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Toxicity to microorganisms

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In the Klimisch 1 GLP test the toxicity on activated sludge microorganisms (Respiration Inhibition Test) according to OECD 209 and EU method C.11. was determined. A range-finding test was performed in a limit test design with the concentrations: 10, 100 and 1000 mg/L. The control and 1000 mg/L were prepared with three replicates whereas the 10 and 100 mg/L treatments were prepared as single replicates. Additionally, for each concentration and replicate of the test item assay and of the reference concentrations a nitrification control with ATU was prepared. Since statistical significant effects were observed for the range-finding test at the highest test item concentration a main test was performed with the following concentrations: 9.54, 30.5, 97.7, 312.5 and 1000 mg/L. All test item concentrations were performed with three replicates whereas the control was performed with six replicates. Additionally a second test setup was prepared and ATU was added to each mixture of one set. The test item had a toxic effect on the nitrifying microorganisms at the highest concentration tested (1000 mg/L). Hence, the EC50 of the test item for the nitrifying organisms was estimated to be ≥ 1000 mg/L and the NOEC was observed to be 312.5 mg/L. No toxic effects were observed for the total and heterotrophic microorganisms.