Bipyridylium herbicide

Suleiman, S.A. and J.B. Stevens. 1987. Bipyridylium herbicide toxicity effects of paraquat and diquat on isolated rat hepatocytes. Jour. Environ. Pathol. Toxicol. Oncol. 7 73-84. 

Sugarcane Sower initiation is dependent on day length, temperature, age, moisture, and variety, and can be prevented by chemical applications at, or very close to, the date of floral initiation. The effective chemicals have been of two types (a) photosynthetic inhibitors, such as 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), or (b) leaf-burning, contact chemicals. The very effective bipyridylium herbicides 6,7-dihydrodipyrido[l,2-a 2, r-c]pyrazidinium dibromide (diquat) and 1, l -dimethyl-4,4 -bipyridinium bis (methyl sulfate) (paraquat) combine the two properties, although the... 

Senesi, N., Dorazio, V. D., and Miano,T. M. (1995). Adsorption mechanisms of s-triazine and bipyridylium herbicides on humic acids from hop field soils. Geoderma 66(3 4), 273-283. 

Bipyridylium Herbicides Di methyln i trosami ne Diethyl nitrosamine... 

Bipyridylium herbicides and insecticides containing activated azomethine group are also suitable for LCEC methods of analysis. The bipyridylium herbicide, methyl viologen (MV, paraquat), undergoes two, one-electron processes. 

Tomita M. Comparison of one-electron reduction activity against the bipyridylium herbicides, paraquat and diquat, in microsomal and mitochondrial fractions of liver, lung and kidney in vitro). Biochemical Pharmacol 1991 42(2) 303-309. 

Atrazine, first of the triazine herbicides, introduced together with paraquat, the first bipyridylium herbicide... 

Khan, S. U. (1973). Interaction of humic substances with bipyridylium herbicides. Can. J. Soil Sci. 53, 199-204. 

Atrazine, a triazine herbicide, blocks electron transport between QA and QB in PSD. DCMU (3-(3,4-dichlorophenyl)-l,l-dimethylurea) also blocks electron flow between the two molecules of plastoquinone. Paraquat is a member of a family of compounds called bipyridylium herbicides. Paraquat is reduced by PSI but is easily reoxidized by 02 in a process that produces superoxide and hydroxyl radicals. Plants die because their cell membranes are destroyed by radicals. Of the herbicides just discussed, determine which, if any, are most likely to be toxic to humans and other animals. What specific damage may occur ... 

The action of both herbicides can be increased by the addition of nonionic surfactants. Anion-active surfactants are incompatible with bipyridylium herbicides. 

The adsorption process also proceeds in organic soils, but the situation is more complicated and not completely clear. Bipyridylium herbicides are strongly adsorbed and thus deactivated by organic soil. However, in peat soils, for example, adsorption is often slow or incomplete, so that residual action must be reckoned with (OToole, 1965). 

Bipyridylium herbicides are absorbed only by the green parts of the plants and cannot penetrate phelloidai parts and woody bark. They can thus be selectively used in orchards and vineyards for weed-killing (Baldwin, 1963 Smith and Sagar,... 

Environmental conditions significantly affect the uptake and translocation of bipyridylium herbicides and thus their phytotoxic action. The quality and intensity... 

Calderbank (1968, 1972, 1976) wrote three excellent and exhaustive reviews on the chemistry and mode of action of bipyridylium herbicides. 

The formation of hydrogen peroxide has been demonstrated by Davenport (1963) and Davenport and Dodge (1969) in a chloroplast suspension treated with diquat. Reduction and oxidation of bipyridylium herbicides are cyclically repeated in the plant, so that catalytic quantities are sufficient to kill the plant. 

But disturbance in photosynthesis leads to slow destruction and does not explain the very rapid phytotoxic action of bipyridylium herbicides, which in the presence of light, is manifested within hours by yellowing, wilting and necrosis. 

Nonphotosynthetic tissues are only slowly attacked and disintegrated by bipyridylium herbicides, so this action is presumably not of primary importance for the mode of action (Bovey and Miller, 1968). 

Bipyridylium herbicides also catalyse the noncyclic and cyclic phosphorylation reactions (Zweig, 1965 Jagendorf and Avron, 1968), but it is rather improbable that the inhibition of relevant NADPH formation plays a role in their phytotoxic action (Corbett, 1974). 

Bipyridylium herbicides also produce changes in other biological processes of plants. It has been shown experimentally that they have an effect on the respiration of plants, photosynthetic oxygen production and the intake of carbon dioxide and that they inhibit transpiration (Mees, 1960 Funderburk and Lawrance, 1964 van Oorschot, 1966 Dodge, 1971). 

Bipyridylium herbicides are not metabolised by plants (Kearney and Helling,... 

Bipyridylium herbicides are broken down in the soil by microorganisms (Bayley and White, 1964 Bozarth et al. 1966 Funderburk and Bozarth, 1967 Calderbank and Tomlinson, 1968 Akhavein and Linscott, 1968). 

In the concentrations used for aquatic weed control (diquat 1 ppm, paraquat 5 ppm) bipyridylium herbicides are not toxic to fish. The tolerance limit for the diquat cation is 6-12 ppm, for paraquat 125 pmm. The sensitivity of single fish species differs considerably. Owing to adsorption on mineral and organic colloids, rapid inactivation occurs in natural waters (Wurtz and Arlet, 1964 Howe and Wright,... 

Diquat and paraquat are not toxic to bees (Beran, 1970) and are harmless to earthworms. Bipyridylium herbicides have virtually no harmful side-effects on the microflora and microfauna of soils. They inhibit the growth of soil bacteria and soil fungi slightly but they have no significant effect on the microbes necessary for soil fertility. The same is true for the microarthropode fauna of the soil (Rodriguez-Kabana et al., 1966 Calderbank and Tomlinson, 1968 Tu and Bollen, 1968 Wallnofer, 1968 Mathure/u/., 1976). 

The mode of action of cyperquat is unknown presumably, being a bipyridylium herbicide, it inhibits photosynthesis. 

Hydrophobic interactions and trapping of molecules in a molecular sieve formed by humic materials have been hypothesized as retention mechanisms for prometryn. It has been shown that fluridone, fluazifop, and bipyridylium herbicides penetrate into intedamellar spaces of smectites and can become trapped. 

The bipyridylium herbicides, used as a substitute for ploughing in erosion-prone country, are contact herbicides. Because they are not appreciably translocated, weeding with them produces a razor-sharp boundary. The most potent of these is paraquat 4.65), l,r-dimethyl-4,-4 -bipyridylium cation (used as the dichloride). This substance has long been in use in another connection, namely as an indicator for low reduction potentials. This colourless substance, known as methyl viologen, functions by forming a violet-coloured stable free radical 4.66) when the potential falls to —446 mV (Michaelis and Hill, 1933). 

The bipyridyl free radicals are not a direct cause of death, but just a stage in a rapid cycle of reduction and re-oxidation. In the course of this cycle much hydrogen peroxide is formed, and some superoxide free radical which is considered to be the true toxic agent (Fridovich, 1975). When monuron (see above) is used to inhibit photosynthesis, diquat loses most of its effect. Although paraquat is completely safe in normal usage, large oral doses cause fibrosis of the lungs, and death may follow. For a book on bipyridylium herbicides, see Summers (1980). 

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