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Toxicity to microorganisms

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Reference
Endpoint:
toxicity to microorganisms, other
Remarks:
Toxicity control from biodegradation study.
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:
other: OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: The solution of the reference substance in mineral medium (100 mg/L) was prepared using a stock solution (10 g/L). Required amounts of the test item were added directly to the test vessels and the mineral medium was added subsequently.
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Source of inoculum/activated sludge: 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
Test type:
static
Water media type:
freshwater
Total exposure duration:
28 d
Test temperature:
22 ± 1 °C
pH:
7.4 ± 0.2 (test start)
7.8 (test end)
Nominal and measured concentrations:
20, and 100 mg/L test item (nominal) corresponding to 61, and 305 mg ThOD/L
Details on test conditions:
TEST SYSTEM
- Toxicity control: Containing 100 mg/L test item and 100 mg/L reference item (2 replicates)
- Test vessel: Respirometer flasks (SAPROMAT respirometer (VOITH Inc.)
- Material, size, headspace, fill volume: 500 mL respirometer flasks filled with 250 mL test solution.
- Aeration: The suspension was aerated during the whole test.
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 2
- No. of vessels per abiotic control (replicates): 2
- Sludge concentration: 29.6 mg dry mass/litre
- Other: The solutions were stirred throughout the test.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Deionized water, free from inhibitory concentrations of toxic substances (e.g. Cu2+ ions)

OTHER TEST CONDITIONS
- Adjustment of pH: Before test start the pH of all solutions were determined and adjusted to 7.4 ± 0.2 with H2SO4 (50 g/L).
- Photoperiod: 24 h darkness

EFFECT PARAMETERS MEASURED:
Oxygen consumption was measured and recorded continuously throughout the duration of the test using a SAPROMAT respirometer (VOITH Inc.).
Reference substance (positive control):
yes
Remarks:
sodium benzoate
Duration:
14 d
Dose descriptor:
NOEC
Effect conc.:
>= 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks on result:
other:
Remarks:
Toxicity control from a biodegradation study.
Details on results:
In absence of a microbial inhibition test, a NOEC for microbial toxicity can be derived from a ready biodegradability test. According to Chapter R.7b: Endpoint specific guidance (ECHA, 2017) if a compound degrades well in a ready biodegradability test, or does not inhibit the degradation of a positive control at a certain concentration, this concentration can be used as a NOEC value.

The test item had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration.

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
Conclusions:
The test item had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 100 mg/L (nominal).

Description of key information

NOEC (14 d) ≥ 100.0 mg/L for activated sludge microorganisms (OECD 301 F)

Key value for chemical safety assessment

Additional information

There is no respiration inhibition study available assessing the toxicity of Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) to activated sludge microorganisms. However, a standard ready biodegradability test conducted according to OECD guideline 301 F and GLP is available, whose toxicity control can be used to derive a NOEC. According to the Guidance on information requirements and chemical safety assessment (Chapter R.7b: Endpoint specific guidance, ECHA, 2017), a concentration can be used as NOEC value, if a compound degrades well in a ready biodegradability test, or does not inhibit the degradation of a positive control at a certain concentration.

The available ready biodegradability test included a toxicity control containing 100 mg/L test item and 100 mg/L reference item (benzoic acid, sodium salt) to determine the possible toxicity to microorganisms of activated sludge at a concentration of 29.6 mg dry mass/L.

After 14 d, a mean biodegradation of 45.1% was observed and after 28 d a mean biodegradation of 60.8% was recorded in the toxicity control. 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 the suitability of the activated sludge. Hence, Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration and a NOEC (14 d) of ≥ 100.0 mg/L (nominal) was derived.