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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: screening test, other
Remarks:
enhanced ready biodegradability test (60 d)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
13 Apr - 13 Jun 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
1992
Deviations:
yes
Remarks:
60 days duration
GLP compliance:
yes (incl. QA statement)
Remarks:
Staatliches Gewerbeaufsichtsamt Hildesheim, Hildesheim, Germany
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: municipal sewage treatment plant, Hildesheim, Germany
-Pretreatment: activated sludge was washed twice with chlorine free tap water. Thereafter settled sludge was resuspended in mineral salts medium and was aerated for 2 h. Sludge was then homogenized with a blender. After sedimentation the supernatant was decanted and maintained in an aerobic condition by aeration with air for 5 d.
- Concentration of sludge: 10 mL/L were used to initiate inoculation
- Initial cell/biomass concentration: approx. 1.13 x 10^7 CFU/L in the final test solution
Duration of test (contact time):
60 d
Initial conc.:
19 mg/L
Based on:
test mat.
Initial conc.:
52.8 mg/L
Based on:
ThOD
Initial conc.:
2.78 other: mg O2/mg
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral salts medium according to OECD 301 F
- Test temperature: 20 - 21 °C
- pH: 7.60 - 7. 90
- pH adjusted: no
- Concentration of sludge: 10 mL/L were used to initiate inoculation
- Continuous darkness: yes
- Other: continuous stirring

TEST SYSTEM
- Number of culture flasks/concentration: 2
- Measuring equipment: OxiTop® measuring heads, WTW Stirring platform, WTW
- Test performed in closed vessels: yes
- Details of trap for CO2: a rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2
- Other: separate replicates of test item and toxicity control were prepared for measurement of pH at test start

SAMPLING
- Sampling frequency: 1080 measuring points during the 60 d incubation period

CONTROL AND BLANK SYSTEM
- Inoculum control: 2
- Inoculum control with silicone oil: 2 (500 µL silicone oil were pipetted directly into the inoculated test medium)
- Toxicity control: 1
- Functional control: 1

STATISTICAL METHODS: Excel, MICROSOFT CORPORATION, SigmaPlot, SPSS CORPORATION

Reference substance:
benzoic acid, sodium salt
Remarks:
45 mg/L
Parameter:
% degradation (O2 consumption)
Value:
57
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
65
Sampling time:
60 d
Details on results:
- Reference substance: 100% degradation after 23 d (pass level of > 60% was reached after 3 d)
- Toxicity control: 75% degradation after 28 d (82% degradation after 60 d)

VALIDITY CRITERIA:

Table 1: Validity criteria

Criterionfrom the guideline

Outcome

Validity criterion fulfilled

Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.

6% difference on day 28 and 13% on day 60

yes

Percentage degradation of the reference compound has reached the pass levels by day 14.

60% after 3 d

yes

The oxygen uptake of the inoculum blank is normally 20-30 mg O2/L and should not be greater than 60 mg/L in 28 days.

mean oxygen depletion in the inoculum control was 8 mg O2/L on day 28 and 10.8 mg O2/L on day 60

yes

 

 

 

RESULTS:

Both test item replicates reached the 10% biodegradation level on day 4. The 60% pass level was reached by the mean of replicates on day 39. The mean biodegradation on day 60 was 65%.

Table 2: % biodegradation over time.

[d] Functional Control Biodegradation [%] Toxicity Control
Test item
1 2
1 7 0 0 4
2 50 0 0 31
3 62 3 1 37
4 73 16 14 43
5 79 26 25 48
6 82 31 29 52
7 84 35 34 55
8 86 38 35 58
9 88 40 38 61
10 89 42 40 62
11 90 42 42 63
12 91 44 42 64
13 93 45 44 65
14 93 46 44 66
15 94 47 45 67
16 96 48 46 68
17 97 49 48 69
18 98 51 49 70
19 98 52 50 70
20 99 52 50 71
21 98 52 50 71
22 99 52 52 72
23 100 53 52 72
24 100 54 52 73
25 100 54 52 74
26 100 56 53 74
27 100 60 53 74
28 100 60 54 75
29 100 64 53 75
30 100 64 53 76
31 100 63 52 75
32 100 63 53 76
33 100 64 53 77
34 100 64 52 77
35 100 64 52 77
36 100 65 54 77
37 100 65 54 78
38 100 65 54 78
39 100 66 54 78
40 100 66 53 79
41 100 66 54 79
42 100 67 54 79
43 100 67 53 79
44 100 66 53 79
45 100 67 54 80
46 100 68 53 80
47 100 68 54 80
48 100 68 55 80
49 100 68 55 80
50 100 68 55 81
51 100 68 55 80
52 100 69 54 81
53 100 70 54 81
54 100 70 54 81
55 100 70 54 81
56 100 70 54 81
57 100 69 55 81
58 100 70 57 81
59 100 70 58 81
60 100 71 58 82
Validity criteria fulfilled:
yes
Remarks:
For further details please refer to “Any other information on results incl. tables”.
Interpretation of results:
inherently biodegradable
Conclusions:
A biodegradation study according to OECD 301F resulted in a biodegradation of 57% after 28 d and 65% after 60 d.
Endpoint:
biodegradation in water: screening test, other
Remarks:
enhanced ready biodegradability test (60 d)
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to the attached justification below and the overall justification for grouping of substances attached in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Parameter:
% degradation (O2 consumption)
Value:
57
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
65
Sampling time:
60 d
Details on results:
- Reference substance: 100% degradation after 23 d (pass level of > 60% was reached after 3 d)
- Toxicity control: 75% degradation after 28 d (82% degradation after 60 d)

Description of key information

Dimethoxymethyloctadecylsilane (CAS 70851-50-2) is inherently biodegradable (57% after 28 d and 65% after 60 d, OECD 301F) based on read across from CAS 18643-08-8.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

There are no data on biodegradation for dimethoxymethyloctadecylsilane (CAS 70851-50-2). In accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5 “Grouping of substances and read across” and in accordance with the read across assessment framework (RAAF, ECHA 2017) a read-across from the analogue substance chlorodimethyloctadecylsilane (CAS 18643-08-8) has been applied to support the environmental hazard assessment of the substance. Details on the read across justification can be found in the attached justification in the respective target entry and in the overall justification for grouping of substances attached in IUCLID Section 13.

The available study (2016) investigating the biodegradation of the analogue substance chlorodimethyloctadecylsilane (CAS 18643-08-8) was conducted according to OECD guidance 301F and GLP conditions. The inoculum (non-adapted activated sludge from a sewage treatment plant) was exposed for 60 days to 19 mg/L test substance and biodegradation was calculated based on O2-consumption. The substance reached a biodegradation value of 57% after 28 d and 65% after 60 d. Therefore, the read across substance is considered as inherently biodegradable.

Based on the results of the analogue substance, dimethoxymethyloctadecylsilane (CAS 70851-50-2) is assumed to be inherently biodegradable.