Cyclohexyldimethoxymethylsilane

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995-10-10 to 1995-10-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Deviations:

no

Qualifier:

equivalent or similar 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: control, 1, 3.2, 10, 32 and 100 mg/l, both replicates.

- Sampling method: Samples were taken at 0 h and 48 h and extracted eimmediately upon preparation.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: 200 mg was dispersed in reconsituted water with the aid of ultrasonic disruption and the volume adjusted to 2 L to give a 100 mg/l test concentration from which dilutions were made to obtain nominal test concentrations.

- Evidence of undissolved material (e.g. precipitate, surface film, etc): The reports states some degradation product adsorped to the glass vessels used in the study.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Common name: water flea

- Source: strain supplied from Insitut National de Recherche Chimique Appliquee (IRCHA), France. Cutltured in lab.

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

- Method of breeding: Adult daphnia were maintained in propylene vessels containing approx. 2L water at 21degC. Lighting cycle: 16 h light, 8 h dark. Fed algae Chlorella spp. predominantly, daily.

- Feeding during test: no


ACCLIMATION

- Acclimation period: 24 h

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

- Health during acclimation (any mortality observed): not reported

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Test temperature:

21 degC

pH:

7.7

Dissolved oxygen:

7.9-8.4

Nominal and measured concentrations:

Nominal concentrations: 0, 1, 1.8, 3.2, 5.6, 10, 18, 32, 56 and 100 mg/l

Details on test conditions:

TEST SYSTEM

- Test vessel: jar

- Type (delete if not applicable): closed

- Material, size, headspace, fill volume: glass, 250 ml vessel filled with 200 ml test solution

- Aeration: no

- Renewal rate of test solution (frequency/flow rate): static test

- 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 water

- Alkalinity: 270 mg/l as CaCO3

- Conductivity: <5 uS/cm

- Culture medium different from test medium: no

- Intervals of water quality measurement: water temperature was recorded daily. pH and DO were recorded at the start and termination of the study.

OTHER TEST CONDITIONS
- Adjustment of pH: not reported
- Photoperiod: 16 h light, 8 h dark
- Light intensity: not reported

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : any immobilisation or adverse reactions to exposure were measured at 24 h and 48 h.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.8-2

- Range finding study
- Test concentrations: 0.1, 1, 10 and 100 mg/l
- Results used to determine the conditions for the definitive study: immobiliastion only observed at 100 mg/l.

Reference substance (positive control):

no

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

31 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: (27-35)

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

24 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: (21-29)

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

8 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: (7.1-9.0) measured arithmetric average at the end of the study

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

6.9 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: (6.0-7.9) measured arithmetric average at the end of the study

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

13 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

- Behavioural abnormalities: none observed

- Mortality of control: 0%

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: the substance is reported to have adhered to the glassware, but it is unclear if this was observed during the range finding test only or also during the definitive test.

Reported statistics and error estimates:

EC50 values were calculated by moving average method of Thompson (1947)

Table 1. Analytical analysis results.

Nominal concentration	Concentration found (mg/l)
	0 h	% nominal	48 h	% nominal
Control	<LOQ	-	<LOQ	-
1.0	0.973	97	0.288	29
1.8	-	-	0.487	27
3.2	2.91	91	0.830	26
5.6	-	-	1.64	29
10	10.3	103	3.21	32
18	-	-	4.84	27
32	31.0	97	9.78	31
56	-	-	14.3	26
100	200	200*	32.5	32

Analysis of the test preparations at 0 h showed the measured concentrations to be near nominal, with the exception of the 100 mg/l test group which gave a measured value of 200% of nominal. * This was considered to be due to analytical variation given that the 32 mg/l test sample was serially diluted from the 100 mg/l sample, was near to the nominal concentration. Additionally the 48 h value for this concentration was in line with the rest of the concentrations. Analysis of the test preparations at 48 h showed measured concentrations ranging from 26 -32% nominal. This is due to the substance being hydrolytically unstable.

Table 2. Mortality during the 48 h.

Nominal concentration (mg/l)	Percentage mortality
	24 h	48 h
Control	0	0
1.0	0	0
1.8	0	0
3.2	0	0
5.6	0	0
10	0	0
18	0	25
32	55	70
56	100	100
100	100	100

Average of two replicates containing 10 daphnids in each.

Geometric means have been calculated by the reviewer based on the initial and 48-h old measured concentrations:

Nominal concentration (mg/l)	Geometric mean (mg/l)	Factor
Control	<LOQ	-
1.0	0.53	1.88
1.8	-	-
3.2	1.55	2.06
5.6	-	-
10	5.75	1.74
18	-	-
32	17.4	1.84
56	-	-
100*	-	-

* This sample was 200% at the start of the test so the result is not taken into account to calculate the geometric mean. The variation was considered to be due to analytical variation given that the 32 mg/l test sample was serially diluted from the 100 mg/l sample, was near to the nominal concentration.

The EC50 geometric mean is calculated by divding the EC50 value of 24 mg/l times a factor of 1.8 = 13 mg/l

Validity criteria fulfilled:

yes

Conclusions:

A 48 h EC50 nominal value of 24 mg/L, corresponding to a geometric mean value of 13 mg/L parent substance, has been determined for the effects of the test substance on immobility of Daphnia magna. The test substance hydrolyses in water and it is likely that the test organisms were predominantly exposed to the hydrolysis products of the substance because the study was conducted under a static regime. It is unclear if during the definitive test the substance adhered to the glass of the test vessels. The majority of the immobilised organisms 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 have been attributed to the parent substance and not the hydrolysis product.

Description of key information

(48-h) 13 mg/l (parent substance) D. magna, reliability 1

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

13 mg/L

Additional information

A 48-h EC₅₀ nominal value of 24 mg/l, equivalent to 13 mg/l geometric mean of the parent substance, has been determined for the effects of cyclohexyldimethoxymethylsilane on mobility of Daphnia magna (SafePharm Laboratories, 1996d). The test substance hydrolyses in water and it is likely that the test organisms were exposed to a mixture of the parent substance and the hydrolysis products of the substance because the study was conducted under a static regime. The parent substance is thought to be more toxic than the silanol hydrolysis product. While there are no data to confirm this assumption, it is supported by the pattern of observed effects, i.e. no further toxicity was observed beyond the initial 24 hours of exposure, where the organisms would have been predominantly exposed to the parent substance. This interpretation is consistent with the estimated log K_ow values of the substance and hydrolysis product, 4.3 and 1.9 respectively.

This study has been chosen as key as it is the most conservative reliable study available for this substance. Other studies report EC₅₀ values in the range 66-140 mg/l with D. magna.