Michael Dorgerloh

Comparison of zebrafish (Danio rerio) and fathead minnow (Pimephales promelas) as test species in the Fish Sexual Development Test (FSDT).

Results are presented from a validation (with 5 laboratories) of the Fish Sexual Development Test (FSDT) developed to detect endocrine disrupters (EDs) and included in the OECD (Organisation for Economic Co-operation and Development) working program. The aromatase-inhibiting fungicide prochloraz was tested in zebrafish (Danio rerio) and fathead minnow (Pimephales promelas). The fish were exposed during sexual differentiation and development from 0 to 60 days post hatch (dph). After exposure, the vitellogenin (VTG) concentrations were quantified in head/tail homogenate and the sex ratio was determined (defined as female, male, intersex or undifferentiated). NOEC/LOEC and EC(x) designs were compared to optimize the test approach. Results show that both species are highly sensitive to prochloraz during sexual development. They respond by skewing of the sex ratio towards male phenotype and by a VTG decline in females. The NOEC/LOEC approach is preferred because sex ratio is difficult to analyze with a regression model. The mean NOEC/LOEC for prochloraz on the sex ratio was 43.3/134 μg/L and 101/293 μg/L for zebrafish and fathead minnow, respectively. The mean NOEC/LOEC on the decline in female VTG concentration was 65/110 μg/L and ~30/68 μg/L respectively. In conclusion, zebrafish and fathead minnow are suitable species in the FSDT and their sexual differentiation is equally labile to EDs.

Combination of a higher-tier flow-through system and population modeling to assess the effects of time-variable exposure of isoproturon on the green algae Desmodesmus subspicatus and Pseudokirchneriella subcapitata.

A flow-through system was developed to investigate the effects of time-variable exposure of pesticides on algae. A recently developed algae population model was used for simulations supported and verified by laboratory experiments. Flow-through studies with Desmodesmus subspicatus and Pseudokirchneriella subcapitata under time-variable exposure to isoproturon were performed, in which the exposure patterns were based on the results of FOrum for Co-ordination of pesticide fate models and their USe (FOCUS) model calculations for typical exposure situations via runoff or drain flow. Different types of pulsed exposure events were realized, including a whole range of repeated pulsed and steep peaks as well as periods of constant exposure. Both species recovered quickly in terms of growth from short-term exposure and according to substance dissipation from the system. Even at a peak 10 times the maximum predicted environmental concentration of isoproturon, only transient effects occurred on algae populations. No modified sensitivity or reduced growth was observed after repeated exposure. Model predictions of algal growth in the flow-through tests agreed well with the experimental data. The experimental boundary conditions and the physiological properties of the algae were used as the only model input. No calibration or parameter fitting was necessary. The combination of the flow-through experiments with the algae population model was revealed to be a powerful tool for the assessment of pulsed exposure on algae. It allowed investigating the growth reduction and recovery potential of algae after complex exposure, which is not possible with standard laboratory experiments alone. The results of the combined approach confirm the beneficial use of population models as supporting tools in higher-tier risk assessments of pesticides.

Labor-Algentest: Bedeutung der toxikologischen Endpunkte

ZusammenfassungDie Bestimmung der Algentoxizität im Labor ist ein Standardverfahren. Ausgehend von einer Wachstumshemmung unter Stoffeinfluß sind verschiedene toxikologische Endpunkte als Wirkungskennzahlen (EC) zu kalkulieren.Die EC50 für die Wachstumsrate μ wird mit der EC50 für die Biomasse verglichen. Die intrinsische Toxizität eines Stoffes kann allein von der weitestgehend prüfzeit-unabhängigen EC50 für die Wachstumsrate μ richtig wiedergegeben werden.Für die Bewertung algentoxischer Stoffe in der Umwelt ist aus ökologischer Sicht (Populationsdynamik und Produktivität des “Biomassepools” des Phytoplanktons) ebenfalls die Verwendung der Ergebnisse zur Wachstumsrate erforderlich.Die Auswerteunterschiede der nationalen und internationalen Prüfrichtlinien sollten daher auf die alleinige Bestimmung der Wachstumsratenhemmung vereinheitlicht werden.AbstractThe determination of algal toxicity in the laboratory is a standard procedure. Based on a growth inhibition under the influence of particular test substances, different toxic endpoints (EC) are to be calculated.The EC50 for a growth rate μ is compared with the EC50 for the biomass. The intrinsic toxicity of the test substance can only be correctly expressed through the use of a growth rate μ as the sole toxicological constant which is largely independent of the test duration.From an ecological standpoint (population dynamics and productivity of the phytoplanktons “biomass pool”), the use of data for growth rates is also necessary for such risk assessments. The differences in the evaluation of national and international guidelines should therefore be harmonized with regard to the growth rate inhibition alone.