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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:
14 Feb - 17 Feb 2006
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Some observations associated with validity criteria in the equivalent OECD test guideline are not reported.
Qualifier:
according to guideline
Guideline:
other: Circular on Test Methods of New Chemical Substances (Japan), Alga growth inhibition test
Deviations:
no
GLP compliance:
yes
Remarks:
according to the Japanese GLP Standard
Specific details on test material used for the study:
Details on properties of test material:
PHYSICO-CHEMICAL PROPERTIES
- Melting point: < 0°C
- Boiling point: 123°C
- Vapour pressure: < 2.7 kPa at 25 °C
- Water solubility (under test conditions): low
- Stability in water: Test item is hydrolysed (half-life: within 30 min)
Analytical monitoring:
yes
Details on sampling:
- Sampling method: sampled directly by each vessel and pre-treatment was not performed
- Sample storage conditions before analysis: no storage before analysis
- Methanol was measured, since the test item was quickly hydrolysed
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: test item was measured and diluted in dilution water by stirring for 120 min
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Alga
- Strain: ATCC22662
- Source (laboratory, culture collection): American Type Culture Collection
- Age of inoculum (at test initiation): after 4-day preculture
- Method of cultivation: on a shaker

ACCLIMATION
- Acclimation period: 4 days (2006-02-10 ~ 2006-02-14)
- Culturing media and conditions (same as test or not): same as test
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Test temperature:
23.0 - 23.1 °C (23 ± 2 °C), measured at the study initiation, 24, 48 and 72 hours after exposure
pH:
8.0 - 9.9, measured at the initiation and at the end of the study.
Nominal and measured concentrations:
Nominal concentration: 100 mg/L
Measured concentration: 89 mg/L (time-weighted mean; the concentration was determined based on the measured concentration of the hydrolysis product, methanol)
Details on test conditions:
TEST SYSTEM
- Test vessel: 500 mL Erlenmeyer-flask
- Type (delete if not applicable): closed
- Material, headspace, fill volume: glass, 490 mL, 100 mL
- Initial cells density: 5000 cells/mL
- Control end cells density: 855900 ± 20700 cells/mL
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS
- Culture medium different from test medium: same medium

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no adjustment
- Photoperiod: continuously
- Light intensity and quality: 65 µE/m2/s

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: counting chamber; electronic particle counter;

TEST CONCENTRATIONS
- Range finding study: performed twice.
- Test concentrations: 1) 1, 10 and 100 mg/L, 2) 100 mg/L
- Results used to determine the conditions for the definitive study:
1) Inhibition rate was 16% (close system), -42% (open system) in 1 mg/L, 12% (close system), -44% (open system) in 10 mg/L, and 1% (close system), -36% (open system) in 100 mg/L, respectively.
2) Inhibition rate was -14% (close system) and 6% (open system). Measured concentration was 108 mg/L at the study initiation and 87 mg/L in a close system at the end of the study.
Reference substance (positive control):
yes
Remarks:
Potassium dichromate (analytical grade)
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 89 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: the concentration was determined based on the measured concentration of the hydrolysis product, methanol
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
> 89 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: the concentration was determined based on the measured concentration of the hydrolysis product, methanol
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 89 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks on result:
other: the concentration was determined based on the measured concentration of the hydrolysis product, methanol
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
> 89 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks on result:
other: the concentration was determined based on the measured concentration of the hydrolysis product, methanol
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): no abnormality was observed
Results with reference substance (positive control):
- Results with reference substance valid? Yes
- EC50: 0.428 ± 0.0683 mg/L
Reported statistics and error estimates:
Student's t-test, subsequent to F test for homogeneity of variances.

Table 1. Calculated concentration of the test substance using methanol concentration

Nominal concentration

(mg/L)

Mean measured concentration, mg/L

(Percent of nominal)

Mean measured

concentration (*), mg/L

 

0 hour

24 hours

48ours

72ours

 

Control

< 0.03

< 0.03

< 0.03

< 0.03

 

100

105

(105

100

(100

75.3

(75)

80.2 (80)

89

(89)

*: Time-weighted mean measured concentration

Table 2. Growth inhibition (%)

Nominal conc. (mg/L)

[Mean measured conc. *]

Inhibition rate (%)

Growth rate

Inhibition rate (%)

Biomass

Control

-

-

100

[89]

0.3

0.5

*: Time-weighted mean measured concentration

Conclusions:
A 72-hour NOEC value of >89 mg/l has been determined for the effects of the test substance on biomass and growth rate Pseudokirchneriella subcapitata. Due to the rapid rate of hydrolysis, the concentration was determined based on the measured concentration of the hydrolysis product, methanol.

Description of key information

72 hour EC50 value of >89 mg/L and NOEC of =89 mg/L, effects of the test substance on growth rate of Pseudokirchneriella subcapitata. Under the conditions of the test is likely that the test organisms were primarily exposed to the hydrolysis products of the substance. The EC50 and NOEC are equivalent to >64 mg/L and =64 mg/L respectively, when expressed in terms of the silanol hydrolysis product vinylsilanetriol.

Key value for chemical safety assessment

Additional information

A 72 hour EC50 value of >89 mg/L and NOEC of =89 mg/L (nominal concentration) (highest concentration tested) has been reported for the effects of the test substance on growth rate of Pseudokirchneriella subcapitata (MOE, 2006). Under the conditions of the test, it is likely that the test organisms were primarily exposed to the hydrolysis products of the substance. The results may be expressed in terms of the silanol hydrolysis product, by adjusting for the respective molecular weights: MW hydrolysis product/MW parent * E(L)C50 or NOEC value, thus 106.15/148.24 * EC50 of >89 mg/L and NOEC of =89 mg/L = EC50 >64 mg/L and NOEC =64 mg/L as vinylsilanetriol.

A second algal study has been carried out with the test substance which was previously considered in Weight of Evidence with the MOE, 2006 test. A 7-day EC50 value of 210 mg/L and NOEC of approximately 25 mg/L have been reported for the effects of the test substance on final yield of Pseudokirchneriella subcapitata. However, the test is no longer considered to be reliable because the 7-day duration means that it is unlikely that the algae maintained exponential growth throughout the test. In addition, the result is expressed in terms of yield as opposed to growth rate, which is the relevant endpoint.

The following result is from a reliable study included as supporting data:

72-hour EC50 >957 mg/L and NOEC =957 mg/L determined for effects of the test substance on growth rate of Desmodesmus subspicatus (Huls, 1993).

Other toxicity to algal tests are available with the registration substance. The key study has been selected because it gives the lowest reliable limit value. The results of the three further studies, for which their reliability could not be ascertained or were deemed unreliable, are as follows:

72-hour EC50 >100 mg/L and NOEC =10 mg/L determined for effects of the test substance on growth rate of Desmodesmus subspicatus (Bement, 2001).

72-hour EC50 >100 mg/L and NOEC =10 mg/L determined for effects of the test substance on biomass of Desmodesmus subspicatus (Chandra 1997 and Dow Corning Corporation, 1997).

72-hour EC50 210 mg/L and EC10 32 mg/L determined for effects of the test substance on final yield of Pseudokirchneriella subcapitata (Dow Corning Corporation, 1979).