Trichloro(hexadecyl)silane

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

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 attached justification for grouping of substances in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Parameter:

% degradation (O2 consumption)

Value:

57

Sampling time:

28 d

Remarks on result:

other: Based on results in enhanced OECD 301F study (Noack Laboratories, 2016)

Parameter:

% degradation (O2 consumption)

Value:

65

Sampling time:

60 d

Remarks on result:

other: Based on results in enhanced OECD 301F study (Noack Laboratories, 2016)

Parameter:

% degradation (O2 consumption)

Value:

65

Sampling time:

28 d

Remarks on result:

other: Based on results in enhanced OECD 301F study (Maischak, 2019)

Parameter:

% degradation (O2 consumption)

Value:

81

Sampling time:

60 d

Remarks on result:

other: Based on results in enhanced OECD 301F study (Maischak, 2019)

Validity criteria fulfilled:

not applicable

Interpretation of results:

inherently biodegradable

Reference 2

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.

Reference 3

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, based on read-across to CAS No. 16415-12-6).

Inherently biodegradable (57% after 28 d and 65% after 60 d, OECD 301F, based on read-across to CAS No. 18643-08-8).

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Type of water:

freshwater

Additional information

There is no reliable ready biodegradation data available for the parent substance trichloro(hexadecyl)silane (CAS No. 5894-60-0) or its silanol hydrolysis product, therefore good quality data has been read across from the structurally analogue substances trimethoxy(hexadecyl)silane (CAS No. 16415-12-6) and octadecyldimethylchlorosilane (CAS No. 18643-08-8). Both source substances hydrolyse in the aquatic environment to form the identical silanol hydrolysis product (trimethoxy(hexadecyl)silane) or a similar silanol hydrolysis product (octadecyldimethylchlorosilane) as the target compound trichloro(hexadecyl)silane. The second hydrolysis products formed being hydrochloric acid (target and octadecyldimethylchlorosilane) and methanol (trimethoxy(hexadecyl)silane). The alcohol hydrolysis product methanol is known to be readily biodegradable (OECD SIDS, 2004), while hydrochloric acid is an inorganic substance and thus not susceptible to biodegradation (OECD SIDS, 2002). While the target substance trichloro(hexadecyl)silane and the source substance octadecyldimethylchlorosilane both show a rapid hydrolysis (DT50 << 2 min), the source substance trimethoxy(hexadecyl)silane has a much slower hydrolysis rate under environmental conditions with a DT50 value of > 14 d at pH 7. Therefore, the parent compound of the source substance trimethoxy(hexadecyl)silane can be expected to be the predominant form, which was present during the study, while for the source substance octadecyldimethylchlorosilane the respective silanol hydrolysis product can be expected to be the predominant form within the study. More information can be found in the attached read-across justification in IUCLID Section 13.

In the available study for the analogue substance octadecyldimethylchlorosilane (CAS No. 18643-08-8, C18 alkyl side chain), biodegradation was assessed in an enhanced ready biodegradability test according to OECD guideline 301F and GLP criteria. The non-adapted activated sludge was exposed to 19 mg/L test substance for 60 days. Biodegradation was calculated based on O2-consumption.

The substance reached a biodegradation of 57% after 28 d and 65% after 60 d. Therefore, the read across substance is assessed as being inherently biodegradable.

In the available study for the analogue substance trimethoxy(hexadecyl)silane (CAS No. 16415-12-6, C16 alkyl side chain), biodegradation was assessed in an enhanced ready biodegradability test according to OECD guideline 301F and GLP conditions. Domestic, non-adapated sludge was exposed to 20 mg/L test item for 60 d. Silicone oil was used as a solubilizing agent. Biodegradation was assessed based on O2-consumption.

After 28 d and 60 d, a biodegradation of 65% and 81% was recorded, respectively. However, the 10-day window criterion was not fulfilled. Therefore, the substance qualifies as "readily biodegradable but failing the 10-day window". Furthermore, the toxicity control showed that the substance is not inhibitory to activated sludge microorganisms.

Hence, biodegradation is expected for the silanol hydrolysis product and it can be regarded as inherently biodegradable.

References:

OECD SIDS, 2002. Hydrogen Chloride - SIDS Initial Assessment Report for SIAM 15, Boston, USA: UNEP Publications.

OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.