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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:
2010-04-20 to 2010-04-30
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study according to GLP. There were some acceptable deviations from the Guideline.
Qualifier:
according to guideline
Guideline:
OECD Guideline 203 (Fish, Acute Toxicity Test)
Version / remarks:
2010
Deviations:
yes
Remarks:
(Only 2 concentrations were tested and multiple exposures were used to define a single test.)
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
Biological Monitoring: All test vessels were examined after 0, 24, 48, 72 and 96 hours of exposure as follows: mortalities were recorded and dead fish removed, biological observations, including adverse effects (e.g., lethargy, loss of equilibrium) of the exposed rainbow trout, and observations of the physical characteristics of the test solutions (e.g., presence of precipitate, film on the solution's surface) were made and recorded. Effects for this study were based on death, defined as the lack of movement by the exposed organisms (i.e., absence of gill movement and reaction to gentle prodding).
Test organisms (species):
Oncorhynchus mykiss (previous name: Salmo gairdneri)
Details on test organisms:
Oncorhynchus mykiss, SSL Lot No. 10A39
Mean total length = 26 mm (range: 22 to 30 mm); N = 30
Mean wet weight = 0.12 g (range: 0.040 to 0.18 g); N = 30
Source: TroutLodge, Inc., Sumner, Washington
Test type:
flow-through
Water media type:
freshwater
Total exposure duration:
96 h
Hardness:
Total hardness as (CaCO3): 44 mg/L

Test temperature:
First exposure: 14-15°C
Second exposure: 6.4-7.4°C
pH:
First exposure: 6.3-6.5
Second exposure: 6.4-7.4
Dissolved oxygen:
First exposure: 8.9-10 mg/l
Second exposure: 8.4-9.5 mg/l
Salinity:
Not applicable
Nominal and measured concentrations:
100% of a water accommodated fraction (WAF)
Details on test conditions:
Test Conditions:
96-hour duration, 14 to 15 oC
Illumination of 66 to 96 footcandles (710 to 1000 lux)
Photoperiod of 16 hours light and 8 hours darkness
Dilution Water:
Laboratory well water
Total hardness as (CaCO3): 44 mg/L
Total alkalinity as (CaCO3): 20 mg/L
Specific conductance: 500 µmhos/cm
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
1.3 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mortality (fish)
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
1.9 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
mortality (fish)
Duration:
96 h
Dose descriptor:
LC100
Effect conc.:
2.9 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
mortality (fish)
Sublethal observations / clinical signs:

A definitive flow-through exposure was initiated on 20 April 2010 utilizing a flow rate of 48 mL/minute of dilution water (test substance application at a rate of 6 mL per 12 hours), but was terminated after 24 hours due to 100% mortality. The measured concentration of 2.9 mg a.i./L at test initiation is considered to represent actual exposure conditions. This exposure was included in the determination of the LC50 value.

A definitive exposure was conducted from 26 to 30 April 2010 using individual mixing chambers (i.e., 4-L Mariotte bottles equipped with side drains) to deliver control and treatment solutions.
 Each mixing chamber received approximately 96 mL/minute of dilution water from an individual FMI pump and delivered the test solution into the exposure vessels via an FMI pump and silicone tubing. Test substance was applied at a rate of 1 mL per 12 hours. Following 96 hours, no mortality or sub-lethal effects were observed. The geometric mean measured concentration (1.3 mg a.i./L) was considered to represent actual exposure concentrations. This exposure was used in the determination of the LC50 value.

The water quality parameters (pH, dissolved oxygen concentration, temperature) were unaffected by the concentrations of tetramethylsilane tested and remained within acceptable ranges for the survival of rainbow trout.

Analytical Results: The toxicant delivery system functioned properly during the pretest period and throughout the exposures.
 Analyses of the solutions during the pretest period established that the delivery apparatus functioned properly. Throughout the exposure periods, the control mixing vessel and all test solutions were observed to be clear and colorless with no visible evidence of undissolved test substance. The test substance mixing vessel(s) were observed to be clear and colorless with a visible layer of undissolved test substance on the surface of the solution(s).

The results of the analysis of the exposure solutions for tetramethylsilane concentration during the in-life portion of the exposures showed that eight of the nine quality control samples resulted in measured concentrations which were consistent with the predetermined range and ranged from 88.7 to 118% of the nominal fortified levels (0.00667, 0.100 and 1.00 mg a.i./L).
 These results established that the appropriate precision and quality control were maintained during the analysis of the exposure solutions. One of the nine QC samples was measured at 51.1% recovery. QC samples can be out of the acceptable range due to a number of factors, some of which are spiking, handling or instrument errors.

Biological Results:
The measured concentrations tested, the corresponding percent mortality, and observations recorded during the exposures are presented below:

Measured
             Cumulative
Conc.
                Percent
(mg a.i./L)
            Mortality(a)
               
Initiated 20 April 2010:
     
Control
              24 hr: 0 (0)
2.9
                      24 hr: 100 (5)
               
Initiated 26 April 2010
      
Control
              24, 48, 72, 96 hr: all were 0 (0)
1.3
                      24, 48, 72, 96 hr: all were 0 (0)
where (a) = Actual number of mortalities is presented in parentheses.

Validity criteria fulfilled:
yes
Conclusions:
The LC50 value was determined to be 1.9 mg a.i./L, using Spearman Karber estimates. Two data points (i.e., 100% mortality at 2.9 mg a.i./L and 0% mortality at 1.3 mg a.i./L) were used in determining the LC50 value. Due to the extremely steep dose response observed with this test substance, no data points with partial responses were generated. The No-Observed-Effect Concentration (NOEC) was determined to be 1.3 mg a.i./L.

Description of key information

A 96-hour LC50 value of 1.9 mg/l and NOEC of 1.3 mg/l have been determined for the effects of the test substance on Oncorhynchus mykiss.

Key value for chemical safety assessment

Additional information

Tetramethylsilane (TMS) is a highly volatile material with a very low boiling point. Due to the characteristics of the test substance and its behaviour in water, the study was conducted in a temperature-controlled room using a flow-through, closed system specifically designed for this testing in an attempt to minimize volatilization of tetramethylsilane during the 96-hour exposure.

The LC50 value was determined to be 1.9 mg active ingredient/L (mg a.i./L), using Spearman Karber estimates. Two data points (i.e., 100% mortality at 2.9 mg a.i./L and 0% mortality at 1.3 mg a.i./L) were used in determining the LC50 value. Due to the extremely steep dose response observed with this test substance, no data points with partial responses were generated. The No-Observed-Effect Concentration (NOEC) was determined to be 1.3 mg a.i./L.