CURRENT RESEARCH Adsorption Catalyzed Chemical Hydrolysis of Atrazine Darid E. Annshong Department of Civil Eggineerin& Water Chemistry Laboratory, University of Wisconsin, Madison, Wis. 53706
Gordon Cbestm Department of Soils, University of Wisconsin, Madison, Wis. 53706
The adsorption of atrazine on soil and model adsorbents as it affects a& hydrolysis was determkd. Of the adsorbents investigated only the soil and a carboxylic resin affected the rate of a& hydrolysis. A phenolic resin, cellulose acetate, and m o n t m u d h i t e clay exhibited high atrazine adsorption capacities but did not affect the rate of ahazine hydrolysis. For the soil and the carboxyl resin, the ht-order rate coustant for atrazine hydrolysis was related directly to the extent (%) of atrazine adsorption; for the same extent of adsorption the hydrolysis rate was higher in the presence of the carboxyl resin than soil. Adsorption catalyzed hydrolysis appaxntly resulted from hydrogen bonding between the adsorbent carboxyl and atrazine ring nitrogen atom. This conclusion was supported by the ability of the carboxyl resin to catalyze hydrolysis, the decrease in atrazine adsorptionwith incxeasedresin carboxyl group ionization or atrazine ring nitrogen atom protonation, and the direct relationship between hydrolysis rate and the extent of adsorption on the carboxyl resin and soil. I
P
revious investi&ons
have shown that atrazine is hydrolyzed to hydroxyatrazine in soil system (Armstrong, Ckstcm, et d., 1%7; Harris, 1%7) by a nonbiological reaction catalyzed apparently by adsorption at soil colloidal surfaces (Armstrong cbesters, et d-, 1%7). The possibility that adsorption catdyms atrazine hydrolysis in soil is s u p portedbyrecentevkkmx that montmorillonite, a common soil mineral promotes atrazine hydrolysis (Russell, Cnrz, et d.,1W). Several types of pesticides, other than triadnes, are also y ~ ~ c e p t i to l e chemical degradation in the presence of soil particles (Ked, 1%7; Konrad, Armstrong, et ul., 1%7). Chemical hydrolysis of atrazine to hydroxyatrazine is of consickable importance in soils in view of the nonphytotoxicity of hydroxyatrazine and the resistance of atrazine to
microbial attack (Armstrong, Chesters, et al., 1%7; Skipper, Gilmour, et ul., 1%7). Because adsorption catalyzed reactions are of importance in determining the rates of degradation of several pesticides in the environment, it is essential to arteanpt to evaluate the factors controlling these reactions.Such information will be of value in future attempts to synthesize degradable pesticides, for predicting rates of pesticidal degradation under different environmental conditions, and for recommending remedial measures for pesticide residue problems. This investigation was designed to clarify the relationship between atrazine adsorption and hydrolysis rates in soils and to establish the types of adsorption sites conducive to catalyzing atrazine hydrolysis. Materials Purified and I C ring-labeled a& (2-chlor04ethylamin6isopropylaminePtriazk) were obtained courtesy of the G e i chemical Cop. Hydroxyatrazine (2-hydroxy analog of atrazine) was prepared by acid hydrolysis of atrazine (Armstrong,C h e s s et d.,1967). The ~ ~ b o x resin, yl Bio-Rex 70 (5@ to IOO-mesh), was obtained from Bio-Rad Laboratories, and the phenolic resin, Durez 11078 (
