Shea. Lincoln, Nebraska: April, 2011

Copyright (c) 2011 Hsin-Ro Wei

Abstract

The products of xenobiotic reactions in environmental mammalian systems may pose risks equal to or greater than parent compounds. Products of concern include nitrosamines, which can be carcinogenic, mutagenic, and teratogenic. Nitrosamines may form in soil, lake water, and sewage; they also can form in agricultural soils treated with agrichemicals containing amine moieties and nitrogen fertilizer. The nitrosamine-forming reaction of amines with nitrite is promoted at acidic pH. The widely used herbicide atrazine has secondary amine groups that can react with nitrite to form N-nitrosoatrazine (NNAT). The primary objective of this research was to characterize the formation, stability, and adsorption of NNAT in water and soil. NNAT formed most readily in acidic solution (pH 2-4) and in soil at pH ≤ 5. Acetate and fulvic acid promoted NNAT formation in water at pH 4 to 7. NNAT was relatively stable in solution in a two-month experiment. However, under light, NNAT rapidly 3 degraded in solution, and atrazine concentration increased, indicating hydrolysis (denitrosation) of NNAT to atrazine. In soil containing atrazine and nitrite, NNAT formed after 7 d at pH 4 and after 14 d at pH 5, but no NNAT was found at pH 6 and 7. No NNAT was detected in pH 4 soil under oversaturated or anaerobic conditions, indicating the importance of oxygen in the nitrosation reaction. Adsorption K_d and K_oc values show greater adsorption of NNAT (average K_d = 5.93 and K_oc = 495) than atrazine (average K_d = 2.71 and K_oc = 123) in Aksarben silty clay loam at agronomic soil pH. Adsorption coefficients decreased in the order: NNAT in Aksarben > NNAT in Rosebud silt loam > atrazine in Aksarben > atrazine in Rosebud > NNAT in Valentine sand > atrazine in Valentine soil. Larger desorption K_d values indicate greater hysteresis of NNAT than atrazine. NNAT half-life in Aksarben soil was approximately 9 d, with degradation to atrazine and other compounds. This information is important when evaluating atrazine fate and impacts in oil-water environments.