APPLICATION METHODS OF PESTICIDES TO AN AQUATIC MESOCOSM IN ORDER TO SIMULATE EFFECTS OF SPRAY DRIFT

A treatment procedure was developed to mimic spray drift deposition of pesticides on the water surface of outdoor experimental ditches. The performance of this procedure was evaluated in two studies (using the pesticides chlorpyrifos and linuron, respectively) by testing the capability to apply pesticides to the ditches accurately, without contaminating adjacent control ditches. This was done by measuring the volume and concentration of the spray, by chemical analysis of the compounds in the ditch water and by measuring spray deposition on the water surface. After the first study some slight modifications were made to the treatment procedure. In the second study, in which eight ditches were treated with a fixed volume of spray of varying pesticide concentrations, it could be shown that the actual volumes dosed closely matched the intended volume (mean value per treatment within 1% of intended value; coefficient of variation <2%). Also, the measured concentrations of the pesticide in the water, as well as the concentrations calculated from spray deposition measurements, closely approximated the intended concentrations. It is concluded that using the newly developed treatment procedure, pesticides are applied to mesocosms in an accurate and reproducible manner without contaminating controls. This may be relevant, especially if mesocosm studies are carried out for registration purposes. © 1998 Elsevier Science Ltd. All rights reserved