Triethoxy(3-thiocyanatopropyl)silane

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991-06-10 to 1991-06-14

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.

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

yes

Remarks:

Three test media were assessed: 1)by direct addition of the substance and also using stock solutions of the test substance prepared in 2)tertiary butyl alcohol (TBA) and 3)in dimethylsulfoxide (DMSO). The exposure period was extended to 96-hours (nominal)

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 (TBA) and in dimethylsulfoxide (DMSO) and used to treat the test media prepared for independent tests (N.B. the highest concentrations in these tests was prepared by direct dispersion of the test substance into the algal growth medium). The final concentration of TBA and DMSO in each of the test substance concentrations was 100 μL/L. Test media were also prepared by direct addition followed by ultrasonication for 30 minutes.

- Controls: Dilution water, Dilution water + 100 μl/l TBA and Dilution water + 100 μl/l DMSO

- Chemical name of vehicle (organic solvent, emulsifier or dispersant): Tertiary butyl alcohol (TBA) and Dimethylsulfoxide (DMSO)

- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)): 100 μl/l

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM

- Strain: SAG 86.81

- Source (laboratory, culture collection): Collection of algal cultures, Institute for Plant Physiology, University of Göttingen, Germany.

- Method of cultivation: a pre-culture of algae in the exponential growth phase was prepared as described in the OECD test guideline using the medium described in Dutch Standard NPR 6505.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Remarks on exposure duration:

nominal

Hardness:

not reported

Test temperature:

23 +/-1ºC

pH:

The pH of the test media in which algae were not present was in the range 8.0-8.3 throughout the test.

The pH of the test media that did contain algae was in the range 8.2-8.4 after 3 days and 8.4-9.4 after 4 days.

Dissolved oxygen:

not reported

Salinity:

not applicable

Nominal and measured concentrations:

Nominal concentrations by direct addition: 0(Control), 0.032, 0.1, 0.32, 1.0, 3.2, 10, 32 and 101 mg/l.

Nominal concentrations using TBA solvent: 0(Control), 0(Control + 100 μl/l TBA), 0.032, 0.1, 0.32, 1.0, 3.2, 10, 32 and 126 mg/l. The latter concentration was prepared by direct dispersion of the test substance into the algal growth medium.

Nominal concentrations using DMSO solvent: 0(Control), 0(Control + 100 μl/l DMSO), 0.032, 0.1, 0.32, 1.0, 3.2, 10, 32 and 150 mg/l. The latter concentration was prepared by direct dispersion of the test substance into the algal growth medium.

Details on test conditions:

TEST SYSTEM

- Test vessel: Conical flask

- Type: covered with silicone sponge caps

- Material, size, headspace, fill volume: glass, 200 ml with 100 ml of test medium

- Aeration: none

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

- Initial cells density: 10000 cells/mL

- Control end cell density: 440000 - 526000 cells/ml after approximately 72 hours, 1332000 - 2220000 cells/ml after approximately 96 hours

- No. of vessels per concentration (replicates): 3

- No. of vessels per control (replicates): 6

- No. of vessels per vehicle control (replicates): 6


GROWTH MEDIUM

- Standard medium used: yes


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Algal growth medium prepare by adding nutrients and salts to Milli-Q filtered water. The medium was filter-sterilized before use.

- Culture medium different from test medium: no

- Intervals of water quality measurement: Start of the test and after 72 and 96 hours (nominal) incubation.


OTHER TEST CONDITIONS

- Sterile test conditions: yes

- Adjustment of pH: no

- Photoperiod: continuous

- Light intensity and quality: 60-120 μmol/s/m2 from fluorescent lamps


EFFECT PARAMETERS MEASURED: cell numbers after 24, 48, 72 and 96 hours (nominal)

- Determination of cell concentrations: Coulter Counter TAII


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 3.2

- Range finding study

- Test concentrations: 0.0003, 0.004, 0.06, 0.70 and 9.6 mg/l

- Results used to determine the conditions for the definitive study: Mean cell concentrations (cells/ml) after 72 hour incubation were: 1170000 (Control), 1350000 (Solvent control), 1360000 (0.0003 mg/l), 1020000 (0.004 mg/l), 700000 (0.06 mg/l), 700000 (0.7 mg/l) and 320000 (9.6 mg/l).

Reference substance (positive control):

no

Key result

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

160 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

direct dispersion

Basis for effect:

growth rate

Remarks on result:

other: 99-270

Key result

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

180 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

with TBA

Basis for effect:

growth rate

Remarks on result:

other: 150-210

Key result

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

200 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

with DMSO

Basis for effect:

growth rate

Remarks on result:

other: 120-360

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

80 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

direct dispersion

Basis for effect:

biomass

Remarks on result:

other: 32-101

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

86 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

with TBA

Basis for effect:

biomass

Remarks on result:

other: 32-126

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

98 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

with DMSO

Basis for effect:

biomass

Remarks on result:

other: 32-150

Duration:

96 h

Dose descriptor:

EC10

Effect conc.:

80 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

direct dispersion

Basis for effect:

growth rate

Duration:

96 h

Dose descriptor:

EC10

Effect conc.:

85 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

with TBA

Basis for effect:

growth rate

Duration:

96 h

Dose descriptor:

EC10

Effect conc.:

110 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

with DMSO

Basis for effect:

growth rate

Key result

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

32 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: growth rate and biomass

Details on results:

- Exponential growth in the control: yes

- Observation of abnormalities: no abnormalities were observed

Reported statistics and error estimates:

ECx values with respect to growth rate were calculated using a parametric model developed by Kooijman et al. ECx values relating to growth rate were calculated using the method described in the OECD test guideline.

NOEC values were determined by visual comparison of the growth curves of Control and treated cultures.

Kooijman, S.A.L.M., A.O. Hanstveit and H. Oldersma. (1983). Parametric analysis of population growth in bioassays. Water Research, 17: 527-538.

The EC50 values determined for effects on growth rate are above the highest test concentrations.

Table 1. Test results - test media prepared by direct dispersion

Nominal test substance concentration (mg/l)	Mean cell concentration after 92.5 hours incubation (cells/ml)
0 (Control)	2075000
0 (Control)	2225000
0.032	2190000
0.10	1901000
0.32	1844000
1.0	2008000
3.2	2127000
10	1982000
32	1929000
101	817000

Table 2. Test results - test media prepared using TBA as solvent

Nominal test substance concentration (mg/l)	Mean cell concentration after 94 hours incubation (cells/ml)
0 (Control)	1817000
0 (TBA control)	1773000
0.032	1735000
0.10	1810000
0.32	1913000
1.0	1910000
3.2	1931000
10	2254000
32	1999000
126 (without TBA)	426000

Table 3. Test results - test media prepared using DMSO as solvent

Nominal test substance concentration (mg/l)	Mean cell concentration after 95.5 hours incubation (cells/ml)
0 (Control)	1922000
0 (DMSO control)	2061000
0.032	2212000
0.10	2059000
0.32	2055000
1.0	2165000
3.2	2006000
10	2062000
32	1914000
150 (without DMSO)	591000

Validity criteria fulfilled:

yes

Conclusions:

96-hour EC50 values in the range 160-200 mg/l have been determined for the effects of the test substance on growth rate of Desmodesmus subspicatus (tested as Scenedesmus subspicatus) cultures. These values have been determined by extrapolation to above the highest test concentrations. The method of test medium preparation did not have a significant effect on the test result. A NOEC of 32 mg/l has been estimated from the test results. 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 primarily exposed to a mixture of the parent compound and the hydrolysis products of the substance. The test results are consistent with those of a related study (TNO, 1992b).

Description of key information

E_rC₅₀ (96 h): 160 mg/l (nominal) and NOE_rC (96 h): 32 mg/l, based on growth rate of Desmodesmus subspicatus (OECD Guideline 201).

Key value for chemical safety assessment

EC50 for freshwater algae:

160 mg/L

EC10 or NOEC for freshwater algae:

32 mg/L

Additional information

A 96-hour E_rC₅₀ value of 160 mg/l and NOE_rC value of 32 mg/l (nominal) have been determined for the effects of the registered substance, triethoxy(3-thiocyanatopropyl)silane (CAS 34708-08-2; EC No. 252-161-3), on growth rate of Desmodesmus subspicatus (reported as Scenedesmus subspicatus) (TNO, 1992a).

The value was obtained by extrapolation to above the highest test concentration from results obtained in test media prepared by direct dispersion of the test substance. The use of other methods of test media preparation did not have a significant effect on the test result. A NOEC of 32 mg/l has been estimated from the test results.

In a separate study, conducted by the same laboratory, a 72-hour E_rC₅₀ value of >10 mg/l and NOE_rC value of ≥10 mg/l have been determined for the effects of the test substance on growth rate and of Desmodesmus subspicatus (TNO, 1992b).

The test solutions were prepared using tert-butyl alcohol (TBA) (TNO, 1992a and b) and dimethyl sulfoxide (DMSO) (TNO 1992a only) as solvents. The recommended solvent concentration (100 mg/l) was not exceeded during the test, and it is therefore unlikely that TBA or DMSO 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 in both tests.

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 these tests.

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.