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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:
2017-02-07 to 2017-03-08
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
July 1992
GLP compliance:
yes (incl. QA statement)
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): Municipal wastewater treatment plant Breisgauer Bucht
- Method of cultivation: The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge.
- Pretreatment: none
- Concentration of sludge: 30 mg dry solids per litre
- Initial cell/biomass concentration: The dry solid content of the activated sludge was 3.5 g/L.
- Other: sampling date: 2017-02-06
Duration of test (contact time):
ca. 28 d
Initial conc.:
ca. 20 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium:
A: Potassium dihydrogenphosphate KH2PO4 8.50 g
Dipotassium hydrogenphosphate K2HPO4 21.75 g
Disodium hydrogenphosphate dihydrate Na2HPO4 * 2 H2O 33.40 g
Ammonium chloride NH4Cl 0.50 g
are dissolved in demineralised water and made up to 1 litre. pH was 7.4 and had not to be adjusted.

B: Calcium chloride dihydrate CaCl2 * 2H2O 36.4 g
is dissolved in demineralised water and made up to 1 litre.

C: Magnesium sulfate heptahydrate MgSO4 * 7H2O 22.5 g
is dissolved in demineralised water and made up to 1 litre.

D: Iron (III) chloride hexahydrate FeCl3 * 6H2O 0.25 g
is dissolved in demineralised water, stabilised with one drop of concentrated HCl and made up to 1 litre.

For preparation of the mineral medium 10 mL of solution (A) is mixed with 900 mL demineralised water, 1 mL each of solutions (B), (C) and (D) are added and the volume is made up to 1 litre.

- Test temperature: 21.3 – 22.4°C
- Continuous darkness: diffuse light
- Others: Dry solid concentration: 12.9 mL activated sludge was filled up to 1500 mL with 1487.1 mL mineral medium corresponding to 30 mg/L dry solids.

TEST SYSTEM
- Culturing apparatus: Gas wash bottles (2000 mL volume) with lateral connecting pieces for butyl rubber septums were used as reactors. The liquid volume was fixed as 1500 mL each. Mixing was performed by magnetic stirrers with 2 cm stir bars.
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: The test vessels are aerated by the passage of carbon dioxide-free air.
- Measuring equipment: IC measurement was performed with a total carbon analyser (TOC-L Shimadzu with an autosampler ASI-L) by purging the inorganic carbon with H3PO4 (25%) using a non-dispersive infrared (NDIR) detector.
- Details of trap for CO2 and volatile organics if used: The CO2 produced in the reactors was absorbed in two 250 mL gas wash bottles in series each filled with 200 mL 0.2 M NaOH.

SAMPLING
- Sampling frequency: 3rd, 7th, 10th, 14th, 21st and 28th day
- Sampling method: 6 mL NaOH from the first of two CO2-absorber flasks connected in line was sampled and the IC's were determined. The vials were immediately closed with sealing film in order to avoid CO2 uptake from the air.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: no
- Toxicity control: yes
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (CO2 evolution)
Value:
97.7
Sampling time:
28 d
Details on results:
The degradation extent of the test substance at the end of the test was 97.7% (28 d after acidification, mean of three replicates).
The degradation extent in the toxicity control was 93.3% within 14 days. The test substance had no inhibitory effect on the inoculum.
The mean CO2-evolution of the blank flasks was 27.6 mg/L on day 28.
Results with reference substance:
The reference compound sodium benzoate reached the pass levels for ready biodegradability (60% ThCO2 by day 7) within 3 days.

Table 1: Ultimate biodegradation after x days [% of ThCO2]

Reactor

Day

0

3

7

10

14

21

28

29

15

Test flasks

0

53.9

80.6

86.7

90.5

91.6

95.0

94.9

16

0

50.9

78.0

86.5

91.8

93.4

94.4

97.0

17

0

60.7

83.8

92.8

96.5

100.3

102.1

101.3

4

Reference flasks

0

67.6

82.7

88.8

91.0

93.4

94.4

94.4

5

0

67.4

86.5

91.0

92.7

95.3

95.8

95.1

6

0

64.3

84.2

85.8

86.1

88.9

92.2

92.0

18

Toxicity control

(Test item and Reference item)

0

53.4

80.3

86.7

93.3

95.0

98.2

97.6

Table 2: Mean CO2-evolution of blank flasks after x days

Day

0

3

7

10

14

21

28

29

CO2-evolution [mg/L]

0

7.5

13.7

17.4

20.8

23.9

26.7

27.6

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The biodegradation of Nonane-1,9-diol was determined according to OECD 301 B under GLP conditions. Within the test period of 28 days, a degradation of 97.7% was determined for the test substance. Within 7 days the degradation of the test item reached 80.8%. The 10 -days window was therefore fullfilled. Nonane-1,9 -diol further showed no inhibitory effects on the microorganisms at the tested concentration as observed in the toxicity control. According to OECD criteria the substance is readily biodegradable.

Description of key information

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The biodegradation of Nonane-1,9-diol was determined according to OECD 301 B under GLP conditions. Within the test period of 28 days, a degradation of 97.7% was determined for the test substance. Within 7 days the degradation of the test item reached 80.8%. The 10 -days window was therefore fullfilled. Nonane-1,9 -diol further showed no inhibitory effects on the microorganisms at the tested concentration as observed in the toxicity control. According to OECD criteria the substance is readily biodegradable.