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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:
2016-12-15 to 2017-04-20
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Test material information:
Composition 1
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: 201601004
- Expiration date of the lot/batch: 01 January 2019

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Keep container tightly closed in a cool, well ventilated place
- Stability under test conditions: stable
- Solubility and stability of the test substance: Slightly soluble (information from the SDS)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Activated sludge from the municipal wastewater treatment plant Breisgauer Bucht was used. The treatment plant clarifies predominantly domestic wastewater and has a capacity of 600.000 inhabitant equivalents.
- Pretreatment: The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge.
- Concentration of sludge: 30 mg/L dry solids. The dry solid content of the activated sludge was 5.1 g/L. It was determined by weight measurements after drying at 105 °C for 3.75 hours (mean of triplicate measurements).
Duration of test (contact time):
28 d
Initial conc.:
>= 101.2 - <= 104 mg/L
Based on:
ThOD
Remarks:
164 mL mineral medium were filled into the test vessels, the test item was weighed onto weighing paper and poured into the bottles. 10.5 – 10.8 mg of the test item were added, corresponding to a concentration of 101.2 – 104.0 mg ThOD/L.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium:
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. Before use, the mineral medium is aerated for about one hour and the pH is adjusted to 7.4 ± 0.2.

A: Potassium dihydrogenphosphate (KH2PO4): 8.50 g,
Dipotassium hydrogenphosphate (K2HPO4): 21.75 g,
Disodium hydrogenphosphate dihydrate (Na2HPO4 * 2 H2O): 33.40 g, and
Ammonium chloride (NH4Cl): 0.50 g are dissolved in demineralised water and made up to 1 litre.
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.

- Test temperature: The temperature was 21.8 – 22.3 °C throughout the whole study.
- pH: 7.4 ± 0.2.
- pH adjusted: yes
- Continuous darkness: not reported


TEST SYSTEM
- Number of culture flasks/concentration: In total three reactors containing the test item. Narrow mouth bottles (500 mL volume) were used. The liquid volume was fixed as 164 mL each.
- Test performed in open system: No


CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes, 3 replicates
- Abiotic sterile control: Yes, 1 replicate
- Toxicity control: Yes, 1 replicate
- Other: Reference: 3 replicates




Reference substance:
other: Sodium acetate
Key result
Parameter:
% degradation (O2 consumption)
Value:
49.4
Sampling time:
28 d
Remarks on result:
other: mean of three replicates
Details on results:
Summary of results: Please refer also to the tables below, shown in "Any other information on results incl. tables"

- Test item:
The biodegradation of the test item was 49.4 % within 28 days (mean of three replicates, see table 2 and figure 1 attached).
The pH in the test vessels at the end of the test was 7.3.

- Toxicity control:
The degradation in the toxicity control reached 50.3 % within 4 days (see table 2) and was thus above the criterion for inhibition effects to the inoculum (<25% on day 14). The pH in the toxicity control vessel at the end of the test was 8.5.

- Abiotic control:
In the abiotic control degradation values between 8.1 % (day 4) and 2.7% (day 28) were determined (see table 2 and figure 1 attached). No significant abiotic degradation could be detected.The pH in the abiotic control vessel at the end of the test was 8.9.

- Reference item:
The reference compound sodium acetate reached the pass level for ready biodegradability (60 % ThOD within a 10-day window) within 8 days (see table 2).
The pH in the reference vessels at the end of the test was 8.6 - 8.7.

- Blank:
The oxygen consumption of the blanks was 32.8 mg/L in 28 days (mean of three replicates, see table 1).
The pH in the blank vessels at the end of the test was 7.3.
Results with reference substance:
The reference compound sodium acetate reached the pass level for ready biodegradability (60 % ThOD within a 10-day window) within 8 days. The pH in the reference vessels at the end of the test was 9.0.

Table 1: Propyl gallate - measured oxygen consumption

 

Test item

Toxicity control

Reference item

Blank

Abiotic
control

Test item [mg/164 mL]

10.5

10.6

10.8

10.7

 

 

10.7

Reference item
[mL/164 mL]*

 

164

164

164

164

 

ThOD [mg/L]

101.2

102.1

104.0

203.0

99.9

99.9

99.9

 

103.1

Day

Oxygen consumption [mg O2/L]

0

0

0

0

0

0

0

0

0

0

0

0

4

42.2

42.2

42.2

118

70.3

67.5

73.2

16.9

14.1

16.9

8.4

8

53.5

53.5

56.3

143

84.4

84.4

92.8

22.5 

22.5 

22.5 

8.4

12

67.5

67.5

67.5

158

95.7

95.7

104

28.1 

28.1 

28.1 

8.4

16

73.2

73.2

73.2

166

104

101

110

25.3 

28.1 

28.1 

8.4

20

78.8

78.8

78.8

172

110

107

115

25.3 

28.1 

33.8 

2.8

24

81.6

81.6

84.4

177

113

110

118

28.1 

28.1 

36.6 

2.8

28

81.6

84.4

84.4

180

113

110

118

28.1 

30.9 

39.4 

2.8

pH on day 28

7.3

7.3

7.3

8.5

8.6

8.7

8.7

7.3

7.3

7.3

8.9

*stock solution with 128.1 mg/L

Table 2: Propyl gallate - Biodegradation in % of ThOD

Test item

Toxicity control

Reference item

Abiotic
control

Test item [mg/164 mL]

10.5

10.6

10.8

10.7

 

10.7

Reference item
[mL/164 mL]*

 

164

164

164

164

 

ThOD [mg/L]

101.2

102.1

104.0

203.0

99.9

99.9

99.9

103.1

Day

Degradation (%)

0

0

0

0

0

0

0

0

0.0

4

25.9

25.7

25.2

50.3

54.4

51.6

57.3

8.1

8

30.6

30.4

32.5

59.4

62.0

62.0

70.4

8.1

12

38.9

38.6

37.9

64.0

67.7

67.7

76.0

8.1

16

45.5

45.1

44.2

68.4

76.9

73.9

82.9

8.1

20

49.2

48.7

47.8

70.4

81.0

78.0

86.0

2.7

24

50.1

49.6

51.4

72.0

82.1

79.1

87.1

2.7

28

48.2

50.5

49.6

72.5

80.3

77.3

85.3

2.7

*stock solution with 128.1 mg/L

Figure 1: Degradation Propyl gallate in the respirometry test (mean values) refer to "Illustrations" below.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The degradation of the test item within 28 days was 49.4 % of ThOD (mean of three replicates).
The test item did not reach the criteria for ready biodegradability (60% ThOD within a 10-d window).
The degradation of the toxicity control after 14 days was >25%. The test item had no inhibitory effect on the inoculum according to the criterion of the guideline.
No abiotic degradation could be detected.
The test is valid according to OECD 301 F (July 1992).


Executive summary:

A manometric tespirometry test according to OECD 301 F (July 1992) was conducted in order to investigate the ready biodegradability of propyl gallate.

The biodegradation of propyl gallate was studied in reconstituted water inoculated with activated sludge from a municipal wastewater treatment plant with a concentration corresponding to 30 mg dry solids per litre.The manometric respirometry test determines the ready biodegradability of test items following their oxygen consumption in closed flasks at a constant temperature (±1 °C) in a range of 20–24 °C. The consumption of oxygen is determined by measuring the negative pressure in the flasks after absorption of the evolved carbon dioxide in sodium hydroxide. A solution or suspension of the test item in a mineral medium, corresponding to 100 mg/L test item giving at least 50–100 mg/L of theoretical oxygen demand (ThOD), is inoculated with activated sludge (30 mg d.s./L) for 28 days. The amount of oxygen taken up by the microbial population during the biodegradation of the test item (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of the ThOD or the chemical oxygen demand (COD). The pass level for ready biodegradability is 60 % of ThOD and must be reached within a 10-d window. The 10-d window begins when the degree of biodegradation reaches 10 %.

The test method is suitable for water soluble and non-soluble test items that are non-volatile and not toxic under the test conditions.

The mean degradation rate of propyl gallate was 49.4 % within 28 days. Therefore, propyl gallate is considered not to be readily biodegradable based on ThOD.

The test is valid according to OECD Test Guideline 301F (July 1992):

• The oxygen uptake of the inoculum blank was 32.8 mg O2/L and did not exceed 60 mg O2/L in 28 days.

• The pH value in the test and blank bottles was 7.3–1.4.

• The difference of extremes of replicate values was less than 20 %.

• The biodegradation of the reference item reached the pass level of 60 % ThOD by day 8.

• The degradation extent in the toxicity control was above 25 % in 14 days based on ThOD

Description of key information

The biodegradation of propyl gallate determined according to OECD guideline 301 F within 28 days was 49.4 % of ThOD (mean of three replicates). The test item did not reach the criteria for ready biodegradability (60 % ThOD within a 10-d window).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window
Type of water:
freshwater

Additional information