Deethylated 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)... 

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). 

Seven chlorotriazines (simazine, cyanazine, hydroxy- and deethyl-atrazine, atra-zine, deisopropylatrazine, chlorodiamino-.r-triazine) were baseline resolved in <14 min using a Cg column (thermospray MS) and a 20/80 —> 55/45 methanol/ water (50 mM ammonium acetate with 1% formic acid) gradient [216], Excellent peak shapes and good resolution were obtained. Detection limits in the 20 ng injected range were reported. The authors noted that these detection limits could not be achieved on a Cjg column. 

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. 

The major degradation of atrazine in soil was its conversion to hydroxyatrazine by loss of the chlorine atom (2-5). Dealkylation also occurred with deethylation predominating over deisopropyla-tion (5,6). Only small amounts of the radioactivity of the ring labeled atrazine was converted to C02 by soil (6,8-10). Geller (11) found that the percentages of evolved "from C-labeled... 

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... 

A GC/ion trap MS method was used for the trace analysis of atrazine and its deethylated degradation product deethylatrazine in environmental water and sediment samples. The isotope dilution technique was applied for the quantitative analysis of atrazine at parts-per-trillion levels <2003ANA263>. 

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