Atrazine mechanisms

These high levels were sporadic and transitory. However, some of them were high enough to have caused phytotoxicity, and more work needs to be done to establish whether herbicides are having adverse effects upon populations of aquatic plants in areas highlighted in this study. It should also be borne in mind that there may have been additive or synergistic effects caused by the combinations of herbicides found in these samples. For example, urea herbicides such as diuron and chlortoluron act upon photosynthesis by a common mechanism, so it seems likely that any effects upon aquatic plants will be additive. Similarly, simazine and atrazine share a common mechanism of action. 

Laird DA, Barriuso E, Dowdy RH, Koskinen WC (1992) Adsorption of atrazine on smectites. Soil Sci Soc Am J 56 62-67 Laird DA, Fleming PD (1999) Mechanisms for adsorption of organic bases on hydrated smectite surfaces. Environ Toxicol Chem 18 1668-1672 Lambert SM (1967) Functional relationship between sorption in soil and chemical structure. J Agric Food Chem 15 572-576 Lambert SM (1968) Omega, a useful index of soil sorption equilibria. J Agric Food Chem 16 340-343... 

Gunkel, G. and B. Streit. 1980. Mechanisms of a herbicide (atrazine, s-triazine) in a freshwater mollusc (Ancylus fluviatilis Mull.) and a fish (Coregonus fera Jurine). Water Res. 14 1573-1584. 

Li Q, Snoeyink VL, Mariaas BJ, Campos C (2003) Elucidating competitive adsorption mechanisms of atrazine and NOM using model compounds. Water Res 37 773-784... 

Li GC, Felbeck Jr. GT (1972) A study of the mechanism of atrazine adsorption by humic acid from muck soil. Soil Sci 113 140-148... 

Atrazine was not carcinogenic to mice or Fischer rats after oral administration in the diet. An increase incidence of mammary tumors has been found in female Sprague-Dawley females treated similarly. The lARC has determined that the mammary tumors associated with atrazine exposure involve a mechanism that is non-DNA-reactive and hormonally mediated. They further stated that this mechanism is not relevant to humans. The lARC concluded that there was sufficient evidence for the carcinogenicity of atrazine in experimental animals and inadequate evidence of carcinogenicity in humans. ... 

Atrazine is still one of the most widely used herbicides. Estimate the fraction of total atrazine present in truly dissolved form (a) in lake water exhibiting 2 mg POC-L1, (b) in marsh water containing 100 mg solids-L-1, if the solid s organic carbon content is 20%, and (c) in an aquifer exhibiting a porosity of 0.2 by volume, a density of the minerals present of 2.5 kg-L l, and an organic carbon content of 0.5%. Assume that partitioning to POM is the major sorption mechanism. You can find Kioc values for atrazine in Fig. 9.9. Comment on which value(s) you select for your calculations. 

To summarize, in flow regime I the maximum atrazine concentation atx = 10 km is reduced to (0.20/0.63) 100% = 32% of its original value. This reduction is significantly larger than that from any other possible mechanism to reduce the concentration. In contrast, in flow regime II dispersion is not yet felt at x = 10 km. 

Three different degradation mechanisms were proposed. In the first mechanism, the hydroxyl radical attacks atrazine by hydrogen abstraction from the secondary carbon of the ethylamino side chain, producing a free radical as shown in Equation (6.135). 

At pH less than 3, the reaction will occur slowly enough for kinetic models to be true. Thus, a pH 2 or 7 can be utilized for the slow kinetics of atrazine oxidation by UV /ozone processes, while rapid reactions will take place at pH 12. All of the three reaction mechanisms will be affected by other variables such as temperature, pH, and bicarbonate ion concentrations. 

Sorption mechanism of atrazine by SOM has been a subject of controversy. The early works (Weber et al., 1969 Hayes, 1970) showed that the sorption process is inhibited due to the low pKa value of herbicide, along with the proton transfer between carboxylic groups as well as the charger transfer at low pH values. These were discussed as probable retention mechanisms by organic colloids. However, Martin-Neto et al. (1994b, 2001) observed by FTIR (Figure 16.16) and UV-vis spectra that a charge-transfer mechanism was not operative in the HA-atrazine (HA-AT) interaction. FTIR showed that in pH <4, the carboxylate band (1610 cm-1) was observed in HA-AT spectrum, but a decrease in the wavenumber of C-H... 

Martin-Neto, L., Vieira, E. M., and Sposito, G. (1994b). Mechanism of atrazine sorption by humic acid A spectroscopic study. Environ. Sci. Technol. 28,1067-1073. 

Shimabukuro et al. (1966) identified 2-chloro-4-amino-6-isopropylamino-i-triazine (G-30033) as a major metabolite in shoots of mature pea plants. These results indicated that a second mechanism for tolerance to atrazine existed in some moderately susceptible plants. Later, Shimabukuro (1967a) was able to demonstrate that atrazine could be metabolized independently in both roots and shoots of young pea plants to 2-chloro-4-amino-6-isopropylamino-.t-triazine. This metabolite was much less phytotoxic than the parent compound. The metabolism of atrazine in resistant com and sorghum, in intermediately susceptible pea, and in highly susceptible wheat was reported by Shimabukuro (1967b). This study revealed two possible pathways for metabolism of atrazine in higher plants. All species studied were able to metabolize atrazine by TV-deal kyI ation of either of the two alkyl groups present. Com and wheat that contain the cyclic hydroxyamate (2,4-dihydroxy-7-methoxy-l,4-benzoxazine-3-one) also metabolized atrazine by conversion to hydroxy-atrazine (G-34048). Subsequent metabolism was postulated to be by conversion to more polar compounds. 

The third metabolic pathway discovered for degradation of triazine herbicides in plants was first reported by Shimabukuro et al. (1970) and involved conjugation of atrazine with glutathione in corn nutrient uptake, excised leaves, and leaf disc experiments. This new degradation mechanism was postulated to be the primary factor in the... 

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