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Toxicity to microorganisms

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Description of key information

EC50 (3h) > 1000 mg/l

Key value for chemical safety assessment

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

Additional information

The purpose of the 3-hour test was to evaluate the influence of theDirect Violet 51on the activity of the activated sludge by measuring the respiration rate according to the OECD guideline 209.

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.

This preliminary test was used to estimate the range of concentrations of the test item needed in a possible definite test for determining the inhibition of oxygen consumption.

TheDirect Violet 51was investigated in this study at the nominal concentrations of 10, 100 and 1000 mg/L. Defined amounts of the test item were added directly into the test vessels.

Triplicate vessels were prepared and investigated at the highest examined test item concentration.

In parallel with the test item treatments 3,5-Dichlorophenol as positive reference control in concentrations of 2, 7 and 24.5 mg/L; furthermore, blank (inoculum) control, nitrification controls and abiotic controls were investigated.

Abiotic controls (investigated in three parallels) were prepared containing the test item in the concentration of 1000 mg/L, synthetics sewage feed, but no inoculum. In this test no abiotic oxygen consumption was noticed.

This experiment was performed without pH adjustment. The test item did not have any effect on the pHwithin the test system and additional neutralization step of test item containing mixtures before inoculum addition was not necessary.

All validity criteria of the study were met. The average specific respiration rate of the blank was 44.27 mg O2/ g activated sludge (based on dry weight) in an hour with a coefficient of variation of 2.27 %. The 3-hour EC50of the reference item 3,5-Dichlorophenol was 15.66 mg/L within the range of 2 mg/L to 25 mg/L, that was required for total respiration (in this study the differentiation between heterotrophic respiration and nitrification was considered as not necessary).

The observed oxygen consumption rates and consequently the specific respiration rates in all examined test item concentrations remained in the range of the blank controls (the average specific respiration rate at 1000 mg/L: 43.56 mg O2/gh). No inhibitory effect of the test item was observed. The noticed 3.61 % inhibition obtained at the test item concentration of 100 mg/L and the average of 1.60 % inhibition obtained at 1000 mg/L remained well within the biological variability range of the applied test system.

Based on measured oxygen consumption values and calculated specific respiration rates it can be stated that the 3-hour EC10and EC50values of the test item are greater than 1000 mg/L. The NOEC was determined to be 1000 mg/L, the highest concentration tested.