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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:
From May 25, 2017 to September 22, 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
1992
Deviations:
yes
Remarks:
No valid microbial counts could be reported for aged inoculum due to high counts on the control plates.
Principles of method if other than guideline:
No valid microbial counts could be reported for aged inoculum due to high counts on the control plates. However, as the soluble reference material (sodium benzoate) degraded by more than 60% in the first 14 days, the test inoculum likely contained a satisfactory population of viable bacteria and this deviation is believed to have had no impact.
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Date of collection: July 05, 2017; Collection point: Stromness Treatment Works, Bu Point; Grid reference: HY 27332 09332; Latitude: 58.964975, Longitude: -3.2653023
- Water filtered: Yes
- Type and size of filter used, if any: Inoculum filtered through 1 μm Whatman filter prior to use in the test
- Volume of inoculum added: 1.3 mL/L

INOCULUM PROPERTIES
- pH: 7.07
- Temperature: 21.7 ºC
- Conductivity: 2.3 µS/cm
- Dissolved oxygen: 4.61 mg O2/l

Duration of test (contact time):
28 d
Initial conc.:
2.737 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium of deionised water. 1 L of medium contains 1 ml of stocks A, B, C, and D (Stock A = KH2PO4: 8.5, K2HPO4: 21.75, Na2HPO4.2HsO: 33.40, NH4Cl: O.5; Stock B = CaCl2: 27.50; Stock C = MgSO4.7H2O: 22.50; Stock D = FeCl3.6H2O: 0.25, EDTA, Di-sodium salt: 0.4)
- Solubilising agent: No, test material is soluble in water
- Test temperature: 22 ± 1 °C
- pH: Test water = 7.71 on collection day; Test inoculum = 7.07
- Aeration of dilution water: Yes, strongly for at least 20 minutes and then allowed to stand for a minimum of 20 hours at test temperature
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: 270-276 ml glass BOD bottles
- Number of culture flasks/concentration: 3 replicate bottles per time-point for test material, oxygen black, reference material, and toxicity control. A minimum of 2 replicates per time-point is required for data processing
- Method used to create aerobic conditions: The solution of the 1- [(2-hydroxyethyl)thio]propan-2-ol in mineral medium was inoculated with microorganisms and kept in completely full, closed bottles in the dark at a constant temperature
- Measuring equipment: A luminescent dissolved oxygen meter (Hach HQ4Od) and probe (Hach LDO10101) were used to measure biodegradation
- Test performed in open system: No, glass BOD bottles were sealed
- Other: Microbial count using the spread plate method = a minimum of 1.0 x 10^1 to 1.0 x 10^3 colony forming units per ml of aged inoculum; Saturation value for dissolved oxygen at normal atmospheric pressure at 22 °C = minimum of ~9 mg/l; Soluble test material preparation = in stock solution (de-ionised water)

SAMPLING
- Sampling frequency: 7 day intervals (0, 7, 14, 21, and 28)
- Sampling method: A luminescent dissolved oxygen meter and probe (Hach HQ4Od and LDO10101) were used to measure luminescent dissolved oxygen

CONTROL AND BLANK SYSTEM
- Inoculum blank: Freshwater inoculum oxygen blank to provide a measure of background oxygen consumption in the test medium
- Toxicity control: A mixture of sodium benzoate (2 mg/l concentration) and test material (addition rate concentration)
Reference substance:
benzoic acid, sodium salt
Remarks:
(Sodium benzoate)
Test performance:
An initial test was conducted on June 07 - July 05, 2017 that met all validity criteria except for the blank oxygen consumption which exceeded the limit. The test was therefore repeated on July 12 - August 09, 2017 in accordance with the study plan and assessed for compliance, as previously, by the validity criteria outlined in OECD Guideline 301D (1992). The reference material, sodium benzoate, underwent > 60 % biodegradation in 14 days (76 %), the oxygen consumption blank (freshwater inoculum) had a reported dissolved oxygen depletion of 0.5 mg/l), and in the inhibition test, the test and reference material in sum underwent > 25 % degradation in 14 days (29%). No valid microbial counts were reported for aged inoculum due to high counts on the control plates, however, this deviation was not thought to have had an impact as the soluble reference material degraded by > 60 % in the first 14 days, indicating that the test inoculum contained a satisfactory population of viable bacteria. No other deviation in the test was reported. All relevant validity criteria were met.
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
0 d
Parameter:
% degradation (O2 consumption)
Value:
3
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
3
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
15
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
15
Sampling time:
28 d
Details on results:
Only two data points are required for data analysis. Replicates that reported a difference in biodegradation greater than 20 % were deemed abnormal and removed.
Key result
Parameter:
ThOD
Value:
1.995 other: mg O2/mg test mat.
Results with reference substance:
Sodium benzoate exhibted 99 % biodegradation after a 28 day period.

Control Test Data

Average control dissolved oxygen concentrations (mg O2/l):

Material Day
0 7 14 21 28
Oxygen consumption blank 8.95 8.46 8.10 7.96 7.67
Sodium benzoate (2 mg/l concentration) 8.95 6.11 5.95 5.20 5.18

Average control net oxygen consumption (BOD, mg O2/l):

Material Day
7 14 21 28
Oxygen consumption blank 0.50 0.85 0.99 1.28
Sodium benzoate  2.35 2.50 3.26 3.28

Reference material percentage biodegradation:

Material 100% BOD (mg/l) Day
0 7 14 21 28
Sodium benzoate  3.32 0 71 76 98 99

Blank oxygen demand:

Day Mean dissolved oxygen (mg/l) Mean BOD (mg/l) BOD (%)
0 8.95 - -
7 8.46 0.50 6
14 8.10 0.85 9
21 7.96 0.99 11
28 7.67 1.28 14

1-[(2-hydroxyethyl)thio]propan-2-ol Analysed Test Data

Analysed test material percentage biodegradation for all replicates:

Material 100% BOD (mg/I) Day
0 7 14 21 28
Test material 5.46 0.0 5.3 0.7 18.1 10.9
0.0 4.0 6.5 6.9 21.5
0.0 0.0 1.9 19.2 12.4
Difference between replicates 0.0 5.3 5.8 12.3 10.6
Test material + Sodium benzoate 8.78 0.0 27.2 29.9 29.5 26.4
0.0 27.9 27.1 - 29.4
0.0 27.2 29.5 26.6 34.3
Difference between replicates 0.0 0.7 2.8 2.9

7.9

Average analysed test material dissolved oxygen concentrations (mg O2/l):

Material Day
0 7 14 21 28
Test material 8.95 8.29 7.94 7.16 6.86
Test material + Sodium benzoate 8.95 6.05 5.58 5.51 5.04

Average analysed test material net oxygen consumption (BOD, mg O2/l):

Material Day
7 14 21 28
Test material 0.17 0.16 0.80 0.81
Test material + Sodium benzoate 2.41 2.53 2.46 2.63

Analysed 1-[(2-hydroxyethyl)thio]propan-2-ol percentage biodegradation:

Material 100% BOD (mg/l) Day
0 7 14 21 28
Test material 5.46 0 3 3 15 15
Test material + Sodium benzoate 8.78 0 28 29 28

30

Assessment of potential inhibition of inoculum due to 1-[(2-hydroxyethyl)thio]propan-2-ol:

Day Test material BOD (mg/l) Sodium benzoate BOD (mg/l) Sum of separate BODs (mg/l) Inhibition control BOD (mg/l) Percentage inhibition
7 0.17 2.35 2.51 2.41 4
14 0.16 2.5 2.67 2.53 5
21 0.8 3.26 4.06 2.46 39
28 0.81 3.28 4.1 2.63

36

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
After a 28 day period the percentage biodegradation for 1-[(2-hydroxyethyl)thio]propan-2-ol was reported as 15 % (based on O2 consumption). The registration substance does not fit the criteria of readily biodegradable.
Executive summary:

The ready biodegradation of 1-[(2-hydroxyethyl)thio]propan-2-ol in an aerobic aqueous environment was determined in line with OECD Guideline 301 D - Ready Biodegradability: Closed Bottle Test. The study satisfied all validity criteria and a minor deviation, in which no valid microbial count could be obtained for aged inoculum, was not believed to have had an effect on the final result. After 28 days, percentage biodegradation of 1-[(2-hydroxyethyl)thio]propan-2-ol was report as 15 % (based on O2 consumption). This result did not achieve the pass removal level of 60 % of theoretical maximum within the 10 (or 14) day window. It is possible to conclude, therefore, that 1-[(2-hydroxyethyl)thio]propan-2-ol is not readily biodegradable under test conditions. As the degradation (%) of test material plus reference on day 14 equated to 29 %, it is further summarised that the substance is not inhibitory to bacteria (at the concentration used) as the study value is >25 %.

Description of key information

The ready biodegradation of 1-[(2-hydroxyethyl)thio]propan-2-ol in an aerobic aqueous environment was determined in line with OECD Guideline 301 D - Ready Biodegradability: Closed Bottle Test. The study satisfied all validity criteria and a minor deviation, in which no valid microbial count could be obtained for aged inoculum, was not believed to have had an affect on the final result. After 28 days, percentage biodegradation of 1-[(2-hydroxyethyl)thio]propan-2-ol was report as 15 % (based on O2 consumption). This result did not achieve the pass removal level of 60 % of theoretical maximum within the 10 (or 14) day window. It is possible to conclude, therefore, that 1-[(2-hydroxyethyl)thio]propan-2-ol is not readily biodegradable under test conditions. As the degradation (%) of test material plus reference on day 14 equated to 29 %, it is further summarised that the substance is not inhibitory to bacteria (at the concentration used) as the study value is >25 %.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information