Effects of the insecticide Dursban 4E (active ingredient chlorpyrifos) in outdoor experimental ditches: I. comparison of short-term toxicity between the laboratory and the field

By means of the insecticide chlorpyrifos, results of acute single-species toxicity tests were compared with direct effects in outdoor mesocosms. In the mesocosms, chlorpyrifos concentrations between 0.1 and 44 Šg/l were sprayed once. Acute effects were observed on arthropods. Effects could be quantified for seven species. For these species, EC50s were similar to their laboratory EC50s. The most sensitive standard test species was about representative of susceptible indigenous species. Effects were negligible at 0.1 Šg/l. A factor of 0.1 * 48-h LC50 of Daphnia magna may have protected most species in the community from direct effects. A safety factor of 0.01 may have protected the most susceptible taxa we found.