AbstractA review of the acute, subacute and chronic effects of four synthetic pyrethroids —permethrin, cypermethrin, deltamethrin and fenvalerate —on freshwater zooplankton is presented. Acute toxicities in the laboratory were found to range from 0.12 to 5.0 μg/L for cladocerans and copepods. Lower concentrations of pyrethroids (≤0.01 μg/L) reduced reproduction and rates of filtration of food by daphnids. Similar results were observed in field experiments. Simulation of direct overspray of aquatic ecosystems resulted in subsurface concentrations of pyrethroids greater than the levels known to be toxic in the laboratory (>1 μg/L). At these concentrations, populations of cladocerans were reduced. At concentrations of 0.05 μg/L or greater, rates of filtration by cladocerans were depressed. Indirect effects on communities included increases in populations of rotifers and green algae (Chlorophyta). Higher levels of contamination (>10 μg/L) caused reductions in copepods, rotifers and ostracods. Levels of pyrethroids of 0.01 μg/L or less were found to have no detectable effects on zooplankton i
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