A COMPARISON OF THE FATE AND EFFECTS OF 2 PYRETHROID INSECTICIDES (LAMBDA-CYHALOTHRIN AND CYPERMETHRIN) IN POND MESOCOSMS

The fate and effects of two pyrethroid insecticides (lambda-cyhalothri n and cypermethrin) were investigated in replicated 25 m(3) pond mesoc osms. Three pesticide treatments which simulated spray drift depositio n were examined: 0.7 ga.i. ha(-1) cypermethrin and 0.17 and 1.7 ga.i. ha(-1) lambda-cyhalothrin. Based on the use rate and pesticidal activi ty of the chemicals, the cypermethrin and lower lambda-cyhalothrin rat es were approximately equivalent. After applications, pyrethroid resid ues in the water column declined rapidly. Treatment-related effects we re observed on some macroinvertebrate taxa, most notably the Asellidae and Gammaridae. Surface-dwelling insects also suffered initial knock- down, particularly in the 1.7 ga.i. ha(-1) lambda-cyhalothrin treatmen t, but there was recovery after the spray period. No adverse effects o ccurred on algae, macrophytes or zooplankton, but there were occasiona l enhancements (e.g. algal biomass and abundances of copepod nauplii a nd Rotifera) which may have been indirect effects. An overall comparis on of the treatments indicated that the higher lambda-cyhalothrin rate had the greatest effects, whilst the cypermethrin application had a s omewhat greater impact than the lower lambda-cyhalothrin treatment rat e (due to effects on peracarid crustaceans). The study indicated that should spray drift occur at the levels expected for either pyrethroid' s normal use patterns, potential impacts on natural aquatic ecosystems would be minor and transient.