Verbleib und Wirkung von Pflanzenschutzmitteln in Oberflächengewässern. Aquatische Mikrokosmosuntersuchungen: Abschlußbericht, Forschungsvorhaben 126 05 111

In an integrated approach for the determination of fate and effects of pesticides in stagnant aquatic systems used in the higher tier risk assessment concept for pesticides aquatic microcosm systems were developed and optimized regarding the expenditure of effort and time. The suitability for the pesticides registration procedure was proved with respect to quality and limitations of applicability. The objective of the first part of the project (Final Report of Project 126 05 105, of January 28, 1996) was to develop the test system and to prove its principal suitability for microcosm studies. In the second part of the project (present report) open questions related to the influence of sediment quality and mode of application on the test results should be investigated. Contrary to the first study unit, loamy sediments were used. Potential impact by spraydrift and runoff was simulated for sparingly soluble and water soluble pesticides, and the resulting effects were comparatively investigated. As in the first part of the project, isoproturon and azocyclotin were applied as test substance. The conclusions drawn from the results of both study units have been integrated in a guidance document on the applicability of aquatic microcosms in the scope of pesticides' registration. For both substances the degradation rate in the sandy system was higher compared to the loamy system, where the substances are absorbed more strongly. Due to the considerably slower water flow through the sediment core only low amounts of isoproturon were transported offsite. A comparison of effects was done only for the studies with azocyclotin varying sediment quality, regulation of macronutrient concentrations, limiting of the periphyton as well as light conditions and duration of the preincubation period. Despite these differences, with respect to the primarily affected biocoenoses (zooplankton) the same conclusions were drawn from the obtained results. This shows that the test systems are comparatively stable towards varying test conditions. To achieve a higher reproducibility the variability can be further decreased by regulating the system according to the proposals given in the guidance document presented in the Annex. For all studies a comparison of the sensitivity of the phyllopodes occurring in the microcosms with the daphnids from standard laboratory tests related to the actual effects concentrations in the water did not differ with 1,5 - 4 µm/l (decrease of abundances in the microcosms) and 5,7 µg/l (EC50, laboratory)