The 6 d solid-phase toxicity test using freshwater ostracods of the species Heterocypris incongruens has been commercialised since 2002 and an ISO standard has been published recently (ISO14371 (2012)). It reveals many advantages compared to traditional sediment toxicity tests: Test organisms can be obtained from cysts so culturing is avoided, it requires a small quantity of sediment sample and bench space and it is easy to run and interpret. However, there still exists scarcity of data on the in uence of physicochemical sediment properties on the test and the sensitivity of H. incongruens to organic micropollutants. In this thesis, clay content in increasing proportions (0% to 80%) was tested as a confounding factor on the endpoints mortality and growth. It was found to have an e ect on growth of the ostracod, not on survival, indicating better growth of H. incongruens in coarse than in fine sediments. Toxicity thresholds were derived considering natural variability of the endpoints accounting for the presence of clay in test sediments. They were set to 10% for mortality and 20% for growth. Sensitivity of H. incongruens to Cypermethrin, Irgarol, Triclocarban and Triclosan was tested and e ect concentrations (LC₅₀, EC₅₀ and EC₁₀) were determined. The substances were selected according to their high partitioning coecients and environmental relevance. Based on nominal concentrations, results revealed highest sensitivity of the organism to Cypermethrin followed by Triclocarban, Triclosan and Irgarol. Effect concentrations causing a 50% effect on mortality or growth ranged from 2:33 µg g^-1 to 53:83 µg g^-1, being higher than environmental concentrations of individual substances detected in sediments. The ostracod test was also included in a battery that contained a growth inhibition test with the plant Myriophyllum aquaticum and an emergence success test with the midge Chironomus riparius testing contaminated and uncontaminated natural sediments. The ostracod test was most sensitive in detecting toxicity among the sediments assessed, according to the di erent characteristics of the test organisms and varying sensitivity to certain groups of contaminants. Both endpoints, mortality and growth, seem suitable for this purpose.