Atrazine photolysis: Mechanistic investigations of direct and nitrate mediated hydroxy radical processes and the influence of dissolved organic carbon from the Chesapeake Bay

Direct and nitrate-mediated hydroxy radical photoprocesses were examined with respect to atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) transformation. Irradiation (lambda > 290 nm) of aqueous solutions of atrazine in the presence of nitrate, which generates (OH)-O-., 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-s-triazine (CDIT), 3% of 4-acetamide-2-chloro-6-ethyiamino-s-triazine (CDET), 16% of chlorodiamino-s-triazine (CAAT), and 3% of hydroxy atrazine (DIET, 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% DIET 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 DIET 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)-O-. processes.