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

Understanding the fate of agrochemicals in surface: and sub-surface environ ments is of vital importance for the protection of water quality and for re sponsible environmental stewardship of crop-protection products. This paper demonstrates the need for a versatile approach to study experimental desig ns, aimed at a fuller understanding of the mobility and degradation of part icular 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 laborato ry studies to establish the routes of degradation and key degradates, suppo rted by non-radiolabelled small-scale field studies to quantify key degrada tes under field conditions; (b) small-plot radiolabelled field studies for tracking the fate of products with low usage rates or those exhibiting rapi d and extensive metabolism; (c) small-scale prospective ground-water studie s (PGWs) to assess the potential for a compound's sub-surface mobility in v ulnerable ground-water settings, and (d) large-scale ground-water monitorin g studies to measure actual environmental concentrations of an in-use produ ct. The determination of which studies are required is product-specific. Ex amples include radiolabelled laboratory and field studies conducted to inve stigate the rapid dissipation of the post-emergence herbicide tralkoxydim a nd its subsequent metabolites in surface soil. A PGW approach is illustrate d, used to assess the degradation and mobility of the contact herbicide fom esafen under vulnerable ground-water conditions. Finally, large-scale monit oring studies are described which are used to assess the impact of the sele ctive post-emergence herbicide fluazifop-P-butyl and fomesafen in vulnerabl e ground-water regions of northern Italy and Germany. These examples illust rate how flexibility and diversity of study design are essential to the dev elopment of a meaningful database of environmental fate information for cro p-protection products. Such a database provides critical data for risk asse ssments and predictive modelling, and enhances our fundamental understandin g of environmental science. (C) 1998 Society of Chemical Industry.