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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Based on measured oxygen consumption values and calculated specific respiration rates it can be stated that the 3-hour EC10 and EC50 values of the test item are higher than 1000 mg/L and the NOEC can be statistically determined as 1000 mg/L.

Key value for chemical safety assessment

EC50 or LC50 for microorganisms:
1 000 mg/L
EC10, LC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

The purpose of the 3-hour test was to evaluate the influence of the test item cesium iodide on the activity of the activated sludge by measuring the respiration rate under defined conditions. The respiration rates (total, heterotrophic and nitrification oxygen uptake rates) of samples of activated sludge fed with synthetic sewage were measured in an enclosed cell containing an oxygen electrode after a contact time of 3 hours.

Based on the preliminary information about the test item caused effect on the activated sludge inoculum, the test item cesium iodide was investigated at the concentration of 1000 mg/L as a limit concentration, only. 2, 7 and 24.5 mg 3,5-Dichlorophenol /L as positive reference control, a Blank (inoculum) control and a nitrification controls were used.

Based on the preliminary information about the abiotic oxygen consumption, the main test was performed without abiotic controls.

All validity criteria of the study were met.

The test item was investigated at one (limit) concentration level of 1000 mg/L. The observed oxygen consumption rates consequently the specific respiration rates were in the range of the blank controls, no inhibitory effect of the test item was observed.

Based on measured oxygen consumption values and calculated specific respiration rates it can be stated that the 3-hour EC10 and EC50 values of the test item are higher than 1000 mg/L. The EC50 value was determined as: EC50 > 1000 mg/L.

The specific respiration rates were compared with the blank control values using 2 Sample t-Test (α=0.05). No statistical significant differences were observed in the comparison with the blank control values, consequently based on the results of this study the NOEC can be statistically determined as 1000 mg/L.