Estimating buffer zone widths for pesticide applications

Abstract

AbstractA technique for estimating the width of buffer zones required around sensitive areas during pesticide applications has been devised and tested. The technique has been used to estimate the buffer width required around water bodies during ground‐based permethrin applications in Canadian forests to prevent significant impact on fish and their food populations. A worst‐ case scenario was developed for environmental impact in water bodies result ing from ground‐based permethrin applications, and a spray application was made under these worst‐case conditions. Permethrin deposit on ground sheets was measured downwind of overlaid crosswind swaths. From these measurements the deposit at various downwind distances from a single crosswind swath was calculated, and a curvilinear regression line fitted to these values. Permethrin deposit downwind of multiple‐swath applications was computed by adding the contributions from individual swaths. Mortality resulting from various permethrin concentrations was measured for Aedes aegypti larvae. Although these larvae are not an important food species for the fish species of interest, salmon and trout, they are more sensitive to permethrin than most aquatic invertebrates. Predicted mortality in populations of this species and Salmo gairdneri, rainbow trout, at various downwind distances from the permethrin application was calculated from the toxicological and spray‐cloud dispersal data. Buffer width was estimated by choosing an acceptably low mortality, and determining the downwind distance at which this value was obtained. For example, a 20 m swath width was found to be adequate to limit mortality in A. aegypti andS. gairdneri populations to 10 and 0.1% during ground‐based permethrin applications.