Impact of Fenvalerate on Enclosed Freshwater Planktonic Communities and on in situ Rates of Filtration of Zooplankton

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Abstract
The treatment of large-volume (~ 125 m3) in situ lake enclosures with fenvalerate at realistic field levels of agricultural contamination by drift or overspray (0.4–4.0 g fenvalerate∙ha−1) resulted in the disruption of the structure and function of the planktonic communities. The toxic effects ranged from short-term changes in the feeding behaviour of several species of zooplankton (Daphnia spp. and Ceriodaphnia lacustris) at 0.05 μg fenvalerate∙L−1 to a drastic reduction in the densities of most of the major groups of zooplankton at 0.1 μg fenvalerate∙L−1 for periods of up to 3 wk following treatment. In addition, indirect effects of toxicity were observed, e.g. populations of rotifers and phytoplankton increased in enclosures after the removal of the large-bodied cladocerans. This is thought to be the result of a reduction in competition and grazing, respectively. The emulsifying agents used in the emulsifiable concentrate formulation of fenvalerate were not found to be toxic to zooplankton at concentrations expected after agricultural use. The half-life of fenvalerate in an enclosure treated with a nominal concentration of 0.1 μg∙L−1 was estimated to be4.1 d by first-order reaction kinetics.