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Environmental fate & pathways

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:
24 July 2013 to 15 October 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted in accordance with international guidelines (OECD 301F) and in accordance with GLP. All relevant validity criteria were met. The study is considered suitable for use as a key study for the endpoint.
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic, non-adapted
Details on inoculum:
A mixed population of activated sewage sludge micro-organisms was obtained on 16 September 2013 from the secondary treatment stage of the sewage treatment plant at Villette (STEP Villette, av. de Thonex 105, 1226 THONEX (Geneva, Switzerland), which treats predominantly domestic sewage.
The sample of activated sludge was maintained on continuous aeration upon receipt. A sample of the activated sewage sludge was washed three times by settlement (centrifuge: Heittich rotenta 460 RS) and suspended in culture medium. To remove any excessive amounts of DOC that may have been present, the solution was stirred and maintained with pure oxygen at room temperature. Determination of dry weight is made to inoculate the final solution with 30 mg/L dry weight activated sludge.
The culture medium used in this study was in accordance with OECD 301F.
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
On Day 0, the following solutions were inoculated in 1,000 mL glass culture vessels (total volume when full = 1,145 mL) each containing 200 mL of solution:
- Duplicate controls, consisting of inoculated culture medium
- The test item, in triplicate, in inoculated culture medium
- The reference material (sodium benzoate) in inoculated culture medium
- The test item and the reference item in inoculated culture medium as a toxicity control
The system comprised a sample flask sealed by a sensor head/CO2 trap in a temperature controlled incubator. The samples were stirred for the duration of the study with a magnetically coupled stirrer.
Biodegradation was monitored by net reduction in gas pressure in the sample flask when the microorganisms convert oxygen to carbon dioxide which is absorbed in sodium hydroxide. The WTW oxitopC instrument automatically calculated the consumption of oxygen. Oxygen consumption was converted to biological oxygen demand for the purpose of calculating degradation.
In order to determine the theoretical oxygen demand, the total amount of oxygen required to oxidise a chemical substance completely is calculated from the molecular formula (assuming no nitrification occurs) and expressed as mg oxygen required per mg test item as described in OECD 301F.
Reference substance:
benzoic acid, sodium salt
Preliminary study:
Not applcable
Test performance:
The test performed adequately with no unusual or unexpected observations.
Parameter:
% degradation (O2 consumption)
Value:
6
St. dev.:
1.15
Sampling time:
1 d
Parameter:
% degradation (O2 consumption)
Value:
19
St. dev.:
0
Sampling time:
2 d
Parameter:
% degradation (O2 consumption)
Value:
61
St. dev.:
2.08
Sampling time:
9 d
Remarks on result:
other: 60 % (ThOD) achieved within 10-day window
Parameter:
% degradation (O2 consumption)
Value:
76
St. dev.:
3.79
Sampling time:
28 d
Details on results:
Calculated theoretical oxygen demand for the test item and reference item are as follows: DThODNH3 = 16[2c+1/2(h-cl-3n)+3s+5/2p+1/2na-o]mg/mg / MW DThONH3 Test item = 2.984 mg O2/mg substance DThONH3 Reference Item = 1.665 mg O2/mg substance. Cumulative BOD values for the test item, reference item, and toxicity control aare presented in Tables 1, 2 and 3 respectively.
Results with reference substance:
The results with the reference item were valid, with 60 % degradation (O2 consumption) achieved by day 14 (achieved by day 4).

Table 1. Cumulative BOD and % degradation of the test item in 3 replicates

Day BOD (mg O2/mg test item) % Degradation
R1 R2 R3 R1 R2 R3 Mean SD
0 0.00 0.00 0.00 0 0 0 0 0.00
1 0.22 0.22 0.16 7 7 5 6 1.15
2 0.56 0.56 0.56 19 19 19 19 0.00
3 0.74 0.80 0.87 25 27 29 27 2.00
4 0.96 1.02 1.03 32 34 35 34 1.53
5 1.20 1.27 1.28 40 43 43 42 1.73
6 1.39 1.51 1.46 47 51 49 49 2.00
7 1.55 1.67 1.56 52 56 52 53 2.31
8 1.63 1.83 1.65 55 61 55 57 3.46
9 1.76 1.89 1.78 59 63 60 61 2.08
10 1.79 1.97 1.87 60 66 63 63 3.00
11 1.88 2.00 1.96 63 67 66 65 2.08
12 1.91 2.04 1.99 64 68 67 66 2.08
13 1.88 2.01 2.03 63 67 68 66 2.65
14 1.94 2.07 2.03 65 69 68 67 2.08
15 1.94 2.07 2.09 65 69 70 68 2.65
16 2.01 2.13 2.09 67 71 70 69 2.08
17 2.01 2.19 2.09 67 73 70 70 3.00
18 2.01 2.25 2.15 67 75 72 71 4.04
19 2.01 2.25 2.15 67 75 72 71 4.04
20 2.01 2.25 2.15 67 75 72 71 4.04
21 2.01 2.32 2.15 67 78 72 72 5.51
22 2.07 2.32 2.21 69 78 74 74 4.51
23 2.07 2.32 2.21 69 78 74 74 4.51
24 2.10 2.35 2.24 70 79 75 75 4.51
25 2.07 2.32 2.21 69 78 74 74 4.51
26 2.13 2.38 2.21 71 80 74 75 4.58
27 2.19 2.32 2.27 73 78 76 76 2.52
28 2.19 2.38 2.21 73 80 74 76 3.79

Table 2. Cumulative BOD and % degradation of the reference item in 1 replicate

Day BOD (mg O2/mg test item) % degradation
0 0.00 0
1 0.28 17
2 0.68 41
3 0.93 56
4 1.02 61
5 1.20 72
6 1.27 76
7 1.30 78
8 1.27 76
9 1.33 80
10 1.36 82
11 1.39 83
12 1.42 85
13 1.39 83
14 1.39 83
15 1.46 88
16 1.46 88
17 1.46 88
18 1.46 88
19 1.46 88
20 1.52 91
21 1.52 91
22 1.52 91
23 1.52 91
24 1.55 93
25 1.52 91
26 1.52 91
27 1.52 91
28 1.52 91

Table 3. Cumulative BOD and % Degradation of the toxicity control in 1 replicate

Day BOD (mg O2/mg test item) % degradation
0 0.00 0
1 0.34 7
2 1.17 25
3 1.67 36
4 1.95 42
5 2.20 47
6 2.45 53
7 2.54 55
8 2.69 58
9 3.00 65
10 3.09 66
11 3.24 70
12 3.34 72
13 3.37 72
14 3.43 74
15 3.43 74
16 3.49 75
17 3.56 77
18 3.56 77
19 3.56 77
20 3.56 77
21 3.62 78
22 3.62 78
23 3.68 79
24 3.71 80
25 3.68 79
26 3.68 79
27 3.74 80
28 3.74 80
Validity criteria fulfilled:
yes
Remarks:
All validity criteria fulfilled in accordance with OECD 301F
Interpretation of results:
readily biodegradable
Conclusions:
The test item attained a mean degradation of 76 % over the 28 -day study period, achieving 10 - 60% degradation within the 10 -day window. The substance is therefore considered to be readily biodegradable.
Executive summary:

The study was performed to assess the ready biodegradability of the test item under aerobic conditions. The study was conducted in accordance with OECD Guideline 301F (1992) and Council Regulation (EC) No. 440/2008 of 30 May 2008, Publication No. L142, Part C.4 -D. The test item was exposed to activated sewage sludge microorganisms with culture medium in sealed culture vessels in diffused light at 22 °C ± 1 °C for 28 days. The test item addition rate was 100 mg/L. The degradation of the test item was assessed by daily measurement of oxygen consumption. Control solutions with inoculum and the reference material sodium benzoate, together wit a toxicity control were also used for study validation purposes. The test item attained 73%, 80% and 74 % degradation in replicates 1, 2 and 3 respectively (mean = 76 %) after 28 -days and satisfied the 10 -day window ready biodegradability criteria (10 -60 % degradation observed in ~8 days). Under the conditions of this test the test item can be considered to be readily biodegradable.

Description of key information

Ready biodegradability: 28-day % biodegradation = 76 % (10-day window satisfied); OECD TG 301F, 2013

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

Key data : OECD TG 301F, 2013 : The study was performed to assess the ready biodegradability of the test item under aerobic conditions. The study was conducted in accordance with OECD Guideline 301F (1992) and Council Regulation (EC) No. 440/2008 of 30 May 2008, Publication No. L142, Part C.4 -D. The test item was exposed to activated sewage sludge microorganisms with culture medium in sealed culture vessels in diffused light at 22 °C ± 1 °C for 28 days. The test item addition rate was 100 mg/L. The degradation of the test item was assessed by daily measurement of oxygen consumption. Control solutions with inoculum and the reference material sodium benzoate, together wit a toxicity control were also used for study validation purposes. The test item attained 73%, 80% and 74 % degradation in replicates 1, 2 and 3 respectively (mean = 76 %) after 28 -days and satisfied the 10 -day window ready biodegradability criteria (10 -60 % degradation observed in ~8 days). Under the conditions of this test the test item can be considered to be readily biodegradable.