Environmental sulfonylurea

LC/MS/MS is the preferred means of detection, quantitation, and confirmation of sulfonylurea herbicides in biological and environmental matrices. Therefore, recommendations for establishing and optimizing LC/MS/MS analyses common to all matrices are given first, followed by specific rationales for methods and sample preparation techniques for plant, soil, and water matrices. 

J. Strahan, Development and application of an enzyme-linked immunosorbent assay method for the determination of multiple sulfonylurea herbicides on the same microwell plate, in Environmental Immunochemical Methods, ed. J.M. Van Emon, C.L. Gerlach, and J.C. Johnson, American Chemical Society, Washington, DC, pp. 65-73 (1996). 

It is desirable to determine the chemical properties of irrigation water, paddy water in the field, and adjacent streams and rivers. Since especially the pH of the paddy water fluctuates diurnally (high in daytime and low at night), this may affect the water solubility of certain chemicals, e.g., sulfonylureas, which have dissociation constants (p/fa) in an environmentally relevant range. 

Only a few models applicable to paddy field conditions have been developed. RICEWQ by Williams, PADDY by Inao and Kitamura," and PCPF-1 by Watanabe and Takagi are useful for paddy fields. EXAMS2 by the United States Environmental Protection Agency (USEPA), a surface water model, can also be used to simulate paddy fields with an appropriate model scenario and has been used for the prediction of sulfonylurea herbicide behavior in paddy fields. The prediction accuracy of PADDY and PCPF-1 is high, although these models require less parameter... 

The environmental impact of sulfonylurea herbicides is also of significance. Based on hydrolytic studies, Dinelli et al. [168] predicted the dissipation rate of four herbicides following aquifer contamination. The chemical... 

The sulfonylureas described here are new herbicides with unprecedented activity. Activity at extraordinarily low rates of application has been demonstrated by both preemergence and postemergence applications (Ref. 1). These rates are best describee in grams per hectare compared to kilograms per hectare for most herbicides currently marketed. Furthermore, the combination of low application rates, half lives of generally less than two months in the soil (Ref. 2) and excellent safety to mammals [LD5o s of generally >5000 mg/kg for technical material in male rats] (Ref. IC) makes these compounds attractive products from an environmental viewpoint. 

Application of molecular modeling techniques to the biorational design of selective and environmentally safe crop protection chemicals is addressed. Sulfonylurea herbicides are used as an example to illustrate the kinds of biological information that can be known with modern technologies. An example of selective inhibitor design using computer graphics is presented. 

The sulfonylurea herbicides are a new family of chemical compounds, some of which are selectively toxic to weeds but not to crops. The selectivity of the sulfonylureas results from their metabolism to non-toxic compounds by particular crops, but not by weeds. In addition to efficient weed control, the sulfonylurea herbicides provide environmentally desirable properties such as field use rates as low as two grams/hectare and very low toxicity to mammals. The high specificity of the herbicides for their molecular target contributes to both of these properties. In addition, the low toxicity to mammals results from their lack of the target enzyme for the herbicides. Sulfonylureas inhibit the enzyme acetolactate synthase (ALS), also known as acetohydroxyacid synthase (AHAS), which catalyzes the first common step in the biosynthesis of the branched chain amino acids leucine, isoleucine and valine. In mammals these are three of the essential amino acids which must be obtained through dietary intake because the biosynthetic pathway for the branched chain amino acids is not present. The prototype structure of a sulfonylurea herbicide is shown in Figure 1. 

Research work in the US potentially offers herbicide-resistant sunflower varieties that have been developed by non-biotechnological techniques. Express , being developed by DuPont and Pioneer, shows resistance to sulfonylurea herbicide. Another variety, Clearfield , is resistant to imazamox. The key decision on these products depends on the decision under Section 18 of the Environmental Protection Agency. Should Section 18 label be approved, Micogen CO. already has enough Clearfield seeds to plant 15000 acres next year. Other companies will have Clearfield seeds ready in 2003. Express is expected to be commercially available in a few years (The Sunflower, December, 2001). 

The last ten years have seen important developments in this respect in the three most important families of pesticides fungicides of the triazole group applied at about 100 g/ha, insecticides of the synthetic pyrethroid type at 20 g/ha and herbicides of the sulfonylurea type at 30 and even as little as 5 g/ha exert an effect which could be achieved with the pesticides of 15-20 years earlier only at rates of a few kilograms per hectare. These modern highly efficient preparations form only a small part of the selection of pesticides available today, but a rapid increase in their share of the total is to be expected as a result of purposeful research work. Another approach toward diminishing environmental contamination by chemicals is the development of new active substances which are less volatile, are degraded more rapidly or are more readily adsorbed by soil particles. 

The visible signs of herbicide action after postemergent application of sulfonylurea herbicides are an almost immediate arrest of growth, followed by leaf yellowing (chlorosis), stimulation of anthocyanin production (leading to the typical reddish coloration of weed leaves), and finally, progressive shoot death. Depending on the weed species and environmental conditions, plant death will usually occur between seven and twenty days after herbicide application. 

Imidazolinones, diphenyl ethers, sulfonylureas, aryloxyphenoxypropionic acids, triazolopyrimidines, sulfonanilides LC/MS/MS TISP ( + ) (MRM) ngmr level Environmental water... 

The ultimate success of this discovery is demonstrated by the fact that there are fourteen commercialized and advanced candidate sulfonylurea herbicides. These compounds are useful in crops such as cereals, soybeans, rice, com, and canola as well as for noncrop use. TTieir low use rates favorable soil half-lives and low mammalian toxicity make them ideal products environmentally. These factors arc discussed in more detail by Brown and Kearney in the following chapter. 

Plant Biochemistry, Environmental Properties, and Global Impact of the Sulfonylurea Herbicides... 

The remainder of this chapter will describe the mode of action, crop selectivity mechanisms and environmental properties of the sulfonylurea herbicides. Other issues including resistant weeds and recropping intervals will also be discussed. 

Conclusion. In this chapter, we have attempted a broad overview of the biochemical and environmental properties of the sulfonylurea herbicides. The history of these herbicides is distinguished by the apparently endless variation in structure leading to new weed control spectra, crop selectivities and soil degradation properties. They have already achieved significant use in j ctice, and it is likely that Dr. Levitt s discovery will continue to yield new herbicide tools offering viable solutions to the needs of world agriculture and of society. 

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