Toxicity of fenvalerate to caddis¯y larvae: chronic eects of 1- vs 10-h pulse-exposure with constant doses Ralf Schulz * , Matthias Liess Zoological Institute, Technical University, Fasanenstrasse 3, D-38092 Braunschweig, Germany Received 20 May 1999; accepted 27 March 2000 Abstract Episodic pollution events such as runo or spraydrift can lead to a short-term (few hours) contamination of aquatic ecosystems with pesticides. So far, dierent short-term exposures with respect to long-term eects have not been studied. In the present study, caddis¯y larvae, typical for agricultural streams (Limnephilus lunatus Curtis, 2nd and 3rd instar) were exposed for 1- vs 10-h to three dierent equivalent doses (lg h) of fenvalerate. After transfer into an ar- ti®cial stream microcosm with pesticide-free water, chronic eects were observed over 240 days. Comparison of 1- and 10-h exposure revealed that 1-h contamination leads to stronger eects. The dierences were signi®cant for the sublethal endpoints emergence pattern and dry weight of adults (ANOVA ANOVA, Fisher's PLSD; P < 0:05). In terms of exposure dose, the dierence between 1- and 10-h exposure equals a factor of 6 as a mean of all endpoints studied. The following signi®cant eect levels for the 1-h exposure were obtained for the dierent endpoints investigated: reduced emergence success and production at 0.1 lgl 1 , temporal pattern of emergence at 0.001 lgl 1 , dry weight of adults at 0.01 lgl 1 . Ó 2000 Elsevier Science Ltd. All rights reserved. Keywords: Acute; Production; Pyrethroid; Runo; Short-term exposure; Spraydrift; Trichoptera 1. Introduction Episodic pollution events cannot adequately be ad- dressed by conventional toxicity testing methods with ®xed duration continuous exposure. For example, the introduction of agricultural pesticides with a low water solubility, e.g., pyrethroids, into streams due to runo, leads to short-term peak concentrations (Baughman et al., 1989; Kreuger, 1995; Schulz et al., 1998; Liess et al., 1999). Concentrations in streams decrease quickly because of adsorption processes and the permanent water renewal (Kreutzweiser and Sibley, 1991; Zwick, 1992). To obtain toxicity data relevant to the ®eld situ- ation, dierent short-term exposure scenarios must be compared and assessed. To assess the eects of dierent short-term exposure times, equivalent doses (lg h) of chemicals can be compared. An increase of acute toxicity with decreasing exposure time has been demonstrated e.g., for Gamma- rus pulex and lindane (Abel, 1980) and for Aedes aegypti and dierent insecticides (Parsons and Surgeoner, 1991). Similar results exist for the chronic eects of brief ex- posure of Chironomus riparius to equivalent doses of cadmium (McCahon and Pascoe, 1991). Recent eco- toxicological studies have increasingly emphasized the importance of long-term observations of eects after short-term contamination (Liess and Schulz, 1996; Brent and Herricks, 1998; Hosmer et al., 1998). However, no information is available on the comparison of dierent short-term exposure times of aquatic invertebrates to insecticides with respect to long-term eects. Chemosphere 41 (2000) 1511±1517 * Corresponding author. Tel.: +49-531-391-3184; fax: +49- 531-391-8201. E-mail address: R.Schulz@tu-bs.de (R. Schulz). 0045-6535/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 5 - 6 5 3 5 ( 0 0 ) 0 0 1 0 7 - 7