The mobility and degradation of pesticides in soils and the pollution of groundwater resources

Pesticides, the most cost-effective means of pest and weed control, allow the maintenance of current yields and so contribute to economic viability. Concern about the environmental impact of repeated pesticide use has prompted research into the environmental fate of these agents, which can emigrate from treated fields to air, other land and waterbodies. How long the pesticide remains in the soil depends on how strongly it is bound by soil components and how readily it is degraded. It also depends on the environmental conditions at the time of application, e.g., soil water content. Pesticide use must ensure public safety and environmental protection with regards to both the chemical itself and their potentially harmful metabolites. This paper reviews what is known of the influence of the physical and chemical characteristics of the soil system, such as moisture content, organic matter and clay contents, and pH, on the sorption/desorption and degradation of pesticides and their access to groundwater and surface waters. An understanding of the fate of pesticides is essential for rational decision-taking regarding their authorization. To reach an adequate understanding will require the concourse of soil science, clay mineralogy, physical chemistry, surface chemistry, environmental microbiology, plant physiology and, no doubt, other disciplines. Only through a multidisciplinary approach to environmental research will it be possible to plan, manage, pursue and integrate the results of the studies that will be necessary for the development of tools and techniques allowing effective environmental decision-making. There seems to be a great potential to develop microbially derived pesticides, which are effective, reliable and have a low environmental risk. In addition, new application techniques, for example precision band spraying, can reduce the dose, which can be a very effective way to minimize transport and emission but also to avoid a build-up of resistance in target organisms. Improved formulations will also be needed to reduce off-target deposition, improve retention on target, and enhance uptake and translocation.