Assessing the ground-water contamination potential of agricultural chemicals: a flexible approach to mobility and degradation studies†

Abstract

Understanding the fate of agrochemicals in surface and sub-surface environments is of vital importance for the protection of water quality and for responsible environmental stewardship of crop-protection products. This paper demonstrates the need for a versatile approach to study experimental designs, aimed at a fuller understanding of the mobility and degradation of particular compounds in surface and sub-surface environments. Where appropriate, the environmental profile of a crop-protection product is built up using a combination of the following four study types: (a) radiolabelled laboratory studies to establish the routes of degradation and key degradates, supported by non-radiolabelled small-scale field studies to quantify key degradates under field conditions; (b) small-plot radiolabelled field studies for tracking the fate of products with low usage rates or those exhibiting rapid and extensive metabolism; (c) small-scale prospective ground-water studies (PGWs) to assess the potential for a compound's sub-surface mobility in vulnerable ground-water settings, and (d) large-scale ground-water monitoring studies to measure actual environmental concentrations of an in-use product. The determination of which studies are required is product-specific. Examples include radiolabelled laboratory and field studies conducted to investigate the rapid dissipation of the post-emergence herbicide tralkoxydim and its subsequent metabolites in surface soil. A PGW approach is illustrated, used to assess the degradation and mobility of the contact herbicide fomesafen under vulnerable ground-water conditions. Finally, large-scale monitoring studies are described which are used to assess the impact of the selective post-emergence herbicide fluazifop-P-butyl and fomesafen in vulnerable ground-water regions of northern Italy and Germany. These examples illustrate how flexibility and diversity of study design are essential to the development of a meaningful database of environmental fate information for crop-protection products. Such a database provides critical data for risk assessments and predictive modelling, and enhances our fundamental understanding of environmental science. © 1998 Society of Chemical Industry