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United States Department of Agriculture - page 25 / 36





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SAMPLE PETITIONHerbicide-Tolerant Plants

VI. Environmental Consequences of Introduction of the Transformed Cultivar

A. The Herbicide Glyphosate

N-(phosphonomethyl)glycerine (glyphosate) is an extremely effective broad-spectrum herbicide. The primary mode of action of the herbicide appears to be competitive inhibition of 5-enolpyruvylshikimic acid-3- phosphate (ESPS) synthase, an enzyme in the shikimic acid pathway of aromatic amino acid biosynthesis. Glyphosate provides effective control for the majority of the world’s worst weeds. It is translocated in the plant via both phloem and xylem. The broad-spectrum herbicidal activity is evident only when glyphosate is applied to foliage because there is little penetration of bark or woody stems (Franz 1983). Glyphosate becomes nontoxic upon contacting soil. Its degradation appears to be mainly microbial. Glyphosate is essentially nontoxic to mammals and birds (Anonymous 1983). Environmental impact studies indicate that the herbicide has little direct effect on animal communities (Sullivan and Sullivan 1979, 1981, 1982). However, some bird communities may show decreased population densities due to destruction of habitat caused by use of the herbicide (Morrison and Meslow 1984). Fish and invertebrates are more sensitive to the herbicide, especially to the commercial formulations, as a result of the surfactants in the formulation (Anonymous 1983). Effects of the herbicide on soil invertebrates in field situations appear to be minor (Eijsackers 1985). Although there are numerous reports of the effects of glyphosate on microbial respiration, nitrogen cycling, and cellulolytic activity in soils, no significant effects on any of these microbial processes should be observed at recommended field application rate of the herbicide (Carlisle and Trevors 1988). There have been no reports of groundwater contamination problems (Goldburg et al. 1990).


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