Registration Dossier

Administrative data

Endpoint:
short-term toxicity to fish
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: OECD/EU guideline study conducted to the principles of good laboratory practice

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2009

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 203 (Fish, Acute Toxicity Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.1 (Acute Toxicity for Fish)
Deviations:
no
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Pre-study solubility work indicated that it was not possible to obtain a testable solution of the test material using traditional methods (e.g. ultrasonication, high-shear mixing). The test material is poorly water soluble and known to rapidly degrade in water to give t-butyldimethylsilanol and 3-(dimethoxymethylsilyl)-propane-1-thiol. As such, and in accordance with the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (OECD 23, 2000), it was considered appropriate to expose the test organisms to the test material degradation products. Due to the volatility of 3-(dimethoxymethylsilyl)-propane-1-thiol, chemical analysis of the test preparations was conducted for t-butyldimethylsilanol alone.

Sampling and analysis

Analytical monitoring:
yes
Details on sampling:
Nominal concentrations of 10, 18, 32, 56, and 100% v/v saturated solution
Semi-static test with complete renewal of medium every 24h. Media analysed at start and end of each 24h period.
Concentrations of t-butyldimethylsilanol were as follows
0h (new): 23.9, 45.5, 72.1, 129, 241mg/l respectively
24h (old): 22.9, 44.3, 75.4, 131, 234mg/l respectively
24h (new): 24.7, 43.8, 76.8, 258mg/l respectively (56% nominal not analysed)
48h (old): 20.8, 36.2, 68.2mg/l respectively (56% & 100% nominal not analysed)
48h (new): 24.5, 44.2, 79.3, 262mg/l respectively (56% nominal not analysed)
72h (old): 23.5, 33.5, 70.7mg/l respectively (56% & 100% nominal not analysed)
72h (new): 26.0, 44.2, 68.9, 218mg/l respectively (56% nominal not analysed)
96h (old): 20.6, 29.7, 63.7mg/l respectively (56% & 100% nominal not analysed)

Test solutions

Vehicle:
no
Details on test solutions:
An amount of test material (11.25g) was dispersed in 22.5l of dechlorinated tap water using a propellor stirrer at approximately 1500rpm at 14°C for 24h. Undissolved test material was removed via filtration through a 0.2µm Sartorius Sartopore filter, with the initial 500ml being discarded to precondition the filter, to produce a 100% v/v saturated solution of the test material degradation products, which was also the highest test concentration. A sample was immediately taken for chemical analysis. Aliquots of the saturated solution (2.0, 3.6, 6.4, and 11.2l) were then further diluted to 20l, by mixing with a flat-bladed mixer for 1min, to prepare the remainder of the test series.

Test organisms

Test organisms (species):
Oncorhynchus mykiss (previous name: Salmo gairdneri)
Details on test organisms:
Supplier: Brow Well Fisheries Ltd, Hebden, near Skipton, Yorkshire, UK

Juveniles were maintained in a glass fibre tank with a single pass water renewal system. There was less than 1% mortality in the stock fish population during the 7 days prior to the start of the test. They were fed commercial trout pellets that were discontinued approximately 24h prior to the start of the definitive test. Test fish had a mean standard length and weight of 5.6cm and 2.69g at the end of the definitive test. They were acclimatised to test conditions from 15 July 2009 to 26 July 2009.

Test conditions: 16h/8h light/dark lighting cycle with 20min dawn/dusk transition periods; 14°C; dissolved oxygen 8.8mgO2/l; water hardness approximately 140mg/l as CaCO3.

Study design

Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Post exposure observation period:
None

Test conditions

Hardness:
ca. 140mg/l as CaCO3
Test temperature:
14°C
pH:
7.6-8.0
Dissolved oxygen:
8.8mg/l
Nominal and measured concentrations:
Nominal concentrations: 10%, 18%, 32%, 56%, 100% saturated solution

Concentrations of t-butyldimethylsilanol were as follows
0h (new): 23.9, 45.5, 72.1, 129, 241mg/l respectively
24h (old): 22.9, 44.3, 75.4, 131, 234mg/l respectively
24h (new): 24.7, 43.8, 76.8, 258mg/l respectively (56% nominal not analysed)
48h (old): 20.8, 36.2, 68.2mg/l respectively (56% & 100% nominal not analysed)
48h (new): 24.5, 44.2, 79.3, 262mg/l respectively (56% nominal not analysed)
72h (old): 23.5, 33.5, 70.7mg/l respectively (56% & 100% nominal not analysed)
72h (new): 26.0, 44.2, 68.9, 218mg/l respectively (56% nominal not analysed)
96h (old): 20.6, 29.7, 63.7mg/l respectively (56% & 100% nominal not analysed)
Details on test conditions:
TEST SYSTEM
- Test vessel: 20l, glass exposure vessels, covered to reduce evaporation
- Aeration: via narrow bore glass tubes
- Renewal rate of test solution (frequency/flow rate): 24h (semi-static test)
- No. of organisms per vessel: 7
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- Biomass loading rate: 0.94g/l


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: tap water dechlorinated by passage through activated carbon filter (Purite Series 500) and partly softened (Elga Nimbus 1248D Duplex Water Softener)


OTHER TEST CONDITIONS
- Adjustment of pH: not applicable
- Photoperiod: 16h/8h light/dark cycle with 20min transition periods


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : mortalities and sublethal effects of exposure were recorded at 3, 6, 24, 48, 72, and 96h after the start of exposure. The criteria of death were taken to be the absence of both respiratory movement and response to physical stimulation.
Reference substance (positive control):
no

Results and discussion

Effect concentrationsopen allclose all
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
26 other: % v/v
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality
Remarks on result:
other: 95%CL=22-30%
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
18 other: % v/v
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality
Details on results:
No deaths occurred during the study at 0%, 10%, or 18% nominal. 0% mortality.
At 32% nominal, there were 6/7 found moribund after 0.5h exposure. These fish were killed and classed as mortalities for the following (3h) observational time point. 86% mortality.
All 7 fish were found dead after 0.5h exposure at the 56% and 100% nominal concentration levels. 100% mortality.
Reported statistics and error estimates:
Lc50 and CL were calculated by the trimmed Spearman-Karber method using ToxCalc computer software

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
Given that the test organisms were exposed to a mixture of degradation products and that toxicity cannot be attributed to a single degradation product or mixture of such products but to the test material and its degradation products as a whole, the results are based on the nominal test material degradation products concentrations only.

The 96h LC50 is 26% v/v (95% CL 22-30% v/v). The NOEC is 18%.