Hexadecyltrimethoxysilane

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Remarks:

prolonged to 60 d

Type of information:

experimental study

Adequacy of study:

key study

Study period:

26 Jul - 24 Sep 2018

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:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Staatliches Gewerbeaufsichtsamt Hildesheim

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: Sludge was washed twice with chlorine free tap water. After the second washing settled sludge was resuspended in mineral salts medium and was maintained in an aerobic condition by aeration with CO2 free air until test start (2 d). The amount of inoculum used to initiate inoculation was 3.83 mg/L (25 mg/L dw)
- Initial cell/biomass concentration: Colony Forming Units (CFU) of the inoculum were determined prior to test start by standard dilution plate count. The CFU concentration of the inoculum corresponds to approx. 0.52 x 10^7 CFU/L in the final test solution.
- Water filtered: no

Duration of test (contact time):

60 d

Initial conc.:

20 mg/L

Based on:

test mat.

Initial conc.:

51.2 other: mg O2/L

Based on:

ThOD

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: according to guideline
- Solubilising agent: silicone oil (500 µL in 250 mL test solution, 100 mg test item / 10 mL silicone oil)
- Test temperature: 21 - 21.7 °C
- pH: inoculum control: 7.51 - 7.65, functional control: 7.64 - 7.68, inoculum control with silicone oil: 7.51 - 7.73, test item: 7.5 - 7.71, toxicity control: 7.64 - 7.73
- pH adjusted: no
- Continuous darkness: yes
- Other: continuous stirring

TEST SYSTEM
- Culturing apparatus: 500 mL brown glass bottles filled with 250 mL
- Number of culture flasks/concentration: 2
- Measuring equipment: OxiTop measuring heads
- Test performed in open system: no
- Details of trap for CO2 and volatile organics if used: A rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2.

SAMPLING
- Sampling frequency and method: The oxygen consumption was determined in the incubation vessels by the OxiTop measuring system at 360 measuring points (every 240 min) during the 60 d incubation period.

CONTROL AND BLANK SYSTEM
- Inoculum control: 2 replicates (test medium without test and / or reference item)
- Inoculum control with silicone oil: 2 replicates (test medium without test and / or reference item and 500 µL silicone oil)
- Toxicity control: 1 replica (test item (incl. 500 µL silicone oil) and reference item)
- Functional control: 1 replica
- Functional control with silicone oil: 1 replica

Reference substance:

benzoic acid, sodium salt

Remarks:

30 mg/L

Reference substance:

benzoic acid, sodium salt

Remarks:

30 mg/L sodium benzoate and 500 µL silicone oil / 250 mL test solution

Parameter:

% degradation (O2 consumption)

Value:

65

Sampling time:

28 d

Parameter:

% degradation (O2 consumption)

Value:

81

Sampling time:

60 d

Details on results:

- The biodegradation of the substance failed the 10 - d window criterion.
- O2 depletion in inoculum control with silicon oil: 28.6 mg O2/L on Day 28 and 33.5 mg/L on Day 60.
- Toxicity control: 47% degradation of test item after 14 d and 86% after 60 d.

Results with reference substance:

- Functional control: 86% biodegradation of sodium benzoate on Day 14.
- Functional control with silicone oil: 98% biodegradation on Day 60.

Table 1: % Biodegradation of test item, functional control and toxicity control during 60 d.

[d]	% Biodegradation
	Functional Control	Functional control with silicon oil	Test Item 1	Test Item 2	Tox. Control
2	30	30	3	1	14
4	64	66	3	3	33
6	75	78	3	3	39
8	83	86	4	4	43
10	84	90	9	9	45
12	85	90	23	20	46
14	86	90	36	34	47
16	81	90	40	41	48
18	78	93	46	45	55
20	77	94	51	52	62
22	78	94	56	57	67
24	78	93	59	60	70
26	78	94	62	64	72
28	79	94	64	66	74
30	80	95	65	68	76
32	80	94	67	70	78
34	80	96	67	72	79
36	79	96	70	74	80
38	77	97	70	74	80
40	80	95	71	76	80
42	81	94	72	78	81
44	80	96	73	79	82
46	82	97	75	79	83
48	82	96	75	80	83
50	81	96	75	80	83
52	80	97	76	80	84
54	80	97	76	81	84
56	78	97	76	81	84
58	79	97	78	81	85
60	77	98	79	83	86

Table 2: Validity criteria for OECD 301 F.

Criterion from 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%.	4%	yes
Percentage degradation of the reference compound reached the pass level by day 14 (≥ 60%).	Functional control: 86% Functional control with silicone oil: 90%	yes
The toxicity control should degrade to at least 35% (based on DOC) or at least 25% (based on ThOD or ThCO2) within 14 d.	47%	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.	Functional control: 32% Functional control with silicone oil: 28.6%	yes
the pH value should be in the range 6-8.5.	7.47 – 7.64	yes

Validity criteria fulfilled:

yes

Remarks:

For further details please refer to “Any other information on results incl. tables”.

Interpretation of results:

readily biodegradable, but failing 10-day window

Description of key information

Readily biodegradable but failing the 10 -day window (65% and 81% biodegradation after 28 and 60 d respectively, OECD 301 F)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable but failing 10-day window

Additional information

One study is available testing the biodegradability of Hexadecyl(trimethoxy)silane (CAS 16415-12-6) according to the OECD guideline 301 F and GLP standards. Domestic, non-adapted, activated sludge was exposed to 20 mg/L test item for 60 d. Silicone oil was used as a solubilizing agent. A toxicity control containing test substance, reference substance and silicon oil was run in parallel. A biodegradation of 65% and 81% was recorded in the treatments with the test item after 28 and 60 d respectively. However, the 10-day window criterion was not fulfilled. Therefore the substance is readily biodegradable but failing the 10-day window. Furthermore, the substance was not inhibitory to activated sludge microorganisms as shown by the toxicity control (47% degradation of the reference substance after 14 d and 86% after 60 d).