1,1,1,3,5,5,5-heptamethyltrisiloxane

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:

2011-05-30 to 2011-06-10

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

For the determination of the actual test item concentrations in this semi-static test, quadruplicate samples were taken from the test item treatment just before the start of the first and of the last renewal periods (Days 0 and 3). At the end of these renewal periods (Days 1 and 4), additional quadruplicate samples were taken for determination of the stability of the test item during the renewal periods of 24 hours. At each sampling date, one sample was also taken from the solvent control.

The samples were taken via septum, without opening the Schott flasks. All samples were analysed immediately after sampling.

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

The preparation of the test medium was based on the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures, 2000.

Due to the low solubility of the test item, the organic solvent N,N-dimethylformamide (DMF) was used for the test item dosage. The solvent was chosen based on its solubilising properties and its relative non-toxicity to fish.

An application solution was prepared just before the start of the test and before the start of each test medium renewal by dissolving 22 mg of test item (dosed in the range: 22.01 and 22.07 mg) in 11 mL of DMF. Until application, the application solution was kept in a completely filled glass flask tightly closed with a septum lid.

For application, 1070 µL of the application solution was taken from the flask using a Hamilton syringe, without opening the flask (through septum), and was injected (via septum in the Schott flask) into 10.7 litres of the test water to prepare the test medium with the concentration of 0.20 mg/L. Thus, the concentration of the solvent DMF in the test water was 100 µL/L. For homogeneous distribution of the test item in the test water, the Schott flask was smoothly shaken.

For the solvent control, the same amount of DMF was injected as for the test medium. For the control, test water without addition of test item or solvent was used.

The test medium was freshly prepared just before the introduction of the fish (=start of the test) and before each test medium renewal.

Test organisms (species):

Danio rerio (previous name: Brachydanio rerio)

Details on test organisms:

TEST ORGANISM
The study was performed with zebra fish (Brachydanio rerio). The fish were obtained from a breeding culture at Harlan Laboratories. No medication was applied during holding and acclimatization. Prior to test start, the test fish were acclimated for one week to the test water and temperature. During holding and acclimatization until one day before the start of the test, the fish were fed with a commercial fish diet (Tetra Min® Hauptfutter, supplied by TETRA-Werke, 49304 Melle / Germany). During holding and acclimatization, no fish died in the test fish batch and all fish were healthy.

From the acclimated test fish batch, 10 fish were measured at the start of the test. The mean body length of the fish was 2.7 ± 0.09 cm (Mean ± SD), the mean body wet weight was 0.12 ± 0.03 g (Mean ± SD).

The test method and test species are recommended by the international test guidelines.

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

96 h

Hardness:

125 mg/L as CaCO3

Test temperature:

21 °C

pH:

7.0 to 7.3

Dissolved oxygen:

at least 7.8 mg/L

Salinity:

n/a

Nominal and measured concentrations:

At the start of the test medium renewal periods, the measured test item concentrations were 0.199 and 0.189 mg/L, corresponding to 99 and 95% of the nominal value (0.200 mg/L), respectively. At the end of the medium renewal periods, the measured test item concentrations were 0.046 and 0.076 mg/L corresponding to 23 and 38% of the nominal value, respectively. The mean measured test concentration (calculated as the average of the geometric means of the concentrations of the start and end of each medium renewal period) was 0.108 mg/L.

Details on test conditions:

Study design: A limit test was performed in accordance with the threshold approach requiring that the fish test should be performed with a single concentration close to or slightly higher than the lowest EC50 value obtained in tests with algae and daphnia. The threshold approach (based on the Guidance on Information Requirements and Chemical Safety Assessment, ECHA (2008) was used to demonstrate, that zebra fish is not the most sensitive species for 1,1,1,3,5,5,5 Heptamethyltrisiloxane up to the maximum solubility of the test item in the used test water.

The EC50 values for 1,1,1,3,5,5,5-Heptamethyltrisiloxane obtained in the algal and daphnia toxicity tests (Harlan Laboratories Studies B62875 and B62853, respectively) were above the nominal value of 200 µg/L, and thus, above the maximum solubility of the test item in test water. Solubility of the test item in HPLC grade water determined in Harlan Laboratories Study B79727 was determined to be 0.020 mg/L. Based on these previous information, the concentration chosen for the fish limit test was nominal 0.200 mg/L.

The test item is known to be highly volatile. Therefore, a semi-static test with daily test medium renewal was performed to keep the concentration of the test item in the test medium as stable as possible during the test period of 96 hours.

During this semi-static test, the test fish were daily placed into a new test vessel with freshly prepared and air saturated test medium of the corresponding treatment.

At the start of the exposure, 7 fish were introduced into each test vessel in a random order. The loading rate was 0.8 g fish wet weight per litre test medium. Thus, the requirement of a loading rate not exceeding 1 g fish/L was fulfilled.


Test vessels: Since the test item is highly volatile, the test was performed in a closed system. One Schott flask with a volumetric capacity of 10.7 L was used for each treatment. Each Schott flask was completely filled with test medium to avoid any headspace in the flask and was tightly sealed with a septum lid.

Dilution water: Reconstituted test water was used in the study. It consisted of analytical grade salts dissolved in purified water to obtain the following nominal concentrations:
CaCl2 × 2H2O: 147 mg/L
MgSO4 × 7H2O: 61.5 mg/L
NaHCO3: 32.5 mg/L
KCl: 2.9 mg/L
Water Hardness: 125 mg/L as CaCO3
Alkalinity: 0.4 mmol/L

Conditions: The water temperature in the test vessels was maintained at 21 °C. Since the test item is highly volatile and a closed system with a septum lid was used (see Section 3.5), the test media were saturated with air prior application of the test item and introduction of the fish. No aeration during the exposure period was performed. However, the oxygen saturation was monitored on a regular basis.

A 16 hour light to 8-hour dark photoperiod, with a 30-minute transition period was used (light intensity during the light period was approximately within the range of 180 to 480 Lux).

The test duration was 96 hours and the fish were not fed during the test.

The ratio of Ca:Mg and Na:K was 4:1 and 10:1, respectively, based on molarity. The test water was aerated prior to the preparation of the test medium until oxygen saturation was reached.

Observations: The test fish were observed for mortality and visible abnormalities after approximately 3, 24, 48, 72 and 96 hours test duration.

Water quality: The water temperature, pH values and oxygen concentrations were measured for each treatment at the start of the test and in each freshly prepared and old test medium. The pH was measured with Handylab pH 11, (serial number 08460020, Schott AG, Hattenbergstr. 10, 55122 Mainz, Germany). The dissolved oxygen concentrations and water temperature were measured with Oxi 330i (serial number 03090010, WTW GmbH, Dr. Karl-Slevogt-Str.1, 82362 Weilheim, Germany).

Reference substance (positive control):

no

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 0.108 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 0.108 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Reported statistics and error estimates:

The NOEC and LC0 were determined directly from the raw data. The LOEC, LC100 and LC50 at the observation times could not be quantified due to the absence of a toxic effect of the test item at the tested concentration.

Sublethal observations / clinical signs:

Table 1. Test results

Loading rate [mg/L]	Mean measured concentration [mg/L]	Number of abnormal and dead fish / number of dead fish Type of visible abnormalities
		Observation time
		3 hours	24 hours	48 hours	72 hours	96 hours
Control	--	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0
Solvent control	--	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0
0.200	0.108	0 / 0	0 / 0	0 / 0	0 / 0	0 / 0
LC50*		>0.108mg/L

Validity criteria fulfilled:

yes

Conclusions:

A 96-hour LC50 value of >0.108 mg/L and a NOEC of ≥0.108 mg/L have been determined for the effects of the test substance on mortality of Brachydanio rerio (new name Danio rerio) based on geometric mean measured concentrations.

Description of key information

Short-term toxicity to fish: 96-h LC₅₀: >0.108 mg/l (measured) (highest concentration tested) (OECD Guideline 203 (Fish, Acute Toxicity Test)).

Additional information

A 96-hour LC₅₀ value of >0.108 mg/l has been determined for the effects of the registration substance on mortality of Brachydanio rerio (new name Danio rerio) based on geometric mean measured concentrations.

It is likely that the test organisms were exposed to the parent substance.

The water solubility limit of the test substance has been determined in a separate study to be 0.02 mg/l.

A 96-hour LC₅₀ of >100 mg/l and NOEC of ≥100 mg/l have also been determined for the effects of the read-across substance, trimethoxysilane (CAS 2487-90-3) on mortality of Oncorhynchus mykiss. It is likely that the test organisms were exposed to the hydrolysis products of the substance. Read-across from trimethoxysilane is not used to fulfil any data-gap, but is used to demonstrate that presence of the Si-H bond does not cause toxic effects. These data indicate that Si-H further reactions with electrophilic compounds are not likely to occur or do not affect short-term toxicity.