Isoproturon - Occurrence in shallow groundwater under fine-textured soils

The objective of the monitoring study was to examine the presence of the he rbicide isoproturon (IPU) in shallow groundwater under fine-textured soils which are prone to exhibit macropore flow. 97 groundwater sites were select ed and sampled in 1998 in different parts of Germany covering a wide range of environmental conditions. The suitability of each sampling site was asse ssed with regard to IPU use, soil texture and the depth of the groundwater table. IPU use was confirmed for the spraying season in 1997/98 with most o f the application conducted very close to the sampling sites. Fine-textured soils with predominantly loam texture classes were selected. Groundwater w as sampled at depths ranging from 1 to 28 m with the majority taken at 1 to 8 m below the surface. None of the 97 ground water samples contained concentrations of isoproturon greater than 0.1 mu g/L, showing that isoproturon can be used safely on fi ne-textured soils without posing a risk to ground water. Only two of the sa mples contained detectable residues (0.06 and 0.08 mu g/L) of isoproturon. At these two sampling locations, the movement of these small amounts of iso proturon to ground water may have been influenced by nearby topographical f eatures (a ditch at one of the locations and a sand and gravel pit at the o ther).