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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:
07 October 1999 to 20 December 1999
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:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (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)
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 5 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):
74 d
Initial conc.:
50 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Test temperature: 22 ± 1 °C

PRINCIPLE OF THE MANOMETRIC RESPIROMETRY TEST
The Manometric Respirometry Test is a static method for testing the ultimate aerobic biodegradability of a test material in water. Mixtures of the test material, 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 material (biochemical oxygen demand, BOD) is continuously produced and measured by the test apparatus.

In addition to the assays with test material (in triplicate) the following investigations are required: blank values (BC), biodegradation of a reference substance (RS), inhibition of the inoculum (I H) and abiotic elimination (PC).

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 material and indicated as biodegradation degree in per cent. Since the micro-organisms oxidise only part of the test material 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 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 material 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:
other: %BOD/ThOD
Value:
>= 30 - <= 40
Sampling time:
28 d
Results with reference substance:
Degradation degree of the reference substance was > 60% after 14 days and therefore met the validity criteria.

TEST INFORMATION

No pre-adapted inoculum used.

Test duration: 74 days

Duration of adaptation phase: 8 days

Duration of degradation phase: 22 days

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

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

Degradation degree of the test material at the end of the test (%BOD/ThOD): 40-50

Degree of degradation of the test material in abiotic control at the end of the test (%BOD/ThOD): 0-10

Degradation degree of the reference substance after 14 days (%BOD/ThOD): 80-90

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

Data results from study report:

Calculated specific BOD values (cumulative, by day sampled), in mg/g:

[data are reported as reference (aniline), followed by each test material replicate]

1d: -40, 20, 0, 40

4d: 1460, 141, 79, 160

7d: 2020, 242, 159, 280

10d: 2060, 423, 357, 520

13d: 2080, 504, 536, 700

16d: 2140, 565, 694, 820

19d: 2260, 605, 754, 840

22d: 2360, 645, 774, 900

25d: 2400, 665, 813, 980

28d: 2440, 685, 813, 1020

*74d: 2700, 1028, 853, 1600

* - incubation time was increased to 74 days as biodegradation of the test material was shown to be a comparatively slow process

BOD of blank (after 74 days) = 50 mg/L

Biodegradation in relation to ThOD (cumulative, by day sampled), in %:[data are reported as reference (aniline), followed by each test material replicate]

1d: -2, 1, 0, 2

4d: 61, 6, 3, 7

7d: 84, 10, 7, 12

10d: 86, 18, 15, 22

13d: 87, 21, 23, 30

16d: 89, 24, 30, 35

19d: 94, 26, 32, 36

22d: 99, 27, 33, 38

25d: 100, 28, 35, 42

28d: 102, 29, 35, 43

*74d: 113, 44, 36, 68

* - incubation time was increased to 74 days as biodegradation of the test material was shown to be a comparatively slow process

Test material was degraded 29-43% in 28 days and was determined to be not readily biodegradable.

Degradation products: not measured

Validity criteria fulfilled:
yes
Remarks:
with the minor exception noted in "Overall remarks"
Interpretation of results:
not readily biodegradable
Conclusions:
Under the conditions of this study, the test material was not biodegradable (e.g. BOD > 60% of ThOD) within a 10-d window within the 28-d period, as required by OECD 301 to be considered "readily biodegradable." However, biodegradation continued after 28 d and thus measurements continued to 74 d. At 74 d, triplicate results ranged 40-50%. Thus the test material may be considered somewhat biodegradable, but not "ready biodegradable".
Executive summary:

The biodegradability of the test material was investigated in the Manometric Respirometry Test according to OECD Guideline 301 F, EU Method C.4 -D and ISO Standard 9408.

Biodegradation degree (BOD of THOD) after 28 days was 30-40 % and the biodegradation degree (BOD of THOD) after 74 days was 40-50 %.

Biodegradation of the test material was shown to be a comparatively slow process. Therefore the test duration was prolonged. After a test period of 74 days biodegradation processes were still ongoing.

Under the conditions of this study, the test material was not biodegradable (e.g. BOD > 60% of ThOD) within a 10-d window within the 28-d period, as required by OECD 301 to be considered "readily biodegradable." However, biodegradation continued after 28 d and thus measurements continued to 74 d. At 74 d, triplicate results ranged 40-50%. Thus the test material may be considered somewhat biodegradable, but 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 from Dioctyltin bis (2-ethylhexylmercaptoacetate) (DOTE) (CAS No. 15571-58-1), see attached justification.
Reason / purpose for cross-reference:
read-across source
Key result
Parameter:
other: %BOD/ThOD
Value:
>= 30 - <= 40
Sampling time:
28 d

Description of key information

Read-across to structurally similar substance Dioctyltin bis (2-ethylhexylmercaptoacetate) (DOTE) (CAS No. 15571-58-1).

Under the conditions of the study, DOTE (CAS No 15571-58-1) was not biodegradable (e.g. BOD > 60% of ThOD) within a 10-d window within the 28-d period, as required by OECD 301 to be considered "readily biodegradable." However, biodegradation continued after 28 d and thus measurements continued to 74 d. At 74 d, triplicate results ranged 40-50%. Thus the test material may be considered somewhat biodegradable, but not "ready biodegradable".

Key value for chemical safety assessment

Additional information

Read-across to structurally similar substance Dioctyltin bis (2-ethylhexylmercaptoacetate) (DOTE) (CAS No. 15571-58-1). Read-across from DOTE can be justified by structural analogy (dioctyltin and two thiogylocolate ligands).

The biodegradability of the test material was investigated in the Manometric Respirometry Test according to OECD Guideline 301 F, EU Method C.4 -D and ISO Standard 9408.

Biodegradation degree (BOD of THOD) after 28 days was 30-40 % and the biodegradation degree (BOD of THOD) after 74 days was 40-50 %.

Biodegradation of the test material was shown to be a comparatively slow process. Therefore the test duration was prolonged. After a test period of 74 days biodegradation processes were still ongoing.

Under the conditions of this study, the test material was not biodegradable (e.g. BOD > 60% of ThOD) within a 10-d window within the 28-d period, as required by OECD 301 to be considered "readily biodegradable." However, biodegradation continued after 28 d and thus measurements continued to 74 d. At 74 d, triplicate results ranged 40-50%. Thus the test material may be considered somewhat biodegradable, but not "readily biodegradable".

The Baumann, 1992a, and Baumann, 1992b, studies are presented here as supporting information only. Both studies were conducted according to EC Method C.5 (84/449/EEC) and under good laboratory practice conditions. The results of the Baumann, 1992a, and Baumann, 1992b, studies were 11 -19% degradation after 28 days and 23% degradation after 28 days respectively and support that DOTE is not readily biodegradable.