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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
11 November 1999 to 20 December 2000
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
other: read-across target
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Qualifier:
according to guideline
Guideline:
ISO DIS 9408 (Ultimate Aerobic Biodegradability - Method by Determining the Oxygen Demand in a Closed Respirometer)
Principles of method if other than guideline:
The Manometric Respirometry Test is a static method for testing the ultimate aerobic biodegradability of a test substance in water. Mixtures of the test substance, a defined inorganic medium and an inoculum, which is not pre-adapted (e.g. activated sludge or effluent of a municipal or laboratory waste water treatment plant), are incubated and aerated in a respirometer (Sapromat) at room temperature up to 28 days regularly. The test period may be expanded if biodegradation processes are still ongoing after 28 days. The oxygen used for the biodegradation of the test substance (biochemical oxygen demand, BOD) is continuously produced and measured by the test apparatus.

In addition to the assays with test substance (in triplicate) the following investigations are required: blank values (BC), biodegradation of a reference substance (RS), inhibition of the inoculum (IH) and abiotic elimination (PC).
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Municipal activated sludge from the waste water treatment plant of Mannheim, stored for 12 days in laboratory waste water treatment plant (WWTP) No. 1 which was fed with municipal waste water. One day before the start of the test the sludge from laboratory WWTP No.1 was washed and aerated for 24 hours and then added to the test vessels to obtain a sludge concentration of 30 mg/l dry solids.
Duration of test (contact time):
39 d
Initial conc.:
50 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Evaluation of Test Results

The biochemical oxygen demand gives unequivocal evidence for biodegradation. The measured BOD is compared with the calculated theoretical oxygen demand (ThOD) or the measured chemical oxygen demand (COD) of the test substance and indicated as biodegradation degree in per cent. Since the micro-organisms oxidize only part of the test substance and incorporate the rest as biomass, substances with a degree of >60 % biodegradation are considered to be sufficiently biodegradable. The relation BOD to ThOD or COD is considered by the author as follows:
>60 % in 10 days - "readily biodegradable (OECD criteria)"
>60% - "biodegradable"
20-60% - "in this test primarily biodegradable"
<20% - "in this test poorly biodegradable"

One of the OECD criteria for ready biodegradable substances is the threshold value of 60% biodegradation within a period of 10 days during a total test period of 28 days. If a test substance is biodegradable in this test, it can be assumed that it will be biodegraded in the environment, especially in wastewater treatment plants and surface waters.
Reference substance:
aniline
Test performance:
No unusual observations
Key result
Parameter:
% degradation (O2 consumption)
Value:
>= 30 - <= 40
Sampling time:
28 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
>= 50 - <= 60
Sampling time:
39 d
Details on results:
Calculated specific BOD values (cumulative, by day sampled), in mg/g:
[data are reported as reference (aniline), followed by each test substance replicate]
1d: -40, 20, -60, -20
4d: 580, 60, 20, 79
7d: 1620, 79, 119, 139
10d: 1880, 179, 238, 258
13d: 2140, 278, 317, 317
16d: 2600, 397, 437, 397
19d: 2820, 516, 595, 516
22d: 2900, 556, 734, 595
25d: 2940, 635, 853, 655
28d: 3020, 694, 972, 774
*39d: 3120, 1052, 1409, 1151
* - incubation time was increased to 39 days as biodegradation of the test substance was shown to be a comparatively slow process

BOD of blank (after 39 days) = 16 mg/L

Biodegradation in relation to ThOD (cumulative, by day sampled), in %:
[data are reported as reference (aniline), followed by each test substance replicate]
1d: -2, 1, -3, -1
4d: 24, 3, 1, 4
7d: 68, 4, 5, 6
10d: 79, 8, 11, 12
13d: 89, 13, 14, 14
16d: 109, 18, 20, 18
19d: 118, 23, 27, 23
22d: 121, 25, 33, 27
25d: 123, 29, 39, 30
28d: 126, 32, 44, 35
*39d: 130, 48, 64, 52
* - incubation time was increased to 39 days as biodegradation of the test substance was shown to be a comparatively slow process

The reference substance (aniline) was degraded more than 60% in 10 days and the BOD of the blank after 39 days was 16 mg/L (within the test method criteria of 60 mg/L).

Octyltin tris(EHMA) was degraded 32-44% after 28 days and was determined to be not readily biodegradable.

Kinetic of test substance (in %):
= 8 ... 12 after 10 day(s)
= 32 ... 44 after 28 day(s)
= 48 ... 64 after 39 day(s)
Kinetic of control substance (in %):
= ... 79 after 10 day(s)
> ... 100 after 39 day(s)
Degradation products: not measured
Results with reference substance:
Degradation degree of the reference substance was >60% after 14 days and therefore met the validity criteria. Degradation degree of the inoculum control was also <60% after 14 days.

No pre-adapted inoculum used

Test duration (days): 39

Duration of adaptation phase (days): 10

Duration of degradation phase (days): >29

Degradation of the test substance at the end of the ten-day window (% BOD/ThOD): --

Degradation degree of the test substance after 28 days (% BOD/ThOD): 30 -40

Degradation degree of the test substance at the end of the test (% BOD/ThOD): 50 -60

Degree of degradation of the test substance in the abiotic control after 20 days of the test (main study) (% BOD/ThOD): 3*

Reference substance: aniline

Degradation degree of the reference substance after 14 days (% BOD/ThOD): 90 -100

Degradation degree in the inhibition control after 14 days (% BOD/ThOD): 40-50

Remarks: *Increasing BOD values of the abiotic test assay (PC) after 20 days might be due to microbial biodegradative activities. Therefore this assay was validated for a test period of 20 days only. Further abiotic test assays did not show any significant degradation during the usual test period of 28 days.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
Under the conditions of this study the test material is not readily biodegradable.
Executive summary:

The biodegradability of the test material was determined in accordance with the standardised guidelines OECD 301 F, EU Method C.4-D and ISO DIS 9408 under GLP conditions.

The test material was not biodegradable (e.g. BOD >60 % of ThOD) within a 10 day window within the 28 day period, as required by OECD 301 to be considered "readily biodegradable." However, biodegradation continued after 28 day and thus measurements continued to day 39. At day 39, biodegradation ranged from 50 to 60 %. Thus the test material may be considered somewhat biodegradable, but not "ready biodegradable".

Under the conditions of this study the test material is not readily biodegradable.

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted on read-across material
Justification for type of information:
Read across to Octyltin tris(2-ethylhexylmercaptoacetate) (MOTE) (EC Number 248-227-6 and CAS No 27107-89-7) based on structural similarity and hydrolytical behaviour, see attached justification.
Reason / purpose for cross-reference:
read-across source
Key result
Parameter:
% degradation (O2 consumption)
Value:
>= 30 - <= 40
Sampling time:
28 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
>= 50 - <= 60
Sampling time:
39 d

Description of key information

Read-across to structurally similar substance Octyltin tris(2-ethylhexylmercaptoacetate) (MOTE) (CAS No 27107-89-7)

Under the conditions of this study the test material is not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Read-across to structurally similar substance Octyltin tris(2-ethylhexylmercaptoacetate) (MOTE).

The biodegradability of the test material was determined in accordance with the standardised guidelines OECD 301 F, EU Method C.4-D and ISO DIS 9408 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

The test material was not biodegradable (e.g. BOD >60 % of ThOD) within a 10 day window within the 28 day period, as required by OECD 301 to be considered "readily biodegradable." However, biodegradation continued after 28 day and thus measurements continued to day 39. At day 39, biodegradation ranged from 50 to 60 %. Thus the test material may be considered somewhat biodegradable, but not "ready biodegradable".

Under the conditions of this study the test material is not readily biodegradable.

The Baumann, 1992, study is presented as supporting information only. The percentage biodegradation results of the study were as follows: 11.7 mg/L test material = 40 % in 28 days and 22.7 mg/L test material = 28 % in 28 days. Based upon these results it is considered that the test material does not meet the EU criteria for classification as a readily biodegradable substance.