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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1995-07-03 to 1995-07-06
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 10, 20, 40, 80, 160, 319 and 639 mg/L and the fresh stock solution used to prepare the test media.

- Sampling method: Concentrations of test substance hydrolysis products determined in fresh media at all concentrations after preparation and again before renewal after 24 hours. The concentrations of the fresh stock solution used to prepare the test media was also determined.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Seven nominal concentrations 10, 20, 40, 80, 160, 319 and 639 mg/L. Test media prepared by dilution of a 1000 mg/l stock solution prepared by mixing for 18 h followed by filtration. TOC concentration of stock solution determined and used as the basis for determining the nominal test concentrations.

- Controls: Dilution water (algal growth medium)
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM

- Strain: 86.81.SAG

- Source (laboratory, culture collection): Institute for Water, Ground and Air Hygiene, Berlin (Germany)

- Age of inoculum (at test initiation): 3 days

- Method of cultivation: A pre-culture is produced from an original culture by super-inoculation three days before the test begins. From this culture the test cultures are inoculated at a density of about 20000 cells/ml.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
not reported
Test temperature:
23.0 - 23.3 degrees C
pH:
8.2 - 8.7 at start of test

7.6 - 9.3 at end of test
Dissolved oxygen:
not reported
Salinity:
not applicable
Nominal and measured concentrations:
Nominal test concentrations: Control (0), 10, 20, 40, 80, 160, 319 and 639 mg/L.

Measured test concentrations at start of test: 0, 9.8, 19, 38, 76, 150, 332 and 596 mg/L.

Measured test concentrations at end of test: 0, 9.2, 19, 38, 73, 147, 296 and 577 mg/L.

The measured concentrations were with +/-20% of nominal. The results are therefore presented and interpreted with reference to nominal concentrations.
Details on test conditions:
TEST SYSTEM

- Test vessel: Erlenmeyer flasks

- Type: open

- Material, size, headspace, fill volume: glass

- Aeration: none

- Initial cells density: 1260000 cells/mL

- Control end cells density: 20000 cells/mL

- No. of vessels per concentration (replicates): 5

- No. of vessels per control (replicates): 8

GROWTH MEDIUM

- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS

- Culture medium different from test medium: no

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

OTHER TEST CONDITIONS

- Sterile test conditions: yes

- Adjustment of pH: no

- Photoperiod: continuous

- Light intensity and quality: 8000 Lux

EFFECT PARAMETERS MEASURED:

- Determination of cell concentrations: spectrophotometer (absorption at 685 nm)

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2
Reference substance (positive control):
no
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
931 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
growth rate
Remarks on result:
other: the concentration exceeds the highest treatment level in the test
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
267 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
biomass
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
92 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
36 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
biomass
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
40 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
growth rate
Details on results:
- Exponential growth in the control (for algal test): yes
Reported statistics and error estimates:
The area under the growth curve (biomass) and growth rate parameters were calculated from the cell concentration data in accordance with the description of the test method.

ECx values were determined by probit analysis (Cavalli-Sforza, 1972. Biometrie. Gustav Fischer Verlag, Stuttgart).

NOEC values were determined directly from the raw data.

Table 1. Results of analysis of test media

 Nominal test substance concentration (mg/L)  Measured concentration at start of test (mg/L)  Measured concentration at end of test (mg/L)
 0 (Control) - -
 10 9.8 9.2
 20 19  19
 40  38 38
 80  76 73
 160 150 147
 319 332 296
 639  596 577

Table 2. Test results

 Nominal test substance concentration (mg/L)  Mean cell concentration at start of test (cells/ml)  Mean cell concentration after 24 hours (cells/ml) Mean cell concentration after 48 hours (cells/ml)  Mean cell concentration after 72 hours (cells/ml) 
 0 (Control)  20000  90000  350000  1260000
 10  20000  80000  260000  1020000
 20  20000  100000  350000  1290000
 40  20000  90000  300000  1040000
 80  20000  90000  310000  920000
 160  20000  100000  270000  610000
 319  20000  90000  200000  350000
 639  20000  100000  170000  260000
Validity criteria fulfilled:
yes
Conclusions:
A 72-h EC50 value of 931 mg/L and a NOEC of 40 mg/L have been determined for the effects of the test substance on growth rate of Scenedesmus subspicatus based on nominal concentrations of the substance. The test substance hydrolyses in water and it is therefore likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

Description of key information

Toxicity to algae: 72-hour ErC50 931 mg/l and ErC10 92 mg/l (nominal) (EC Guideline 92/69/EWG C3), growth rate of Scenedesmus subspicatus. The ErC50 and ErC10 are equivalent to 732 and 72 mg/l, respectively, when expressed in terms of the silanol hydrolysis product.

Key value for chemical safety assessment

EC50 for freshwater algae:
732 mg/L
EC10 or NOEC for freshwater algae:
72 mg/L

Additional information

A 72-hour ErC50 value of 931 mg/l and ErC10 of 92 mg/l (nominal) have been determined for the effects of the registration substance on growth rate of Scenedesmus subspicatus (new name: Desmodesmus subspicatus) conducted in accordance with EU Method C.3 (Algal Inhibition test) and in compliance with GLP (Hüls 1995). A NOEbC of 40 mg/l (nominal) was determined in the same test, for biomass effects. In view of the test media preparation method and exposure regime, it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance.

At the loading concentration used in preparation of stock, it is expected that oligomers and/or cross-linked aggregates may have been present to some extent, though no specific evidence of precipitation or physical effects on test animals is described. While this is an uncertainty, it is considered that the study results are suitable to be used (with caution), with effects attributed in principle to intrinsic ecotoxicity of silanol (and oligomers).

The results may be expressed in terms of concentration of the hydrolysis product, 3-(trihydroxysilyl)propanethiol, by applying a molecular weight correction: (MW of silanol = 154.26 / MW of parent = 196.34) * ErC50 931 and ErC10 92 = ErC50 732 mg/l and ErC10 72 mg/l.

The reliability of another ErC50 value of 43 mg/l, that was obtained from the open literature, could not be determined.

To support the proposed long-term read-across data, short-term aquatic toxicity data with 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1) are included, for comparison of aquatic effects between the registered and read-across substances.

A 72-hour ErC50 value of 32.2 mg/l, an ErC10 value of 11.8 mg/l and a NOErC of 4.8 mg/l have been determined for the effects of 3-(triethoxysilyl)propanethiol on growth rate of Pseudokirchneriella subcapitata, based on time weighted average measured concentrations of the substance, conducted in accordance with OECD TG 201 and in compliance with GLP (Noack 2020). The ErC50, ErC10 and NOErC values are equivalent to 20.8, 7.6 and 3.1 mg/l respectively, when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.  

Due to the static nature of the algal test, it is likely that the algae were exposed to the parent at the beginning of the test, with the hydrolysis products dominating towards the end.

Refer to IUCLID Section 6, CSR Section 7.0, for further discussion of the approach to chemical safety assessment for this registration substance.