Two years of pesticides monitoring in a Belgian watershed

A monitoring study was carried out in 1998-1999 on a medium-sized (c. 4580 km(2)) watershed of the Dyle (or Dijle) river in central Belgium, composed of both rural and urbanized areas. This watershed may be considered as representative of a large part of the country. Samples were taken each month from seven sites along the course of the river, plus one from its major affluent the Demer. The eight molecules monitored were the main herbicides used on the major crops in the area, plus some used in nonagricultural sectors. The concentrations found were mostly in the 0-3 mug/L range, with some peaks between 3 and 14 mug/L. The averages over all spring and summer samples analyzed ranged from 0.14 (bentazone) to 1.54 mug/L (diuron). Time and space specific patterns could be observed.