3-(triethoxysilyl)propanethiol

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2021-12-07 to 2022-06-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)

Version / remarks:

2014

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Reference substance: Sodium benzoate
Test facility ID: 70144_1
Batch number: BCBX0430
CAS RN: 532-32-1
Purity: 100%
Expiry date: 2026-09-03
Replicates: 3 /5 for each sampling day
Test concentration: 30 mg/L
ThTOC: 0.583 mg/L
ThCO2: 2.14 mg CO2/mg
Carbon content in vessel: 17.5 mg C/L

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Municipal sewage treatment plant, 31137 Hildesheim, Germany. Activated sludge from the sewage plant at Hildesheim is well suited as it receives predominantly municipal sewage and hardly any industrial chemical waste.
- Storage conditions: Aerobic condition by aeration with CO2-free air
- Storage length: 3 days
- Pre-treatment: The activated sludge was washed twice with chlorine free tap water. After the second washing the settled sludge was resuspended in mineral salts medium and was maintained in an aerobic condition by aeration for 2 hours. Thereafter, the sludge was homogenized with a blender. After sedimentation the supernatant was decanted and was maintained in an aerobic condition by aeration with CO2-free air for 3 days until test start.
- Concentration of sludge: 7.48 mL/L were used to initiate inoculation (4 mg/L dry weight)
- Water filtered: yes
-Colony forming units in the test solution: 10^5 - 10^8 CFU/L

Duration of test (contact time):

28 d

Initial conc.:

24 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

inorg. C analysis

Details on study design:

Study of ready biodegradability over a period of 60 days with a non-adapted inoculum from activated sludge in order to check the rate of biodegradation in % by determination of the total inorganic carbon (TIC). Since the test item biodegradation has already reached a plateau on day 28, this study is evaluated after 28 days.

TEST CONDITIONS
- Test temperature: Nominal 20 ± 1 °C, actually measured 18.8 – 21.8 °C. The temperature has slightly exceeded the range. It is considered that this deviation has no impact on the study.
- pH adjusted: pH-adjustment was not necessary.

SAMPLING
- Sampling frequency: 3 / 5 for each sampling day
- Sampling method: Analysis was carried out at test start, and on 7 further sampling times. The inoculum control and test item replicates were sampled at test start and on day 1, 4, 7, 11, 14, 21, 28, 35, 42, 49, 56 and 60. The functional control and toxicity control were sampled at test start and on day 7, 14 and 28.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Mineral salts medium with inoculum without test / reference item.
- Toxicity control: Mineral salts medium with inoculum and test and reference item in test concentration.

Reference substance:

benzoic acid, sodium salt

Preliminary study:

Pre-tests were carried out to determine the most suitable method of preparation. Different techniques and chemicals were applied.

Key result

Parameter:

% degradation (inorg. C analysis)

Value:

47

Sampling time:

28 d

Remarks on result:

other: 95 % confidence interval on day 28 was 28 – 65 %

Results with reference substance:

To check the activity of the test system sodium benzoate was used as functional control. The percentage degradation of the functional control reached the pass level of 60 % within 7 days and came to a maximum of 91 % on day 28. The 95 % confidence interval on day 28 was 90 – 92 % (Table 2).

Table 1. CO₂-Production and Biodegradation in the Test Item Samples

CO2-Production in mg C/L
Day	P1	P2	P3	P4	P5	Mean	Net MP	Degr.[%]
0	2.37	2.33	2.35			0.00
1	2.65	2.54	2.58			0.74	0.28	3
4	4.17	4.30	4.26			2.41	1.88	17
7	5.65	6.46	6.97			4.42	3.86	36
11	6.68	7.11	7.38			4.94	4.55	42
14	7.21	6.77	7.84			5.27	4.65	43
21	8.02	8.20	8.20			6.09	5.48	51
28	8.19	24.54*	14.65*	8.23	6.81	5.76	5.03	47
35	9.66	8.59	8.02			6.79	6.12	57
42	8.41	7.98	8.08			6.06	5.44	50
49	8.08	7.97	6.68			5.33	4.73	44
56	8.14	7.59	8.32			6.05	5.24	49
60	8.41	3.25	7.94	8.45	10.22	5.61	4.85	45

Mean = mean values (NaOH corrected)

Net MP = net mean production (corrected for inoculum control values)

Degr. = degradation

*) Replicates two and three are not included in the evaluation on day 28 and are regarded as outliers, since the theoretical maximum CO2 production was far exceeded

 

Table 2. Biodegradation and Confidence Interval of the Test Item 3-(Triethoxysilyl)propanethiol in Comparison to the Functional Control and the Toxicity Control

Replicates	Biodegradation [%] on Day 28					Confidence Interval on Day 28 P = 95%
	1	2	3	4	5
Functional Control	91	91	90	92	92	90-92
Test Item	51	-*	-*	51	38	28-65
Toxicity Control, Test Item + Reference Item	79	75	76	72	76	73-79

*) Replicates two and three are not included in the evaluation on day 28 and are regarded as outliers, since the theoretical maximum CO₂ production was far exceeded

 

Table 3. CO₂-Production in the Inoculum Control Samples

		CO2-Production in mg C/L
Day	NaOH	C1	C2	C3	C4	C5	Mean	MP
0	2.37	2.13	2.21	2.16			0.00	--
1	1.85	2.33	2.25	2.36			0.46	0.46
4	1.83	2.42	2.3	2.35			0.53	0.53
7	1.94	2.51	2.45	2.53			0.56	0.56
11	2.12	2.47	2.54	2.51			0.39	0.39
14	2.00	2.64	2.65	2.58			0.62	0.62
21	2.05	2.68	2.72	2.57			0.61	0.61
28	1.98	2.67	2.80	2.69	2.68	2.72	0.73	0.73
35	1.97	2.61	2.6	2.72			0.67	0.67
42	2.1	2.67	2.83	2.67			0.62	0.62
49	2.25	2.81	2.85	2.88			0.60	0.60
56	1.97	2.73	2.82	2.79			0.81	0.81
60	2.04	2.72	2.85	2.75	2.78	2.92	0.76	0.76

Mean = mean values (NaOH corrected)

MP = mean production

 

Table 4: CO₂-Production and Biodegradation in the Functional Control Samples

	CO2-Production in mg C/L
Day	R1	R2	R3	R4	R5	Mean	Net MP	Degr. [%]
0	2.67	2.64	2.67			0.29	-	-
7	17.85	17.86	18.05			15.98	15.13	86
14	18.69	18.69	18.77			16.72	15.81	90
28	18.96	18.86	18.78	19.17	19.04	16.98	15.96	91

Mean = mean values (NaOH corrected)

Net MP = net mean production (corrected for inoculum control values)

Degr. = degradation

 

Table 5: CO₂-Production and Biodegradation in the Toxicity Control Samples

	CO2-Production in mg C/L
Day	T1	T2	T3	T4	T5	Mean	Net MP	Degr. [%]
0	2.65	2.78	2.69			0.32	--
7	21.63	20.96	21.72			19.5	18.62	66
14	23.8	24.25	23.67			21.91	20.97	74
28	25.3	24.29	24.52	23.51	24.46	22.44	21.39	76

Mean = mean values (NaOH corrected)

Net MP = net mean production (corrected for inoculum control values)

Degr. = degradation

Validity criteria fulfilled:

yes

Remarks:

The reference substance degradation was > 60 % after 7 days (90% on day 14) and the inorg. carbon produced for the control samples was < 3 mg C/L (0.73 mg C/L on day 28)

Interpretation of results:

not readily biodegradable

Conclusions:

The test substance attained 47% degradation in 28 days in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Biodegradation in water: ready biodegradability: 47% after 28 days (OECD 310)

No significant biodegradation of the silanol hydrolysis product is expected.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Additional information

A biodegradation of 47% in 28 days (CO₂ evolution) was determined in a reliable study conducted according to OECD test guideline 310 and in compliance with GLP. The result is considered to be reliable and is selected as the key study.

 

The substance, 3-(triethoxysilyl)propanethiol, is expected to hydrolyse within the timescale of the ready biodegradation study (half-life of 32.1 hours at pH 7 and 20°C) to produce 3-(trihydroxysilyl)propanethiol and ethanol. Furthermore, ethanol is readily biodegradable (OECD 2004). Therefore, the biodegradation observed in the key study is attributable to the biodegradation of the ethanol hydrolysis product.

 

No significant biodegradation is expected for the silanol hydrolysis product.

 

References: 

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.