Trichloro(hexadecyl)silane

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2002-04-15 to 2002-07-25

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

yes

Remarks:

Test media were not prepared in accordance with OECD guidance for testing difficult substances

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Nominal treatments: 100 mg/L and 10 mg/L (10% concentration of 100 mg/L water-soluble fraction)

- Sampling method: A sample of test media were taken from all treatments at the start (before introducing the test organisms) and at the end of the test.

- Sample storage conditions before analysis: Not reported

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A water-soluble fraction of the test substance was prepared by mixing 100 mg/l of the test substance with dilution water for 48 hours and then filtering (0.45 μm) to remove undissolved test substance. The water-soluble fraction was tested undiluted and at one-tenth of its original concentration.

- Controls: Dilution water

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Strain: IRCHA

- Source: LPT Laboratory Culture

- Age at study initiation (mean and range, SD): 6-24 hours

ACCLIMATION

- Acclimation period: at least one week

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

- Type and amount of food: algae (Scenedesmus subspicatus) plus a small quantity of sewage from the aerated phase of treatment

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

250 mg/L as CaCO3

Test temperature:

20+/-1ºC

pH:

7.61-8.15

Dissolved oxygen:

≥80% ASV

Nominal and measured concentrations:

Nominal loading rates: 0(Control), 100 mg/L and 10 mg/L (10% concentration of 100 mg/L water-soluble fraction).

A loading rate of 100 mg/L is above the expected solubility of the substance in the test medium. Measured dissolved organic carbon concentrations were below 5% of the theoretical values at the start and end of the test.

Details on test conditions:

- Aeration: none

- No. of organisms per vessel: 5

- No. of vessels per concentration (replicates): 4

- No. of vessels per control (replicates): 4

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: aerated reconstituted water

- Alkalinity: 0.8 mmol/L

- Ca/mg ratio: 4:1

- Culture medium different from test medium: no

- Intervals of water quality measurement: Start and end ot test

OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 h light/8 h dark

- Light intensity: 500 Lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Mobility after 24 and 48 hours

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 10

Reference substance (positive control):

no

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Duration:

48 h

Dose descriptor:

NOELR

Effect conc.:

< 10 other: percent concentration of the 100 mg/l water-soluble fraction

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Conclusions:

An EL50 of >100 mg/l was reported for the test substance. The result is considered reliable.

Reference 2

Endpoint:

short-term toxicity to aquatic invertebrates

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 attached justification for grouping of substances in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Reference 3

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

disregarded due to major methodological deficiencies

Study period:

2002-05-07 to 2003-02-14

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

yes

Remarks:

Test media were not prepared in accordance with OECD guidelines for testing difficult substances

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Nominal treatments: 0(Control), 0.464, 1.00, 2.15, 4.64, 10.0 and 100 mg/l.

- Sampling method: An aliquot of test medium from all test concentrations at the start of the test before filling the test vessels. A combined aliquot was collected from the test media from all four exposure vessels of all test concentrations at the end of the test (48 hours).

- Sample storage conditions before analysis: The samples were stored at -20ºC prior to analysis.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Two sets of test media were prepared. The first set were prepared from a stock solution of the test substance prepared by adding 100 mg/l of the test substance to dilution water and stirring for 4 hours followed by passage through a 0.45 μm cellulose acetate filter. Other treatments were prepared by dilution of the filtrate. The second set were prepared from a stock solution prepared in a similar way except that it had been shaken for 48 hours.

- Controls: Dilution water

- Evidence of undissolved material (e.g. precipitate, surface film, etc): It is likely that the solubility of the test substance will have been exceeded in the stages of test media preparation prior to filtration of the stock solutions.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Source: IRChA, France

- Age at study initiation (mean and range, SD): 6-24 hours

- Method of breeding: Laboratory stock culture

- Feeding during test: None

ACCLIMATION

- Acclimation period: At least 7 days

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

- Type and amount of food: Unicellular algae (Scenedesmus subspicatus) and a small amount of aerated sewage.

- Feeding frequency: no data

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

250 mg/l as CaCO3

Test temperature:

20+/-1ºC

pH:

First set of test media: 7.06-8.09 in 0.464 to 10.0 mg/l nominal treatments and <5.6 in 100 mg/l nominal treatment.

First set of test media: 7.59-8.00 in 0.464 to 10.0 mg/l nominal treatments and approximately 5.0 in 100 mg/l nominal treatment.

It is likely that pH effects will have contributed to effects observed in the 100 mg/l nominal treatments in both tests.

Dissolved oxygen:

≥80% ASV

Salinity:

not applicable

Nominal and measured concentrations:

Nominal treatments: 0(Control), 0.464, 1.00, 2.15, 4.64, 10.0 and 100 mg/l.

Measured DOC concentrations in the test media prepared from the stock solution that had been shaken for 48 hours were <5% of the theoretical values. The test media prepared from the other stock solution were not analysed.

The results are reported and interpreted in the test report with reference to the nominal concentrations. The results have also been interpreted here with reference to the estimated concentration corresponding to the 48-h EC50 value. This is considered appropriate given the disparity between the measured and theoretical concentrations.

Details on test conditions:

TEST SYSTEM

- Test vessel:

- Type: no data

- Material, size: glass, 50 ml

- Aeration: none

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

- No. of organisms per vessel: 5

- No. of vessels per concentration (replicates): 4

- No. of vessels per control (replicates): 4

- Biomass loading rate: 1 daphnid/10 ml

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Reconstituted fresh water prepared by adding salts to demineralised water.

- Alkalinity: 0.8 mmol/l

- Ca/mg ratio: 4:1

- Culture medium different from test medium: no

- Intervals of water quality measurement: Start and end of test

OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 hours light, 8 hours dark

- Light intensity:500 lux (+/-20%)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Mobility after 24 and 48 hours

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2.2-10

- Range finding study: no

Reference substance (positive control):

no

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

7 mg/L

Nominal / measured:

nominal

Conc. based on:

other: hydrolysis product (first test)

Basis for effect:

mobility

Remarks on result:

other: 4-13

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

14 mg/L

Nominal / measured:

nominal

Conc. based on:

other: hydrolysis product (second test)

Basis for effect:

mobility

Remarks on result:

other: 9-24

Duration:

48 h

Dose descriptor:

NOELR

Effect conc.:

0.464 mg/L

Nominal / measured:

nominal

Conc. based on:

other: hydrolysis product (first and second test)

Basis for effect:

mobility

Details on results:

- Behavioural abnormalities: no data

- Mortality of control: First test = 2.5%, Second test = 0

- Other adverse effects control: none

- Other adverse effects in treatments: It is likely that low pH will have contributed to the effects observed in the highest (nominal 100 mg/l) treatment in both tests.

Reported statistics and error estimates:

The EL50 value based on nominal loading rates was calculated by linear regression employing probit analysis (Probit Program Version 1.5, U.S. Environmental Protection Agency, 1992).

The EC50 value determined on the basis of measured concentrations and the NOEC (NOELR) values were obtained directly from the raw data.

Table 1. Test results (first and second tests)

Nominal test substance concentration (mg/l)	Mean percentage immobilisation after 24 hours - first test	Mean percentage immobilisation after 48 hours - first test	Mean percentage immobilisation after 24 hours - second test	Mean percentage immobilisation after 48 hours - second test
0 (Control)	0	2.5	0	0
0.464	0	0	0	0
1.00	0	10	5	5
2.15	10	40	5	5
4.64	15	45	15	20
10.0	40	60	15	25
100	45	90	100	100

Table 2. Measured dissolved organic carbon (DOC) concentrations in the test media prepared for the second test.

Nominal concentration of test substance (mg/l)	Theoretical DOC concentration (mg/l)	Actual DOC concentration at start of test (mg/l)	Actual DOC concentration at end of test (mg/l)
0.462	0.2	<1.0	1.3
1.00	0.5	<1.0	<1.0
2.15	1.1	<1.0	<1.0
4.64	2.5	1.1	1.6
10.0	5.3	1.3	<1.0
100	53.4	1.4	2.0

Limit of Quantitation (LOQ) = 10 mg/l

Limit of Detection (LOD) = 1.0 mg/l

Validity criteria fulfilled:

no

Conclusions:

48-h EL50 values of 7 and 14 mg/l and a NOELR of 0.464 mg/l have been determined in two tests for the effects of the test substance on mobility of Daphnia magna based on nominal test substance concentration. The study was severely compromised by significant methodological deficiencies or use of unsuitable test system; results not fit for purpose.

Description of key information

EL50 (48) > 100 mg/L (nominal, Daphnia magna, OECD 202, based on read across to CAS No. 16415-12-6)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

> 100 mg/L

Additional information

A study is available for the registered substance, which reported two EL50 values of 7 and 14 mg/l from two separate experiments. However, due to deficiencies in the methodology, the reliability could not be determined. Therefore, data was read-across from the structural analogue substance trimethoxy(hexadecyl)silane(CAS No. 16415-12-6) for the assessment of acute toxicity towards aquatic invertebrates. Both substances hydrolyse in the aquatic environment, but with very different hydrolysis rates (DT50 = << 2 min at room temperature and pH 7 (target); DT50 > 14 d at pH 7 (source)). However, both form the same silanol hydrolysis product hexadecylsilanetriol. The second hydrolysis product of the target substance is hydrochloric acid, while the second hydrolysis product of the source compound is methanol. Hydrochloric acid and methanol are both well described substances in the public domain literature and both are not expected to contribute to the overall aquatic toxicity of target and source substances (OECD SIDS, 2002; OECD SIDS 2004). Therefore, hydrochloric acid and methanol can be disregarded in the environmental hazard assessment. Further information can be found in an attached read-across justification in Section 13 of IUCLID.

 

In the valid acute toxicity test on aquatic invertebrates according to OECD guideline 202 and under GLP conditions, Daphnia magna was exposed to trimethoxy(hexadecyl)silane over 48 h to the nominal loading rates of 0 (control), 100 mg/L and 10 mg/L (10% concentration of 100 mg/L water-soluble fraction). The test solutions were analytically monitored via DOC analysis. Since the tested substance is poorly water soluble analytical results showed that measured DOC concentrations were <5% of nominal. An EL50 value of >100 mg/L (nominal loading rate) was determined in this study.

The result was obtained under static test conditions. In view of the slow hydrolysis rate and exposure regime it is likely that the test organisms were exposed predominantly to the parent of the tested source substance.

 

References:

OECD, 2002. Hydrogen Chloride - SIDS Initial Assessment Report for SIAM 15, Boston, USA: UNEP Publications.

OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.