Alkali salt of sulfonated aryl azo amino sulfonyl aryl azo sulfonyl aryl azo aryl sulfonate

Biodegradation in water: screening tests

Description of key information

The test substance Reactive Brown DYHY 0331/0334 was not readily biodegradable under the present test conditions. In a test for inherent biodegradability, the test substance was found to be primary biodegradable but not ultimate biodegradable, and was not proved to be inherent degradable under the present test conditions.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater

Additional information

The study was conducted according to the guidelines of “OECD, Guidelines for the Testing of Chemicals. Ready Biodegradability 301F: Manometric Respirometry Test, 1992”.

Under specific experimental conditions, the ready biodegradability of Reactive Brown DYHY 0331/0334 (DSDS20140530-0914) was determined in a 28-day dissolved oxygen depletion test using activated sludge from a domestic waste water treatment plant.

The test substance is very good soluble in water. Due to the fact that the substance is a milticonstituent, ThOD_NO3 could not be calculated and COD replaced ThOD_NO3 for calculating the rate of biodegradability in percent.The tested concentration of the test substance was100 mg/L (i.e.76.9 mg COD/L). The concentration of sludge inoculum in the test system was 30 mg/L. The tested concentration of sodium benzoate, used as reference substance, was 100 mg/L (i.e. 167 mg ThOD/L). A toxicity control was included in the study conduct.

During the test, the temperature was maintained at 22.0-23.5℃. The mean total O₂ uptake in the inoculum blanks at the end of the test was less than 60 mg O₂/L in 28 days, meeting the guideline requirement. Biodegradation of the reference substance (sodium benzoate) reached an average of 86% by Day 14 and was therefore within the validity criteria of the ready biodegradation test (>60% within 14 days). The variability of maximum biodegradability between replicate values of the removal of the test substance during the 28-day test period was less than 20%. The results of the toxicity control showed that the test substance met the criteria for not being inhibitory to the microbial inoculum. Thus, the test is valid.

During the 28-day test period, the biochemical oxygen demand (BOD) of the test substance did not show a significant increase, and the mean biodegradation percentage of the test substance at Day 28 was 6%.Thus, the test criteria of 60% BOD in 28 days within the 10-day window was not met.

Therefore, the test substance cannot be considered to be readily biodegradable under the experimental conditions according to this test method.

The study of inherent biodegradation of Reactive Brown DYHY 0331/0334 was performed according to the modified MITI test II “OECD, Guidelines for the Testing of Chemicals, 1981,Inherent Biodegradability: Modified MITI Test (II)”.

The results of biochemical oxygen demand (BOD) indicated that the cumulative oxygen consumption level of three replicates of test substance group were 95.80 mg/L, 97.20 mg/L and 98.60 mg/L, respectively. The mean oxygen consumption of blank controls was 86.65 mg/L. The calculated percentage biodegradation based on the BOD was determined to be 46% after 28 days. Primary biodegradation occurred during the 28-day testing period, but there was no ultimate inherent biodegradability of the test substance based on the criteria of “The guidelines for the hazard evaluation of new chemical substances (HJ/T 154-2004)” and “OECD guidelines for the testing of chemicals: revised introduction to the OECD guidelines for testing of chemicals, section 3, 2006”.

The results of DOC determination showed that the DOC of inoculum control group (IB), test substance group (TS) and abiotic control group (AC) at zero-time were 1.79 mg/L, 8.72 mg/L and 8.70 mg/L, respectively. The DOC of IB was 3.38 mg/L, the average DOC of TS was 6.89 mg/L and the DOC of AC was 9.18 mg/L on the 28^thday. Hence, the DOC removal of the test substance on the 28^thday was 49%.

The test substance was primary biodegradable but not ultimate biodegradable, and was not proved to be inherent degradable under the present test conditions.