Dissipation of herbicides

Fang, C.H. Studies on the degradation and dissipation of herbicide alachlor on soil thin layers, J. Chin. Agric. Chem. Soc., 17 47-53, 1979. 

Chen, Y-L., Chen, J-S. (1979) Degradation and dissipation of herbicide butachlor in paddy fields. J. Pest. Sci. 4, 431. 

Dissipation in Static Water. The pathways which lead to dissipation of herbicidal residues in static water depend largely upon the nature of... 

Dissipation of Herbicidal Residues in Flowing Water. Acrolein and emulsified xylene are used extensively to control submersed weeds in irrigation canals. The three principal routes by which residues of these herbicides are dissipated are volatilization, dilution, and absorption by plants. Volatility accounts for the greatest loss. Typical reductions of xylene residue levels range from 50-60% during a distance of water flow of 5 miles. No precise data are available for the dissipation of acrolein. 

Urea and uracil herbicides tend to be persistent in soils and may carry over from one season to the next (299). However, there is significant variation between compounds. Bromacil is debrominated under anaerobic conditions but does not undergo further transformation (423), linuron is degraded in a field soil and does not accumulate or cause carryover problems (424), and terbacd [5902-51-2] is slowly degraded in a Russian soil by microbial means (425). The half-hves for this breakdown range from 76 to 2,475 days and are affected by several factors including moisture and temperature. Finally, tebuthiuron apphed to rangeland has been shown to be phytotoxic after 615 days, and the estimated time for total dissipation of the herbicide is from 2.9 to 7.2 years (426). 

Wu, T.L. 1980. Dissipation of the herbicides atrazine and alachlor in a Maryland cornfield. Jour. Environ. Qual. 9 459-465. 

In crop protection as well, understanding plant metabolism is of paramount importance to increase selectivity and to address resistance of chemical compounds. Moreover, dissipation of a compound in the aquatic ecosystem is very similar to the excretion phenomena of the bodies. An extensive amount of evidence has been accumulated to support the involvement of CYPs in the metabolism and detoxification of herbicides, fungicides and insecticides. The understanding of their biotransformations at the molecular level may be extremely helpful for herbicide- or insecticide-synergistic development. 

G. Dinelb, A. Vicari, A. Bonetti, P. Catizone, Hydrolytic Dissipation of Four Sulfonylurea Herbicides , J. Agric. Food Chem. 1997, 45, 1940-1945. 

Soil. The major soil metabolite is 2,6-dichlorobenzamide which degrades to 2,6-dichloro-benzoic acid. The estimated half-lives ranged from 1 to 12 months (Hartley and Kidd, 1987). Under field conditions, dichlobenil persists from 2 to 12 months (Ashton and Monaco, 1991). The disappearance of dichlobenil from a hydrosol and pond water was primarily due to volatilization and biodegradation. The times required for 50 and 90% dissipation of the herbicide from a hydrosol were approximately 20 and 50 d, respectively (Rice et al., 1974). Dichlobenil has a high vapor pressure and volatilization should be an important process. Williams and Eagle (1979) found... 

Surface Water. The time required for 50 and 90% dissipation of the herbicide from New York pond water was approximately 21 and 60 d, respectively (Rice et al., 1974). 

Nash, R.G. Dissipation from soil, in Environmental Chemistry of Herbicides. Volume TR. Grover, Ed. (Boca Raton, FL CRC Press, Inc. 1988), pp. 131-169. 

Newton, M., Roberts, R, Allen, A., Kelpas, B., White, D.,and Boyd, P. Deposition and dissipation ofthree herbicides in foliage, litter, and soil of brushfields of southwest Oregon. J. Agric. Food Chem., 38 574-583,1990. 

Muir DCG (1991) Dissipation and transformation in water and sediment. In Grover R (ed). Environmental Chemistry of Herbicides, Volume 2. CRC Press, Boca Raton, pp 3-88... 

Rouchard, J., O. Neus, R. Bulche, K. Cools, H. Ealen, and T. Dekkers (2000). Soil dissipation of diuron, chlorotoluron, simazine, pro-pyzamide and diflufenican herbicides after repeated applications in fruit tree orchards. Arch. Environ. Contam. Toxicol., 39 60-65. 

Triazine herbicides absorb sunlight weakly at wavelengths >290 nanometers (nm), thus, dissipation of the triazine herbicides in the atmosphere and in surface waters via photodegradation occurs mainly by indirect photolysis or photosensitized reactions. 

Current information on the photochemical dissipation of the triazine herbicides in the atmosphere is very limited. No studies concerning the vapor-phase photolysis of these herbicides have been reported, and only two studies have investigated the phototransformation of triazine herbicides when associated with atmospheric aerosols. Photodegradation of atrazine and terbuthylazine was observed in these studies, but the significance of photodegradation in the dissipation of atmospheric concentrations of these herbicides has yet to be established. 

The increased rates of photodegradation of the triazine herbicides observed in the presence of naturally occurring sensitizers indicate that photodegradation plays a significant role in the dissipation of these herbicides in natural waters. With most of the sensitizers studied thus far, cyanuric acid was the stable end product, rather than complete mineralization of the triazine herbicide. 

Although hydrolysis of the triazine herbicides is temperature and pH dependent, these herbicides are considered to be hydrolytically stable under the pH and temperature conditions encountered in natural waters. However, the relatively slow hydrolysis rates in natural waters may be enhanced somewhat by the presence of dissolved organic carbon (DOC) (in the form of fulvic acids and a variety of low-molecular-weight carboxylic acids and phenols) that has been shown to catalyze the hydrolysis of several triazine herbicides. Although microbial degradation is probably the most important mechanism of dissipation of the triazine herbicides in soils, abiotic hydrolysis of these herbicides also occurs. Hydrolysis in soils is affected by the pH, organic matter (humic acid) content, and the type and content of clay in the soil. 

Several processes may play a role in the environmental dissipation of -triazine herbicides. Dissipation processes can include microbial or chemical degradation in soil metabolism or conjugation in plants photodegradation in air, water, and on soil and plant surfaces and volatilization and transport mechanisms. This chapter will address photolytic degradation and abiotic hydrolysis of the currently used triazine herbicides, the triazinone herbicides (metribuzin and metamitron), and the triazinedione herbicide hexazinone. 

Hubbs, C.W. and T.L. Lavy (1990). Dissipation of norflurazon and other persistent herbicides in soil. Weed Sci., 38 81-88. 

Wang, Y.-S., J.-R. Duh, Y.-F. Liang, and Y.-L. Chen (1995). Dissipation of three s-triazine herbicides atrazine, simazine, and ametryn in subtropical soils. Bull. Environ. Contam. Toxicol., 55 351-358. 

Beestman, G.B., Demming, J.M. (1974) Dissipation of acetamide herbicides from soils. Agron. J. 66, 308-544. 

West, S.D., Burger, R.O., Poole, G.M., Mowrey, O.H. (1983) Bioconcentration and field dissipation of the aquatic herbicide fluridone and its degradation products in aquatic environments. J. Agric. Food Chem. 31, 579-585. 

DineUi G., Vicari A., Bonetti A., and Catizone P. (1997) Hydrolytic dissipation of four sulfonylurea herbicides. J. Agn. Food Chem. 45(5), 1940-1945. 

Nash R. G. (1988) Dissipation from soil. In Environmental Chemistry of Herbicides (ed. R. Grover). CRC Press, Boca Raton, FL, vol. 1, pp. 132-169. 

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