Atrazine transformation

The possible environmental fate of chemical transformation products is dependent on various factors. Once formed under certain conditions, transformation products are distributed between four major environmental media air, water/sediment, soil, and biota. Therefore, environmental fate of transformation products is primarily influenced by the properties of the chemical and conditions of environmental media. Differences in fate are clearly due to variance in environmental media with different physical, chemical, and biological properties including temperature, soil type, light intensity, organic matter, moisture, pH, aeration, and microbial activity. For example, mobilities of flve atrazine transformation products, deethylatrazine, deisopropyl-atrazine, didealkyatrazine, hydroxyatrazine, and ammeline, were negatively correlated with soil organic matter content and positively correlated with sand content [43]. 

H-Dealkylation. This is commonly observed as a primary transformation of pesticides with A/-alkyl substituents, such as atrazine [1912-24-9] (3) (eq. 5), trifluraHn [1582-09-8] (4) (eq. 6) (16), and 3 -ethyl dipropylthiocarbamate [759-94-4] (EPTC) (5) (eq. 7) (18). These reactions are catalyzed by a variety of bacterial strains, including Noeardia, Pseudomonas, Phodococcus, and Streptomyces. 

The product-ion spectra of the (M - - H)+ ions of atrazine, the structure of which is shown in Figure 3.29, and three of its transformation products showed that if the isopropyl side-chain was present in the structure a constaut neutral... 

Figure 3.29 Structure of atrazine. Reprinted from J. Chromatogr., A, 915, Steen, R. J. C. A., Bobeldijk, I. and Brinkman, U. A. Th., Screening for transformation products of pesticides using tandem mass spectrometric scan modes , 129-137, Copyright (2001), with permission from Elsevier Science.

Atrazine is successively transformed to 2,4,6-trihydroxy-l,3,5-triazine (Pelizzetti et al. 1990) by dealkylation of the alkylamine side chains and hydrolytic displacement of the ring chlorine and amino groups (Figure 1.3). A comparison has been made between direct photolysis and nitrate-mediated hydroxyl radical reactions (Torrents et al. 1997) the rates of the latter were much greater under the conditions of this experiment, and the major difference in the products was the absence of ring hydroxylation with loss of chloride. 

This example illustrates the difficulty of showing pesticides mutagenic activity. For example, mutagenic activity was clearly expressed not in the sym-triazine herbicides atrazine and cyanazine, but in their transformation products formed in corn husks ... 

Janthinellum yielded 2-chloro-4-amino-6-isopropylamino-5-triazine and Rhizopus stolonifer yielded 2-chloro-4-(ethylamino)-6-amino-5-triazine (Paris and Lewis, 1973). Atrazine was transformed by the culture Nocardia forming 2-chloro-4-amino-5-triazine (Giardina et al, 1980,1982). 

Plant. In tolerant plants, atrazine is readily transformed to hydroxyatrazine which may degrade via dealkylation of the side chains and subsequent hydrolysis of the amino groups with some evolution of carbon dioxide (Castelfranco et al, 1961 Roth and Knuesli, 1961 Humburg et al, 1989). In corn juice, atrazine was converted to hydroxyatrazine (Montgomery and Freed, 1964). In both roots and shoots of young bean plants, atrazine underwent monodealkylation forming 2-chloro-4-amino-6-isopropylamino-s-triazine. This metabolite is less phytotoxic than atrazine (Shimabukuro, 1967). 

Minero, C., Pramauro, E., Pelizzetti, E., Dolci, M.,andMarchesini, A. Photosensitized transformations of atrazine under simulated sunlight in aqueous humic acid solution, Chemosphere, 24(11) 1597-1606, 1992. 

Winkelmann, D.A. andKlaine, SJ. Atrazine metabolite behavior in soil-core microcosms, in Pesticide Transformation Products. Fate and Significance in the Environment, ACS Symposium Series 459, Somasundaram, L. and Coats, J.R., Eds. (Washington, DC American Chemical Society, 1991), pp. 75-92. 

A preemergence herbicide used for general weed control including grasses and broad-leaved weeds in a range of crops Chemical transformation product. Parent simazine and atrazine Chemical transformation product. Parent atrazine... 

N-dealkylation results from an alkyl substitution on an aromatic molecule, which is one of the first places where microorganisms initiate catabolic transformation of atrazine, a xenobiotic molecule (Fig. 15.2). It is a typical example of a reaction leading to transformation of pesticides like phenyl ureas, acylanihdes, carbamates, s-tri-azines, and dinitranilines. The enzyme mediating the reaction is a mixed-function oxidase, requiring a reduced nicotinamide nucleotide as an H donor. 

Crop protection chemicals are an important group of contaminants that exhibit biologically mediated transformation in aerobic or anaerobic subsurface environments. We consider two well-known contaminants the insecticide parathion, which is an organophosphate compound, and the herbicide atrazine, from the triazine group. 

The persistence (half-life) of atrazine in the subsurface is governed by chemically and biologically mediated transformations. Because the solubility of atrazine is relatively high ( 30mg/L) compared to its toxicity level in water (5 Lig/L), atrazine has become a hazard to groundwater quality. Atrazine has been detected in groundwater more than any other crop protection chemical two examples of atrazine persistence-transformation in aquifer environments are discussed next. 

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