Dodecamethylcyclohexasiloxane

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:

2009-09-04

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)

- Method: 52 µl of the test substance, corresponding to 50 mg, was pipetted below the surface of the purified tap water and stirred.

Test organisms (species):

activated sludge

Details on inoculum:

- Source: Municipal sewage treatment plant: ‘Waterschap de Maaskant', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage

- Preparation of inoculum for exposure: coarsely sieved then washed.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

Oxygen consumption was measured and recorded for approximately 10 minutes.

Test temperature:

19.0-20.4°C

pH:

8.1-8.4

Nominal and measured concentrations:

100 mg/L
Performance of a limit concentration at 100 mg/l is acceptable, because 100 mg/l is far above the water solubility of Dodecamethylcyclohexasiloxane and thus exceeds the expected concentration in a Sewage Treatment Plant.

Details on test conditions:

TEST SYSTEM

- Test vessel:

- Material, size, headspace, fill volume: 1L test bottle

- Aeration: continuous vigorous aeration during contact time

- No. of vessels per concentration (replicates): Two

- No. of vessels per control (replicates): One at the initial, one at the final test points.

- Biomass loading rate: activated sludge: 3.8 g/l

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q) (Millipore Corp.).

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Details on results:

The two control had a difference in respiration rate of 15%, which is the limit for a valid study.

Results with reference substance (positive control):

A positive control test with 3,5-dichlorophenol yielded an EC50 of 7.2 mg/L. The validity criteria of the Guideline were fulfilled.

Test sample	Nominal concentration of test substance (mg/l)	Oxygen conc. At start (mg O2/l)	Oxygen consumption (mg O2/l/h)	% Inhibition respiration rate	pH
Initial control	0	7.5	33	-	8.4
Final control	0	7.0	38	-	8.3
Dodecamethylcyclohexasiloxane (1)	100	5.4	38	-7	8.2
Dodecamethylcyclohexasiloxane (2)	100	4.2	39	-10	8.1
3,5-dichlorophenol	5	-	-	43	-
	12	-	-	61	-
	30	-	-	67	-

Validity criteria fulfilled:

yes

Conclusions:

An EC50 >100 mg/l for toxicity to microorganisms was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Toxicity to microorganisms: EC₅₀ > 100 mg/L (OECD 209)

Additional information

A 3-hour EC₅₀ >100 mg/l for toxicity to microorganisms was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.