Soil Column Leaching of Pesticides: Fid-Bau Portal

Soil Column Leaching of Pesticides

Katagi, Toshiyuki

Groundwater (GW) constitutes the most important source of drinking water, and despite the benefit of pesticides in food production, the contamination of GW by biologically active pesticides at unacceptable levels should be avoided. A number of pesticides and their degradation products have frequently been detected in field GW monitoring programs (Cohen et al. 1984; Hancock et al. 2008; Kolpin et al. 2000). Regulatory agencies in each country are responsible for preventing contamination of GW by pesticides or their degradates. Regulators have developed methods to assess both existing and newly developed pesticides for any tendency to leach in soil. The US EPA has performed monitoring studies to determine if pesticides contaminate GW (Wells et al. 1995) and has recently introduced a conceptual environmental model to better evaluate GW contamination (USEPA 2008b). In Europe, a stepwise evaluation procedure for regulating GW contamination by pesticides and their degradates is used, and this has recently been updated; the revision not only utilizes computer simulations of predicted environmental concentrations to determine if the 0.1 ppb trigger level is exceeded, but also relies on data from higher-tier field experiments (Boesten et al. 2009). To estimate the leaching behavior of a pesticide in soil or to compare its relative mobility with other pesticides, the sophisticated simulation approaches used generally require considerable data on the environmental fate of the pesticide. Because the cost of conducting field experiments over extended time periods can be extremely high, it is useful to collect relevant information on pesticide soil mobility by first using experimental laboratory approaches. For soil mobility, such approaches include batch adsorption studies, soil thin-layer chromatography, and soil column leaching (Häfner 1994; Helling and Dragun 1981; USEPA 2008a). Although laboratory soil column leaching and batch adsorption/desorption studies have been performed on many pesticides, the results of these studies do not always reflect what actually occurs in the field. Nevertheless, such studies normally provide valuable information on the potential mobility of pesticides in soil if they are well-controlled and focused, and the results are mathematically analyzed using an appropriate model.