Hexamethyldisiloxane

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991-10-14 to 1991-10-24

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Guideline study; GLP. Most test concentrations tested were above the limit of water solubility for this compound.  Measured concentrations were significantly lower than nominal concentrations, reflecting the low water solubility of the compound.

Qualifier:

according to guideline

Guideline:

EPA OTS 797.1400 (Fish Acute Toxicity Test)

Qualifier:

according to guideline

Guideline:

other: EEC Directive 79/831

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling: Analytical determination of concentration was performed at the beginning of the test in the stock solutions and the test media at the beginning and end of the test. Water samples were taken from a point approximately midway between the surface, bottom and sides of each aquarium by means of glass pipettes of 20 mL volume carefully dipped into the solution. The samples were filled into volumetric flasks of 20 mL nominal volume. 0.5 mL n-decane containing the toluene used as internal standard for gas chromatography is added. The flask is closed and then shaken for about one minute. The above operations were performed immediately to minimize the losses of the test substance (M2) due to evaporation and reactions at the water interface. From the n-decane phase on top of the water phase, approximately 0.3 mL was taken by a suitable syringe and filled into a 1 mL vial. The vials were stored in a refrigerator until analysis. The procedure for sampling and preparing the stock solution samples were very similar to those used for the test solutions.
water.

Vehicle:

yes

Details on test solutions:

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

- Method: Seven stock solutions were prepared using iso-propanol as a co-solvent. These stock solutions were dosed into the water inlet of the aquaria under the test medium level. The stock solutions were continuously agitated during the test by magnetic stirrers and were dosed at intervals of 36 sec into the water flowing into the respective aquarium by HAMILTON dispensers controlled by a computer. The volurne per dosing cycle was 10 μL.

Test water continuously flowed into the aquaria via an inlet tube at a rate of 10 L/h regulated by a flow-meter. The aquaria were made of glass and had a size of 32 x 36 x 38 cm (L x D x H). The test volumes amounted to 40 L. Thus, the test volume was exchanged 6 times per day. In all the aquaria with the exception of the control, the iso-propanol concentration was 0.1 ml/L. The control aquarium contained only test water. Stock solutions were weighed prior to the start of the dosing system and at test termination to determine the total consumption of stock solution per aquarium.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM

- Length at study initiation (length definition, mean, range and SD): 5.4 +/- 0.4 cm

- Weight at study initiation (mean and range, SD): 1.5 +/- 0.4 g

- Culture conditions: Fish were held and tested under a 16/8 light/dark cycle.

- Observations: Fish were monitored daily for mortality and symptoms of intoxication.

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

40 - 60 mg/L as CaCO3

Test temperature:

12+/-1°C

pH:

7.4 - 7.6

Dissolved oxygen:

10.8 - 11.7 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 0 (Solvent control; iso-propanol), 0.16, 0.28, 0.50, 0.89, 1.58, 2.81, and 5.00 mg/L.

Analytical results confirm that stock solutions were 80-90% of nominal values and the test substance was stable for the duration of the test. Measured concentrations ranged from 13-56% of nominal concentrations. The lower percentages were at the higher test concentrations, at or above the limit of water solubility (~0.93 mg/L).

Details on test conditions:

TEST SYSTEM

- Test vessels: The aquaria were made of glass and had a size of 32 x 36 x 38 cm (L x D x H). The test volumes amounted to 40 L. About 4 hours before the start of the test the aquaria were filled with the respective test medium by starting the water flow and the dosing system.
Immediately before the start of the test.

- No. of organisms per vessel: 10

- No. of vessels per concentration (replicates): 1

- No. of vessels per control (replicates): 1

- No. of vessels per vehicle control (replicates): 1

TEST MEDIUM / WATER PARAMETERS

- Culture medium different from test medium: No. Reconstituted water prepared by adding salt stock solutions to demineralized
water (conductivity < 0.2 μmho/cm).

- Intervals of water quality measurement: Dissolved oxygen and pH were also measured daily.  Water temperature was monitored and recorded hourly in the control aquaria.

Reference substance (positive control):

not specified

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

0.11 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

0.46 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Remarks on result:

other: calculated independently of report author

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

0.28 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

3.02 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Remarks on result:

other: 95% CL 1.58-5.00

Details on results:

- Mortality of control: No mortalities or symptoms of intoxication occurred in the control or solvent control groups.

- Effect concentrations exceeding solubility of substance in test medium: Most test concentrations tested were above the limit of water solubility for this compound.  Measured concentrations were significantly lower than nominal concentrations, reflecting the low water solubility of the compound.

Reported statistics and error estimates:

The LC50 value was calculated by the binomial probability method.

Sublethal observations / clinical signs:

Table 1. Results of analysis of test media

 

Nominal concentration (mg/L)	Day 0 measured concentration (mg/L)	Day 4 measured concentration (mg/L)	Mean measured concentration (mg/L)
0 (Control)	-	-	-
0 (Solvent control)	-	-	-
0.16	0.08	0.09	0.09
0.28	0.10	0.12	0.11
0.50	0.07	0.28	0.18
0.89	0.26	0.21	0.24
1.58	0.37	0.37	0.37
2.81	0.32	0.56	0.44
5.00	0.43	0.74	0.59

 

 Table 2. Test results – percentage mortalities throughout the test

 

Nominal concentration (mg/L)	4 hours	24 hours	48 hours	72 hours	96 hours
0 (Control)	0	0	0	0	0
0 (Solvent control)	0	0	0	0	0
0.16	0	0	0	0	0
0.28	0	0	0	0	0
0.50	0	0	0	0	0
0.89	0	0	0	0	0
1.58	0	0	0	0	0
2.81	0	0	10	20	40
5.00	0	0	10	70	100

 

Validity criteria fulfilled:

yes

Conclusions:

A 96-hr LC50 value of 3.02 mg/L and NOEC of 0.28 mg/L have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss based on nominal concentrations. A 96-hr LC50 value of 0.46 mg/L and NOEC of 0.11 mg/L have been re-calculated based on mean measured concentrations.

Description of key information

A 96-hr LC₅₀ value of 3.02 mg/L and NOEC of 0.28 mg/L have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss based on nominal concentrations. A 96-hr LC₅₀ value of 0.46 mg/L and NOEC of 0.11 mg/L have been re-calculated based on mean measured concentrations. The results of this test have been selected as the lowest definitive value from two reliable tests.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.46 mg/L

Additional information

A 96-hour LC₅₀ value of 3.02 mg/l and NOEC value of 0.28 mg/l have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss based on nominal concentrations. A 96-hr LC₅₀ value of 0.46 mg/l and NOEC value of 0.11 mg/l have been re-calculated based on mean measured concentrations (Bayer, 1991).

The results of this test have been selected as key because they give the lowest definitive value from two reliable tests.

In the second reliable test with HMDS:

A 48-hour LC₅₀ value of 1.27 mg/l has been determined for the effects of HMDS on mortality of Oryzias latipes based on nominal concentrations (Kurume Research Laboratories, 1995).

Two further studies are available but they are of unassignable reliability:

A 96-hour LC₅₀ value of >13.5 mg/l has been determined for the effects of HMDS on mortality of Cyprinus carpio based on measured concentrations (Huls Infracor, 1999).

A 9-day LC₅₀ value of >0.095 mg/l has been determined for the effects of HMDS on mortality of Oncorhynchus mykiss based on measured concentrations (DCC, 1990).