Effect on Hyalella azteca after pulse exposure to environmentally realistic concentrations of permethrin

Exposure of non-target aquatic organisms to pesticides is likely to occur in short pulses following periods of drain flow, surface run-off or spray drift. However, standard aquatic toxicity tests are primarily based on continuous and maintained exposure periods of 24 to 96 hours for acute effect assessment. There is therefore a mismatch between laboratory and field exposure patterns, which has implications for standard risk assessments and could result in over- or underestimation of toxicity. The aim of the present study was to examine the short-term and delayed effects of different environmentally realistic pulse exposure and concentration of a pyrethroid pesticide, permethrin, on the freshwater amphipod Hyalella azteca.
Permethrin is a pyrethroid insecticide used in mosquito control and to control a wide range of insect pests on various crops and is known to be highly toxic to aquatic invertebrates. H. azteca is widely distributed through North America where it is common as a food source for birds, fish and large invertebrates and is therefore considered as an ecologically important organism. In addition H. azteca has been extensively used as a test organism and is generally sensitive to contaminants. The toxicity of permethrin to H. azteca was first estimated in a 96 hour test with constant exposure. Then the toxicity and delayed effects after 10 days were tested with different concentrations and pulse lengths. The exposure pulses lasted for 1, 3 or 24 hours simulating a realistic run-off event. After exposure, the organisms were transferred to clean water and survival was recorded immediately after the pulse and again after 10 days from the start of the experiment.