Hexamethyldisiloxane

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:

2001-02-15 to 2001-03-07

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method:  Tertiary butyl alcohol was used as a solvent in the five lower test solutions. HMDS was dosed directly in the 2 highest concentrations.

Test organisms (species):

activated sludge, domestic

Details on inoculum:

Activated sludge from a domestic sewage oxidation ditch situated at the district of Hazerswoude Dorp, The Netherlands, taken on 5th March 2001.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

The oxygen concentration was recorded every minute during a period of about 10 minutes.

Test temperature:

20 ± 2 °C

pH:

8.1 to 8.3

Nominal and measured concentrations:

Nominal concentrations were 0, 0.10, 0.32, 1.0, 3.2, 11, 39 and 100 mg/l.

Details on test conditions:

TEST SYSTEM
- Test vessel: One litre glass beaker and BOD bottle

- Aeration: All suspensions were aerated vigorously.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Dilution water prepared by adding 1 ml of stock 1 to 4 to each litre of ultrapure water and store at 20 deg C in the dark with aeration. Prescription according to NEN 6634 [3].

- Vehicle: Tertiary butyl alcohol (TBA)

- Particulate matter: Activated sludge = 4.0 g (dw)/l

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The two controls had a difference in respiration rate of 2.6%, less than the 15% limit for a valid study.  The validity criteria of the Guideline were fulfilled.

Results with reference substance (positive control):

A positive control test with 3,5-dichlorophenol yielded an EC50 of 13.1 mg/l.  The validity criteria of the Guideline were fulfilled.

No inhibition of the respiration rate was observed within the entire concentration range. Based on nominal test concentrations, the NOEC of HMDS was >= 100 mg/l. The EC50 was >100 mg/l.

Table 1: Results of the activated sludge respiration inhibition test

Test sample	Nominal concentration of test substance (mg/l)	Respiration rate (mg O2/g/h)	Coefficient of determination	% Inhibition respiration rate	pH
Hexamethyldisiloxane
Initial control	0	18.6	-1.0000	-1.3	8.2
Final control	0	18.1	-0.9999	1.3	8.2
	0.1	19.8	-1.0000	-0.8	8.2
	0.32	20.0	-1.0000	-9.1	8.2
	1	19.5	-1.0000	-6.4	8.1
	3.2	19.6	-1.0000	-6.9	8.1
	11	20.6	-1.0000	-12.0	8.1
	39	21.0	-1.0000	-14.1	8.1
	100	20.7	-1.0000	-12.9	8.1
3,5-dichlorophenol
Initial control	0	15.7	-0.9999	7.0	8.2
Final control	0	18.1	-0.9999	-7.0	8.2
	5	14.6	-0.9998	13.7	8.3
	12	8.9	-1.0000	47.7	8.3
	30	3.5	-0.9743	79.4	8.3

 

Validity criteria fulfilled:

yes

Conclusions:

A NOEC of >=100mg/l and EC50 >100 mg/l for toxicity to microorganisms were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Toxicity to microorganisms: 3hr ASRI NOEC >=100mg/l; EC50 >100 mg/l (OECD 209)

Additional information

Three reliable studies are available for toxicity to microorganisms.

Two reliable studies are ASRI (activated sludge respiration inhibition) studies. The key study (Mayer 2001) was chosen as the most recent study. This study gave a result of NOEC (3 h) ≥100 mg/l; EC₅₀>100 mg/l. The result from the other reliable ASRI study (Diefenbach 1998) was EC₅₀(3 h) >2000 mg/l.

A reliable study for growth inhibition for Pseudomonas putida is also available (Hanstveit 1999). The result was EC₅₀(17 h) >100 mg/l.