Pesticide mobility on a hillside soil in St. Lucia

Pest control technology, developed for temperate countries was introduced i nto the Caribbean without any consideration for the fragility of the island s ecosystem. A significant increase in the utilization of pesticides by ban ana farmers in St. Lucia occurred during recent years. The mobility of two commonly used pesticides, 'ametryn' [N-2-ethyl-N-4-isopropyl-6-methylthio-1 ,3,5-triazine-2,4-diamine] and 'pirimiphos-ethyl' [O-2-diethylamino-6-methy lpyrimidin-4-yl O,O-diethyl phosphothiorate] on two different soils on bana na cultivated hillsides in St. Lucia was studied. Ametryn and pirimiphos-et hyl were applied to both sites, and soil samples were collected at differen t time intervals and were analyzed using gas chromatography. At both sites and on both soil types, quite early in the season, both pesticides leached down to 0.4 m depth. However, there appeared to be equal or greater leachin g and downslope transport of pesticides on hillside 2. Pesticide concentrat ion showed a reducing trend with respect to time and depth in both soil typ es at both sites. However, because of runoff interference, the half-life of pirimiphos-ethyl could not be properly defined, but half-life for ametryn was estimated to be 3 to 8 days. The short half-life for ametryn indicates the fast degradation of this pesticide under tropical conditions which coul d reduce the risk of environmental pollution. The environmental mobility of both pesticides suggests that leaching of ametryn and pirimiphos-ethyl may , in some circumstances create surface and groundwater pollution problems. (C) 1999 Elsevier Science B.V. All rights reserved.