Triazine herbicides simazine

The triazine herbicides simazine, atrazine, and hexazinone are commonly used in Christmas tree plantings in North America. Hexazinone is widely used in certain pines and on other conifer species in natural stands in regions where the organic matter content in soil is adequate to prevent excessive leaching to conifer root zones. Simazine and... 

These landmarks in American agriculture, and many others dated from before 1600 to 1990, are documented by Smith and Roth (1990). In 1958 and 1959 another major milestone in com production was attained when the triazine herbicides (simazine and atrazine) were registered for weed control in com. 

The widespread application of herbicides in agriculture has resulted in many polluted surface waters. As a result, numerous pesticides/herbicides have been treated in bench-scale laboratory studies with 03/UV/H202 processes during the last 10 years (see Table 10). Among them, many studies focused on the treatment of atrazine and other. v-triazine herbicides (simazine, prop-azine, etc.). Atrazine is a priority pollutant that similar to other individual pesticides has a very low maximum contaminant level (MCL) (0.1 pg L 1 for the European Environmental Commission according to Directive 80/778/ EEC). In some countries atrazine cannot be used but it is still found in many surface waters. In France, for example, atrazine was banned on September 28, 2001. From applied technologies, only carbon adsorption [180] and possibly advanced oxidations can be recommended to remove some of these... 

Numerical solutions of these relations have been obtained using the data from column studies and the estimates of / and 2 have been derived, making the assumption that sorption at site-1 is very rapid with ki = 1000 day. Results with a common triazine herbicide, Simazine, in different soils are summarized in... 

Triazines. Triazine herbicides are one of several herbicide groups that are heterocycHc nitrogen derivatives. Triazine herbicides include the chloro-, methylthio-, and methoxytriazines. They are used for the selective pre-emergence control and early post-emergence control of seedling grass and broadleaved weeds in cropland (299). In addition, some of the triazines, particularly atrazine, prometon [1610-18-0] and simazine [122-34-9] are used for the nonselective control of vegetation in noncropland (2). Simazine may be used for selective control of aquatic weeds (2). 

Depending on the duration of heating yellow-green to dark green chromatogram zones were produced on a weakly colored background. The detection limits of the triazine herbicides cyanazine (h/Jf 25-30), simazine (h/Jf 30-35), atrazine (h/Jf 40-45), terbutylazine (h/Jf 45-50) and anilazine (h/Jf 60-65) were 20 ng substance per chromatogram zone. 

Thus it is significant that for such si/m-triazine herbicides as simazine, atrazine, etc., the health and hygiene MPC (toxicity to warm-blooded animals, including humans) and phytotoxic MPC (toxicity to plants) differ by more than an order of magnitude 0.2-0.5 mg/kg for warm-blooded animals, and 0.01 mg/ kg for plants [89]. Warm-blooded animals and arthropods have a difference in sensitivity to many pyretroids that can reach tens of thousands of times [90]. 

After use, herbicides decompose slowly, and so affect cultivated plants for many years. In 1990, investigations in many regions of the USSR detected herbicides phytotoxic effects, especially among the si/m-triazine class, on different cultivars in many varied situations [13]. These sym-triazine herbicides, such as protrazin, simazin, atrazine, metazin, and prometrin, were used in different oblasts of the Ukraine, Kirgizia, Kazakhstan, Russia and Moldavia in previous years, especially on corn. Residual herbicide aftereffects led to the suppression and death of crops such as winter wheat, oats, barley, rye, potatoes, beets and sugar beets, linen, onions, watermelons and other melons, and sunflowers. 

Kulshrestha, G., N.T. Yaduraju, and V.S. Mani. 1982. The relative toxicity of the s-triazine herbicides atrazine and simazine to crops. Jour. Environ. Sci. Health B17 341-354. 

Beynon, K.I., Stoydin, G, and Wright, A.N. A comparison of the breakdown of the triazine herbicides cyanazine, atrazine, and simazine in soil and in maize, Pestic. Biochem. Physiol, 2 153-161,1972. 

In 1977, when the above review was presented and published, the history of the s-triazine herbicides was already 25 years old, with the first synthesis of these chemicals completed in 1952. The filing of the first basic triazine patent case in Switzerland was on August 16, 1954, and the first commercial products appeared on the market in 1956, following the approval of simazine for use in corn by federal authorities in Switzerland on December 3, 1956. Several other agrochemical companies started immediately to work with their own s-triazine variations, using other radicals or amino-functions on the s-triazine ring. This further research was also briefly reviewed in Knusli s 1977 paper. 

June Compound G-27692 (simazine) was found to be two to four times more herbicidally active than the first selected lead compound, G-25804 (chlorazine). The selectivity for corn of G-27692 was confirmed in new tests with outstanding results. The selection of simazine as the new com herbicide was a decisive step towards the first marketable triazine herbicide. 

Most producers concentrated their production on the major triazines (e.g., atrazine, simazine, terbuthylazine, ametryn, and terbutryn). The producers of triazine herbicides through the 1990s are presented in Table 3.1, and producers since 2000 are listed in Table 3.2. 

The triazine herbicides have revolutionized agricultural production of corn and more than 40 other crops. The yield increases, less labor-intensive production, and use for erosion control in conservation tillage are all benefits of the tri-azines, especially atrazine and simazine. Registered since the late 1950s, atrazine is still a mainstay of corn production and likely the most studied herbicide by regulatory agencies. 

The triazine herbicides can be divided into four different structural classes chlorotriazines, methylthiotriazines, methoxytriazines, and atypical or asymmetrical triazines. The chlorotriazine group includes atrazine, simazine, pro-pazine, terbuthylazine, and cyanazine. The methylthiotriazine group includes ametryn, prometryn, and terbutryn. The methoxytriazine group will include prometon and secbumeton. Hexazinone and metribuzin were chosen to represent the atypical triazine group. The plant metabolism of the most researched member of each triazine group will be discussed in detail to cover all major biological and chemical transformations reported in the literature. 

The metabolism of s-triazines has been the subject of extensive research since the 1950s to the present time. Much of this research has been the subject of review articles published over the years since s-triazines were introduced. The metabolism of -triazine herbicides in animals and plants and their degradation in soil were the subject of a review by Knuesli et al. (1969), later updated and revised by Esser et al. (1975) as a second edition. The metabolism of. v-triazines in plants was also reviewed by Shimabukuro et al. (1971a). Naylor (1976) published a review of herbicide metabolism in plants that included the. v-triazines. Lamoureux et al. (1998) reported on the identification of several plant metabolites of atrazine and simazine. 

Finally, certain triazine herbicides can be used selectively in orchards and in some horticultural crops. In this case, selectivity is not based only on physiological differences between species, but on physical selectivity associated with the location of the herbicide and the roots of the crop and weed species in the soil. Triazine herbicides such as simazine, which has very low solubility in water, remain close to the soil surface in most mineral soils. Careful application of simazine in horticultural or fruit crops can result in the herbicide being available to control shallow-rooted weed species without harming the deeper-rooted perennial species. The success of this use is dependent not only on the relative rooting depths of the tolerant and susceptible species, but also on soil conditions and other factors that may affect herbicide fate and movement. 

Weed resistance to the triazine herbicides was first identified in the late 1960s, with a biotype of common groundsel that was resistant to simazine (Ryan, 1970). Since then, resistance to triazine herbicides has been reported in many weed species (Holt and LeBaron, 1990 LeBaron and McFarland, 1990 Gronwald, 1994). Most cases of triazine resistance have been reported in the US, Canada, and Europe, where triazine herbicides have been used extensively in corn monocultures (LeBaron and McFarland, 1990 Stephenson et al., 1990 LeBaron, 1991). Most of the. v-triazinc-resistant weed species have been selected against atrazine and usually show a high level of cross-resistance to other. v-triazine herbicides. In most cases, these weeds also show a low level of resistance to as-triazinones (e.g., metribuzin). Triazine-resistant weeds are often less vigorous than nonresistant weeds, which facilitates their management. 

Soon after the discovery of triazine-resistant common groundsel, another equally important discovery was made. Radosevich and DeVilliers (1976) found that the mechanism of resistance in this weed was due to insensitive chloro-plasts that were capable of photosynthesis, even in the presence of simazine or atrazine. This was surprising because earlier research had confirmed that there were no differences in plant selectivity or susceptibility due to the origin of chloroplasts. Moreland (1969) had reported that isolated chloroplasts were equally inhibited to simazine whether they came from tolerant com or susceptible spinach. Radosevich and Appleby (1973) had confirmed there were no differences between the susceptible and resistant biotypes of common groundsel due to herbicide uptake, distribution, or metabolism, whereas it is known that com metabolizes triazine herbicides (Shimabukuro, 1985). 

During late 1994, the United States Environmental Protection Agency (USEPA) published a public document (PD-1) relative to the use of triazine herbicides by American farmers. In doing so, they placed atrazine and simazine in Special Review. USEPA s PD-1 triggered a benefits study of unprecedented proportions on the following issues benefits of atrazine and simazine use economic and biological impact of the loss of these products feasibility and efficacy of alternatives environmental benefits associated with atrazine and simazine use best management practices and comparative performance of alternatives. 

Triazine herbicides, principally simazine, have been an integral part of this change in management practice. Simazine is used alone and in combination with other preemergence herbicides for weed control in the plant row. It has low water solubility, low volatility, long residual activity, and gives a broad spectrum of annual weed control. 

Triazine herbicide soil activity, movement, and residues depend primarily on content of organic matter, and to a lesser extent, clay colloids (Nearpass 1965 Day et al, 1968 Weber et al, 1969). Soils that are low in organic matter or clay usually require lower herbicide rates, but result in more potential phytotoxicity (Lange et al, 1969a). Simazine (4.0kg/ ha) or diuron (5.0kg/ha) gave season-long weed control in soils of the Northwest (Hogue and Neilsen, 1987). 

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