Triethoxy(3-thiocyanatopropyl)silane

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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP. However, there was no analysis of exposure concentrations, the solvent concentration was higher than recommended by the OECD guideline and exposure duration was only 24 hours rather than the guideline 48 hours.

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

yes

Remarks:

The concentration of tertiary butyl alcohol (TBA) used in the preparation of the test media (320 μl/l) exceeded the maximum (100 mg/l) recommended in the OECD guideline.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Stock solutions of the test substance were prepared in tertiary butyl alcohol at concentrations of 100, 180 and 320 g/l. The stock solutions were added to 100 ml of dilution water in amounts required to produce the desired test concentrations. The final concentration of TBA in the media (320 μl/l) exceeded the maximum concentration recommended in the OECD test guideline (100 mg/l).

- Controls: Dilution water and Dilution water+ Tertiary butyl alcohol at 100 μl/l.

- Chemical name of vehicle (organic solvent, emulsifier or dispersant): tertiary butyl alcohol (TBA)

- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)): 320 μl/l.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Source: Laboratory culture in the testing laboratory

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

- Feeding during test: none

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

215 mg/l as CaCO3

Test temperature:

20 +/-1ºC

pH:

7.8-7.9

Dissolved oxygen:

≥8.4 mg/l

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 0+320 μl/l TBA (Solvent control), 10, 18, 32, 58 and 100 mg/l.

Test concentrations all contained 320 μl/l TBA

Details on test conditions:

TEST SYSTEM

- Test vessel: Beakers

- Type: open

- Material, size, headspace, fill volume: glass, 150 mL with 100 ml of test medium

- Aeration: none

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

- No. of organisms per vessel: 5

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

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

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

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Reconstituted freshwater (DSWL standard water) prepared by adding salts to groundwater from Linschoten, the Netherlands.

- Ca/mg ratio: 1.37 mmol/l Ca3+ : 0.78 mmol/l Mg3+

- 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 h light, 8 h dark

EFFECT PARAMETERS MEASURED: mobility after 24 and 48 hours

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 1.8

- Range finding study: yes but results not reported.

Reference substance (positive control):

no

Key result

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

29 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 21-39

Duration:

24 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:

EC100

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Reported statistics and error estimates:

The EC50 values and their confidence intervals were calculated using a parametric model (Kooijman, 1981).

Kooijman, S.A.L.M. (1981). Parametric analyses of mortality rates in bioassays. Water Research, 15: 107-119.

Table 1. Test results

Nominal test substance concentration (mg/l)	Mean percentage immobilisation after 24 hours
0 (Control)	0
0 (TBA control)	0
10	0
18	55
32	65
58	55
100	90

Validity criteria fulfilled:

yes

Conclusions:

A 24-hour EC50 value of 29 mg/l (21-39 mg/L) and NOEC of 10 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna. The results are interpreted with reference to nominal concentrations of the test substance. However, the test substance is susceptible to hydrolysis and it is likely that the test organisms were exposed to a mixture of the parent compound and the hydrolysis products of the substance.

Description of key information

EC₅₀ (24 h): 29 mg/l (nominal), based on mobility of Daphnia magna (OECD Guideline 202).

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

29 mg/L

Additional information

A 24-hour EC₅₀ value of 29 mg/l (nominal) has been determined for the effects of the registered substance, triethoxy(3-thiocyanatopropyl)silane (CAS 34708-08-2; EC No. 252-161-3), on mobility of Daphnia magna (TNO, 1990b). In view of the test media preparation method and exposure regime it is likely that the test organisms were exposed to a mixture of the parent substance and its hydrolysis products.

The exposure duration during this test was only 24 hours rather than 48 hours as recommended by OECD TG 202. It is therefore possible that the toxicity of the substance could have been underestimated and the EC₅₀ value may have been lower, had the test duration been 48 hours. A long-term toxicity to aquatic invertebrates study is ongoing, conducted according to OECD TG 211 and in compliance with GLP. In this study it is proposed to conduct a Dose Range Finding study, the results of which will be compared with the current short-term aquatic invertebrate toxicity study by TNO (1990b).

The test solution was prepared using tert-butyl alcohol (TBA) as a solvent. The recommended solvent concentration (100 mg/l) was exceeded during the test, with TBA at a concentration of approximately 250 mg/l (based on a density of 0.781 g/ml). However, TBA is a low molecular weight (MW = 74.123 g/mol), highly water soluble (1000 g/l at 25°C) solvent with a low log K_ow value (0.32 at 22.5°C) (ECHA Substance Evaluation Conclusion document, 2019). The substance is not classified as toxic to the aquatic environment according to the harmonised classification and labelling (CLP) or CLP inventory for this substance and E(L)C₅₀ values are >100 mg/l, indicating low toxicity (WHO, 1987; ECHA Substance Evaluation Conclusion document, 2019). The lowest E(L)C₅₀ value according to the REACH disseminated dossier is 933 mg/l for invertebrates, which is higher than the concentration of TBA used in this study (ECHA, 2022). It is therefore unlikely that TBA significantly affected the results of the test.

In addition, the test substance is susceptible to hydrolysis and it is likely that the test organisms were exposed to a mixture of the parent compound and the hydrolysis products of the substance.

Above a concentration of approximately 1000 mg/l, dimeric/oligomeric, cyclic or cross-linked condensation products could potentially form over time in the aqueous test media. There was no report of undissolved material (parent substance or precipitated by products) indicated in the study report for this test.

A functional group associated with ecotoxicity by a specific mode of action (thiocyanate) is present in both the registration substance and the silanol hydrolysis product, and the effects seen are attributed to this. It is therefore reasonable to conclude that both the parent and hydrolysis product could contribute to any effects observed.

References:

WHO (1987) International Programme on Chemical Safety, Environmental Health Criteria 65, Butanols: Four Isomers. World Health Organisation, Geneva. Report date: 1987. Available at: https://iris.who.int/bitstream/handle/10665/37266/9241542659-eng.pdf?sequence=1&isAllowed=y

ECHA (2019) Substance Evaluation Conclusion as required by REACH Article 48 and Evaluation Report for 2-methylpropan-2-ol (tertiary butyl alcohol) EC No 200-889-7, CAS No 75-65-0. Evaluating Member State(s): United Kingdom. Report date: October 2019. Available at: https://echa.europa.eu/documents/10162/528c3841-87b8-d5c9-4269-d7cef27d815b

ECHA (2022) 2-methylpropan-2-ol. Available at: https://echa.europa.eu/registration-dossier/-/registered-dossier/14112/6/2/1. Date accessed: 3 May 2022.