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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:
2017-10-25 to 2017-11-22
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
yes
Remarks:
Temperature range was 19.9 – 21.1°C instead of 20.0 – 24.0°C. As degradation of the positive control was in the normal range, this is considered as uncritical concerning the outcome of the study.
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
yes
Remarks:
Temperature range was 19.9 – 21.1°C instead of 20.0 – 24.0°C. As degradation of the positive control was in the normal range, this is considered as uncritical concerning the outcome of the study.
GLP compliance:
yes (incl. certificate)
Remarks:
Landesamt für Umwelt, Wasserwirtschaft und Gewerbeaufsicht, Mainz (8.04.2015)
Specific details on test material used for the study:
Storage in test facility:
The test item was stored in a tightly closed vessel at room temperature (20 ± 5°C).
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Activated sludge from a municipal biologic sewage treatment plant was used. The chosen plant is treating mostly household sewage. The sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant, Im Altenschemel, NW-Lachen-Speyerdorf. Date of collection: 25. Oct. 2017, batch no: 20171025.
- Laboratory culture: The sludge was filtrated, washed with medium 2x, and re-suspended in test medium. It was then aerated.
The dry matter was determined as 4560 mg suspended solids/L.
Duration of test (contact time):
28 d
Initial conc.:
37 mg/L
Based on:
ThOD
Remarks:
equivalent to a theoretical oxygen demand of 99.95 mg O2/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium:
Test Medium
The medium was freshly prepared (volumes were adapted to final volume needed in the test).
Composition:
Solution a 10 mL
Solution b 1 mL
Solution c 1 mL
Solution d 1 mL
H2O demin ad 1000 mL

Solution a
Potassium dihydrogen phosphate (KH2PO4): 8.5 g
Dipotassium hydrogen phosphate (K2HPO4): 21.75 g
Disodium hydrogenphosphate dihydrate (Na2HPO4*2H2O): 33.4 g
Ammonium chloride (NH4Cl): 0.5 g
H2O demin.: ad 1000 mL
The pH was 7.4

Solution b
Calcium chloride (CaCl2): 27.5 g
H2O demin.: ad 1000 mL

Solution c
Magnesium sulphate heptahydrate (MgSO4*7H2O): 22.5 g
H2O demin. ad 1000 mL
Solution d
Iron(III) chloride hexahydrate (FeCl3*6H2O): 0.25 g
Disodium ethylene-diaminetetraacetate dihydrate (Na2EDTA*2H2O): 0.4 g
H2O demin.: ad 1000 mL

- Test temperature: 19.9 – 21.1 °C
- pH: 7.4
- Suspended solids concentration: 25 mg/L

TEST SYSTEM
- Culturing apparatus: 500 mL flasks
- Number of culture flasks/concentration: 3
- Measuring equipment: OxiTop®-C measuring heads
- Test performed in closed vessels: yes
- Details of trap for CO2 and volatile organics if used: Evolved carbon dioxide is absorbed in soda lime (mixture of sodium hydroxide and calcium hydroxide). The soda lime isfilled in the OxiTop®-C measuring heads


CONTROL AND BLANK SYSTEM
- Inoculum blank: 3 test vessels (medium and inoculum)
- Abiotic sterile control: 1 test vessel (test item and 10 mL 1% HgCl2 solution/L)
- Toxicity control: 1 test vessel (200 mg/L ThOD, 100 mg/L ThOD each of test item and positive control)

Reference substance:
benzoic acid, sodium salt
Remarks:
60 mg/L sodium benzoate (corresponding to a ThOD of 99.86 mg/L)
Test performance:
The oxygen which was consumed by the content of the vessels was measured automatically by the test apparatus. After 28 days, the test was ended. Because the test item and positive control do not contain nitrogen, presence of nitrate and nitrite was not checked.
Key result
Parameter:
% degradation (O2 consumption)
Value:
69
Sampling time:
28 d
Details on results:
The degree of biodegradation reached 69 % after 28 days. The degradation phase, the interval between the end of the lag phase and the reaching of 90 % of the highest degree of degradation was reached on day 11. The 10-day-window began on day 1 (this time period is stated as lag phase), at its end (day 11), 63 % were reached.
Parameter:
ThOD
Value:
2.716 g O2/g test mat.
Remarks on result:
other: calculated based on molecular weight
Results with reference substance:
The degree of biodegradation of sodium benzoate reached 85 % after 28 days

Table 2      pH-values on day 0 and day 28 and Oxygen demand and degradation values on day 28

Flask

Blank

control 1

Blank

control 2

Blank

control 3

Positive control 1

Positive control 2

Positive control 3

pH at day 0

7.4

7.4

7.4

7.4

7.4

7.4

pH at day 28

7.3

7.3

7.3

7.7

7.7

7.7

Oxygen demand in mg/L at day 28

19.8

18.0

14.4

104

102

101

Oxygen demand in mg/L after deductions

--

--

--

86.6

84.6

83.6

% biological degradation

--

--

--

86.7

84.7

83.7

Table 3     pH-values on day 0 and day 28 and Oxygen demand and degradation values on day 28, continuation

Flask

Test item 1

Test item 2

Test item 3

Mean

Test item

Abiotic Control

Toxicity Control

pH at day 0

7.4

7.4

7.4

--

7.2

7.4

pH at day 28

7.4

7.4

7.4

--

7.1

7.7

Oxygen demand in mg/L at day 28

84.4

88

88

--

1.8

82.3

Oxygen demand in mg/L after deductions

67.0

70.6

70.6

--

1.8

64.9

% biological degradation

67.0

70.6

70.6

69.4

1.8

59.0

Table 4      Validity

Parameter

Criterion

Found

Assessment

Degradation of positive control > 60%

< 14 days

3 days

valid

Mean O2demand of the controls

< 60 mg/L

17.4 mg/L

valid

Degradation in the toxicity flask on day 14

> 25 %

32.4 % 

valid

pH at the end of the test

6.0 – 8.5

7.1 – 7.7

valid

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The degree of biodegradation reached 69 % after 28 days. The degradation phase, the interval between the end of the lag phase and the reaching of 90 % of the highest degree of degradation was reached on day 11. The 10-day-window began on day 1 (this time period is stated as lag phase), at its end (day 11), 63 % were reached, surpassing the pass level of 60 % given in the OECD guideline. Therefore, when applying the 10-day-window, the test item hexanal 0,05 % TOCO is readily biodegradable following OECD 301F/EU C.4-D.
Executive summary:

The test item hexanal (+ 0,05 %, alpha-Tocopherol as stabilizer) was tested under aerobic conditions in the Manometric Respirometry Test following OECD 301F / EU C.4-D using a concentration of 37 mg test item/L (equivalent to a theoretical oxygen demand of 99.95 mg O2/L). The study was conducted following GLP. Activated sludge was used as inoculum. The test was left running for 28 days. All validity criteria were met. The positive control reached the pass level of 60 % on day 3 (criterion: < 14). 

The following data could be determined for the test item hexanal 0.05 % TOCO:

 

10-day-window: day 1–11

degradation at the end of 10-day-window: 63 %

degradation at the end of the test: 69 %

 

Therefore, when applying the 10-day-window, hexanal is classified as readily biodegradable following OECD 301F/EU C.4-D.

Description of key information

The test item hexanal (+ 0,05 %, alpha-Tocopherol as stabilizer) was tested under aerobic conditions in the Manometric Respirometry Test following OECD 301F / EU C.4-D using a concentration of 37 mg test item/L (equivalent to a theoretical oxygen demand of 99.95 mg O2/L). Activated sludge was used as inoculum. The test was left running for 28 days. All validity criteria were met. The positive control reached the pass level of 60 % on day 3 (criterion: < 14). 

The following data could be determined for the test item hexanal 0,05 % TOCO:

 

10-day-window: day 1–11

degradation at the end of 10-day-window: 63 %

degradation at the end of the test: 69 %

 

Therefore, when applying the 10-day-window, hexanal is classified as readily biodegradable following OECD 301F/EU C.4-D.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information