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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:
10 Aug - 07 Sep 2016
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)
Version / remarks:
1992
Deviations:
no
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 (e.g. location, sampling depth, contamination history, procedure): sewage treatment plant Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany
- Date of sampling: 10th August 2016
- Storage conditions: No storage
- Preparation of inoculum for exposure: No washing, the concentration was adjusted to 3.0 g/L and verified by dry mass measurement.
- Pretreatment: Kept aerobic until use
- Concentration of sludge in the test: 29.6 mg dry mass/litre
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Remarks:
corresponding to 305 mg ThOD / L
Initial conc.:
20 mg/L
Based on:
test mat.
Remarks:
corresponding to 61 mg ThOD / L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
- The concentration in the test assays were 100 and 20 mg per litre mineral test medium (25 and 5 mg/250 mL), respectively. 100 mg test item correspond to 305.3 mg ThOD. 20 mg test item correspond to 61.1 mg ThOD. The required amount of test item was added directly on a weight basis via Teflon discs. Subsequently, the required volume of aqueous reference stock solution (if applicable) and mineral medium were added to the vessels.
- The concentration in the test vessels with reference item (procedural control, toxicity control) was 100 mg per litre mineral test medium (25 mg/250 mL).
- A further solution containing both test and reference item at the same concentrations as in the individual solutions (test item 100 mg/L, reference item 100 mg/L) was prepared to determine the possible toxicity of the test item against the inoculum.
- Further flasks with mineral medium only were prepared for inoculum controls.
- Abiotic controls were also prepared to measure any possible abiotic degradation; a solution of the test item at about 100 mg/L was sterilized by the addition of 1 mL/L HgCl2 (10 g/L).
- In all test assays except of the abiotic controls, 2.47 mL of the inoculum stock solution were transferred for inoculation (per 250 mL) resulting in a concentration of 29.6 mg dry mass/litre (7.4 mg dry mass/250 mL).
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
86
St. dev.:
3.5
Sampling time:
28 d
Remarks on result:
other:
Remarks:
for 20 mg test item /L test assays
Details on results:
The biodegradation of isocetyl stearoyl stearate after 28 days of incubation in the static test was found to be 66 % (SD = 1.4 %) and 86 % (SD = 3.5 %) in the assays with 100 mg/L and 20 mg/L, respectively. The biodegradation within the 10-day-window was 43 % and 80 % in the assays with 100 mg/L and 20 mg/L, respectively. The 10-day-window started at day 3 in the assays with 100 mg/L and at day 2 - 3 in the assays with 20 mg/L.
Results with reference substance:
The reference item sodium benzoate was degraded to 86 % within the first 14 days. At the end of the test
(Day 28), the reference item was degraded by an average of 91 %.

Percent degradation. Degradation (%) after 14 days.

vessel

 

Test suspension 100 mg/L

Test suspension 20 mg/L

Abiotic
control

Procedural control

Toxicity
control

1

 

45.2

88.4

0.0

86.5

42.8

2

 

45.9

78.6

0.0

84.7

47.5

Mean

 

45.5

83.5

0.0

85.6

45.1

SD

 

0.5

6.9

0.0

1.3

3.3

Percent degradation. Degradation (%) after 28 days.

vessel

 

Test suspension 100 mg/L

Test suspension 20 mg/L

Abiotic
control

Procedural control

Toxicity
control

1

 

67.5

88.4

0.0

91.3

57.4

2

 

65.5

83.5

0.0

91.3

64.2

Mean

 

66.5

86.0

0.0

91.3

60.8

SD

 

1.4

3.5

0.0

0.0

4.8

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
According to the OECD guideline 301F, the test item can be considered as readily biodegradable.
Executive summary:

The ready biodegradability of the test item was investigated according to the manometric respirometry test design and carried out according to the OECD guideline for Testing of Chemicals No. 301 F (1992) and the Council Regulation (EC) No 440/2008 of 30 May 2008. The ready biodegradability of the test item was investigated at a concentration of at a concentration of 100 mg/L (ThOD = 305 mg/L) and 20 mg/L (ThOD = 61 mg/L), respectively, in a manometric respirometry test using domestic aerobic activated sewage sludge incubated at 22°C in the dark over 28 days under continuous stirring. The biochemical oxygen demand (BOD) was measured daily and the percentage degradation was calculated from the theoretical oxygen demand (ThOD) after correcting for the BOD of inoculum controls. The biodegradation of the test item in the static test was found to be at mean 66 % with a standard deviation of 1.4 % for a concentration of 100 mg test item per liter and at mean 86 % with a standard deviation of 3.5 % for a concentration of 20 mg test item per liter after 28 days. For a concentration of 100 mg test item per liter biodegradation within the 10-day-window was found to be 43 %. For a concentration of 20 mg test item per liter biodegradation within the 10-day-window was found to be 80 %. The test item had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration. In the procedural controls, the reference substance sodium benzoate was degraded by an average of 86 % by exposure day 14, and reached an average biodegradation of 91 % by the end of the test (day 28), thus confirming suitability of the activated sludge.

Description of key information

Readily biodegradable: 86.0% in 28 d (OECD 301 F)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There is one GLP study available investigating the ready biodegradability of Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) according to the OECD guideline 301 F (1992).

In a manometric respirometry test, a nominal concentration of 20 and 100 mg/L test item (corresponding to 61 and 305 mg/L ThOD, respectively) was inoculated with 29.6 mg dry mass/L activated sludge at 22 °C in the dark for 28 d under continuous stirring. Procedural and toxicity controls were run in parallel. The biochemical oxygen demand (BOD) was measured daily and the percentage degradation was calculated from the theoretical oxygen demand (ThOD) after correcting for the BOD of inoculum controls.

After 28 d, the biodegradation of the test item reached a mean of 86% in the 20 mg/L treatment and the 10-d window started on Days 2 to 3. In the 100 mg/L treatment a mean biodegradation of 66% was reached after 28 d and the 10-d window started on Day 3, reaching a mean biodegradation of 43% at the end of the 10-d window. 100 mg test item correspond to 305 mg ThOD, which is clearly above the value of 50-100 mg ThOD/L recommended by the guideline. The author of the study stated that some substances with high ThODs have gently inclined degradation curves, even when they are completely degradable. Thus, the test item concentration of 20 mg/L (corresponding to 61 mg ThOD/L) was considered appropriate to conclude on the ready biodegradability of the test substance.  The test item had no inhibitory effects on the activity of the activated sludge microorganisms. The procedural controls confirmed the suitability of the inoculum.

Therefore, Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) is readily biodegradable according to OECD criteria.