Environmental Behavior Of Glyphosate In Soils

Glyphosate [N-(phosphonomethyl) glycine] (GPS) is currently, and has been for some time, the most commonly applied herbicide worldwide. As such, considerable effort has been put forth to investigate the herbicide's behavior in the environment. In this review, an overview of the existing literature involving GPS is provided, with emphasis placed on recent studies completed in the past 10 years. As this chapter will illustrate, experimental results are highly variable and often contradictory, indicating a need for the behavior of GPS to be considered within the context of a set of specific environmental conditions. The affinity of a soil for solvated GPS is highly dependent upon the physiochemical properties of the matrix, although the herbicide is generally considered as strongly sorbed in most cases. Although the results of laboratory studies suggest that the mobility of GPS is highly limited in soils, the environmental occurrence of the herbicide in surface and groundwater is well documented. Leaching of GPS may be of concern in field soils with well-developed structure, where preferential flow through macropores is often responsible for rapid vertical transport. Recent studies indicated that the transport of GPS along with windblown sediment may also be a significant mechanism of off-site deposition. GPS has been traditionally considered as essentially non-toxic; however, more contemporary evidence suggests that it does indeed impart toxic effects to certain aquatic organisms as well as vertebrates. Overall, results presented here suggest that traditional presumptions of the immobility and non-toxicity of GPS may need to be re-evaluated.