Registration Dossier

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:
20 November 2009-28 January 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Modern GLP study conducted in accordance with OECD test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Qualifier:
equivalent or similar to
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: activated sewage sludge
Details on inoculum:
The activated sewage sludge sample was washed three times by settlement and resuspension in culture medium to remove any excessive amounts of dissolved organic carbon (DOC) that may have been present. The washed sample was then maintained on continuous aeration in the laboratory at a temperature of approximately 21ºC and used on the day of collection. Determination of the suspended solids level of the activated sewage sludge was carried out by filtering a sample (100 ml) of the washed activated sewage sludge by suction through pre-weighed GF/A filter paper* using a
Buchner funnel. Filtration was then continued for a further 3 minutes after rinsing the filter three successive times with 10 ml of deionised reverse osmosis water. The filter paper was then dried in an oven at approximately 105ºC for at least 1 hour and allowed to cool before weighing. This process was repeated until a constant weight was attained. The suspended solids concentration was equal to 4.6 g/l prior to use.
Duration of test (contact time):
42 d
Details on study design:
DETAILS ON PRETREATMENT
The test material was added to the test vessels using two methods of preparation. For both methods the test material was prepared using silica gel with one of the methods having a surfactant added. An amount of test material (40.5 mg) was dissolved in diethylether (50 ml) prior to adding to 10 g of granular silica gel (200-500 mesh Fluka Lot No #0001418794) in a round bottomed flask. The contents of the round bottomed flask were swirled prior to the solvent being evaporated off using a rotary evaporator set at 30°C for 15 minutes and then the temperature was increased to 80°C for 60 minutes. In order to ensure that all the solvent had been removed from the silica gel the ‘treated’ silica gel was placed in an oven at approximately 105°C over night prior to being stored in labelled sealed glass containers at approximately 21°C in darkness until use in the test. This whole process
was performed in duplicate for each test material series.On Day 0 of the test, the test material coated silica gel was dispersed in inoculated culture medium and the volume adjusted to 3 litres to give a final concentration of 13.5 mg/l, equivalent to 10 mg carbon/l. For the series containing surfactant, an aliquot (45 ml) of Tween® 85 (Polysorbate 85) was also added was also added to give a surfactant concentration of 75 mg/l. A test concentration of 10 mg carbon/l was employed in the test. Control vessels were prepared for each series containing 10 g silica gel per 3 litres of inoculated culture medium in order to maintain consistency between the control and test material vessels. The silica gel was prepared in a similar manner to the test material with the omission of the test material. For the series containing surfactant, an aliquot (45 ml) of Tween® 85 (Polysorbate 85) was also added to give a surfactant concentration of 75 mg/l.


Parameter:
% degradation (CO2 evolution)
Value:
67
Sampling time:
42 d
Details on results:
Points of degradation plot (test substance):

9% degradation after 2 days
6% degradation after 6 days
16% degradation after 8 days
22% degradation after 10 days
37% degradation after 14 days
39% degradation after 21 days
63 % degradation after 24 days
51% degradation after 28 days
61 % degradation after 31 days
71% degradation aftter 38 days
61% degradation after 42 days
67% degradation after 43 days (*)
(*)- values corrected to include any carry-over of CO2 detected in Absorber 2

Results with reference substance:
Points of degradation plot (in the presence of the surfactant):

0% degradation after 2 days
32% degradation after 6 days
0% degradation after 8 days
8% degradation after 10 days
0% degradation after 14 days
22% degradation after 21 days
40% degradation after 24 days
50% degradation after 28 days
53 % degradation after 31 days
55% degradation after 38 days
62 % degradation after 42 days
72 % degradation after 43 days (*)
(*)- Day 43 values corrected to include any carry-over of CO2 detected in Absorber 2
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable, but failing 10-day window
Conclusions:
Where no surfactant was present the test material attained 67% degradation after 42 days (63 % degradation after 24 days) . In the presence of the surfactant, the test material attained 72% degradation after 42 days. Under the strict terms and conditions of OECD Guideline No 301B the test material was considered to be rapidly biodegradable but it failed to satisfy the 10-Day window validation criterion.
Executive summary:

The study was performed to assess the ready biodegradability of the test material in an aerobic aqueous medium. The test material, at a concentration of 10 mg Carbon/l, was exposed to activated sewage sludge micro-organisms with culture medium in sealed culture vessels in the dark at approximately 21 degrees Celsius for 42 days. At the request of the Sponsor the study was extended from 28 days to 42 days. To aid dispersion in the test medium and increase the surface area exposed to the test organisms, the test material was dissolved in solvent prior to being adsorbed onto the granular silica gel. Two different series of vessels were prepared using silica gel alone and the other using silica gel with the addition of a surfactant (Tween® 85 (Polysorbate 85)). The addition of a surfactant aids in solubilizing the test material in the test media. The degradation of the test material was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and surfactant, where applicable, and the standard material, sodium benzoate, together with a toxicity control were used for validation purposes.

Where no surfactant was present the test material attained 51% degradation after 28 days and a final degradation of 67% after 42 days. In the presence of the surfactant, the test material attained 50% degradation after 28 days and a final 72% degradation after 42 days. With and without surfactant, the test did not meet the validity criteria - reaching 60% threshold degradation within 10 days of meeting 10% degradation, within 28 days from test initiation. Under the strict terms and conditions of OECD Guideline No 301B the test material cannot be considered to be readily biodegradable as the test material failed to meet the validation criterion. However, the test material has exhibited rapid degradation.

Description of key information

A key GLP study conducted in accordance with the OECD 301B guideline,  biodegradation in water-  rapidly biodegradable but failing the 10-day window

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

A key GLP study was conducted in accordance with the OECD 301B guideline to assess the ready biodegradability of the test material in an aerobic aqueous medium. The test material was dissolved in solvent prior to being adsorbed onto granular silica gel prior to dispersion in the test medium to aid dispersion of the test material in the test medium and to increase the surface area of the test material exposed to the test organisms.

Where no surfactant was present the test material attained 67% degradation after 42 days (63 % degradation after 24 days). In the presence of the surfactant, the test material attained 72% degradation after 42 days. The OECD guideline criteria for classification of a chemical as readily biodegradable are as follows: 1) percent biodegradation must reach 60% within 28 days, and 2) the 60% degradation must be attained within 10 days of exceeding 10% biodegradation.

Under the strict terms and conditions of OECD Guideline No 301B the test material was considered to be rapidly biodegradable but it failed to satisfy the 10-Day window validation criterion.