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Short-term toxicity to fish

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Reference
Endpoint:
short-term toxicity to fish
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003-11-17 to 2003-11-21
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to the appropriate OECD guideline, in accordance with GLP and analytical monitoring was carried out. However turbidity was observed in test media from 48 h.
Qualifier:
according to guideline
Guideline:
OECD Guideline 203 (Fish, Acute Toxicity Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: all

- Sampling method: direct from vessels

- Sample storage conditions before analysis: samples were analysed shortly after collection.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: 2000 mg of test substance was dissolved in 2 litres of dechlorinated tap water with ultrasonication to give a 1000 mg/L stock solution. Aliquots of this stock solution (360 and 640 ml) were each separately dispersed in a final volume of 20 litres of dechlorinated tap water and stirred using a flat bladed mixer for approximately 1 minute to give the 18 and 32 mg/L test concentrations respectively. To prepare the remaining test concentrations, amounts of test material (1120, 2000 and 3600 mg) were each separately dissolved in a final volume of 2 litres of dechlorinated tap water with the aid of ultrasonication prior to dispersion in a final volume of 20 litres of dechlorinated tap water and stirred using a flat bladed mixer for approximately 1 minute to give the 56, 100 and 180 mg/L test concentrations respectively. Stock solutions were inverted several times to ensure adequate mixing.

- Evidence of undissolved material (e.g. precipitate, surface film, etc): turbidity was reported in all concentrations after 48 h.
Test organisms (species):
Oncorhynchus mykiss (previous name: Salmo gairdneri)
Details on test organisms:
TEST ORGANISM

- Common name: rainbow trout

- Source: from Brow Well Fisheries Limited, Hebden, near Skipton, Yorkshire, UK and maintained in-house since 23 October 2003.

- Length at study termination: mean standard length = 4.4. cm (sd = 0.3)

- Weight at study termination: mean weight 1 g (sd = 0.25)

- Feeding during test: no


ACCLIMATION

- Acclimation period: 5-11-2003 to 17-11-2003

- Acclimation conditions (same as test or not): same as test

- Type and amount of food: commercial trout pellets were fed to the fish up to 24 h prior to the start of the test

- Health during acclimation (any mortality observed): 0% in the 7 days prior to the test
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Hardness:
100 mg/L as CaCO3
Test temperature:
ca. 14°C
pH:
range: 7.7-8.2
Dissolved oxygen:
≥9.4 mg
Nominal and measured concentrations:
Nominal concentrations: 18, 32, 56, 100 and 180 mg/L
Measured concentrations: Analysis of the test solutions at 0 hours showed measured concentrations of parent test material to range from 68% to 145% of nominal. Analysis at 96 hours showed a marked decline in measured concentrations of parent test material with concentrations ranging from 2% to 5% of nominal.
Details on test conditions:
TEST SYSTEM

- Test vessel: covered aquaria to reduce evaporation

- Material, size, headspace, fill volume: 20 L glass exposure vessels

- Aeration: yes, via a narrow bore glass tube

- No. of organisms per vessel: 10

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

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

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: dechlorinated tap water

- Culture medium different from test medium: not reported

- Intervals of water quality measurement: daily


OTHER TEST CONDITIONS

- Adjustment of pH: not reported

- Photoperiod: 16 h light, 8 h darkness


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : The number of mortalities and any sub-lethal effects of exposure in each test and control vessel were determined 3 and 6 hours after the start of exposure and then daily throughout the test until termination after 96 hours. Sub-lethal effects observed were swimming at the bottom of the test vessels with increased pigmentation and swimming at the bottom of the test vessels.

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

- Range finding study

- Test concentrations: 18 and 180 mg/L, semi-static

- Results used to determine the conditions for the definitive study: 100% fish were moribund at 180 mg/L after 48 h, these fish were killed.
Reference substance (positive control):
no
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
ca. 180 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality (fish)
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
ca. 37.4 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Remarks:
parent substance
Basis for effect:
mortality (fish)
Details on results:
- Behavioural abnormalities: Sub-lethal effects of exposure were observed at test concentrations of 100 mg/l and above.

- Other biological observations: The results of the definitive test differ slightly compared to the results of the second range-finding test which showed 100% mortality at 180 mg/l after 48 hours exposure. This difference was considered to be due to the fact that the second range-finding test was conducted under semi-static conditions, as evidence of instability was observed in the first range-finding test, whilst the definitive test was conducted under a static regime. However, the sub-lethal effects observed at 100 mg/L in the definitive test were comparable with those observed at 100 mg/L in the rangefinding test. Therefore, this was considered not to have affected the outcome or validity of the test.

- Mortality of control: 0%

- Other adverse effects control: none

- Abnormal responses: Throughout the test it was observed that the severity and number of sub-lethal effects observed in the fish at 100 and 180 mg/l declined over time. This was considered to possibly be due to instability of the test media.

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: the half life of the test material was determined to be less than 3 hours. In addition this work showed that the hydrolysis products themselves were possibly unstable. Therefore it was determined that the test organisms would be exposed to parent test material and hydrolysis products. After 96 h the test medium was cloudy and the turbidity increased with increasing concentrations. See Any other information on test material and methods for further details.
Reported statistics and error estimates:
No statistical analysis was undertaken because there was unsufficent data. However 50% mortality was achieved at the highest concentration and this was indicative to be the LC50.
Sublethal observations / clinical signs:

Analytical analysis results: Analysis of the test substance is presented in the table below. Examination of the chromatography indicated the presence of hydrolysis products in the 0 hour samples. As analytical standards for the hydrolysis products were not available their concentrations could not be determined.

The hydrolysis product of the substance is subject to further hydrolysis (epoxide ring opening). It is the opinion of the reviewer that this explains the difference between measured hydrolysis and expected concentration of hydrolysis product.

Table 1. Analytical monitoring data.

 Sample     Nominal concentration (mg/L)     Hydrolysis product     Parent Test Material      Total Peak Area    Geometric mean HP (0 -24 h) Geometric mean Parent (0 -24 h)
measured (mg/L)  % nominal  measured (mg/L)  % nominal  measured (mg/L)  % nominal    
 0 h  Control  <LOQ  -  <LOQ  -  <LOQ  -  <LOQ  <LOQ
 18  0.419  2  12.2  68  12.6  70  0.44  3.1
 32  1.1  3  21.9  68  23.0  72  3.1  6.1
 56  1.71  3  41.3  74  43.0  77  0.61  11.2
 100  7.27  7  133  133  140  141  1.37  19.9
 180  15.7  9  261  145  277  154  3.2  37.4
 96 h  Control  <LOQ  -  <LOQ  -  <LOQ  -  see above  see above
 18  0.0188  0.1  0.762  4  0.781  4  see above see above 
 32  0.162  0.5  1.43  4  1.59  5  see above  see above
 56  0.220  0.4  2.69  5  2.91  5  see above  see above
 100  0.259  03  2.57  3  2.83  3  see above  see above
 180  0.658  0.4  4.39  2  5.05  3  see above  see above

Mortality effects: At the 24-Hour time point, after approximately 29 hours exposure and at the 48-Hour time point two out of ten fish, one out of eight fish and one out of seven fish respectively were observed to be moribund at 180 mg/L. Due to the approach of the substantial severity limit (Animals (Scientific Procedures) Act 1986) these fish were killed and classed as mortalities for the following observational time point.

Table 2. Cumulative mortality data.

 Nominal concentrations (mg/L)     Cumulative mortality                 % mortality
 3 h  6 h  24 h  48 h  72 h  96 h  96 h
 Control  0  0  0  0  0  0  0
 18  0  0  0  0  0  0  0
32   0  0  0 0  0  0  0
 56  0  0  0  0  0  0  0
 100  0  0  0  0  0  0  0
 180  0  0  0  3  4  5  50
Validity criteria fulfilled:
yes
Conclusions:
A 96 h LC50 value of ca. 37 mg/l geometric mean of the parent substance, and 180 mg/l nominal, has been reported for the effects of the test substance on the mortality of the freshwater fish O. mykiss. 50% mortality was achieved at the highest concentration tested (180 mg/L) however, the test medium was observed to increase in turbidity with increasing concentration from 72h to 96h. Due to behavioural effects being observed from 3 h (consistent with epoxides) and mortalities being recorded from 48 h, it is thought that the effects are due to the toxicity of the substance rather than the turbidity observed. The reviewer of the report considers the turbidity to be caused by the formation of less soluble polymers in solution.

Description of key information

Short-term toxicity to fish: 96 h LC50 180 mg/l (nominal), 37 mg/l (measured parent, geometric mean) (OECD 203). The LC50 is equivalent to 139 mg/l when expressed in terms of the hydrolysis product [3-(2,3-epoxypropoxy)propyl]methylsilanediol.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Effect concentration:
139 mg/L

Additional information

A 96 h LC50 value of approximately 37 mg/l, geometric mean measured concentration of the parent substance, and 180 mg/l nominal concentration, has been reported for the effects of the registration substance on the mortality of the freshwater fish Oncorhynchus mykiss. 50% mortality was achieved at the highest concentration tested (180 mg/l).

However, the test medium was observed to increase in turbidity with increasing concentration from 48 h. The reviewer of the report considers the turbidity to be caused by the formation of less soluble polymers in solution.

 

Due to behavioural effects being observed from 3 h (consistent with epoxides) and mortalities being recorded from 29 h, it is thought that the effects are due to the toxicity of the substance rather than physical effects associated with undissolved materials. This is the only study available for this substance and has been chosen as key.

The study report discusses the potential for two hydrolysis reactions of the different functional groups and concludes that the substance had a hydrolysis half-life for removal of parent of approximately 3 hours under the test conditions. This is attributed by the reviewer to the reaction of alkoxy groups under elevated pH conditions of the test media (pH 7.7-8.2). Therefore the effects seen in the test are attributed to [3-(2,3-epoxypropoxy)propyl]methylsilanediol.

In view that the analytical results are for parent substance, it is appropriate to interpret the results in terms of nominal concentration.

 

The results may be expressed in terms of concentration of the hydrolysis product, (2,3-epoxypropoxy)propyl]methylsilanediol, by applying a molecular weight correction: (MW of silanol = 192.28 / MW of parent = 248.40) * 180 mg/l = 139 mg/l.

 

[3-(2,3-epoxypropoxy)propyl]methylsilanediol is susceptible to further hydrolysis reactions and the ultimate hydrolysis product 3-{3-[dihydroxy(methyl)silyl]propoxy}propane-1,2-diol is considered unlikely to exhibit significant ecotoxic effects based on QSAR estimated E(L)C50s >>100 mg/l (ECOSAR). The rate of reaction under environmental conditions is uncertain but the half-life is not expected to be more than a few days.