Trisiloxane, 3-ethyl-1,1,1,3,5,5,5-heptamethyl-

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2005-06-13 to 2005-11-09

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)

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

- Preparation of inoculum for exposure: The activated sludge was washed by cetrifugation and the supernatant liquid phase was decanted, this procedure was repeated twice. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 1.5 g dry material per litre were mixed with test water and then aerated until use.
- Concentration of sludge in the test: 30 mg suspended solids/L

Duration of test (contact time):

28 d

Initial conc.:

25 mg/L

Based on:

test mat.

Initial conc.:

25.1 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: according to guideline
- Test temperature: 21.5 - 22.0°C
- pH: 7.6 at test start, 7.2 - 7.6 at test end
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: Manometric Test System with test flasks containing a volume of 500 mL
- Number of culture flasks/concentration: 1
- Method used to create aerobic conditions: continuous stirring
- Test performed in closed vessels due to significant volatility of test substance: yes

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 flasks
- Abiotic sterile control: 25.1 mg test item with sterile water
- Toxicity control: 25 mg test item and 25 mg reference substance (Aniline) with acivated sludge
- Other: procedure control: 25.1 mg reference substance (Aniline) with activated sludge

Reference substance:

aniline

Key result

Parameter:

other: % degradation (BOD/ThODNH4)

Value:

0

Sampling time:

28 d

Details on results:

Points of degradation plot (test substance):
0% degradation after 1 d
1% degradation after 7 d
2% degradation after 14 d
2% degradation after 21 d
0% degradation after 28 d

Points of degradation plot (toxicity control):
0% degradation after 1 d
23% degradation after 7 d
48% degradation after 14 d
52% degradation after 21 d
53% degradation after 28 d

Results with reference substance:

Points of degradation plot (reference substance):
0 % degradation after 1 d
61 % degradation after 7 d
105 % degradation after 14 d
109 % degradation after 21 d
109 % degradation after 28 d

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The degradation rate of the test item did not reach 60% within the 10-day window and after 28 days of incubation. Therefore, the test item is considered to be not readily biodegradable. Furthermore, no inhibitory effects of the activated sludge from the test item were observed in the toxicity control (53% biodegradation after 28 days).

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-07-28 to 2017-03-23

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)

Qualifier:

according to guideline

Guideline:

ISO 14593:1999 (Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium - Method by analysis of inorganic carbon in sealed vessels (CO2 headspace test))

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

other: mixed population of sewage treatment micro-organisms (predominantly domestic sewage)

Details on inoculum:

- Preparation of inoculum for exposure: In order to reduce the inorganic carbon (IC) content of the inoculum, the filtrate was sparged with CO2-free air for approximately 1 hour whilst maintaining its pH at 6.5 using concentrated orthophosphoric acid. After sparging, the pH was restored to its original value of 7.5 using 7 M sodium hydroxide and the inoculum allowed to settle for approximately 1 hour prior to removal of an aliquot (2 liters) of the supernatant for use in the test. The supernatant was maintained on aeration using CO2-free air until use.
- Concentration of sludge: 350 mL inoculum diluted with 3500 mL mineral medium. An aliquot of diluted inoculum (107 mL) was added to each test vessel.

Duration of test (contact time):

28 d

Initial conc.:

46.4 mg/L

Based on:

test mat.

Initial conc.:

20 mg/L

Based on:

TOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: according to guideline
- Test temperature: 20+/- 1°C
- Inoculum concentration: 100 mL/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 125 mL glass Wheaton bottles (total volume when full 160 mL) each containing 107 mL of solution, sealed using Teflon lined silicon septa and aluminum crimp caps
- Number of culture flasks/concentration:
a) inoculum: 33 replicate vessels
b) procedure control: 33 replicate vessels
c) test item: 29 replicate vessels
d) toxicity control: 9 replicate vessels
- Method used to create aerobic conditions: by constant shaking at approximately 125 rpm
- Measuring equipment: CO2 production in the vessels was determined by measuring the increase in the concentration of Inorganic Carbon (IC) in the headspace. The samples were analyzed using a Shimadzu TOC-VCSH TOC analyzer. For DOC analysis, samples (30 mL) were removed from the inoculum control and procedure control vessels (at 0 and 28 days) and filtered through Gelman 0.45 µm Acrocap filters (approximately 5 mL discarded) prior to DOC analysis. The samples were then analyzed using a Shimadzu TOC-VCPH TOC analyzer.

SAMPLING
- Sampling frequency: Triplicate inoculum control, procedure control and test item vessels were sacrificed on Days 0, 3, 7, 10, 13, 15, 17 and 21 for IC analysis. On day 28, five replicate vessels were sacrificed for IC analysis. Triplicate toxicity control vessels were sacrificed on Days 0, 10 and 15 for IC analysis.
- Sampling method: The principle of this method is that after acidification to a pH value of less than 3 and equilibration at 20 ± 1 °C, the equilibrium constant for the distribution of CO2 between the liquid and gaseous phases in the test vessels is 1.0 and hence only the CO2 concentration in the headspace needs to be determined. On Days 0 and 28, samples (30 mL) were removed from the inoculum control and procedure control vessels prepared for DOC analysis

CONTROL AND BLANK SYSTEM
- Inoculum blank: aliquot of diluted inoculum (350 mL inoculumn diluted with 3500 mL mineral medium)
- Toxicity control: reference substance (sodium benzoate) at a concentration of 34.3 mg/L (20 mg C/L), test item at a concentration of 46.4 mg/L (200 mg C/L)
- procedure control: reference substance at a concentration of 34.3 mg/L (20mg C/L)

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (CO2 evolution)

Value:

0

Sampling time:

28 d

Table 1: Inorganic Carbon (IC) Values on Each Analysis Occasion

	Inorganic Carbon (mg IC)
Day	Inoculum Control					Procedure Control					Test Item					Toxicity Control
	R1	R2	R3	R4	R5	R1	R2	R3	R4	R5	R1	R2	R3	R4	R5	R1	R2	R3	R4	R5
0	0.05	0.04	0.04	-	-	0.04	0.04	0.05	-	-	0.07	0.05	0.05	-	-	0.05	0.05	0.04	-	-
3	0.05	0.05	0.05	-	-	1.22	1.21	1.14	-	-	0.05	0.05	0.05	-	-	-	-	-	-	-
7	0.05	0.05	0.05	-	-	1.83	1.74	1.72	-	-	0.05	0.05	0.05	-	-	-	-	-	-	-
10	0.05	0.05	0.05	-	-	1.75	1.79	1.85	-	-	0.05	0.06	0.06	-	-	1.84	1.79	1.73	-	-
13	0.05	0.06	0.06	-	-	1.97	1.94	2.00	-	-	0.06	0.06	0.06	-	-	-	-	-	-	-
15	0.05	0.06	0.05	-	-	2.04	1.97	1.77	-	-	0.06	0.07	0.06	-	-	1.77	1.76	1.71	-	-
17	0.05	0.06	0.05	-	-	1.87	1.86	1.90	-	-	0.06	0.06	0.05	-	-	-	-	-	-	-
21	0.06	0.06	0.06	-	-	1.90	1.77	1.80	-	-	0.05	0.06	0.06	-	-	-	-	-	-	-
28	0.06	0.07	0.06	0.06	0.06	2.03	2.07	2.09	2.10	2.14	0.07	0.08	0.06	0.06	0.06	-	-	-	-	-

Table 2 Percentage Biodegradation Values

	% Biodegradation
Day	Procedure Control	Test Item	Toxicity Control
0	0	1	0
3	53	0	-
7	80	0	-
10	82	0	41
13	89	0	-
15	88	0	40
17	86	0	-
21	82	0	-
28	93	0	-

Table 3: Dissolved Organic Carbon (DOC) Values on day 0 and Day 28

DOC Concentration
Test Vessel		Day 0			Day 28
		mg C/L	mg C/L Corrected for Mean Control Value	% of Nominal Carbon Content	mg C/L	mg C/L Corrected for Mean Control Value	% Biodegradation
Inoculum Control	R1	1.149	-	-	<LOQ	-	-
	R2	1.087	-	-	<LOQ	-	-
Procedure Control	R1	20.26	19.14	96	<LOQ	-	100
	R2	20.12	19.00	95	<LOQ	-	100

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The test item attained 0% biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline 310. Furthermore, no inhibitory effects were observed from the test substance on activated sludge.

Description of key information

Based on the study results, 3-ethylheptamethyltrisiloxane is considered as not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

The biodegradation of 3-ethylheptamethyltrisiloxane was determined in a GLP study according to OECD 301 F and a GLP study according to OECD 310. In both tests the test item was considered to be not readily biodegradable. No inhibitory effects of the activated sludge from the test item were observed.