Strontium hydrogen phosphate

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:

3-6 February 2014

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The study was conducted according to the OECD 201 Guideline and complied with the principles of GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8692 (Water Quality - Fresh Water Algal Growth Inhibition Test with Scenedesmus subspicatus and Selenastrum capricornutum)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Guidance document on aquatic toxicity testing of difficult substances and mixtures, OECD series on testing and assessment number 23, December 14, 2000

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Samples of 4.8 mL for possible analysis were taken from all test concentrations and the control at t=0 h, t=24 h and t=72 h and stored in a freezer until analysis. In addition, the filter containing undissolved residue was retained for possible analysis.
At the end of the exposure period, the replicates with algae were pooled at each concentration before sampling.
On the day of analysis, the test samples were defrosted at room temperature. The samples were diluted in a 25:1 (v:v) ratio with HNO3 and analysed. If necessary, the samples were further diluted with 4% HNO3 in M2-medium to obtain concentrations within the calibration range.

Vehicle:

no

Details on test solutions:

Preparation of test solutions started with a loading rate of 100 mg/l applying a 2-day period of magnetic stirring followed by a filtration through a 0.45 µm membrane filter (rc55, Whatman). The obtained Water Soluble Fraction (WSF) was used as the highest concentration. The lower test concentrations were prepared by subsequent dilutions of the highest concentration in test medium. The final test solutions were all clear and colourless.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM
- Strain: NIVA CHL 1
- Source (laboratory, culture collection): In-house laboratory culture.
- Age of inoculum (at test initiation):
- Method of cultivation: Algae stock cultures were started by inoculating growth medium with algal cells from a pure culture on agar. The suspensions were continuously aerated and exposed to light in a climate room at a temperature of 21-24°C. 3 days before the start of the test, cells from the algal stock culture were inoculated in culture medium at a cell density of 1 x 10^4 cells/mL. The pre-culture was maintained under the same conditions as used in the test. The cell density was measured immediately before use.

ACCLIMATION
- Culturing media and conditions (same as test or not): Pre-culture medium is same as test (M2)

Test type:

static

Water media type:

freshwater

Total exposure duration:

72 h

Post exposure observation period:

None

Hardness:

24 mg CaCO3/L

Test temperature:

21 -23 ºC

pH:

8.1-8.4

Dissolved oxygen:

Not measured

Salinity:

Not applicable

Nominal and measured concentrations:

The actual measured concentration was 16 mg Sr/L at the start of the test in the solution containing the WSF prepared at 100 mg/L. The concentration remained stable during the exposure (105% of initial). The concentration obtained in the undiluted WSF was considered the maximum soluble concentration in the test medium.

Details on test conditions:

TEST SYSTEM
- Test vessel: 100 ml, all-glass, containing 50 ml of test solution
- Aeration: no
- Initial cells density: 1x 10^4 cells/mL
- Control end cells density: 198 x 10^4 cells/mL
- No. of vessels per concentration (replicates): 6 for the highest concentration, 3 for each lower concentration
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes (M2)

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuously
- Light intensity and quality: TLD-lamps with a light intensity within the range of 93 to 94 µE.m-2.s-1.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: At the beginning of the test, cells were counted using a microscope and a counting chamber. Thereafter cell densities were determined by spectrophotometric measurement of samples at 720 nm using a spectrophotometer with immersion probe (pathlength =20 mm). Algal medium was used as blank and the extra replicates as background for the treated solutions.

TEST CONCENTRATIONS
- Test concentrations: combined limit/range-finding test with solutions containing 1.0, 10 and 100% of a WSF prepared at a loading rate of 100 mg/l.

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Duration:

72 h

Dose descriptor:

EC50

Basis for effect:

growth rate

Remarks on result:

other: EC50 > maximum soluble concentration in test medium

Duration:

72 h

Dose descriptor:

EC10

Basis for effect:

growth rate

Remarks on result:

other: EC10 > maximum soluble concentration in test medium

Details on results:

No significant inhibition of growth rate was observed in the diluted WSF (1.0 and 10%). Significant inhibition of growth rate (6.3%) was observed in the undiluted WSF. However, the observed inhibition of growth rate was below 10% and, therefore, considered biologically insignificant. In this case, the EC10 is considered a more reliable parameter than the NOEC.
Microscopic observations at the end in the undiluted of the test revealed a normal and healthy appearance of the exposed cells when compared to the control.

Acceptability of the test:
- In the controls, cell density increased by an average factor of >16 within 2 days.
- The mean coefficient of variation for section-by-section specific growth rates in the control cultures did not exceed 35% (i.e. 32%).
- The coefficient of variation of average specific growth rates during the whole test period in replicate control cultures did not exceed 7% (i.e. 1.8%).

Results with reference substance (positive control):

The EC50 for growth rate inhibition (72h-ERC50) was 1.3 mg/l with a 95% confidence interval ranging from 1.3 to 1.4 mg/l. The historical ranges for growth rate inhibition lie between 0.82 and 2.3 mg/l. Hence, the 72h-ERC50 for the algal culture tested corresponds with this range.

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of the present study with Pseudokirchneriella subcapitata, the 72h-ErC10 and 72h-ErC50 for growth rate inhibition exceeded the maximum solubility of SrHPO4 in test medium.

Executive summary:

A 72-h algae growth inhibition test was performed with SrHPO4 according to OECD 201 and in compliance with GLP principles. The test substance solution was prepared as a water soluble fraction of a loading rate of 100 mg/L. The lower test concentrations were prepared by subsequent dilutions of this WSF in test medium. The actual measured concentration of the WSF prepared at a loading rate of 100 mg/L was 16 mg Sr/L at the start of the test and remained stable during exposure (105% of initial). The 72h-ErC10 and 72h-ErC50 were considered to exceed the maximum solubility of the test substance in medium.

Description of key information

A 72-h algae growth inhibition test was performed with SrHPO4 according to OECD 201 and in compliance with GLP principles. The test substance solution was prepared as a water soluble fraction of a loading rate of 100 mg/L. Preparation started with a loading rate of 100 mg/L applying a 2-day period of magnetic stirring followed by a filtration through a 0.45 µm membrane filter. The lower test concentrations were prepared by subsequent dilutions of this WSF in test medium. The actual measured concentration of the WSF prepared at a loading rate of 100 mg/L was 16 mg Sr/L at the start of the test and remained stable during exposure. No significant inhibition of growth rate was observed in the diluted WSF (1.0 and 10%). Significant inhibition of growth rate (6.3%) was observed in the undiluted WSF. However, the observed inhibition of growth rate was below 10% and, therefore, considered biologically insignificant. The 72h-ErC10 and 72h-ErC50 were considered to exceed the maximum solubility of the test substance in medium.

 

Additional information

Key value for CSA: 72h-ERC10 and 72h-ERC50 are > the maximum solubility of the test substance in medium.