Atrazine corn crops

An herbicide, atrazine, which is commonly used on corn crops in the mid-western United States, was chosen as an example. During the spring, rainfall washes this compound from soil, and concentrations of herbicide in surface water will reach the Environmental Protection Agency s annual maximum contaminant level of 3 gg/L. It is necessary to detect this compound at concentrations as low as 0.05 gg/L. How would one isolate and purify this compound from water for analysis by gas chromatography/mass spectrometry (GC/MS) using SPE Some questions and ideas that come to mind follow ... 

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. 

Atrazine, a triazlne compound, is extensively used as a selective herbicide on corn and sorghum fields for the control of broadleaf and grassy weeds. Depending on soil properties and climatic effects, its persistence from recommended application rates in north central states may extend well beyond one year and crop injury may result when sensitive species are in the rotation (50). 

Of the 44 pesticides and three degradates analyzed for in surface waters of the Lake Erie Basin, 30 were detected at least once [75]. Atrazine was detected in every water sample, including samples from an area with less than 10% row crops (e.g., corn). The atrazine degradate deethylatrazine and the herbicide metolachlor were detected in 99% of the samples (Fig. 11). Eight of the 47 pesticides and degradates were detected in at least 50% of the water samples. All eight of these are herbicides used on row crops, except for prometon, which is used primarily in urban areas. Diazinon and chlorpyrifos were the most frequently detected insecticides, detected in 43% and 22% of the water samples, respectively. The most heavily applied agricultural pesticide not de-... 

Atrazine is by far the mostly widely used of the triazines, and corn is its major crop use. Table 1.3 shows the top five corn-producing countries in the world. Atrazine is a critical component in the herbicide programs of each of these countries. 

One of the reasons the triazines are so important in corn and other crops around the world is their application flexibility and their ability to mix with other herbicides for broad-spectrum weed control. Figure 1.6 demonstrates the relative importance of atrazine in com compared to other herbicides. 

Although simazine was the first triazine to be developed and marketed in corn as well as other crops, the more versatile atrazine quickly became the standard herbicide in corn. Simazine, however, has remained very valuable and is important on forage crops, ornamentals, turf, and several other vegetable, fruit and nut crops, including almond, apple, artichoke, avocado, berries, cherry, citrus, grape, hazelnut, peach, and walnut. There also remains a strong demand for simazine use in corn in some areas based on specific weed pressure. Simazine is manufactured and sold by several companies today in more than 25 countries around the world, with Brazil, the United States, Australia, and Japan ranked as the top four. 

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. 

Survey year Area corn grown (ha) Area corn treated11 (ha) Amount atrazine applied (t a.i.) Amount atrazine applied to all crops (t a.i.)... 

Of all the triazines tested in 1958, atrazine gave the best and most consistent results (Lee, 1958), without negative side effects such as crop injury, drift, serious handling problems, allergic responses, or odors. However, by far the most important characteristic of both simazine and atrazine was their ability to control many weed species for the entire growing season, with no corn injury at even high rates, and under adverse weather conditions (e.g., cold and wet). 

The weed control successes of the triazines led to important discoveries about new and better ways to use herbicides. The remarkable biological success of the triazine herbicides has had a tremendous impact on weed control and crop management over a relatively short time. Sumner (1999) told of his uncle in Hastings, Kansas, who looked over his weed-free com held after he had applied his first atrazine and remarked If I didn t see it with my own eyes, I wouldn t believe it. Such accounts could be repeated many thousands of times in the late 1950s and 1960s. The triazines are still the most important herbicides for weed control in corn, sorghum, and sugarcane. 

The metabolism of atrazine and a series of 2-chloro-.v-lriaz.ines were reported by Lamoureux et al. (1972) in excised leaf or shoot tissue of barley, corn, sorghum, and sugarcane. The authors found that the primary route of metabolism was the displacement of the 2-chloro group with glutathione or 7-glutamylcysteine. The overall rate of metabolism in susceptible barley was much slower than in tolerant crops. 

The 10 separate studies are listed in Table 12.1. The authors, time of completion, crops included, and aggregate economic costs based on atrazine or triazine availability are shown when they were available. Because most of the atrazine used is on corn and sorghum, these studies focus on these crops. 

There are yield and weed control costs in other commodities besides corn and sorghum. Sweet corn and popcorn have similar weed pests, but fewer herbicide substitutes than field corn. Of course, these crops are more valuable crops per area than field corn, so losses per acre are large relative to field corn. Both yield and cost of production changes were computed for sweet com and popcorn using the same agronomic and analytical approach as for field com. Sweet com losses are estimated to be 80.5 million and 62.4 million if triazines or atrazines were not available, respectively. 

Because of its cost, reliability, and superior performance, atrazine s adoption was swift. Surveys of Illinois corn farmers showed that in 1961 approximately 1% of Illinois com received atrazine, but only 8 years later in 1969, 33% of the crop received atrazine. Average com yields rose dramatically during the late 1950s and 1960s. What role did improved weed control and the triazine herbicides play in this rise in com yield Decker (1964) provided an interesting analysis of corn yield changes in the United States during this period ... 

Application versatility, combined with a high level of crop tolerance, led to atrazine being the most widely used corn herbicide in history. In fact, atrazine led the US com herbicide market within several years of its introduction. Illinois corn farmer surveys show a steady increase in the use of atrazine in corn from its debut in 1960, with 75-85% of com being treated with atrazine since 1975. 

Soon after its initial registration, atrazine became a widely used herbicide in the United States (Padgett et al., 2000). In 1994 at the time the USEPA Special Review was initiated, atrazine was used on approximately 67%, 65%, and 90% of US corn, sorghum, and sugarcane acreage, respectively. These 1994 percentages of crop treated remain consistent today. 

Analysis approach - corn and sorghum A two-tiered approach was also used to characterize the benefits associated with uses of atrazine and simazine in corn and sorghum. First, a comparative analysis was made of product labels. The following parameters were considered in this review performance profiles, including efficacy, spectrum, and crop tolerance label comparisons physical and chemical characteristics of the product hazard profiles economic benefits and other relevant issues, such as use restrictions, etc. 

Table 13.4 A computer simulation of projected US regional changes to corn growers if atrazine had not been available for use during the 1995 crop year3...

Performance and market share for competitive herbicide products Since the USEPA Special Review was initiated in 1994, acres treated with various corn herbicides have been carefully monitored. No clear alternative has proved to be a possible replacement to atrazine. Several facts are noteworthy. No corn herbicide introduced between 1994 and 2000 reached a 10% market share, nor did the market share increase for putative atrazine replacements like 2,4-D or bromoxynil (Table 13.6). These new products suffered from one or more of the following limitations limited spectrum of weeds controlled, crop injury potential, or rotational restrictions. Meanwhile, atrazine s total market share remained constant at approximately 70%. To date market retention has been poor when new herbicides are used alone. Virtually all com herbicides introduced since 1994 are used with atrazine, and the percentage of acreage treated in combination with atrazine is increasing (Table 13.6). 

As new herbicides were introduced over the years, weed scientists and farmers looked for the best mixtures, rates, and ratios to determine where the new ones would fit. The objective was always to provide the grower with the most dependable and efficacious control of major weeds, with the least amount of herbicides and cost, and with little or no risk to the applicator, consumers, and environment. With corn, sorghum, sugarcane, and certain other crops, such mixtures most often included atrazine or other triazine herbicides. Many times as weed scientists or farmers would discuss the virtues and performance of new herbicides, they would state The new products performed well, but it sure helped to add a little atrazine. ... 

Atrazine is the key herbicide facilitating ecofallow corn and sorghum production in the semi-arid Great Plains, where crop production is often uncertain and profits to farmers are often marginal. The success of atrazine in ecofallow is attributable to its duration of weed control as a soil-applied herbicide, the broad spectrum of weeds controlled, the low cost per area treated, and its safety to crops. In this semi-arid environment, maintaining weed-free fallow with repeated applications of nonresidual herbicides is not an economically viable alternative to atrazine. 

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