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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
As noted in the hydrolysis section, oximesilanes quicky hydrolyze to the corresponding oxime and reactive silanols which spontaneously cross link to form high molecular weight silicone polymers. The relevant hydrolysis product is MPKO, the substance that was tested.

Data on selected oximes and oxime silanes are summarized in the attached Table. Although data for each endpoint is not available for all products, the available data show similarities between oxime silanes and their hydrolysis products (oxime). These materials show low toxicity to fish, and daphnia. For algal studies, the toxicity shows a structure activity relationship. The smaller oximes are more toxic to alga, the larger oximes and associated oxime silanes are less toxic. The similarities in response between the oximes and oxime silanes provide additional support of the silicone containing moieties do not contribute to the aquatic toxicity of these materials. Due to the rapid hydrolysis, it is appropriate to use the oxime as surrogate data for the oxime silane.
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0, 5.6, 10, 18, 32, 56, and 100 mg/l at 0 and 72 h.

Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The nominal 100 mg l-1 test concentration of methyl propyl ketoxime was prepared in 2000 ml of culture medium. This stock solution was stirred for 30 minutes using a magnetic follower, after which the stock solution was observed to be clear and colourless.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Strain: ATCC 22662
- Source (laboratory, culture collection): laboratory cultures maintained under axenic conditions
- Age of inoculum (at test initiation): 4 days during exponential growth phase


- Culturing media and conditions: same as test
- Any deformed or abnormal cells observed: non observed
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
not reported
Test temperature:
18-22 °C
pH:
7.6 - 7.8
Dissolved oxygen:
not reported
Nominal and measured concentrations:
Nominal test substance concentrations: 5.6, 10, 18, 32, 56 and 100 mg/L
With the exception of the 5.6 mg/l samples, the measured concentrations with 91 - 100% of nomimal
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 ml glass conical flasks closed with foam bungs filled with 100 ml of test solution and 0.75 ml of inoculum culture
- Initial cells density: 0.5 x 10e4 cells/ml
- Control end cells density: at 72 hours, 81.8 x 10e4 cells/ml
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes


OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuous
- Light intensity and quality: "cool-white" illumination of 6708 lux (mean)



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

Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
ca. 54 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
32 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
88 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
32 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): At the 32, 56 and 100 mg l-1 test concentrations the cells were observed to be smaller than those in the control test concentration.
- Any stimulation of growth found in any treatment: none observed
- Effect concentrations exceeding solubility of substance in test medium: none observed
Reported statistics and error estimates:
one way analysis of variance and Duunnett's procedure to identify significant changes from control. Weibull method used to estimate the meane effective concentrations.

Table 1: Validity criteria for OECD 201.

Criterion from the guideline

Outcome

Validity criterion fulfilled

The biomass in the control cultures should have increased exponentially by a factor of at least 16 within the 72-hour test period.

169

yes

The mean coefficient of variation for section-by-section specific growth rates (days 0-1, 1-2 and 2-3, for 72-hour tests) in the control cultures must not exceed 35%

7.9 %

yes4

The coefficient of variation of average specific growth rates during the whole test period in replicate control cultures must not exceed 7% in tests with Pseudokirchneriella subcapitata and Desmodesmus subspicatus. For other less frequently tested species, the value should not exceed 10%.

4.0 %

yes

 

Validity criteria fulfilled:
yes
Remarks:
Please refer to Table 1 at "Any other information on results incl. tables"
Conclusions:
The 72 hr ECy50 is 54 mg/l, and the ECr50 is 88 mg/l. The 72 hour no-observed effect concentration was 32 mg/l based on yield and growth rate.

Description of key information

ErC50 (72 h): 88 mg/L (nominal, OECD 201)

NOErC (72 h): 32 mg/L (nominal, OECD 201)

Key value for chemical safety assessment

Additional information

The toxicity to algae was tested in a GLP-study following OECD guideline 201. Green algae (Pseudokirchneriella subcapitata) were exposed to nominal test substance concentrations of 5.6, 10, 18, 32, 56 and 100 mg/L. The analytical dose verification at 0 and 72 h was conducted using a HPLC method. With the exception of the 5.6 mg/l samples, the mean measured concentrations in the range of 91 - 100% of nominal were determined. The mean growth rate at the substance concentrations 56 mg/L and 100 mg/L was significantly reduced compared to the control growth rate. Thus, the determined ErC50 (72 h) was 88 mg/L (nominal) and the NOErC (72 h) was 32 mg/L.