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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:
This study was conducted between 07 June 2017 and 28 June 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Reliability 1 is assigned because the study conducted according to OECD TG 201 in compliance with GLP, without deviations that influence the quality of the results.
Qualifier:
according to
Guideline:
OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)
Version / remarks:
2006
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.3 (Algal Inhibition test)
Version / remarks:
EC No. 761/2009
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Identification: Formaldehyde, reaction products with aniline, 4,4'-methylenebis[phenol]
Physical state/Appearance: Yellow solid
Batch: AAE0967900
Purity: Not provided
Expiry Date: 24 June 2018
Storage Conditions: Approximately 4 ºC 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. Only the concentration within the range to be used for the definitive test were analyzed.

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:
In view of the difficulties associated with the evaluation of aquatic toxicity of poorly water soluble test items, a modification of the standard method for the preparation of aqueous media was performed. In cases where the test item is a complex mixture and is poorly soluble in water, an approach endorsed by several important regulatory authorities in the EU and elsewhere (ECETOC 1996, OECD 2000 and Singer et al 2000), is to expose organisms to a Water Accommodated Fraction (WAF) of the test item. Using this approach, aqueous media are prepared by mixing the test item with water for a prolonged period. At the completion of mixing and following a settlement period, the test item phase is separated by siphon and the test organisms exposed to the aqueous phase or WAF (which may contain dissolved test item and/or leachates from the test item). Exposures are expressed in terms of the original concentration of test item in water at the start of the mixing period (loading rate) irrespective of the actual concentration of test item in the WAF.

Validation of Mixing Period
Preliminary investigational work was carried out to determine whether stirring for a prolonged period produced significantly higher levels of dissolved test item in the WAF. A WAF of a nominal loading rate of 100 mg/L was prepared in culture medium and stirred using a stirring rate such that a vortex was formed to give a dimple at the water surface. One loading rate was stirred for a period of 23 hours and the other for a period of 95 hours. After a 1-Hour standing period the mixtures were then removed by siphon and samples taken for chemical analysis.
The results are summarized as follows:
Nominal Loading Rate (mg/L) Time (Hours)
24 96
Measured Concentration (mg/L) Measured Concentration (mg/L)
100 A peak was observed in the 96-Hour chromatogram which did not correlate to the test item.
It is evident from this work that increasing the stirring period did not significantly increase the amount of dissolved test item in the WAF and so preparation of the WAF was maintained at 24 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 ± 2”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 10^3 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 10^4 – 10^5 cells/mL.


Culture Medium
NaNO3 25.5 mg/L
MgCl2.6H2O 12.16 mg/L
CaCl2.2H2O 4.41 mg/L
MgSO4.7H2O 14.6 mg/L
K2HPO4 1.044 mg/L
NaHCO3 15.0 mg/L
H3BO3 0.186 mg/L
MnCl2.4H2O 0.415 mg/L
ZnCl2 0.00327 mg/L
FeCl3.6H2O 0.160 mg/L
CoCl2.6H2O 0.00143 mg/L
Na2MoO4.2H2O 0.00726 mg/L
CuCl2.2H2O 0.000012 mg/L
Na2EDTA.2H2O 0.30 mg/L
The culture medium was prepared using reverse osmosis purified deionized water and the pH adjusted to 7.5 with 0.1N NaOH or HCl.
Test type:
semi-static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Hardness:
not reported
Test temperature:
Temperature was maintained at 24 ± 1 °C
pH:
The pH value of the control cultures was observed to increase from pH 7.3 at 0 hours to pH 7.7 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.
Dissolved oxygen:
Not reported
Salinity:
Not reported
Conductivity:
Not reported
Nominal and measured concentrations:
Observations on Test Item Solubility
Observations on the test media were carried out during the mixing and testing of the WAF.
At both the start and end of the mixing period the 100 mg/L loading rate WAF was observed to have formed a clear colorless media column with flakes of test item at the media surface, dispersed throughout the media column and settled on the bottom of the mixing vessel. After standing the WAF was observed to have formed a clear colorless media column with flakes of test item at the media surface and settled on the bottom of the mixing vessel. Microscopic examination of the WAF showed micro-dispersions of test item to be present and hence it was considered justifiable to remove the aqueous phase by filtration through a glass wool plug and one piece of filter paper to remove as much undissolved test item as possible. Microscopic examination after filtration showed there to be no micro-dispersions of test item present.
Details on test conditions:
Experimental Design and Study Conduct
Due to the low aqueous solubility and complex nature of the test item, for the purposes of the study the test medium was prepared as a Water Accommodated Fraction (WAF) of the test item.

Validation of Mixing Period
Preliminary work was carried out to determine whether stirring for a prolonged period produced significantly higher measured test concentrations in the WAF.

Range-Finding Test
The loading rate to be used in the definitive test was determined by a preliminary range-finding test.
The range-finding test was conducted by exposing Pseudokirchneriella subcapitata cells to nominal loading rates of 10 and 100 mg/L for a period of 72 hours.
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.
An aliquot (500 mL) of each of the loading rate WAFs was separately inoculated with algal suspension (10.0 mL) to give the required test concentrations of 10 and 100 mg/L loading rate WAF.
The control group was maintained under identical conditions but not exposed to the test item.
At the start of the range-finding test a sample of each test and control culture was removed and the cell density determined using a Coulter® Multisizer Particle Counter. The flasks were then plugged with polyurethane foam bungs and incubated (INFORS Multitron Version 2 incubator) at 24 ± 1 ºC 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.
After 72 hours the cell density of each flask was determined using a Coulter® Multisizer Particle Counter.
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 0-Hour samples were stored frozen prior to analysis. Only concentrations within the range to be used for the definitive test were analyzed.

Definitive Test
Based on the result of the range-finding test a "limit test" was conducted at a single loading rate of 100 mg/L to confirm that no effect on algal growth was observed.

Experimental Preparation
A nominal amount of test item (200 mg) was added to the surface of 2 liters of culture medium to give the 100 mg/L loading rate 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 mixture allowed to stand for 1 hour. Microscopic observations made on the WAF indicated that a significant amount of dispersed test item was present in the water column and hence it was considered justifiable to remove the WAF by filtering through a glass wool plug (2-4 cm in length). 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. A glass wool plug was inserted into the opposite end of the tubing and the WAF removed by mid-depth siphoning (the first 75-100 mL discarded). After siphoning the aqueous phase was passed through one sheet of filter paper to remove as much undissolved test item as possible. Microscopic observations of the WAF were performed after filtering and showed there to be no micro-dispersions of test item present.
An aliquot (1 liter) of the WAF was inoculated with algal suspension (10.2 mL) to give the required test concentration of 100 mg/L loading rate WAF.
The concentration and stability of the test item in the test preparations were verified by chemical analysis at 0 and 72 hours.

Exposure Conditions
As in the range-finding test 250 mL glass conical flasks were used. Six flasks each containing 100 mL of test preparation were used for the control and 100 mg/L loading rate WAF 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 4.90 x 10^5 cells per mL. Inoculation of 1 liter of test medium with 10.2 mL of this algal suspension gave an initial nominal cell density of 5 x 10^3 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 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.

Assessments
Test Organism Observations
Samples were taken at 22, 45 and 72 hours and the cell densities determined using a Coulter® Multisizer Particle Counter. Three determinations were made for each sample. The nominally inoculated cell concentration (5.00 x 103^ cells/mL) was taken as the starting cell density.
To determine the potential effect of the test item on the appearance of algal cells, a sample was removed from each test and control culture (replicates pooled) at the end of the test. The shape and size of the algal cells was inspected microscopically and any abnormalities recorded.

Water Quality Criteria
The pH of the control and 100 mg/L loading rate WAF test concentration was determined at initiation of the test and after 72 hours exposure. The pH was measured using a Hach HQ30d Flexi handheld meter. The temperature within the incubator was recorded daily.
The appearance of the test media was recorded daily.

Vortex Depth Measurements
The vortex depth was recorded at the start and end of the mixing period.

Chemical Analysis of Test Loading Rates
Samples were taken from the control and the 100 mg/L loading rate WAF test group from the bulk test preparation at 0 hours and from the pooled replicates at 72 hours for quantitative analysis. All 0-Hour samples were stored frozen prior to analysis. Duplicate samples were taken at each occasion and stored frozen for further analysis if necessary.




Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Remarks:
WAF
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Remarks:
WAF
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Remarks:
WAF
Basis for effect:
cell number
Remarks:
Yield
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (dissolved fraction)
Remarks:
WAF
Basis for effect:
cell number
Remarks:
Yield
Details on results:
Validation of Mixing Period
Preliminary investigational work indicated that there was no increase in the amount of dissolved test item when the preparation period was extended for longer than 24 hours. Therefore, for the purpose of testing the WAF was prepared using a stirring period of 23 hours followed by a 1-Hour settlement period.

Range-finding Test
The results showed no effect on growth at 10 and 100 mg/L loading rate WAF.
Based on this information a single loading rate of six replicates of 100 mg/L was selected for the definitive test. This experimental design conforms to a "limit test" to confirm that no effect on growth was observed.
Chemical analysis of the 100 mg/L loading rate WAF test preparations at 0 and 72 hours (see Annex 4) showed measured test concentrations of less than the limit of quantification (LOQ) of the analytical method employed were obtained which was determined to be 0.031 mg/L. This does not infer that no test item was in solution, just that any dissolved test item was at a concentration of less than the LOQ.

Definitive Test
Chemical Analysis of Test Loading Rates
Chemical analysis of the test preparations at 0 and 72 hours (see Annex 4) showed measured test concentrations of less than the limit of quantification (LOQ) of the analytical method employed were obtained which was determined to be 0.031 mg/L. This does not infer that no test item was in solution, just that any dissolved test item was at a concentration of less than the LOQ.
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.

Growth Data
Growth rate and yield values for the control and test cultures after 72 hours and percentage inhibition values are given in Table 1.
From the data it is clear that the growth rate (r) and yield (y) of Pseudokirchneriella subcapitata (CCAP 278/4) were not affected by the presence of the test item over the 72-Hour exposure period.
It was considered unnecessary and unrealistic to test at loading rates in excess of 100 mg/L.
Accordingly the following results were determined from the data:

Inhibition of growth rate
ErL10 (0 - 72 h) : >100 mg/L loading rate WAF
ErL20 (0 - 72 h) : >100 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%.
Statistical analysis of the growth rate data was carried out for the control and 100 mg/L loading rate WAF test group using a Student’s t-test 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 (P0.05), between the control and 100 mg/L loading rate WAF test group and therefore the "No Observed Effect Loading Rate" (NOEL) based on growth rate was 100 mg/L loading rate WAF.

Inhibition of Yield
EyL10 (0 - 72 h) : >100 mg/L loading rate WAF
EyL20 (0 - 72 h) : >100 mg/L loading rate WAF
EyL50 (0 - 72 h) : >100 mg/L loading rate WAF

Where EyLx is the loading rate that reduced yield by x%.
Statistical analysis of the yield data was carried out as above. There were no statistically significant differences between the control and the 100 mg/L loading rate WAF (P>0.05), therefore the "No Observed Effect Loading Rate" (NOEL) based on yield was 100 mg/L loading rate WAF.

Validation Criteria
The following data show that the cell concentration of the control cultures increased by a factor of 226 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.
Nominal cell density of control at 0 hours : 5.00 x 10^3 cells per mL
Mean cell density of control at 72 hours : 1.13 x 10^6 cells per mL

The mean coefficient of variation for section by section specific growth rate for the control cultures was 6% 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 1% and hence satisfied the validation criterion given in the OECD Guideline which states that this must not exceed 7%.

Observations on Cultures
All test and control cultures were inspected microscopically at 72 hours. There were no abnormalities detected in any of the control or test cultures at 72 hours.

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 7.3 at 0 hours to pH 7.7 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.

Vortex Depth Measurements
The vortex depth was recorded at the start and end of the mixing period and was observed to have formed a dimple at the media surface.

Observations on Test Item Solubility
Observations on the test media were carried out during the mixing and testing of the WAF.
At both the start and end of the mixing period the 100 mg/L loading rate WAF was observed to have formed a clear colorless media column with flakes of test item at the media surface, dispersed throughout the media column and settled on the bottom of the mixing vessel. After standing the WAF was observed to have formed a clear colorless media column with flakes of test item at the media surface and settled on the bottom of the mixing vessel. Microscopic examination of the WAF showed micro-dispersions of test item to be present and hence it was considered justifiable to remove the aqueous phase by filtration through a glass wool plug and one piece of filter paper to remove as much undissolved test item as possible. Microscopic examination after filtration 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 and test cultures were observed to be green dispersions.
Results with reference substance (positive control):
A positive control (Envigo Study Number FP48BQ) 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) : 1.4 mg/L; 95% confidence limits 1.2 – 1.5 mg/L
EyC50 (0 – 72 h) : 0.60 mg/L; 95% confidence limits 0.52 – 0.69 mg/L

No Observed Effect Concentration (NOEC) based on growth rate: 0.25 mg/L
No Observed Effect Concentration (NOEC) based on yield: 0.25 mg/L
Lowest Observed Effect Concentration (LOEC) based on growth rate: 0.50 mg/L
Lowest Observed Effect Concentration (LOEC) based on yield: 0.50 mg/L

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

Table 1: Inhibition of Growth Rate and Yield in the Definitive Test

Nominal Loading Rate
(mg/L)

Growth Rate (cells/mL/hour)

Yield (cells/mL)

0 – 72 h

% Inhibition

0 – 72 h

% Inhibition*

Control

R1

0.073

 

9.64E+05

 

R2

0.076

 

1.20E+06

 

R3

0.076

 

1.20E+06

 

R4

0.077

-

1.27E+06

-

R5

0.075

 

1.08E+06

 

R6

0.074

 

1.03E+06

 

Mean

0.075

 

1.12E+06

 

SD

0.001

 

1.17E+05

 

100

R1

0.077

[3]

1.31E+06

 

R2

0.077

[3]

1.28E+06

 

R3

0.075

0

1.12E+06

 

R4

0.076

[1]

1.23E+06

 

R5

0.077

[3]

1.28E+06

 

R6

0.076

[1]

1.20E+06

 

Mean

0.076

[2]

1.24E+06

[10]

SD

0.001

 

7.10E+04

 

*       In accordance with the OECD test guideline only the mean value for yield is calculated

R1-R6= Replicates 1 to 6

SD= Standard Deviation

[ ] = Increase in growth as complared to controls

Validity criteria fulfilled:
yes
Remarks:
The data satisfied the validation criterion given in the OECD Guideline
Conclusions:
The effect of the test item on the growth of Pseudokirchneriella subcapitata has been investigated and gave EL50 values of greater than 100 mg/L loading rate WAF. The No Observed Effect Loading Rate was 100 mg/L loading rate WAF.
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 a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to a Water Accommodated Fraction (WAF) of the test item, at a single nominal loading rate of 100 mg/L (six replicate flasks) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1 °C.

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 and 72 hours showed measured test concentrations of less than the limit of quantification (LOQ) of the analytical method employed were obtained which was determined to be 0.031 mg/L. This does not infer that no test item was in solution, just that any dissolved test item was at a concentration of less than the LOQ.

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 EL50values of greater than 100 mg/L loading rate WAF. The No Observed Effect Loading Rate was 100 mg/L loading rate WAF.

It was considered unnecessary and unrealistic to test at loading rates in excess of 100 mg/L loading rate WAF.

Description of key information

A study was performed to assess the effect of the test item on the growth of Pseudokirchneriella subcapitata. The test was performed according to the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria.

The test item is very low soluble therefore the test solutions was prepared as a Water Accommodated Fraction (WAF).

Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to a WAF of the test item, at a single nominal loading rate of 100 mg/L.

Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group.

Analysis of the test preparations at 0 and 72 hours showed measured test concentrations of less than the limit of quantification (LOQ) of the analytical method employed were obtained which was determined to be 0.031 mg/L.

EL50values > 100 mg/L loading rate WAF. 

NOEL= 100 mg/L loading rate WAF.

According to the results, the test item is not toxic for Daphnia magna under the conditions of the test.

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L

Additional information