1,1,3,3-tetramethyldisiloxane

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

long-term toxicity to aquatic invertebrates

Data waiving:

other justification

Justification for data waiving:

other:

Reference 2

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017-08-28 - 2017-09-13

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Bulk test solution sampled on days 0, 2, 7, 14 and 19
Pooled replicate solutions were sampled on days 2, 5, 9, 16 and 21

Vehicle:

no

Details on test solutions:

The highest (limit) test concentration was prepared by direct addition, solutions were renewed every Monday, Wednesday and Friday

Test organisms (species):

Daphnia magna

Details on test organisms:

in-house cultures, initially obtained from Aquatic BioSystems, Inc., Fort Collins, Colorado

Feed: Day 1-6: 0.4 mL Raphidocelis subcapitata and 0.1 mL yeast, wheat grass and finfish food suspension
Day 7-20: 0.5 mL Raphidocelis subcapitata and 0.1 mL yeast, wheat grass and finfish food suspension

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

21 d

Hardness:

54-64 mg CaCO3/ L

Test temperature:

20-21 degree C

pH:

7.4-8.0

Dissolved oxygen:

7.4-8.9 mg/L

Conductivity:

157-200 uS/cm

Nominal and measured concentrations:

Nominal concentration: 12 mg/L
Measured concentration (time-weighted mean, averaging measured concentration): 12.6 mg/L

Details on test conditions:

TEST SYSTEM
- Material, size, headspace, fill volume: 125 mL glass jars with 90 mL medium
- Renewal rate of test solution (frequency): Monday, Wednesday, Friday
- No. of organisms per vessel: 1
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10
- Biomass loading rate: 0.2 mg C/daphnid/day

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Lake Huron water: flocculated with ferric chloride, sand filtered, carbon filtered, UV-irradiated


OTHER TEST CONDITIONS
- Adjustment of pH: with gaseous CO2
- Photoperiod: 16 h light
- Light intensity: 1042-1484 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : mortality, daily

TEST CONCENTRATIONS
- Results used to determine the conditions for the definitive study: Limit test with 12 mg/L based on short term test with EC>117 mg/L

Reference substance (positive control):

no

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

>= 12.6 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

other: survival, reproduction and growth

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

> 12.6 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

other: survival, reproduction and growth

Nominal conc. (mg/L)	Time weighted mean measured conc. (mg/L)	Percent survival	Average Cumulative Offspring Per surviving Adult (mean +/- SD)	Length in milimeter (mean +/- SD)	Dry weight in Milligrams (mean +/- SD)
0 (water control)	0 (<LLQ)	90	120.7 +/- 9.9	4.19 +/- 0.06	0.53 +/- 0.15
12	12.6	90	118.2 +/- 11.6	4.17 +/- 0.07	0.44 +/- 0.07
	NOEC (mg/L)	12.6	12.6	12.6	12.6
	LOEC (mg/L)	>12.6	>12.6	>12.6	>12.6
	MATC (mg/L)	>12.6	>12.6	>12.6	>12.6

Validity criteria fulfilled:

yes

Conclusions:

A 21 day NOEC value of >= 12.6 mg/L and EC50 value of >12.6 mg/L (based on Time Weighted Average Measured concentrations) have been determined for the effects of the test substance on survival, reproduction and growth of Daphnia magna.

Description of key information

Dimethylsilanol: The endpoint is waived.

Dimethylsilanediol: Long-term toxicity to invertebrates: 21-day EC₅₀ >12.6 mg/l mg/l and NOEC ≥12.6 mg/l (highest concentration tested) (OECD guideline 211), read-across from data on the ultimate hydrolysis product dimethylsilanediol (CAS 1066-42-8).

Additional information

No data are available for the registered substance, which hydrolyses very rapidly to dimethylsilanol during the intermediate hydrolysis. The substance further hydrolyses to dimethylsilanediol (CAS 1066-42-8), however the final hydrolysis rate is >48 hours, therefore as indicated by the REACH guidance (ECHA 2016, R.16), the aquatic chemical safety assessment and PNECs are based on the intermediate hydrolysis product, for which short-term aquatic toxicity data have been read across from the structural analogue trimethylsilanol (CAS 1066-40-6) (structural analogue of dimethylsilanol).

Short- and long-term aquatic toxicity data are also available on the ultimate hydrolysis product, where no effects were reported at the highest concentrations tested, see details below.

Dimethylsilanol:

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a long-term aquatic toxicity to invertebrates study because, as indicated in guidance R.7.8.4.3 (ECHA 2016), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1 and therefore the risk is already adequately controlled and further testing is not justifiable.  

The intermediate hydrolysis product, dimethylsilanol, is very water-soluble, has low bioavailability (based on log Kow <<3) and there is no reason to expect any specific mechanism of toxicity beyond narcosis. Therefore, the occurrence of toxic effects that were not expressed in the existing short-term aquatic studies (conducted at concentrations up to 1000 mg/l with trimethylsilanol) would be considered unlikely.  

Based on the short-term aquatic data set on trimethylsilanol, the most sensitive trophic level is invertebrates, although no toxicity was observed below 100 mg/l. For the purpose of chemical safety assessment, a freshwater PNEC has been derived by applying an assessment factor of 1000 to the short-term data. This high assessment factor to derive the predicted no-effect level already reflects the typically higher value of a short-term EC50 compared to a long-term NOEC. For a narcotic chemical without a specific mode of toxic action, it is unlikely that the aquatic PNEC would be significantly over-estimated using this method.    

In addition, dimethylsilanol is not likely to persist in the environment because it is susceptible to hydrolysis, forming dimethylsilanediol, for which long-term invertebrate toxicity data are available (see below).

Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further in vivo testing is not considered necessary or justified on ethical grounds.    

Dimethylsilanediol:

A 21-day NOEC value of ≥12.6 mg/L and EC₅₀ value of >12.6 mg/L (Time Weighted Average measured concentrations, limit test) have been determined for the effects of dimethylsilanediol (CAS 1066-42-8, the ultimate hydrolysis product) on survival, reproduction and growth of Daphnia magna. The data are used to derive indicative sediment and soil PNECs for the ultimate hydrolysis product, using the Equilibrium Partitioning Method.

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.