Registration Dossier

Diss Factsheets

Environmental fate & pathways

Biodegradation in water: screening tests

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From July 07, 2017 to August 10, 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Lot/batch No.: 0000974911; Scymaris reference No.: 1014.042
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
Activated sludge was obtained from Totnes Sewage Treatment Works, Totnes, Devon, UK on 5 July 2017. This works treats sewage of predominantly domestic origin. At the laboratory, the activated sludge was kept aerated at room temperature and the pH maintained at 7.0 ± 1.0.
Six days prior to the exposure start the activated sludge was centrifuged, washed and re-suspended in the mineral medium and the solids concentration determined. This sludge was then diluted in medium, added to test bottles and stirred until required for use. The seeded mineral medium was pre-conditioned for six days to reduce the blank oxygen uptake readings in the test.
The mineral medium was made up according to the OECD and EC guidelines.
Duration of test (contact time):
ca. 28 d
Initial conc.:
100 mg/L
Based on:
COD
Initial conc.:
16.4 other: mg
Based on:
COD
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
Experimental design

All test bottles contained the prepared activated sludge inoculum in mineral medium.
- Inoculum blanks contained no test or reference substance, in order to demonstrate there was no other carbon source in the medium.
- Positive controls contained the reference substance, sodium benzoate at 100 mg/L, to demonstrate the viability of the inoculum (16.4 mL of 1000 mg/L sodium benzoate solution).
- The test substance bottles contained test substance at 100 mg/L (16.4 mg), to determine its biodegradation.
- Toxicity controls contained the test and reference substances, both at 100 mg/L, and were used to show if there had been any inhibition of the inoculum by the test substance (16.4 mg of the test substance + 16.4 mL of 1000 mg/L sodium benzoate).

Each set of bottles was prepared in triplicate. Additional single replicate of the test substance and toxicity control bottles were prepared for determination of pH at day 0, so undissolved test substance was not removed by the pH probe.

Determination of chemical oxygen demand (COD)

The COD of the test substance was determined using cuvette tests provided by Hach Lange Ltd using a DR2800 spectrophotometer for evaluation. In outline, a predetermined amount of the test substance, dissolved or dispersed in water, is oxidised by potassium dichromate in a strong sulphuric acid medium with silver sulphate as a catalyst, under reflux. The green colour of Cr3+ or the yellow colour of Cr6+ is evaluated spectrophotometrically.

pH and temperature measurements

The pH of the seeded test medium was measured and adjusted as necessary to 7.4 ± 0.2 prior to the acclimation phase. On day 0 the pH was measured in every bottle from the inoculum blanks, a single bottle from the positive controls, and the additional single replicate of the test substance and toxicity control bottles. Determinations were not made on other bottles containing the test substance as undissolved test substance could have adhered to the pH probe. The pH in all of the test bottles was measured on day 28.
The study was performed in an incubator to ensure the test bottle contents were maintained within the range 22 ± 1°C. The temperature of the solutions in a selection of test bottles was measured on days 0 and 28. The temperature of the incubator was continuously monitored throughout the study.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
ca. 122
Sampling time:
28 d
Details on results:
Chemical oxygen demand (COD)
The measured COD value of the test substance was 1.27 g O2/g of substance, and its biodegradation was calculated on the basis of measured COD. The COD was measured on three occasions as it gave a biodegradation of > 100%.

Validity criteria:
Mean oxygen uptake of the inoculum blank was below 60 mg/L, as required in the OECD guideline. The difference between replicate of the test substance extremes was < 20% after the 10-day window, at plateau, and on day 28. Sodium benzoate reached a mean 71% biodegradation by day 14. The average of the mean oxygen consumed in the inoculum blanks was 12.5 mg/L after 28 days. Therefore, this test has satisfied all the validity criteria.
The mean toxicity control degradation achieved on day 14 was 83% (based on combined ThOD/COD), as this is > 25% the test substance is assumed not to be inhibitory at this concentration.
Key result
Parameter:
BOD5
Value:
1.47 g O2/g test mat.
Key result
Parameter:
COD
Value:
1.27 g O2/g test mat.
Results with reference substance:
The ThOD of sodium benzoate was calculated as 1.67 g O2/g of substance, using the formula given in the OECD guideline. Biodegradation of sodium benzoate has been calculated on the basis of calculated ThOD.
Sodium benzoate attained a maximum mean level of biodegradation (based on the BOD:ThOD ratio) of 75%, and the results showed good replication.

pH and temperature measurements

At the end of the 28-day test period, the pH values were 7.3 in the inoculum blank bottles, 6.9 in the sodium benzoate bottles, 6.6 in the test substance bottles and ranged from 6.4 to 6.6 in the toxicity control bottles.

Temperature measurements recorded in several of the test bottles on days 0 and 28 indicated the temperature was within the range 22 ± 1°C. Continuous monitoring of the incubator temperature showed it to have remained within the range 22 ± 1°C throughout the study.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Under the study conditions, the test substance attained a maximum mean level of biodegradation (based on the BOD:COD ratio) of 122% and the results showed good replication. Greater than 60% degradation was achieved within the 10 d window and the test substance was considered to be readily biodegradable.
Executive summary:

A study was conducted to determine the ready biodegradability of the test substance by the measurement of biochemical oxygen demand (BOD) in a manometric respirometry test according to OECD Guideline 301F, in compliance with GLP. The test substance at 100 mg/L was inoculated for 28 d in a pre-aerated, microbial system collected from a domestic sewage plant. Oxygen uptake was measured in Oxitop respirometers. A reference substance, sodium benzoate (at 100 mg/L), was tested simultaneously under the same conditions as the test substance and functioned as a procedure control. Additionally, toxicity and inoculum controls were used. Sodium benzoate reached a mean biodegradation of 71% by Day 14. The average of the mean oxygen consumed in the inoculum blanks was 12.5 mg/L after 28 d. All other validity criteria were met. The COD of the test substance was measured as 1.27 g O2/g and the mean BOD value after 28 d was 1.47 g O2/g. The percentage degradation was calculated as (BOD/COD) x 100. Under the study conditions, the test substance attained a maximum mean level of biodegradation (based on the BOD:COD ratio) of 122% and the results showed good replication. Greater than 60% degradation was achieved within the 10 d window and the test substance was considered to be readily biodegradable (Scymaris, 2017).

Description of key information

Based on the study results, the test substance was considered to be readily biodegradable (122% degradation in 28 d).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

A study was conducted to determine the ready biodegradability of the test substance by the measurement of biochemical oxygen demand (BOD) in a manometric respirometry test according to OECD Guideline 301F, in compliance with GLP. The test substance at 100 mg/L was inoculated for 28 d in a pre-aerated, microbial system collected from a domestic sewage plant. Oxygen uptake was measured in Oxitop respirometers. A reference substance, sodium benzoate (at 100 mg/L), was tested simultaneously under the same conditions as the test substance and functioned as a procedure control. Additionally, toxicity and inoculum controls were used. Sodium benzoate reached a mean biodegradation of 71% by Day 14. The average of the mean oxygen consumed in the inoculum blanks was 12.5 mg/L after 28 d. All other validity criteria were met. The COD of the test substance was measured as 1.27 g O2/g and the mean BOD value after 28 d was 1.47 g O2/g. The percentage degradation was calculated as (BOD/COD) x 100. Under the study conditions, the test substance attained a maximum mean level of biodegradation (based on the BOD:COD ratio) of 122% and the results showed good replication. Greater than 60% degradation was achieved within the 10 d window and the test substance was considered to be readily biodegradable (Scymaris, 2017).

[Type of water: freshwater]

Categories Display