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Short-term toxicity to fish

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Endpoint:
short-term toxicity to fish
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The result was obtained by an appropriate predictive method
Principles of method if other than guideline:
The ECOSAR ‘neutral organics’ QSARs for acute data have been applied and the effect concentrations calculated using log Kow and molar mass as input variables. An additional factor of *0.2 has been applied to the results.

The USEPA model ECOSAR was used as the basis for the estimation. This method is well-validated for ‘neutral organics’, i.e. those which act by a general narcotic mechanism, the potency of which is usually related to log Kow. Its scope is acute and long-term effects for the three standard trophic levels.
The method was validated for use with organosilicon compounds with a high weight percent of Si and limited or no additional functionality. Many of the reliable data for the category are limit values, therefore, the data were considered in terms of the range of theE(L)C50, in accordance with normal classification bands:    
E(L)C50 < 1 mg/l;
E(L)C50 in the range > 1 mg/l to 10 mg/l;
E(L)C50 in the range > 10 mg/l to 100 mg/l;
E(L)C50 > 100 mg/l.

In broad terms ECOSAR predicted correctly for most substances for each trophic level. However, performance was improved significantly by application of a factor of 0.2 to each predicted value (expressed in mg/l). This is equivalent to saying that the organosilicon substances are slightly more toxic than the general ECOSAR ‘neutral organics’ regression lines, although still well within the range of each model. The factor of 0.2 is applicable to fish,Daphniaand algae, across the whole range of log Kowvalues.
It is concluded that the acute effects of the substances in the sub-category can therefore be predicted from ECOSAR, with a minor modification.
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
31.6 mg/L
Remarks on result:
other: Based on O[Si](O)(c1ccccc1)c2ccccc2 and log Kow of -2.4
Conclusions:
A 96 h LC50 value of 31.6 mg/L was obtained for the hydrolysis product of the submission substance using an appropriate calculation method. The results are considered to be reliable.
Endpoint:
short-term toxicity to fish
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2004-02-13 to 2004-02-20
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 203 (Fish, Acute Toxicity Test)
Qualifier:
according to
Guideline:
EPA OPPTS 850.1075 (Freshwater and Saltwater Fish Acute Toxicity Test)
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0 (Control), 6.5, 11, 18, 30, and 50 mg/L.

- Sampling method: Samples were collected from the each test chamber of each concentration at test initiation, mid-point (48-hours), and test termination. Test solution samples were collected at mid-depth, placed in glass vials, and analyzed immediately.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 60L primary stock was prepared in an 80L glass aquarium by mixing diphenylsilanediol in dilution water (Wildlife International, Ltd. well water) at a nominal concentration of 100 mg/L. The test solutions were prepared at nominal concentrations of 6.5, 11, 18, 30, and 50 mg/L by proportional dilution. The primary stock was mixed for approximately 20.5 hours using a top-down, electric mixer. After stirring and before transfer, the stock had a clear and colorless appearance with white particles on the water surface. Test solutions were prepared by transferring primary stock into test chambers that contained the appropriate amount of dilution water. A clean plastic container was used to transfer the primary stock into the appropriate measuring container (e.g. glass graduated cylinder or calibrated glass jar). The measured primary stock was then transferred into the test chamber and stirred with a stainless steel whisk for approximately one minute.

At test initiation, the appearance of test solutions in all test concentrations was clear and colourless, with a slight amount of white particles at the water surface in the 30 and 50 mg/L test concentrations. The number of particles increased with concentration. At test termination, test solutions were clear and colorless with slight amounts of white particles at the water surface in all test concentrations, with the number of particles increasing with concentration. While the particles were visible, they did not appear to affect the measured test concentrations.

- Controls: Dilution water (Wildlife International, Ltd. well water).
Test organisms (species):
Oncorhynchus mykiss (previous name: Salmo gairdneri)
Details on test organisms:
TEST ORGANISM

Rainbow trout used in the test were hatched on December 1, 2003 and were obtained as juveniles from Thomas Fish Company, Anderson, California. Identification of the species was verified by the supplier.

All fish used in the test were from the same source and year class, and the length of the longest fish measured at test termination was no more than twice the length of the shortest. The average total length of 10 negative control fish measured at the end of the test was 5.3 cm, with a range of 4.8 to 5.9 cm. The average wet weight (blotted dry) of 10 negative control fish measured at the end of the test was 1.2 grams, with a range of 1.0 to 1.7 grams. Loading was defined as the total wet weight of fish per liter of test water and was 0.48 g fish/L.

The rainbow trout were held for at least 14 days prior to the test in water from the same source and at approximately the same temperature as used during the test. During the 14-day holding period preceding the test, water temperatures ranged from 11.8 to 12.3°C, measured with a hand-held liquid-in-glass thermometer. The pH of the water ranged from 8.3 to 8.6, measured with a Fisher Scientific Accumet Model 915 pH meter. Dissolved oxygen concentrations ranged from 10.1 to 10.6 mg/L (≥93% of saturation).

During the holding period, the rainbow trout were fed daily a commercially-prepared diet supplied by Zeigler Brothers, Inc., Gardners, Pennsylvania. The fish were not fed for at least two days prior to the test or during the test.

During the 14-day period prior to the test no mortalities occurred and the fish showed no signs of disease or stress. At test initiation, the rainbow trout were collected from the holding tank and impartially distributed two at a time to the test chambers until each contained 10 fish.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Post exposure observation period:
None
Hardness:
132 mg/L as CaCO3


Test temperature:
12.1 - 12.9 ºC



pH:
8.2-8.6
Dissolved oxygen:
7.8-9.7 mg/L
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 0 (Control),6.5, 11, 18, 30, and 50 mg/L.

Mean measured concentrations: -, 5.5, 9.5, 16, 27 and 44 mg/L, representing -, 85, 86, 89, 90 and 88% of nominal concentrations, respectively.

The results of the study are interpreted with reference to the mean measured test concentrations.
Details on test conditions:
TEST SYSTEM

- Test vessel: Test chambers consisted of 38-L stainless steel aquaria containing approximately 25 L of test solution. The depth of test solution in a representative test chamber was 19.6 cm. Each test chamber was labeled with the project number, test concentration and replicate. Test chambers were impartially positioned in a temperature-controlled environmental chamber set to maintain the desired test temperature throughout the test period.

- Renewal rate of test solution: None - static test

- No. of organisms per vessel: 10

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

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

- Biomass loading rate: 0.48 g fish/L


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: The water used for culturing and testing was freshwater obtained from a well approximately 40 meters deep located on the Wildlife International, Ltd. site. The well water is characterized as moderately-hard water. The well water was passed through a sand filter to remove particles greater than approximately 25 μm, and pumped into a 37,800-L storage tank where the water was aerated with
spray nozzles. Prior to use, the water again was filtered (0.45 μm) to remove microorganisms and fine particles.

- Hardness: 120-136 mg/L as CaCO3

- Alkalinity: 174-184 mg/L as CaCO3

- Conductivity: 290-305 mhos/cm

- Culture medium different from test medium: no

- Intervals of water quality measurement: daily


OTHER TEST CONDITIONS

- Adjustment of pH: no

- Lighting: Fluorescent light bulbs (Colortone 50) that emit wavelengths similar to natural sunlight were used for illumination of the culture and test chambers. A photoperiod of 16 hours of light and 8 hours of darkness was controlled with an automatic timer. A 30-minute transition period of low light intensity was provided when lights went on and off to avoid sudden changes in lighting. Light intensity at test initiation was 300 lux at the surface of the water of one representative test chamber.

- Temperature: The target test temperature during the study was 12 ± 1ºC. Temperature was measured in each test chamber at the beginning and end of the test and at approximately 24-hour intervals during the test. Temperature also was measured continuously in one negative control test chamber.

Dissolved oygen, pH and hardness: Dissolved oxygen and pH were measured in each test chamber at the beginning and end of the test and at approximately 24-hour intervals during the test. Hardness, alkalinity and specific conductance were measured in the dilution water at the beginning of the test.


EFFECT PARAMETERS MEASURED: All organisms were observed periodically to determine the numbers of mortalities in each treatment and control group. The numbers of individuals exhibiting signs of toxicity or abnormal behavior also were evaluated. Observations were made approximately 4, 24, 48, 72 and 96 hours after test initiation.


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 1.7
Reference substance (positive control):
no
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
39 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mortality
Details on results:
Biological observations: Rainbow trout in the negative control group appeared healthy and normal throughout the test. After 96-hours of exposure, all fish in the 5.5, 9.5 and 16 mg/L treatment groups also appeared healthy and normal, with no mortality or overt signs of toxicity observed. At 96-hours, four fish in the 27 mg/L treatment group were observed to be surfacing at the water surface for unusually long periods of time, and two fish were exhibiting loss of equilibrium, while all the other fish appeared normal. Percent mortality at test termination in the 44 mg/L treatment group was 75%, with the remaining fish lying on the bottom of the test chambers.




Reported statistics and error estimates:
The mortality data were analyzed using the computer program of C. E. Stephan. The program was designed to calculate the LC50 value and the 95% confidence interval by probit analysis, the moving average method, and binomial probability with nonlinear interpolation. In this study, binomial probability was used to calculate the 96-hour LC50 value. There was <50% mortality at at 24, 48 and 72 hours, which precluded the statistical calculation of LC50 values. Therefore, the 24, 48 and 72-hour EC50 values was determined by visual interpretation of the mortality and observation data.

Table 1. Results of analysis of test media

 

Nominal test substance concentration (mg/L)

Mean measured concentration (mg/L)

Mean measured concentration as percentage of nominal

0 (Control)

-

-

6.5

5.5

85

11

9.5

86

18

16

89

30

27

90

50

44

88

 

Table 2. Test results

 

Mean measured concentration (mg/L)

Mean percentage mortality after 24 hours

Mean percentage mortality after 48 hours

Mean percentage mortality after 72 hours 

Mean percentage mortality after 96 hours 

0 (Control)

0

0

 0  0

5.5

0

0

 0  0

9.5

0

0

 0  0

16

0

0

 0  0

27

0

0

 0  0

44

0

5

 35  75

 

Validity criteria fulfilled:
yes
Conclusions:
A 96-hour LC50 of 39 mg/L have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss based on mean measured concentrations. Due to structural similarities of the subtances, read across of these endpoints to 80-10-4 is considered valid and representative.
Endpoint:
short-term toxicity to fish
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to the attached justification for grouping of substances in IUCLID Section 13.
Reason / purpose:
read-across source
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
39 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mortality

Description of key information

96-hour LC50 = 39 mg/L

Key value for chemical safety assessment

LC50 for freshwater fish:
39 mg/L

Additional information

Data were not available for dichloro(diphenyl)silane (CAS 80-10-4). However due to its rapid rate of hydrolysis (half-life 10 seconds) it is more relevant to consider the hydrolysis product, diphenylsilanediol, as under conditions relevant to ecotoxicity testing, exposure will predominantly be to the hydrolysis product. Measured data were available for the diphenylsilanediol. A 96 hour LC50 of 39 mg/l was determined for Oncorhynchus mykiss based on a study conducted according to OECD guideline 203 (Wildlife international ltd, 2004a). This study is considered reliable and was selected as key. This is supported by QSAR calculated 96 hr LC50 of 31.6 mg/l.