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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The studies were conducted following a recognized guideline (OPPTS 850.5400) and are sufficiently documented for assessment. The most significant restriction is the lack of analytical verification. A concentrated stock solution and carrier solvent were used to prepare the test solutions for the study. Under the conditions described for preparation of the concentrated stock solution, the test material 3-glycidoxypropyl-trimethoxysilane could have significantly hydrolysed to 3-glycidoxypropyl-silanetriol, which could have condensed to insoluble siloxane resins.
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Qualifier:
according to
Guideline:
EPA OPPTS 850.5400 (Algal Toxicity, Tiers I and II)
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 1000 mg a.i./L stock solution was prepared by placing 1.889 mL (2.0212 g based on a density of 1.07 g/mL, 1.9969 g as active ingredient) of glycidoxy in a 2000 mL volumetric flask and diluting to volume with sterile AAP medium containing 0.10 mL/L of dimethyl formamide (DMF, CAS No. 68-12-2).  The resulting stock solution was stirred using a magnetic stir plate and stir for 15 minutes.  Nominal test concentrations were prepared from dilutions of the 1000 mg a.i./L stock solution.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM

- Strain: 1648

- Source (laboratory, culture collection): The alga was obtained from Carolina Biological Supply Co., Burlington, North Carolina, and was maintained in stock culture at Springborn Smithers. 

- Culture conditions: The stock cultures were maintained within the following conditions:  a shaking rate of 100 ± 10 rpm, a temperature of 24 ± 1 °C and continuous illumination at the surface of the medium with an intensity of approximately 300 to 500 footcandles (3200 to 5400 lux).  Lighting was supplied by Duro-Test® Vita-Lite® fluorescent bulbs.  Culture flasks were agitated continuously on an orbital shaker.

- Growth/test medium:  The culture medium used was Algal Assay Procedure (AAP) medium prepared with sterile, deionized water.  
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Hardness:
No data
Test temperature:
23 to 24 °C
pH:
7.0-8.5
Dissolved oxygen:
No data
Salinity:
No data
Nominal and measured concentrations:
Nominal test concentrations: 31, 63, 130, 250, 500 and 1000 mg a.i./L.
Details on test conditions:
TEST SYSTEM

- Growth/test medium:  The culture medium used was Algal Assay Procedure (AAP) medium prepared with sterile, deionized water.  

- Exposure vessel type: The test was conducted in sterile 250-mL Erlenmeyer flasks containing  100-mL of test solution.  All test vessels were fitted with stainless steel caps which permit gas exchange.  

- Water chemistry in test:  TOC concentration of the AAP sample collected in January 2002 was 0.47 mg/L.  The dilution water and solvent control vessels both had a specific conductivity of 90 mmhos/cm at test initiation and at test termination.  pH measured in the dilution water and solvent control vessels were 7.3 and 7.1 respectively, at test initiation and 8.4 and 8.5 respectively, at test termination.  The 1000 mg a.i./L treatment level had a specific conductivity of 70 mmhos/cm at test initiation and 80 mmhos at test termination.  pH measured in the 1000 mg a.i./L treatment level was 7.0 at test initiation and 7.2 at test termination.

- Light levels and quality during exposure:  340 - 440 footcandles (3700 - 4700 lux).  The photosynthetically-active radiation (PAR) of the test area measured at test initiation ranged from 50 to 69 µE/m2/s.

- Test Design:  Approximately 30 minutes after the test solutions were added to the test flasks (100 mL per flask), a 0.216-mL inoculum of Pseudokirchneriella subcapitata cells, at a density of approximately 464 x 104 cells/mL, was aseptically introduced into each flask.  This inoculum provided the required initial (0 hour) cell density of approximately 1.0 x 104 cells/mL.  Three replicate test vessels were established for each treatment level, the dilution water control and the solvent control.
Reference substance (positive control):
no
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
130 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
350 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 170-720
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
350 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
250 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks on result:
other: 140-450
Reported statistics and error estimates:
Statistical methods: Shapiro-Wilks' Test , Bartlett's Test , Williams' Test, Kruskal-Wallis' Test, Bonferroni's test.

Cell Density

Cell densities in the 31, 63, 130, 250, 500 and 1000 mg a.i./L treatment levels averaged 83, 136, 137, 89, 11 and 0 x 10E4 cells/mL, respectively. Statistical analysis based on Williams' Test determined a significant reduction in cell density in all treatment level tested as compared to the pooled control. Based on Williams' Test the NOEC was determined to be <31 mg a.i./L. Additional statistical analysis (Bonferroni's Test) determined a significant

reduction in cell density in the 31, 250, 500 and 1000 mg a.i./L treatments. The effect on the 31 mg a.i./L treatment level is not considered treatment-related since the two higher concentrations (63 and 130 mg a.i./L) were not affected and were less than 10% inhibited. Therefore, the NOEC was determined to be 130 mg a.i./L. The 96 hour EC50 for cell density was calculated to be 260 mg a.i./L, with 95% confidence intervals of 190 and 360 mg a.i./L.

Biomass

Biomass in the 31, 63, 130, 250, 500 and 1000 mg a.i./L treatment levels averaged 35, 53, 37, 20, 3.6 and 0.7 cells·days/mL, respectively. Statistical analysis (Williams' Test) determined a significant difference in biomass in the 250, 500 and 1000 mg a.i./L any treatment levels tested when compared to the biomass in the pooled control. Therefore, the NOEC was determined to be 130 mg

a.i./L. The 72 hour EbC50 was calculated to be 250 mg a.i./L, with 95% confidence intervals of 140 and 450 mg a.i./L.

Growth Rate

The 0- to 72 hour growth rate in the 31, 63, 130, 250, 500 and 1000 mg a.i./L treatment levels averaged 1.17, 1.37,1.24, 0.99, 0.32 and -0.6 days-1, respectively. Statistical analysis (Kruskal-Wallis' Test) did not determine a

significant reduction in any treatment level tested when compared to the growth rate in the pooled control. Since the Kruskal-Wallis' Test did not provide a reasonable NOEC (1000 mg a.i./L), the NOEC was empirically estimated to be

130 mg a.i./L, the highest concentration with less than 10% inhibition. The 72 hour ErC50 was calculated to be 350 mg a.i./L, with 95% confidence intervals of 170 and 720 mg a.i./L.

Validity criteria fulfilled:
yes
Conclusions:
A 96-hour EC50 value of 350 mg/L and NOEC of 130 mg/L have been determined for the effects of the test substance on growth rate of Selenastrum capricornutum (new name: Pseudokirchnerella subcapitata). It is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

Description of key information

Toxicity to algae: 96 hour ErC50 350 mg/l and 96 hour NOEC 130 mg/l (growth rate) (nominal) (OECD 201). The ErC50 and NOEC are equivalent to 288 mg/l and 107 mg/l when expressed in terms of the concentration of the silanol hydrolysis product [3-(2,3-epoxypropoxy)propyl]silanetriol.

Key value for chemical safety assessment

EC50 for freshwater algae:
288 mg/L
EC10 or NOEC for freshwater algae:
107 mg/L

Additional information

A 96 hour ErC50 value of 350 mg/l and NOEC of 130 mg/l (nominal) have been determined for the effects of 3-(2,3-epoxypropoxy)propyltrimethoxysilane on growth rate of Pseudokirchneriella subcapitata (SEHSC, 2002). In view of the media preparation and exposure regime, it is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance.

The results may be expressed in terms of concentration of the hydrolysis product, [3-(2,3-epoxypropoxy)propyl]silanetriol, by applying a molecular weight correction: (MW of silanol = 194.26 / MW of parent = 236.34) * EC50 350 mg/l and NOEC 130 mg/l = EC50 288 mg/l and NOEC 107 mg/l.

 

This study has been selected as key because it has lower effect concentrations than the other reliable study.

 

Supporting data with the registration substance are available:

A 72 hour ErC50 value of >420 mg/l and ErC10 of 190 mg/l have been determined for the effects of 3-(2,3-epoxypropoxy)propyltrimethoxysilane on growth rate of Desmodesmus subspicatus (Hüls, 1993). In view of the media preparation and exposure regime, it is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance.

 

A 7 day EC50 value of 119 mg/l and EC10 value of 40 mg/l have been determined for the effects on growth rate of Anabaena flos-aquae (blue-green algae) (Dow Corning, 1978). The NOEC was 50 mg/l, the lowest test concentration. It is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance. However, the duration of this test is longer than standard, and in the absence of sufficient evidence reported in the original study, it must be assumed that the algal culture may not have remained in exponential growth throughout the exposure period (in accordance with guidance in Part R7b, ECHA, 2017) which would make the results unsuitable for use in the chemical safety assessment. Therefore, this NOEC is not a suitable basis for deriving PNEC and the study has been assigned reliability 4.