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

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2005-06-13 to 2005-07-13

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Version / remarks:

1988

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

1984

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Due to the low solubility of the test item in test water, adequate amounts of the test item were directly weighed into each test flask.

Test organisms (species):

activated sludge, domestic

Details on inoculum:

- Method of cultivation: The sludge was washed by centrifugation and the supernatant liquid phase was decanted. The solid material was resuspended in tap water and again centrifuged. The latter procedure was repeated twice. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge (g) to its dry weight (g) determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 3 g dry material per litre, were made up with tap water. To this mixture, 50 mL synthetic sewage feed per litre was added, starting two days prior use of the activated sludge. The activated sludge was kept at room temperature under continuous aeration until use. The pH of the activated sludge was 7.3, therefore no adjustment was necessary.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

21 - 22°C

pH:

7.2 at test start
8.0 - 8.2 at test end

Dissolved oxygen:

7.8 - 8.1 mg/L at test start
7.4 - 7.9 mg/L at test end

Nominal and measured concentrations:

Nominal: 10, 32, 100, 320 and 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: glass flasks of approximately 1 litre volume and Karlsruher flasks of 250 mL volume
- Aeration: with compressed air (approximately 0.613 litre per minute)
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2
- Sludge concentration (weight of dry solids per volume): 3 g/L

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: inhibition of respiration rate

Duration:

3 h

Dose descriptor:

other: EC20

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: inhibition of respiration rate

Results with reference substance (positive control):

- Results with reference substance valid? yes
- The following nominal concentrations of the positive control 3,5-Dichlorophenol were tested on the same activated sludge and under identical conditions as the test item: 3,2, 10, and 32 mg/L. In comparison to the controls the respiration rate of the activated sludge was inhibited by 24.3 % at the lowest nominal concentration of 3.2 mg/L. At the nominal concentrations of 10 and 32 mg test item/L, the respiration rate was inhibited by 51.4 and 81.1%, respectively.

Table 1: Influence of the test item and the reference item (3,5 -Dichlorophenol, DCP) on oxygen consumption of activated sludge

Flask No.	Treatment	Concentration	Oxygene consumption	Inhibition	pH- values		Oxygene concentration [mg O2/L]
		[mg/L]	[mg O2/L_min]	%	start	end	start	end
1	Control	---	0.350	---	7.2	8.2	8.1	7.9
10	Control	---	0.390	---	7.2	8.0	8.0	7.0
		mean	0.370
	replicate deviation		10.3
2	3,5-DCP	32	0.070	81.1	7.3	8.2	8.1	8.4
3	3,5-DCP	10	0.180	51.4	7.2	8.2	8.1	8.1
4	3,5-DCP	3.2	0.280	24.3	7.2	8.1	8.2	7.6
5	Y-14877	1000	0.340	8.1	7.2	8.0	7.8	7.6
6	Y-14877	320	0.370	0	7.2	8.0	7.9	7.4
7	Y-14877	100	0.380	-2.7	7.2	8.0	8.0	7.4
8	Y-14877	32	0.360	2.7	7.2	8.1	7.9	7.8
9	Y-14877	10	0.370	0	7.2	8.0	8.0	7.4

Validity criteria fulfilled:

yes

Conclusions:

Based on measured inhibition rates, the 3-hour EC20 and EC50 could not be quantified because up to the highest nominal test concentration of 1000 mg/L less than 20 % inhibition was noted after three hours incubation. Nevertheless, the 3-hour EC20 and EC50 are clearly higher than 1000 mg/L under the present test conditions.

Description of key information

Based on the results of a respiration inhibition test, the 3-hour EC20 and EC50 of 3-ethylheptamethyltrisiloxane are concluded to exceed 1000 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L