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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
1. HYPOTHESIS FOR THE ANALOGUE APPROACH
- Read-across hypothesis: "Different compounds have the same type of effect(s)"

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
- Target chemical: 2-Propenoic acid, homopolymer (purity ≥ 99.0%) = UVCB substance composed of acrylic acid monomers (Mw = 72 g/mol) and 2-carboxyethyl acrylate oligomers (average Mw = 208.8 g/mol)
- Source chemical: Acrylic acid = monoconstituent substance composed of acrylic acid monomers (Mw = 72 g/mol)

3. ANALOGUE APPROACH JUSTIFICATION
- Common structure: the constituents of the target and source chemicals share identical functional groups (i.e. one terminal carboxylic acid group and one terminal vinyl group) and only differ in the presence/absence of one or several -CH2-CH2-COO- pattern(s) in their structural backbones. This pattern being introduced as a result of (poly)addition reactions, it is only present in the polymerized units of acrylic acid (average number of -CH2-CH2-COO- patterns per vinyl group: < 3) and is absent from the monomer units.
- Common physico-chemical/fate properties: the target and source chemicals are both hydrophylic substances (log Pow < 1) with a high solubility in water and a low volatility (VP < 5 hPa). Both substances have a low potential for bioaccumulation in living organisms (log Pow < 4) and a low potential for persistence in environmental compartments (rapidly degradable).
- Common mode of action: the toxic effects of the target and source chemicals are expected to result from their acidic character (carboxylic acid group) and from the reactivity of their double bond (vinyl group). As the polyaddition reactions lead only to an increase in the chain length/molecular weight without an increase in the number of reactive functional groups, the low molecular-weight polymerized units of acrylic acid (from the test item) are not expected to exert higher toxicity than the monomer units. As a result, the target chemical, although only partially composed of acrylic acid monomers, is considered at the very worst to be as toxic as the source substance.

Further information (including data matrix) is available in the attached read-across justification document.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.75 mg/L
Basis for effect:
growth rate
Remarks on result:
other: Pseudokirchneriella subcapitata (freshwater sp.)
Remarks:
read-across from acrylic acid
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.03 mg/L
Basis for effect:
growth rate
Remarks on result:
other: Pseudokirchneriella subcapitata (freshwater sp.)
Remarks:
read-across from acrylic acid
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.13 - 0.205 mg/L
Basis for effect:
growth rate
Remarks on result:
other: Desmodesmus subspicatus (freshwater sp.)
Remarks:
read-across from acrylic acid
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.03 - 0.031 mg/L
Basis for effect:
growth rate
Remarks on result:
other: Desmodesmus subspicatus (freshwater sp.)
Remarks:
read-across from acrylic acid
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
105 mg/L
Basis for effect:
growth rate
Remarks on result:
other: Skeletonema costatum (marine sp.)
Remarks:
read-across from acrylic acid
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
36 mg/L
Basis for effect:
growth rate
Remarks on result:
other: Skeletonema costatum (marine sp.)
Remarks:
read-across from acrylic acid
Conclusions:
Using a read-across approach, the REACH substance is expected to exhibit a 76-hour 50% effective concentration EC50 in the range >0.1-1 mg/L, and a 76-hour no-observed-effect concentration NOEC in the range >0.01-0.1 mg/L, when exposed to freshwater algae species. Toxic effects are expected to be lower in marine algae species (i.e. 76h-EC50 > 100 mg/L and 76h-NOEC > 10 mg/L).
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study without detailed documentation
Qualifier:
according to guideline
Guideline:
EU Method C.3 (Algal Inhibition test)
GLP compliance:
yes
Analytical monitoring:
yes
Vehicle:
not specified
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Reference substance (positive control):
not specified
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.13 - 0.205 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.03 - 0.031 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Validity criteria fulfilled:
not specified
Conclusions:
A 50% effective concentration EC50 in the range 0.130-0.205 mg/L and a 10% effective concentration EC10 in the range 0.030-0.031 mg/L were obtained following a 72-hour exposure of freshwater green algae Desmodesmus subspicatus to acrylic acid.
Executive summary:

The toxicity of acrylic acid to freshwater green algae Desmodesmus subspicatus was determined in a GLP-compliant study performed in accordance with standard methods. A 72-hour 50% effective concentration EC50 in the range 0.130-0.205 mg/L and a 72-hour 10% effective concentration EC10 in the range 0.030-0.031 mg/L were obtained based on measured concentrations.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study without detailed documentation
Qualifier:
according to guideline
Guideline:
ISO 10253 (Water quality - Marine Algal Growth Inhibition Test with Skeletonema costatum and Phaeodactylum tricornutum)
GLP compliance:
yes
Analytical monitoring:
yes
Vehicle:
not specified
Test organisms (species):
Skeletonema costatum
Test type:
static
Water media type:
saltwater
Limit test:
no
Total exposure duration:
72 h
Reference substance (positive control):
not specified
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
105 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
36 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Validity criteria fulfilled:
not specified
Conclusions:
A 50% effective concentration EC50 of 105 mg/L and a no-observed-effect concentration NOEC of 36 mg/L were obtained following a 72-hour exposure of marine diatoms Skeletonema costatum to acrylic acid.
Executive summary:

The toxicity of acrylic acid to marine diatoms Skeletonema costatum was determined in a GLP-compliant study performed in accordance with standard methods. A 72-hour 50% effective concentration EC50 of 105 mg/L and a 72-hour no-observed-effect concentration NOEC of 36 mg/L were obtained based on measured concentrations.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study without detailed documentation
Qualifier:
according to guideline
Guideline:
other: The Notice on the Test Method Concerning New Chemical Substances < Algal Growth Inhibition Test, Daphnia Acute Immobilization Test, and Fish Acute Toxicity Test >
GLP compliance:
yes
Analytical monitoring:
yes
Vehicle:
not specified
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Test type:
not specified
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.2-24.2°C
pH:
7.3-8.2 (no pH adjustment)
Nominal and measured concentrations:
Nominal concentrations: control, 0.0032, 0.010, 0.032, 0.10, 0.32, 1.0, 3.2, 10 mg/L
Details on test conditions:
TEST SYSTEM:
- Exposure system: shaking cultivation (100 r/min)
- Material, size, headspace, fill volume: test solution volume 100 mL/vessel
- Initial cells density: ca. 10000 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

TEST MEDIUM / WATER PARAMETERS:
- Source/preparation of dilution water: Used the medium shown in OECD guideline for testing of chemicals: 201 Alga, Growth Inhibition Test (1984)

OTHER TEST CONDITIONS:
- Photoperiod: continuous lighting
- Light intensity and quality: 90 - 95 micromol/m2/s (irradiating continuously and uniformly by using white fluorescent lamp)
Reference substance (positive control):
not specified
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.75 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% CL 0.69-0.82 mg/L
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.03 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
The mean measured concentration obtained by the geometric mean from the measured value of test substance concentration in test solution was used for calculation of result.
Validity criteria fulfilled:
not specified
Conclusions:
A 50% effective concentration EC50 of 0.75 mg/L (95% CL 0.69-0.82 mg/L) and a no-observed-effect concentration NOEC of 0.03 mg/L were obtained following a 72-hour exposure of freshwater green algae (Pseudokirchneriella subcapitata) to acrylic acid.
Executive summary:

The toxicity of acrylic acid to freshwater green algae Pseudokirchneriella subcapitata was determined in a GLP-compliant study performed in accordance with standard methods. A 72-hour 50% effective concentration EC50 of 0.75 mg/L (95% CL 0.69-0.82 mg/L) and a 72-hour no-observed-effect concentration NOEC of 0.03 mg/L were obtained based on measured concentrations.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
no final test / no analytical monitoring / no GLP
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
yes
Remarks:
no final test performed (at the request of the sponsor)
GLP compliance:
no
Specific details on test material used for the study:
- Composition of test material: 2-carboxyethyl acrylate oligomers (= homopolymers of acrylic acid + 2-carboxyethyl acrylate) and acrylic acid
- Analytical purity: 98.4%
- Purity test date: 22 May 2019
- Lot/batch No.: BA9E59810
- Expiration date of the lot/batch: 13 May 2020
- Appearance: Colourless limpid liquid
- Storage: In darkness at room temperature
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
21–24 °C (controlled at ± 2°C)
pH:
7.9-8.9
Nominal and measured concentrations:
Nominal concentrations: 0, 0.0103, 0.047, 0.217 and 1 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: glass Erlenmeyer flasks (300 mL) covered by air-permeable lids
- Fill volume: 100±5 mL
- Initial cells density: 5000 cells/mL
- Control end cells density: 778600 cells/mL
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 2

GROWTH MEDIUM
- Standard medium used: yes (OECD medium)

OTHER TEST CONDITIONS
- Sterile test conditions: not specified
- Adjustment of pH: not specified
- Photoperiod: permanent illumination
- Light intensity and quality: 75.3-76.9 μE m–2s–1

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: at test end
Reference substance (positive control):
not specified
Details on results:
No considerable inhibition of the algal growth was observed at the tested concentration levels (up to 1.0 mg test item/L). In none of the concentration levels, deformed and/or damaged algal cells were observed during microscopic inspection.

Cell number per mL (divided by 104) in Raphidocelis subcapitata as dependent on concentration of the test item and time

Concentrations

[mg test item/L]

Control

0.0103

0.0473

0.217

1.00

0 h

Replicates

2

2

2

2

2

 

Mean [cells]*

0.5

0.5

0.5

0.5

0.5

72h

Replicates

2

2

2

2

2

 

Mean [cells]

77.86

99.17

103.91

105.74

98.25

Mean: arithmetic mean

* nominal initial cell number of 0.5×104cells per mL

Inhibition of Yield: Yield per mL (divided by 104) of Raphidocelis subcapitata in relation to concentration of the test item and % inhibition caused by the test item, after 72 hours.

Nominal

concentration

[mg test item/L]

Mean yield

[cells]

Std. Dev.

[cells]

n

%Inhibition

Control

77.86

1.952

2

 

0.0103

99.17

8.818

2

-27.36

0.0473

103.91

8.217

2

-33.46

0.217

105.74

12.990

2

-35.81

1.00

98.25

9.072

2

-26.18

Mean: arithmetic mean; Std. Dev.: standard deviation; n: number of replicates; negative inhibition represents increas compared to the control values.

Inhibition of Growth Rate: Growth Rate of Raphidocelis subcapitata in relation to concentration of the test item and % inhibition caused by the test item, after 72 hours.

Nominal

concentration

[mg test item/L]

Mean

growth rate

[day-1]

Std. Dev.

[day-1]

n

%Inhibition

Control

1.6848

0.00830

2

 

0.0103

1.7643

0.02953

2

-4.72

0.0473

1.7800

0.02626

2

-5.65

0.217

1.7850

0.04086

2

-5.95

1.00

1.7612

0.03067

2

-4.54

Mean: arithmetic mean; Std.Dev.: standard deviation; n: number of replicates; negative inhibition represents increas compared to the control values.

Validity criteria fulfilled:
yes
Remarks:
Mean biomass increase in the control cultures: factor of at least 16 within the 72-hour test period (found: 157). Coefficient of variation of average specific growth rates during test period in replicate control cultures: up to 7% (found: 0.49%).
Conclusions:
No considerable inhibition of the algal growth was observed at the tested concentration levels (up to 1.0 mg test item/L).
Executive summary:

The toxicity of the test item to freshwater green algae Raphidocellis subcapitata was investigated in a non-GLP compliant study performed in accordance with OECD Guideline No. 201. The aim of the study was to screen the toxicity of the test item; only a range-finding test was therefore performed. The test organisms were exposed to test concentrations in the range 0.01-1 mg/L, as well as to a control without the test item, for a test period of 72 hours. No considerable inhibition of the algal growth was observed at the tested concentration levels (up to 1.0 mg test item/L).

Description of key information

The REACH substance is composed of polymerized units of acrylic acid (identified as "2-carboxyethyl acrylate oligomers") and residual monomers of acrylic acid. As the toxicity of acrylic acid derivates is not expected to increase with their increasing molecular weight, a worst-case analogy was made between the REACH substance and acrylic acid, the latter being considered as its most toxic constituent.

According to the data available on acrylic acid, the REACH substance is expected, by analogy, to exhibit a 72-hour 50% effective concentration ErC50 in the range >0.1-1 mg/L, and a 72-hour no-observed-effect concentration NOErC in the range >0.01-0.1 mg/L, when exposed to freshwater alga species; toxic effects are expected to be lower in marine algae species. This assumption is supported by the results from a range-finding non-GLP study performed to screen the toxicity of the REACH substance to freshwater green algae: no significant inhibition of the algal growth rate was observed at the highest test concentration (1 mg/L) at the end of the 72-hour exposure period. These results confirm that the analogy made between the REACH substance and acrylic acid does not lead to any underestimation of hazards to aquatic algae.

The lowest ErC50 and ErC10 values obtained with acrylic acid (i.e. 0.13 mg/L and 0.03 mg/L, respectively) were used, by analogy, for the environmental hazard assessment of the REACH substance.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.13 mg/L
EC10 or NOEC for freshwater algae:
0.03 mg/L

Additional information

The toxicity of the REACH substance to freshwater green algae was screened in a non-GLP compliant range-finding study performed in accordance with standard methods, with deviations. The study is considered as reliable with restrictions (Klimisch 2) and is selected as a supporting study for the endpoint.