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Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
October 2018 - January 2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
1992
Deviations:
no
Qualifier:
according to
Guideline:
other: Ministry of environmental protection of the people's Republic of China, The Guidelines for the Testing of Chemicals - Degradation and Accumulation, 301F Ready Biodegradability: Manometric Respirometry Test.
Version / remarks:
2013
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
A fresh sample of activated sludge was collected on Nov. 15th, 2018 from the aeration tank of the Long Hua Wastewater Treatment Plant in Shanghai which treats predominantly domestic sewage with Anacrobic-Oxic process (A/O). The activated sludge was kept by aeration until used (non-aeration during transport from the wastewater treatment plant to the laboratory was kept to a minimum). When back to the laboratory, the sludge was washed with mineral medium. After centrifugation, the supernatant was decanted. This procedure was repeated three times (4000 rpm, 4°C, centrifuge 20 minutes). Then 0.400 g of the concentrated sludge was weighed, dried at 105 °C for 1 h and then measured by moisture meter for 1h to determine the dry weight. The dry weight of concentrated sludge was 5.50%. According to the dry weight, 54.55 g of concentrated sludge was calculated and suspended in 1 L mineral medium to yeild a concentration of 3 g suspended solids/L. The final concentration of the activated sludge in the test medium was 30 mg/L.
Duration of test (contact time):
28 d
Initial conc.:
> 50.62 - < 50.78 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium according to OECD 301F
- Additional substrate: no
- Solubilising agent: no
- Test temperature: 21.9 °C-22.3 °C
- pH: 7.33-8.03
- pH adjusted: no
- Suspended solids concentration: 3 g suspended solids/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: airtight test flasks, brown BOD bottles with a volume of 500mL (The pressure drop is detected and converted into an electrical signal by means of an electrode type manometer)
- Number of culture flasks/concentration: 2
- Measuring equipment: Respirometer (WTW, OxiTop 110C, Weilheim, Germany)

CONTROL AND BLANK SYSTEM
- Inoculum blank: inoculum and mineral medium
- Procedure control: reference substance sodium benzoate, inoculum and mineral medium
- Toxicity control: reference substanc sodium benzoate, test substance, inoculum and mineral medium
Reference substance:
benzoic acid, sodium salt
Test performance:
The mean BOD of the inoculum blanks was 29.40 mg O2/L in 28 days, which was less than 60 mg/L, meeting the guideline requirement. During the 28 days, the pH values of the solution in test substance flasks were in the range of 7.51-8.03, which met the requirement of pH 6.0-8.5 of the test substance solution. The difference between replicate values of the removal of the test substance during 28d test period was less than 20 %. The mean biodegradation of the reference substance (Sodium benzoate) was 86 % by Day 14, reaching the pass level of the ready biodegradation test (>60 % within 14 days). The biodegradation percent of the toxicity control was 55 % by day 14, >25% ThOD, which met the guideline requirement. Thus, the test is considered valid.
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
During the 28-day test period, the biochemical oxygen demand (BOD) of test substance didn't increase from test start until test termination after 28d in comparison with that of the blank control group and didn't reach the 10-days window. Therefore, the test substance cannot be considered to be readily biodegradable under the experimental conditions according to this test method.
The percent of biodegradation in the toxicity control, containing both the test substance and reference substance, was calculated based on the sum of the ThODNH3 of the test substance and the ThODNH3 of the reference substance. In the toxicity control, within 14 days of exposure, biodegradation amounted to 55%. Since biodegradation in the toxicity control was greater than 25% within 14 days, the test substance was considered not to have a toxic or inhibitory effect on the activity of the microbial inoculum. The mean BOD of the inoculum blanks was 29.40 mg O2/L in 28 days, which was less than 60 mg/L, meeting the guideline requirement. During the 28 days, the pH values of the solution in test substance flasks were in the range of 7.51-8.03, which met the requirement of pH 6.0-8.5 of the test substance solution. The difference between replicate values of the removal of the test substance during 28 d test period was less than 20%.
Results with reference substance:
The mean biodegradation of the reference substance (Sodium benzoate) was 86% by Day 14, reaching the pass level of the ready biodegradation test (>60% within 14 days).
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The ready biodegradability of the test item was determined according to OECD 301F. No biodegradation occurred during the 28-d test. Therefore, the test substance cannot be considered to be readily biodegradable.
Executive summary:

The ready biodegradability of the test item was determined according to the guidelines of "Ministry of environmental protection of the people's Republic of China, The Guidelines for the Testing of Chemicals-Degradation and Accumulation, 2013, 301F Ready Biodegradability: Manometric Respirometry Test" and "OECD, Guidelines for the Testing of Chemicals. Ready Biodegradability 301F: Manometric Respirometry Test, 1992". Under specific experimental conditions, the ready biodegradability of the test item was determined in a 28-day dissolved oxygen depletion test using activated sludge from a domestic waste water treatment plant. The tested concentrations of test substance were 64.08 mg/L and 64.28 mg/L (i.e. 50.62 mg ThOD/L and 50.78 mg ThOD/L). The concentration of sludge inoculum in test system was 30mg/L, and the tested concentration of sodium benzoate used as reference substance was 100 mg/L (i.e.167.00 mg ThOD/L). A toxicity control was also included. During the test, the temperature was maintained at 21.9 °C-22.3 °C. The mean total O2uptake 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 the pass level of the ready biodegradation test (>60 % within 14 days). Biodegradation of the reference substance (sodium benzoate) reached an average of 86 % by Day 14. The difference of extremes between replicate values of the removal of the test substance during the 28 d 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 test substance didn't increase from test start until test termination after 28 d in comparison with that of the blank control group. No biodegradation occurred during the 28-d test. Therefore, the test substance cannot be considered to be readily biodegradable under the experimental conditions.

Description of key information

The ready biodegradability of the test item was determined according to OECD 301F. No biodegradation occurred during the 28-d test. Therefore, the test substance cannot be considered to be readily biodegradable (reference 5.2.1 -1)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The ready biodegradability of the test item was determined according to the guidelines of "Ministry of environmental protection of the people's Republic of China, The Guidelines for the Testing of Chemicals-Degradation and Accumulation, 2013, 301F Ready Biodegradability: Manometric Respirometry Test" and "OECD, Guidelines for the Testing of Chemicals. Ready Biodegradability 301F: Manometric Respirometry Test, 1992" (reference 5.2.1 -1). Under specific experimental conditions, the ready biodegradability of the test item was determined in a 28-day dissolved oxygen depletion test using activated sludge from a domestic waste water treatment plant. The tested concentrations of test substance were 64.08 mg/L and 64.28 mg/L (i.e. 50.62 mg ThOD/L and 50.78 mg ThOD/L). The concentration of sludge inoculum in test system was 30 mg/L, and the tested concentration of sodium benzoate used as reference substance was 100 mg/L (i.e.167.00mg ThOD/L). A toxicity control was also included. During the test, the temperature was maintained at 21.9 °C-22.3 °C. 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 the pass level of the ready biodegradation test (>60% within 14 days). Biodegradation of the reference substance (sodium benzoate) reached an average of 86% by Day 14. The difference of extremes between replicate values of the removal of the test substance during the 28d 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 test substance didn't increase from test start until test termination after 28d in comparison with that of the blank control group. No biodegradation occurred during the 28-d test. Therefore, the test substance cannot be considered to be readily biodegradable under the experimental conditions.