Deisopropylated atrazine

Photosynthesis inhibition of about 1% (Jones and Winchell 1984) Photosynthesis inhibition 50% atrazine significantly more effective than deethylated atrazine, deisopropylated atrazine, and hydroxyatrazine, in that order, in effecting inhibition (Jones and Winchell 1984)... 

Gascon, J., E. Martinez, and D. Barcelo (1995a). Determination of atrazine and alachlor in natural waters by a rapid-magnetic particle-based ELISA Influence of common cross-reactants deethylatrazine, deisopropyl-atrazine, simazine and metolachlor. Anal. Chim. Acta, 311 357-364. 

Figure 30.5 Concentrations in selected midwestem streams during post-application runoff in 1989, 1990, 1994, 1995, and 1999 for (A) atrazine and cyanazine, (B) propazine and simazine, and (C) cyanazine amide, deethylatrazine, and deisopropyl atrazine.

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]. 

Fig. 4 Removal of atrazine (ATZ) and formation of deethylatrazine (DEA), deisopropyl-atrazine (DIA), and didealkylatrazine (DDA) using ozonation of 3 pg/1 of atrazine in filtered Missouri River water at pH 6 (Jiang and Adams 2006)...

The metabolism of chloro-S-triazines in soil involves reactions of dealkylation, deamination, hydroxylation, and ring cleavage [171]. Dealkylation of chloro -triazines does not remove their toxidly, which has been, instead, attributed to the release by chemical hydrolysis of active chknine [172]. In a study on the effects of atrazine and its degradation products on phototrophic microorganisms, the most toxic degradation product was deethylated atrazine, vdiidi was 2 to 7 times more effective towards cyanobacteria than deisopropylated atrazine. On the contrary, diamino and hydro atrazine were non-toxic [173]. 

In a soil-core microcosm study, Winkelmann and Klaine (1991) observed that the concentration of atrazine decreased exponentially over a 6-month period. Metabolites identified in soil included DEA, deisopropylatrazine, DAA and hydroxyatrazine. The half-life in soil is 71 days (Jury et al., 1987). Under laboratory conditions, the half-lives for atrazine in a Hatzenbiihl soil (pH 4.8) and Neuhofen soil (pH 6.5) at 22°C were 53 and 113 days, respectively (Burkhatd and Guth, 1981). Atrazine degradation products identified in soil were deethylatrazine, deisopropylatrazine, deethyldeisopropylatrazine and hydroxyatrazine (Patumi et al., 1981). Microbial attack of atrazine gave deethylated atrazine and deisopropyl atrazine as major and minor metabolites, respectively (Sirons et al., 1973). 

Excretion of free atrazine in urine is consistent with the pattern of exposure, with maximal excretion rates at the end of the workshift and a rapid decrease after cessation of exposure. This pattern suggests that atrazine does not accumulate in the body (Catenacci et al., 1990). Atrazine metabolism gives rise to bi-dealkylated (80%), deisopropylated (10%), and deethylated (8%) metabolites, which are eliminated in urine over a period slightly longer... 

Other chlorotriazines (simazine, propazine, terbuthylazine) follow the same biotransformation pathway of atrazine therefore, urinary excretion of bi-dealkylated, deisopropylated, and deethylated metabolites is not compound specific. When simultaneous exposure to different chlorotriazines occurs, the unmodified compound measured in urine, even though it represents a minor portion of the absorbed dose, may be useful for a qualitative confirmation of exposure. 

Deethylatrazine (DEA) and deisopropylatrazine (DIA) also have been detected in shallow, unsaturated surface-water runoff from a Eudora silt loam soil with DEA present at higher concentrations (Mills and Thurman, 1994a). Dissolved atrazine, DEA, and DIA concentrations in water samples from two closely spaced lakes indicated large differences in input from watershed nonpoint sources. Levels of these chemicals increased in response to spring and early summer runoff events (Spalding et al., 1994). In studies conducted by Gaynor el al. (1992, 1995), DEA was found in surface runoff samples that contained atrazine. Hydroxyatrazine (HA), deethyl hydroxyatrazine (DEHA), and deisopropyl hydroxyatrazine (DIHA) have also been identified in surface water (Lerch et al., 1995). 

A study was designed to define the relative rates of dealkylation of selected triazine herbicides and two monodealkylated triazine degradation products in the unsaturated zone and in surface runoff. Atrazine and propazine degrade to DEA by deethylation and deisopropylation, respectively. Similarly, atrazine and simazine can both dealkylate to DIA by removal of an isopropyl and ethyl side chain, respectively (Figure 30.12). Differences in the concentration of the dealkylated degradation product from the two different sources should indicate any preferential removal of ethyl versus isopropyl side chain. Furthermore, because monodealkylated DEA and DIA have different side chains remaining, their relative rate of removal should provide additional information on the liability of the ethyl side chain versus an isopropyl side chain. 

This study showed that under field conditions, the removal of an ethyl side chain from atrazine occurred more readily than the removal of an isopropyl side chain. Furthermore, deethylation rates of atrazine and simazine were comparable, and approximately two to three times more rapid than the rates of deisopropylation from atrazine and propazine, regardless of parent triazine. Continued dealkylation of the monodealkylated degradation products at 1 m in the unsaturated zone also shows a preferential removal of ethyl side chains over isopropyl side chains. Therefore, the small concentrations of DIA commonly reported in the environment do not result purely from a smaller production of the degradation product, but from a rapid removal once produced. This substantial turnover rate or flux of DIA in the environment is evidence for the presence of a didealkylated degradation product in the unsaturated zone (Mills and Thurman, 1994 Thurman et al., 1994). 

It is hypothesized that the DAR may be an indicator of point-source versus nonpoint-source contamination of groundwater by atrazine (Adams and Thurman, 1991). The DAR hypothesis is predicated on the assumption that atrazine degrades slowly in an aquifer because of low organic carbon concentrations, small microbial populations, and anaerobic conditions. This is substantiated by Wehtje et al. (1983) who determined that, under aquifer conditions, atrazine did not undergo deethylation or deisopropylation, and only slowly underwent abiotic degradation to... 

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