Atrazine Photolysis:  Mechanistic Investigations of Direct and Nitrate-Mediated Hydroxy Radical Processes and the Influence of Dissolved Organic Carbon from the Chesapeake Bay

Abstract

Direct and nitrate-mediated hydroxy radical photoprocesses were examined with respect to atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) transformation. Irradiation (λ > 290 nm) of aqueous solutions of atrazine in the presence of nitrate, which generates • OH, yielded 20% of 6-amino-2-chloro-4-isopropylamino-s-triazine (CIAT), 10% of 6-amino-2-chloro-4-ethylamino-s-triazine (CEAT), 6% of 4-acetamide-2-chloro-6-isopropylamino-striazine (CDIT), 3% of 4-acetamide-2-chloro-6-ethylaminos-triazine (CDET), 16% of chlorodiamino-s-triazine (CAAT), and 3% of hydroxy atrazine (OIET, 4-ethylamino-6-isopropylamino-2-hydroxy-s-triazine) at 87% atrazine conversion. Direct photolysis of atrazine was much slower and at 23% atrazine conversion gave rise to 14% OIET and ca. 9% of chloroalkyloxidized or chlorodealkylated compounds with the ratio of the reaction rate constants equal to 0.14 (k direct / k indirect ). Results also suggest that OIET was not the product of a hydroxy radical process. The efficiency of the hydroxy radical process decreased more than 85%, with increasing DOC obtained from the surface layer of the Chesapeake Bay. However, only a slight decrease (<15%) in efficiency was observed for direct photolysis, suggesting that in the presence of surface layer DOC direct photolysis may become more important relative to the • OH processes.

Biodegradation of Aged Residues of Atrazine and Alachlor in a Mix-Load Site Soil by Fungal Enzymes

“…The observed rates constants calculated from firstorder rate plots were 0.0960 d −1 and 0.6960 d −1 for direct and indirect photolysis. In the indirect process, the XOH are formed faster, thus the faster degradation rate [24]. This rate was similar to that calculated from the current research data, (0.0882 d −1 versus 0.0960 d −1 ).…”

“…During indirect and direct photolysis of a substrate, the adsorption of UV-visible light energy resulted in the formation of oxidants such as the hydroxy radical (XOH) [24], causing similar reactions as described above. The observed rates constants calculated from firstorder rate plots were 0.0960 d −1 and 0.6960 d −1 for direct and indirect photolysis.…”

Photodegradation kinetics of fenitrothion in various aqueous media and its effect on steroid hormones biosynthesis

“…In light of these results, fenitrothion was more rapidly photodegraded in pure water under indirect photolysis compared to direct photolysis. This result consistently with Torrents et al (1997) reported that in the presence of the nitrate, where the hydroxyl radical was readily formed, a faster degradation of atrazine was observed compared to direct photolysis in distilled water. Therefore, the differences in the degradation rate constant and half-lives of fenitrothion between the two aqueous media are attributed mainly to the presence of nitrate under indirect photolysis, which accelerates the degradation rate of fenitrothion compared with direct photolysis.…”

“…Recent evidence indicates that the nitrate ion also promotes the photochemical oxidation of trace organic compounds in water. As reported by Zepp et al (1987) and Torrents et al (1997), the photolysis of nitrate, which is present in natural water as a natural component, produces hydroxyl radicals. Although hydroxyl radicals can be produced by several mechanisms, including the photolysis of hydrogen peroxide, ozone, nitrite, and dissolved organic matters, several studies have pointed to nitrate as the key source of the hydroxyl radicals in natural waters (Brezonik, 1994).…”

Reaction pathways and mechanisms of photodegradation of pesticides

“…Hapeman et al [252] examined the reaction of HO reaction between atrazine and HO was determined as light from a xenon lamp. The products found were 20% attack on the ethyl group was favoured relative to HO 6-amino-2-chloro-4-isopropylamino-s-triazine, 10% 6-attack on the isopropyl group.…”