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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:
The study was conducted between 25 April 2016 and 17 June 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)
Version / remarks:
2006
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.3 (Algal Inhibition test)
Version / remarks:
2009
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Sponsor Lot/Batch number 5399561P10
- Expiration date of the lot/batch: 25 January 2020
- Purity test date: 25 january 2016



STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature in the dark

Analytical monitoring:
yes
Details on sampling:
Range-finding test

A sample of each loading rate WAF was taken for chemical analysis at 0 and 72 hours in order to determine the stability of the test item over the test duration. All samples were stored frozen prior to analysis.

Definitive test

The concentration and stability of the test item in the test preparations were verified by chemical analysis at 0 and 72 hours
Vehicle:
no
Details on test solutions:
Range-finding test
The initial range-finding test was conducted at nominal loading rates of 10 and 100 mg/L
The test was conducted in 250 mL glass conical flasks each containing 100 mL of test preparation and plugged with polyurethane foam bungs to reduce evaporation. Two replicate flasks were prepared for each control and test concentration.
Nominal amounts of test item (20 and 200 mg) were each separately added to the surface of 2 liters of culture medium to give the 10 and 100 mg/L loading rates respectively. After the addition of the test item, the culture medium was stirred by magnetic stirrer using a stirring rate such that a vortex was formed to give a dimple at the water surface. The stirring was stopped after 23 hours and the mixtures allowed to stand for 1 hour. A wide bore glass tube, covered at one end with Nescofilm was submerged into the vessel, sealed end down, to a depth of approximately 5 cm from the bottom of the vessel. A length of Tygon tubing was inserted into the glass tube and pushed through the Nescofilm seal. The aqueous phase or WAF was removed by mid-depth siphoning (the first 75-100 mL discarded) to give the 10 and 100 mg/L loading rate WAFs. Microscopic inspection of the WAFs showed no micro-dispersions or undissolved test item to be present.

A second range-finding test was conducted at nominal loading rates of 0.10, 1.0 and 10.0 mg/L.
Nominal amounts of test item (20 and 20 mg) were each separately added to the surface of 20 and 2 liters of culture medium to give the 1.0 and 10 mg/L loading rates respectively. After the addition of the test item, the culture medium was stirred by magnetic stirrer using a stirring rate such that a vortex was formed to give a dimple at the water surface. The stirring was stopped after 23 hours and the mixtures allowed to stand for 1 hour. A wide bore glass tube, covered at one end with Nescofilm was submerged into the vessel, sealed end down, to a depth of approximately 5 cm from the bottom of the vessel. A length of Tygon tubing was inserted into the glass tube and pushed through the Nescofilm seal. The aqueous phase or WAF was removed by mid-depth siphoning (the first 75-100 mL discarded) to give the 1.0 and 10 mg/L loading rate WAFs. Microscopic inspection of the WAFs showed no micro-dispersions or undissolved test item to be present. A dilution was made from the 1.0 mg/L loading rate WAF to give the 0.10 mg/L loading rate WAF.

Definitive Test
Based on the results of the range-finding tests the following loading rates were assigned to the definitive test: 1.0, 3.2, 10, 32 and 100 mg/L.

Experimental Preparation
Nominal amounts of test item (10, 32, 20, 64 and 200 mg) were each separately added to the surface of 10, 10, 2, 2 and 2 liters of culture medium to give the 1.0, 3.2, 10, 32 and 100 mg/L loading rates respectively. After the addition of the test item, the culture medium was stirred by magnetic stirrer using a stirring rate such that a vortex was formed to give a dimple at the water surface. The stirring was stopped after 23 hours and the mixtures allowed to stand for 1 hour. A wide bore glass tube, covered at one end with Nescofilm was submerged into the vessel, sealed end down, to a depth of approximately 5 cm from the bottom of the vessel. A length of Tygon tubing was inserted into the glass tube and pushed through the Nescofilm seal. The aqueous phase or WAF was removed by mid-depth siphoning (the first 75-100 mL discarded) to give the 1.0, 3.2, 10, 32 and 100 mg/L loading rate WAFs. Microscopic inspection of the WAFs showed no micro-dispersions or undissolved test item to be present.

The concentration and stability of the test item in the test preparations were verified by chemical analysis at 0 and 72 hours

Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
The test was carried out using Pseudokirchneriella subcapitata strain CCAP 278/4. Liquid cultures of Pseudokirchneriella subcapitata were obtained from the Culture Collection of Algae and Protozoa (CCAP), SAMS Research Services Ltd, Scottish Marine Institute, Oban, Argyll, Scotland. Master cultures were maintained in the laboratory by the periodic replenishment of culture medium (Section 3.3). The master cultures were maintained in the laboratory under constant aeration and illumination at 21 ± 1 ”C.
Prior to the start of the test sufficient master culture was added to approximately 100 mL volumes of culture media contained in conical flasks to give an initial cell density of approximately 103 cells/mL. The flasks were plugged with polyurethane foam stoppers and kept under constant agitation by orbital shaker (100 – 150 rpm) and constant illumination at 24 ± 1 ”C until the algal cell density was approximately 104 – 105 cells/mL.
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Details on test conditions:
250 mL glass conical flasks were used. Six flasks each containing 100 mL of test preparation were used for the control and three flasks each containing 100 mL were used for each treatment group.
The control group was maintained under identical conditions but not exposed to the test item.
Pre-culture conditions gave an algal suspension in log phase growth characterized by a cell density of 4.72 x 105 cells per mL. Inoculation of 1 liter of test medium with 10.6 mL of this algal suspension gave an initial nominal cell density of 5 x 103 cells per mL and had no significant dilution effect on the final test concentration.
The flasks were plugged with polyurethane foam bungs and incubated (INFORS Multitron Version 2 incubator) at 24 ± 1 °C under continuous illumination (intensity approximately 7000 lux) provided by warm white lighting (380 – 730 nm) and constantly shaken at approximately 150 rpm for 72 hours.
Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
>= 10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
LOELR
Effect conc.:
>= 32 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
35 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
other: Yield
Key result
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
other: Yield
Key result
Duration:
72 h
Dose descriptor:
LOELR
Effect conc.:
32 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
other: Yield
Details on results:
Definitive Test
Chemical Analysis of Test Loading Rates
Analysis of the test preparations at 0 hours showed measured test concentrations to range from 0.032 to 0.81 mg/L. A decline in measured test concentrations was observed at 72 hours in the range of less than the limit of quantification (LOQ) of the analytical method employed, determined to be 0.0019 mg/L, to 0.082 mg/L indicating that the test item was unstable over the test duration.
Given that toxicity cannot be attributed to a single component or mixture of components but to the test item as a whole, the results were based on nominal loading rates only.

Inhibition of growth rate
ErL10 (0 - 72 h) : 29 mg/L loading rate WAF
ErL20 (0 - 72 h) : 55 mg/L loading rate WAF
ErL50 (0 - 72 h) : >100 mg/L loading rate WAF**

Where ErLx is the loading rate that reduced growth rate by x%.
It was not possible to calculate an ErL50 value as no loading rate tested resulted in 50% inhibition of growth rate.
Statistical analysis of the growth rate data was carried out for the control and all loading rates using one way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf, 1981) and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett, 1955). There were no statistically significant differences between the control, 1.0, 3.2 and 10 mg/L loading rate WAFs (P0.05), however all other loading rates were significantly different (P<0.05) and, therefore the "No Observed Effect Loading Rate" (NOEL) based on growth rate was 10 mg/L loading rate WAF. Correspondingly the "Lowest Observed Effect Loading Rate" (LOEL) based on growth rate was 32 mg/L loading rate WAF.

Inhibition of Yield
EyL10 (0 - 72 h) : 10 mg/L loading rate WAF
EyL20 (0 - 72 h) : 16 mg/L loading rate WAF
EyL50 (0 - 72 h) : 35 mg/L loading rate WAF; 95% confidence limits 27 - 46 mg/L loading rate WAF

Where EyLx is the loading rate that reduced yield by x%.
There were no statistically significant differences between the control, 1.0, 3.2 and 10 mg/L loading rate WAFs (P0.05), however all other loading rates were significantly different (P<0.05) and, therefore the "No Observed Effect Loading Rate" (NOEL) based on yield was 10 mg/L loading rate WAF. Correspondingly the "Lowest Observed Effect Loading Rate" (LOEL) based on yield was 32 mg/L loading rate WAF.
Results with reference substance (positive control):
A positive control (Envigo Study Number MG09PL) used potassium dichromate as the reference item at concentrations of 0.25, 0.50, 1.0, 2.0 and 4.0 mg/L.

Exposure conditions and data evaluation for the positive control were similar to those in the definitive test.

Exposure of Pseudokirchneriella subcapitata (CCAP 278/4) to the reference item gave the following results:

ErC50 (0 – 72 h) : 1.5 mg/L; 95% confidence limits 1.3 – 1.7 mg/L
EyC50 (0 – 72 h) : 0.79 mg/L; 95% confidence limits 0.70 – 0.89 mg/L

No Observed Effect Concentration (NOEC) based on growth rate: 0.50 mg/L
No Observed Effect Concentration (NOEC) based on yield: 0.50 mg/L
Lowest Observed Effect Concentration (LOEC) based on growth rate: 1.0 mg/L
Lowest Observed Effect Concentration (LOEC) based on yield: 1.0 mg/L

The results from the positive control with potassium dichromate were within the normal ranges for this reference item.

Observations on Cultures

All test and control cultures were inspected microscopically at 72 hours. After 72 hours there were no abnormalities detected in the control or test cultures at 1.0, 3.2 and 10 mg/L loading rate WAFs, however cell debris was observed to be present in the test cultures at 32 and 100 mg/L loading rate WAF.

Water Quality Criteria

Temperature was maintained at 24 ± 1 ºC throughout the test. The pH value of the control cultures was observed to increase from pH 7.7 at 0 hours to pH 8.4 at 72 hours. The pH deviation in the control cultures was less than 1.5 pH units after 72 hours and therefore was within the limits given in the Test Guidelines.

Observations on Test Item Solubility

Observations on the test media were carried out during the mixing and testing of the WAFs. At both the start and end of the mixing period, and following a 1-Hour standing period, all loading rate WAFs were observed to have formed clear colorless media columns with solid test item floating at the media surface. Microscopic examination of the WAFs showed there to be no micro-dispersions of test item present.

At the start of the test all control and test cultures were observed to be clear colorless solutions. After the 72-Hour test period all control, 1.0, 3.2 and 10 mg/L loading rate WAF test cultures were observed to be green dispersions. The 32 mg/L loading rate WAF test cultures were observed to be pale green dispersions whilst the 100 mg/L loading rate WAF test cultures were observed to be extremely pale green dispersions.

Validation Criteria

The following data show that the cell concentration of the control cultures increased by a factor of 245 after 72 hours. This increase was in line with the OECD Guideline that states the enhancement must be at least by a factor of 16 after 72 hours.

Mean cell density of control at 0 hours:        5.00 x 103 cells per mL

Mean cell density of control at 72 hours:       1.22 x 106 cells per mL

The mean coefficient of variation for section by section specific growth rate for the control cultures was 16% and hence satisfied the validation criterion given in the OECD Guideline which states the mean must not exceed 35%. The coefficient of variation for average specific growth rate for the control cultures over the test period (0 – 72 h) was 3% and hence satisfied the validation criterion given in the OECD Guideline which states that this must not exceed 7%.

Validity criteria fulfilled:
yes
Conclusions:
The effect of the test item on the growth of Pseudokirchneriella subcapitata has been investigated over a 72-Hour period and gave the following results:

Response Variable EL50 95% Confidence Limits No Observed Effect Loading Rate Lowest Observed Effect Loading Rate
(mg/L Loading Rate WAF) (mg/L Loading Rate WAF) (NOEL) (mg/L) (LOEL) (mg/L)
Growth Rate >100 * 10 32
Yield 35 27 - 46 10 32
Executive summary:

A study was performed to assess the effect of the test item on the growth of the green alga Pseudokirchneriella subcapitata. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) 761/2009.

Methods

Due to the low aqueous solubility and complex nature of the test item for the purposes of the test the test item was prepared as a Water Accommodated Fraction (WAF). Following preliminary range-finding tests, Pseudokirchneriella subcapitata was exposed to Water Accommodated Fractions (WAFs) of the test item over a range of nominal loading rates of 1.0, 3.2, 10, 32 and 100 mg/L (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1oC.

Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter.

Results

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 0.032 to 0.81 mg/L. A decline in measured test concentrations was observed at 72 hours in the range of less than the limit of quantification (LOQ) of the analytical method employed, determined to be 0.0019 mg/L, to 0.082 mg/L indicating that the test item was unstable over the test duration.

However, given that the toxicity cannot be attributed to a single component or a mixture of components but to the test item as a whole, the results were based on nominal loading rates only.

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results (based on Loading rate WAF):

Growth Rate: EL50 = >100 mg/L NOEL = 10 mg/L LOEL = 32 mg/L

Yield:           EL50 = 35 mg/L NOEL = 10 mg/L LOEL = 32 mg/L

Description of key information

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results (based on Loading rate WAF):

Growth Rate: EL50= >100 mg/L NOEL = 10 mg/L LOEL = 32 mg/L

Yield:           EL50= 35 mg/L NOEL = 10 mg/L LOEL = 32 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
10 mg/L

Additional information