Toxicity of fenvalerate to caddisfly larvae: chronic effects of 1-vs 10-h pulse-exposure with constant doses

Episodic pollution events such as runoff or spraydrift can lead to a short- term (few hours) contamination of aquatic ecosystems with pesticides. So fa r, different short-term exposures with respect to long-term effects have no t been studied, In the present study, caddisfly larvae, typical for agricul tural streams (Limnephilus lunatus Curtis, 2nd and 3rd instar) were exposed for 1- vs 10-h to three different equivalent doses (mu g h) of fenvalerate . After transfer into an artificial stream microcosm with pesticide-free wa ter, chronic effects were observed over 240 days. Comparison of 1- and 10-h exposure revealed that l-h contamination leads to stronger effects. The di fferences were significant for the sublethal endpoints emergence pattern an d dry weight of adults (ANOVA, Fisher's PLSD; P < 0.05). In terms of exposu re dose, the difference between 1- and 10-h exposure equals a factor of 6 a s a mean of all endpoints studied. The following significant effect levels for the l-h exposure were obtained for the different endpoints investigated : reduced emergence success and production at 0.1 mu g l(-1), temporal patt ern of emergence at 0.001 mu g l(-1), dry weight of adults at 0.01 mu g l(- 1) (C) 2000 Elsevier Science Ltd. All rights reserved.