Single-species tests allow the assessment of chronical effects of endocrine disruptors on organisms under laboratory conditions. In the current study, three-generation tests with Ceriodaphnia reticulata and Sida crystallina were carried out to examine the influence of the synthetic hormone 17α-ethinylestradiol (EE) on the reproduction of these cladoceran species. For each species, six different concentrations (10-500 μg/l EE) and two controls were tested with eight replicates for a duration of 4 weeks. The test was initiated by transferring one neonate individual into a test vessel which was incubated under standardized conditions. Every 2 days, the medium was renewed and life history parameters such as survivorship of the adults and juveniles, clutch size, first appearance and number of produced offspring were investigated. Acute toxicity tests showed that C. reticulata (EC50 (24 h) 1814 μg/l) was more sensitive towards the substance compared to S. crystallina (EC50 (24 h) >4100 μg/l). The juvenile phase of S. crystallina was significantly shorter at concentrations above 100 μg/l EE. For C. reticulata, 17α-ethinylestradiol caused a higher mortality of the newly hatched juveniles at EE concentrations above 200 μg/l. No effects were found for mortality of adult animals, birth rate, number of juveniles per female and net reproduction rate of S. crystallina and C. reticulata. Thus, sublethal effects on parental generation exposed to EE lead to disturbances in reproduction and to affection of their offspring. Negative consequences for the population dynamic cannot be excluded, e.g. the decrease of a population. © 2002 Elsevier Science Ltd. All rights reserved.
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