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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2011-02-28 to 2011-03-24
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
For the determination of the actual test item concentrations, three samples (samples were taken out separately from replicate test flasks 1 to 3) were taken from the test medium of the single test concentration at the start and end of each test medium renewal period. At the same time, one sample was also taken from the solvent control.

The concentration of the test substance, 1,1,1,3,5,5,5-Heptamethyltrisiloxane, was analytically determined of each sample immediately after sampling.
Vehicle:
yes
Details on test solutions:
Due to the low solubility of the test item the organic solvent N,N-dimethylformamide (DMF) was used to solubilize the test item. The test substance is highly volatile therefore measures were taken to reduce volatilization (closed containers, no headspace, freshly prepared media).

The application solution was prepared just before each test medium renewal by dissolving 22.13 and 22.14 mg of test item in 10.7 mL of DMF on Day 0 and 1, respectively. Until application, the application solution was kept in a completely filled glass flask tightly closed with a septum lid.

For application, 13µl of the application solution was taken out from the flask with a Hamilton syringe, without opening the flask (through septum), and was injected (via septum) into the test water to prepare the test medium with the concentration of 0.20 mg/L. For homogeneous distribution of the test item in the test water the test flasks were smoothly shaken.

For the preparation of the solvent control, the same volume of DMF (without test item) was injected in the test water.
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Species: Daphnia magna Straus

- Strain: Clone 5

- Source: A clone of Daphnia magna was originally supplied by the University of Sheffield / UK in 1992. Since that time, the clone has been bred at Harlan Laboratories in reconstituted water of the quality identical to the water quality used in the tests (in respect to pH, main ions, and total hardness) and under temperature and light conditions identical to those of the tests.

- Feeding: During breeding, daphnids are generally fed three times a week with an algal suspension of the green algae Desmodesmus subspicatus CHODAT, Strain No. 86.81 SAG, supplied by the Collection of Algal Cultures (SAG, Institute for Plant Physiology, University of Göttingen, 37073 Göttingen / Germany) and cultivated at Harlan Laboratories under standardized conditions or a mixture of this algal suspension and a commercial fish diet (Tetra Min® Hauptfutter, supplied by TETRA-Werke, 49304 Melle / Germany).

- Age at study initiation (mean and range, SD): At the start of the test, the organisms used in the test were 6 24 hours old and were not first brood progeny.

Test type:
semi-static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
48 h
Hardness:
250 mg/l as CaCO3
Test temperature:
20 21 °C
pH:
7.8 - 8.0
Dissolved oxygen:
≥8.0 mg/l
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 0 (Control), 0 (Solvent control) and 0.20 mg/l.

At the start of the test medium renewal periods, the measured test substance concentrations were 0.252 and 0.358 mg/l (mean 0.31 mg/l), corresponding to 126 and 179% (mean 150%) of the nominal values. At the end of the medium renewal periods, the measured test substance concentrations were below LOQ (limit of quantification of the analytical method, LOQbio = 0.006 mg test substance/l). The geometric mean measured substance concentration (calculated as the average of the geometric means of the concentrations of the start and end of each medium renewal period) was 0.030 mg/l, which is approximately the solubility limit of the test substance in water as determined in Harlan Laboratories Study B79727 (0.02 mg/L).

The biological results are related to the geometric mean measured test substance concentration and the mean initial measured test substance concentration.

Details on test conditions:
TEST DESIGN

A semi-static test with test medium renewal after 24 hours was performed to keep the concentration of the test item in the test medium as stable as possible during the test period of 48 hours. After 24 hours, the test organisms were placed in clean test vessels with freshly prepared test medium.

The study design was based on the results of range-finding pre-tests (non-GLP).

For each treatment, 20 daphnids were used divided into four replicates of five daphnids each. The volume of test solution provided for each daphnid was 27 mL. Thus, the requirement of the test guidelines for the minimum volume of 2 mL test medium per daphnid was fulfilled. The daphnids were randomly distributed to the test vessels at initiation of the test.

OBSERVATIONS

The daphnids were observed for immobility after 24 and 48 hours of exposure (daphnids not being able to swim within 15 seconds after gentle agitation of the test beaker are considered to be immobilized).


WATER QUALITY

At the start and end of each test medium renewal period, the pH values, dissolved oxygen concentrations and water temperature were determined at each treatment. At the start of the renewal periods, these parameters were measured in a separate vessel prepared for measurement for each treatment. At the end of the renewal periods, the test medium of the treatment replicates used in the test was pooled for measurement.

The appearance of the test medium was visually recorded at the same time.
Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 0.03 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 0.03 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
- Mortality of control: 0
Results with reference substance (positive control):
For evaluation of the quality of the daphnia clone and the experimental conditions, potassium dichromate is tested as a positive control twice a year. The result of the latest positive control test in October 2010 (48-hour EC50: 0.56 mg/l, study C97643) showed that the sensitivity of the test organisms was within the internal historical range (48-hour EC50 from 2000 to 2010: 0.43 - 1.1 mg/l).
Reported statistics and error estimates:
The NOEC and EC0 were directly determined from the raw data. The EC50 and EC100 could not be calculated due to the absence of a toxic effect.

Table 1      Effect of 1,1,1,3,5,5,5-Heptamethyltrisiloxane on the Mobility of Daphnia magna

Nominal
test substance
concentration

Mean initial measured concentration

Geometric mean measured
concentration

No. of
daphnids
tested

Immobilized
daphnids after
24 hours

Immobilized
daphnids after
48 hours

(mg/l)

(mg/l)

(mg/l)

 

No.

%

No.

%

0 (Solvent Control)

--

--

20

0

0

0

0

0 (Control)

--

--

20

0

0

0

0

0.20

0.31

0.030

20

0

0

0

0

Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of >0.030 mg/l and NOEC of ≥0.030 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna based on geometric mean measured concentrations. The water solubility limit of the test substance has been determined in a separate study to be 0.02 mg/l.

The test substance is highly volatile. It is also likely that the test substance will hydrolyse rapidly in water. It is therefore appropriate to also consider the results with respect to the initial measured concentration. The mean initial measured concentration at the start of the two successive 24 hour exposure periods was 0.31 mg/l and so the corresponding 48-hour EC50 and NOEC values are >0.31 mg/l and NOEC of ≥0.31 mg/l respectively.

Description of key information

Short-term toxicity to invertebrates: 48-h EC50: >0.030 mg/l (geometric mean measured concentration) or >0.31 mg/l (mean initial measured concentration) (highest concentration tested) (OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)).

Key value for chemical safety assessment

Additional information

A 48-hour EC50 value of >0.030 mg/l has been determined for the effects of the test substance on mobility of Daphnia magna 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 48-hour EC50 of >100 mg/l has been determined for the effects of trimethoxysilane (CAS: 2487-90-3) on mobility of Daphnia magna. The test organisms will have been exposed to the hydrolysis products of the substances. Read-across of trimethoxysilane is not used to fulfil any data-gap, it is just used to demonstrate that reaction of the Si-H bond does not cause toxic effects.

Taken together the data indicate that the registered substance does not exhibit short-term toxicity to aquatic invertebrates at its solubility limit and that Si-H further reactions with electrophilic compounds are not likely to occur or do not affect short-term toxicity.