Dichlorocyclohexylmethylsilane

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2002-06-10 to 2002-07-05

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

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: Control and all test concentrations containing surviving fish at 0, 24, 48 and 72 hours in fresh media and at 24, 48, 72 and 96 hours in old media.

- Sample storage conditions before analysis: The samples were extracted immediately after collection.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: The test media were prepared by direct dispersion of the test substance in the dilution water. Amounts of the test substance (0.16, 0.28, 0.50, 0.90 and 1.60 g) were separately dispersed in 20 L of dechlorinated tap water with the aid of propeller stirrers for approximately 5 minutes to give the treatment series of 8.0, 14, 25, 45 and 80 mg/L.

- Controls: Dechlorinated tap water

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM

- Common name: Rainbow trout

- Source: Parkwood trout farm, Wigmoor, Kent, U.K.

- Length at study initiation (length definition, mean, range and SD): 4.2+/-0.2 cm

- Weight at study initiation (mean and range, SD): 0.61+/-0.11 g

- Feeding during test: none


ACCLIMATION

- Acclimation period: 7 days

- Acclimation conditions: same as test

- Type and amount of food: Commercial trout pellets

- Feeding frequency: daily until the day prior to the test.

- Health during acclimation (any mortality observed): approximately 2% mortality in 7 days prior to test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

100 mg/L as CaCO3

Test temperature:

14ºC

pH:

7.3-7.4

Dissolved oxygen:

9.6-9.9 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Dilution water control), 8.0, 14, 25, 45 and 80 mg/L.

Mean measured concentrations in the 24-hour old treated media: 4.47, 6.07, 11.89, 21.87 and 37.80 mg/L. The reduction in concentration is attributed to the hydrolysis of the substance and adsorption to the test vessel.

The mean measured concentrations ranged between 43 and 56% of the nominal concentrations.

The results are interpreted with reference to nominal and mean measured concentrations.

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type: covered
- Material, size, headspace, fill volume: Glass, 20 litres with 20 L of test medium
- Aeration: continuously via narrow bore tube
- Renewal rate of test solution (frequency): daily
- No. of organisms per vessel: 10
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- No. of vessels per vehicle control (replicates): 1
- Biomass loading rate: 0.31 g/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Dechlorinated tap water
- Total organic carbon: 1 mg/l
- Chlorine: 0.22 mg/l (total)
- Conductivity: 382 μS/cm
- Culture medium different from test medium: no
- Intervals of water quality measurement: daily

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 16 h light, 8 h dark with a 20 minute transition period.
- Light intensity: not reported

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): mortality after 3, 6, 24, 48, 72 and 96 hours

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.8
- Range finding study
- Test concentrations: 1, 10 and 100 mg/L and 3.2 and 32 mg/L and 50 and 80 mg/L
- Results used to determine the conditions for the definitive study: no mortality at nominal concentrations of ≤32 mg/L but mortalities at the higher concentrations.

Reference substance (positive control):

no

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

14 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is likely to have been to a mixture of test substance and hydrolysis products

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

9.1 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Remarks:

but exposure is likely to have been to a mixture of test substance and hydrolysis products

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

6.1 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Remarks:

Mean measured concentrations of test material in 24-hour old test media. However exposure is likely to have been to a mixture of test substance and hydrolysis products.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

50 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is likely to have been to a mixture of test substance and hydrolysis products

Basis for effect:

mortality (fish)

Remarks on result:

other: 40-60

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

35 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Remarks:

but exposure is likely to have been to a mixture of test substance and hydrolysis products

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

24 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Remarks:

Mean measured concentrations of test material in 24-hour old test media. However exposure is likely to have been to a mixture of test substance and hydrolysis products.

Basis for effect:

mortality (fish)

Remarks on result:

other: 20-29

Details on results:

- Mortality of control: 0

- Other adverse effects control: none

Reported statistics and error estimates:

LC50 values and associated confidence intervals were calculated by the moving average method of Thompson (1947).

Sublethal observations / clinical signs:

Table 1. Results of analysis of test media

Nominal concentration of test substance (mg/l)	Mean measured concentration of substance in 24 -hour old test media (mg/l)	Mean measured concentration as percentage of nominal
0 (Control)	-	-
8.0	4.47	56
14	6.07	43
25	11.89	48
45	21.87	49
80	37.80	47

Table 2. Test results

Nominal concentration of test substance (mg/l)	Percentage mortality after 24 hours	Percentage mortality after 48 hours	Percentage mortality after 72 hours	Percentage mortality after 96 hours
0 (Control)	0	0	0	0
8.0	0	0	0	0
14	0	0	0	0
25	0	0	0	0
45	30	30	30	30
80	100	100	100	100

Geometric means have been calculated from the reviewer based on the measured concentrations at the start of the test/after each water renewal and 24 h after the water media renewal. The average of the geometric means of measured concentrations in fresh and 24 -h old media are presented in the table below.

Table 3. Geometric means of measured concentrations.

Nominal concentrations (mg/l)	Geometric mean (mg/l)	Factor
8	6.02	1.31
14	9.14	1.53
25	17.28	1.45
45	31.37	1.43
80	55.45	1.44

The LC50 geometric mean has been calculated based on the above factors. Therefore the LC50 nominal value of 50 mg/l has been divided by a factor of 1.4 to determine an LC50 geometric mean value of 35 mg/l.

It is unclear whether a significant part of the 50% of substance seen by the GC-MS is due to poor extraction efficiencies and so a good measure of the concentration in solution. The hexane would extract the non-polar parent and not the polar hydrolysis product.

Validity criteria fulfilled:

yes

Conclusions:

A 96-h LC50 value of 50 mg/L , equivalent to a geometric mean measured value of 35 mg/l, and NOEC of 14 mg/, equivalent to a geometric mean measured value of 9.1 mg/l, have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss based on nominal concentrations. When expressed in terms of mean measured concentrations of the substance in the 24-hour old test media the corresponding values were 24 and 6.1 mg/L. The test substance hydrolyses in water and it is likely that the test organisms were exposed to a mixture of test substance and hydrolysis products.

Description of key information

Short-term toxicity to fish: 96 hour LC₅₀ 50 mg/l and 35 mg/l (nominal and geometric mean measured respectively) (OECD TG 203), read-across from an analogous/structurally related substance, cyclohexyl(dimethoxy)methylsilane (CAS 17865-32-6). Measured analysis indicated loss of parent substance, therefore the observations in this study are attributed to the exposure of test organisms to a mixture of the parent and the hydrolysis products in the test system. The results expressed in terms of the silanol hydrolysis product cyclohexyl(methyl)silanediol are EC₅₀ 43 mg/l.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

43 mg/L

Additional information

There are no reliable short-term fish toxicity data available for dichloro(cyclohexyl)methylsilane (CAS 5578-42-7), therefore good quality data for an appropriate structural analogue, cyclohexyl(dimethoxy)methylsilane (CAS 17865-32-6), have been read across. Both substances share the same silanol hydrolysis product, cyclohexyl(methyl)silanediol. In the test with cyclohexyl(dimethoxy)methylsilane the observations are attributed to the exposure of test organisms to a mixture of the parent and the silanol hydrolysis products in the test system. There is no basis to expect that methanol significantly influenced the results of the test. The toxicity of cyclohexyl(methyl)silanediol is discussed further in the ecotoxicological information overview endpoint summary (additional information).

 

96 hour LC₅₀ values of 50 and 35 mg/l (nominal and geometric mean measured respectively) cyclohexyl(dimethoxy)methylsilane (CAS 17865-32-6) have been determined for the effects of on mortality of Oncorhynchus mykiss. In view of the test media preparation method and exposure regime it is likely that the test organisms were exposed predominantly to a mixture of the parent substance and hydrolysis products of the tested substance. The nominal test concentrations are supported by gas chromatography analysis. Because the relevant assessment entity is the silanol hydrolysis product cyclohexyl(methyl)silanediol, the nominal test substance concentration is used for chemical safety assessment with a molecular weight correction to reflect the concentration of cyclohexyl(methyl)silanediol:

(MW of silanol = 160.29 / MW of parent = 188.34) * [CONCENTRATION OF PARENT = 50] = EC₅₀ 43 mg/l.

This read-across is considered to be a worst-case scenario because the parent test substance, cyclohexyl(dimethoxy)methylsilane (CAS 17865-32-6), hydrolyses much more slowly than the registration substance, therefore organisms will have been exposed to the parent substance during the read-across tests, but would be unlikely to be exposed to parent substance if the registration substance were tested. Due to the log K_ow of cyclohexyldimethoxymethylsilane being 4.3, it is likely that the parent substance is more toxic than the silanol hydrolysis product. In addition, the majority of the immobilised daphnids were observed in the first 24 hours of the study where the organisms would have been exposed predominantly to the parent substance. Therefore the observed effects may be attributed to the parent substance rather than the hydrolysis products. The read-across is therefore very conservative.