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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:
2003-11-18 to 2003-11-20
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
The study was conducted according to the appropriate OECD guideline, in accordance with GLP and analytical monitoring was carried out. However the test medium was prepared from serial dilutions of a stock solution where the parent compound and the hydrolysis product have different water solubilities.
Qualifier:
according to guideline
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: all

- Sampling method: at 0 h and 48 h

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

- Method: The test material was dissolved directly in reconstituted water to make a stock solution of 100 mg/L in 2L volume. Aliquots were taken from this stock solution and dispersed in 2 L reconstituted water to make the rest of the exposure concentrations. Each prepared concentration was inverted several times to ensure adequate mixing and homogeneity.
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Source: in-house laboratory cultures

- Age at study initiation (mean and range, SD): 1st instar, <24 h

- Method of breeding: Adult Daphnia were maintained in polypropylene vessels containing approximately 2 litres of reconstituted water in a temperature controlled room at approximately 21°C. The lighting cycle was controlled to give a 16 hours light and 8 hours darkness cycle with 20 minute dawn and dusk
transition periods. Culture conditions ensured that reproduction was by parthenogenesis.

- Feeding during test: not fed


ACCLIMATION

- Acclimation period: in-house bread in similar conditions to the test

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

- Type and amount of food: Each culture was fed daily with a suspension of algae (Chlorella sp.).
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Test temperature:
approx. 20°C
pH:
8.0-8.1
Nominal and measured concentrations:
Nominal concentrations: 1.0, 1.8, 3.2, 5.6, 10, 18, 32, 56 and 100 mg/L.
Measured concentrations: Analysis of the test solutions at 0 hours showed measured concentrations of parent test material to range from 67% to 97% of nominal with the exception of the 1.0 mg/L test concentration which showed a measured concentration of 1% of nominal. Analysis at 48 hours showed a marked decline in measured concentrations of parent test material with concentrations ranging from
Details on test conditions:
TEST SYSTEM

- Test vessel: jars

- Material, size, headspace, fill volume: 250 ml glass jars filled with 200 ml test medium.

- Aeration: no

- No. of organisms per vessel: 10

- No. of vessels per concentration (replicates): 2

- No. of vessels per control (replicates): 2


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: reconstituted freshwater

- Culture medium different from test medium: no

- Intervals of water quality measurement: temperature was recorded throughout the test; DO and pH were recorded at the start and the end of the test.


OTHER TEST CONDITIONS

- Adjustment of pH: not reported

- Photoperiod: 16 h light, 8 h darkness

- Light intensity: not reported


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : immobility at 24 h and 48 h


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2


- Range finding study

- Test concentrations: 0.1, 1.0,10 and 100 mg/L

- Results used to determine the conditions for the definitive study: 48 h EC50 10-100 mg/L
Reference substance (positive control):
no
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
20 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: 15-29
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
3.1 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Remarks:
parent substance
Basis for effect:
mobility
Details on results:
- Mortality of control: 0%

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: the substance has been reported to hydrolyse rapidly, the hydrolysis product is also though to be unstable. Therefore the organisms were exposed to a mixture of the hydrolysis product and the parent substance. The test medium were all clear.

- Effect concentrations exceeding solubility of substance in test medium: no
Reported statistics and error estimates:
The EC50 value and associated confidence limits at 48 hours were calculated by the maximum likelihood probit method (Finney 1971) using the ToxCalc computer software package (ToxCalc 1999).

Table 1. Cumulative mortality (average of 2 replicates).

 Concentration (mg/L)     Cumulative mortality (%)   
 24 h  48 h
 Control  0  0
 1.0  0  0
 1.8  0  0
 3.2  0  10
 5.6  0  25
 10  0  40
 18  0  45
 32  0  60
 56  0  75
 100  0  85

Table 2. Analytical monitoring data

 Sample     Nominal concentration (mg/L)     Hydrolysis product     Parent test material     Total Peak Area    Geometric mean - hydrolysis product  Geometric mean - parent  
 measured (mg/L)  % nominal  measured (mg/L)  % nominal  measured (mg/L)  % nominal  (0 -24 h)  (0 -24 h)
 0 h  Control  <LOQ  -  <LOQ  -  <LOQ  -  <LOQ  <LOQ
 18  0.419  2  12.2  68  12.6  70  0.09  3.1
 32  1.10 21.9   68  23.0  72  0.42 9.5
 56  1.71  3  41.3  74  43.0  77  0.61  10.5
 100  7.27  7  133 133   140  141  1.37  18.5
 180  15.7  9  261  145  277  154  3.2  33.8
 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  0.3  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

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.

Given that the test material was unstable in test medium and that the hydrolysis products were indicated to be unstable it was concluded that the test organisms were exposed to a mixture of components.

Validity criteria fulfilled:
yes
Conclusions:
A 48 h EC50 nominal value of 20 mg/L, equivalent to 3.1-9.5 mg/l parent substance (measured, geometric mean) has been determined for the effects of the test substance to the freshwater invertebrate Daphnia magna. The test substance hydrolyses rapidly while the hydrolysis product is also subject to further hydrolysis (epoxy ring opening). Therefore the organisms were exposed to a mixture of the test substance and the hydrolysis product. The results are interpreted with reference to the parent substance as the analysis of the study indicates that the hydrolysis half life is between 16 and 24 hours.

Description of key information

Short-term toxicity to invertebrates: 48 h EC50 value of 20 mg/l (nominal), 3.1-9.5 mg/l (measured parent, geometric mean) (OECD 202). The EC50 is equivalent to 15.5 mg/l when expressed in terms of the hydrolysis product [3-(2,3-epoxypropoxy)propyl]methylsilanediol.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
15.5 mg/L

Additional information

A reliable 48 h EC50 value of 20 mg/l (nominal), equivalent to measured concentrations of 3.1-9.5 mg/l parent substance (geometric mean), has been determined for the effects of the test substance to the freshwater invertebrate Daphnia magna.

The test substance hydrolyses rapidly while the hydrolysis product is also subject to further hydrolysis (epoxy ring opening). Therefore the organisms were exposed to a mixture of the test substance and the hydrolysis product. The study report discusses the two hydrolysis steps and concludes that the substance had a hydrolysis half-life 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 8.0 - 8.1). 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) * 20 mg/l = 15.5 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.