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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003-03-18 to 2003-11-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
Analytical samples (approximately 10 mL) were collected into 40 mL glass VOA vials that contained 2 mL of 0.01M H2SO4 and 0.5 mL methanol in HPLC water. Samples collected at the start of the toxicity test were collected from test solutions just prior to the addition of algae and distribution of the test solutions to sealed test vessels. Samples collected at the end of the toxicity test were centrifuged to remove algal cells from pooled replicate test vessels. Samples outside the calibration range were diluted into the range with 50/50 acetonitrile/HPLC water.
Vehicle:
no
Test organisms (species):
Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Algae
- Strain: Selenastrum capricornutum, UTEX 1648
- Source (laboratory, culture collection): The culture was originally procured from the Culture Collection of Algae at the University of Texas at Austin and delivered to T.R. Wilbury Laboratories on July 17, 2001.
- Age of inoculum (at test initiation): 8 days
- Method of cultivation: No data

ACCLIMATION
- Acclimation period: at least 14 days
- Culturing media and conditions (same as test or not): Yes
- Any deformed or abnormal cells observed: No data
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Post exposure observation period:
Not applicable
Hardness:
No data
Test temperature:
24 ± 2 °C
pH:
Initial: 7.4 - 7.6
Final: 7.1 - 9.9
Dissolved oxygen:
No data
Salinity:
No data
Nominal and measured concentrations:
- Nominal test concentrations: 0, 0.25, 0.50, 1.0, 2.0, 4.0 and 8.0 mg/L
- Initial measured concentrations: 0, 0.196, 0.453, 0.759, 1.47, 3.20 and 6.41 mg/L
- Final estimated test concentration after 72 h (because the instrument response was less than the lowest standard): 0, ND, <0.00440, 0.0187, 0.0530, 0.212 and 0.373 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Type: closed (sealed with Teflon-lined caps)
- Material, size, headspace, fill volume: clear glass 40 mL vials were filled to capacity to eliminate any head space
- Aeration: No
- Initial cells density: approximately 10000 algal cells/mL
- Control end cells density: 222000 cells/mL after 72 h
- No. of vessels per concentration (replicates): 11
- No. of vessels per control (replicates): 20
- A stability sample, prepared with a nominal concentration of 8.0 mg/L but not inoculated with algae, was incubated among the test vessels during the 72 hour exposure.

GROWTH MEDIUM
- Standard medium used: yes (freshwater AAP medium)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Sterile deionised water used to formulate the freshwater AAP medium
- Total organic carbon: Not detected (ND)
- Particulate matter: No data
- Metals:
- Aluminium: 0.02 mg/L
- Arsenic: ND
- Boron: ND
- Cadmium: ND
- Calcium: ND
- Chromium: ND
- Cobalt: 0.0034 mg/L
- Copper: ND
- Iron: ND
- Lead: 0.001 mg/L
- Magnesium: ND
- Mercury: ND
- Nickel: ND
- Potassium: ND
- Silver: ND
- Sodium: ND
- Zinc: 0.010 mg/L
- Pesticides: No data
- Chlorine: No data
- Alkalinity: No data
- Ca/mg ratio: ND
- Conductivity:No data
- Culture medium different from test medium: No
- Intervals of water quality measurement: Full analysis of the water was performed twice per year. The temperature in a representative vessel of water incubated with the test vessels was recorded continuously during the test. The pH of test solutions was measured and recorded in the single solution of each concentration prior to its distribution to test vessels at the beginning of the test, and in all test vessels used for the determination of the number of algal cells/mL at the end of the test.

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: pH was adjusted to 7.5 ± 0.1
- Photoperiod: 24 hour light maintained with cool-white fluorescent lights
- Light intensity and quality: approximately 400 footcandles (approximately 52 to 54 μEin/m²sec)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
The number of algal cells/mL in each test vessel and the occurrence of relative size differences, unusual cell shapes, colors, flocculations, adherence of cells to test containers, or aggregation of cells was determined visually by means of direct microscopic examination with a hemocytometer. At 24, 48, and 72 hours, three treatment vessels and six control vessels were randomly selected and sacrificed (opened to the atmosphere) to allow daily determination of the number of algal cells/mL. The remaining two vessels at each concentration were used for the determination of nonanal concentration at the end of the test.

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: 0, 0.01, 0.10, 1.0, 10 and 100 mg/L
- Results used to determine the conditions for the definitive study: At the conclusion of the range-finding test, the percent of control growth was as follows; 0.01, 0.10, and 1.0 mg/L = >100%, 10 mg/L = 9%, and 100 mg/L = <3%. A definitive test was initiated with a control and six concentrations of nonanal (0.50, 1.0, 2.0, 3.8, 7.5, and 15 mg/L). The test was terminated after 48 hours and repeated because analytical recoveries in samples collected at the start of the test were unacceptably low.
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
4.5 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% CL 4.03 - 5.02 mg/L
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
2.6 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
cell number
Remarks on result:
other: 95% CL 2.17 - 3.11 mg/L
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.79 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
biomass
Remarks on result:
other: 95% CL 1.36 - 2.37 mg/L
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.759 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
other: growth rate, cell number & biomass
Details on results:
- Exponential growth in the control: yes
- Observation of abnormalities: No effects (relative size differences, unusual cell shapes, colors, flocculations, adherence of cells to test containers, or aggregation of cells) were noted during the test.
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: Insoluble material was not observed during the test. Initial measured concentrations of nonanal ranged from 74 to 91% of the nominal concentrations and were used to calculate median effective concentrations (EC50s). Final measured concentrations were <1 to 5% of nominal concentrations. Initial measured concentrations were used for all calculations.
- At the conclusion of the definitive toxicity test, a 0.5 mL aliquot of test media from each test vessel where growth was maximally inhibited (the 3.20 and 6.41 mg/L nonanal concentrations) was combined with 100 mL of fresh media in a 250-mL flask. The cultures were incubated under test conditions for 72 hours. During this period the number of algal cells increased from an initial concentration of 1,600 cells/mL to approximately 580,000 cells/mL at 3.20 mg/L and from 330 cells/mL to 198,000 cells/mL at 6.41 mg/L, indicating that the toxic effects were algistatic rather than algicidal.

Analytical confirmation of the test substance in test solutions was performed to assess whether exposure to the test organism was maintained. Initial measured concentrations in the 6 dose levels were 0.196, 0.453, 0.759, 1.47, 3.2 and 6.41 mg/L (74 to 91% of the nominal concentrations). The final measured concentrations were respectively
Validity criteria fulfilled:
yes
Conclusions:
Exposure of Selenastrum capricornutum to nonanal for 72 h resulted in an EC50 of 4.50 mg/L when calculated using the average specific growth rate. The 72 h NOEC is 0.759 mg/L.
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The read-across hypothesis is based on different compounds which have similar properties. It is covered by scenario 2 in the ECHA Read-Across Assessment Framework [RAAF, ECHA 2017]. The source and target substance have similar ecotoxicological properties as a result of structural similarity, the same mode of action for aquatic toxicity and similar bioavailabilities (e.g. lipophilicity as modelled by log Kow).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
See section 3 in attached "Algal Inhibition Read-Across justification for Decanal (RAAF 2017 version)".

3. ANALOGUE APPROACH JUSTIFICATION
For details see attached "Algal Inhibition Read-Across justification for Decanal (RAAF 2017 version)". In summary, important considerations for the use of the read-across are:
• Decanal (target substance) is structurally similar to nonanal (source substance). Both are linear mono-aldehydes. The only structural difference is the chain length, C10 and C9 respectively
• Both substances are expected to act via the same mode of action for aquatic toxicity. Characterization using the OECD QSAR Toolbox shows that the 5 primary profilers relevant to acute aquatic toxicity are identical
• There are no impurities that are expected to affect the ecotoxicological properties of the source and target substance
• Both substances have similar physico-chemical properties relevant for fate and behaviour of the substance under aquatic toxicity test conditions (e.g. vapour pressure, water solubility and log Kow). Thus both substances are expected to exhibit similar exposure to the test organisms under similar test conditions.
• Uptake / lipophilicity (as modelled by log Kow) is a known determinant of the toxicity in aquatic organisms. Nonanal and decanal, which vary only by one carbon atom in chain length, have similar measured log Kow values of 3.4 and 3.8 respectively, and therefore the strength of aquatic toxicity for the two substances is expected to be similar.
• Both chemicals have been tested for ready biodegradability, toxicity to aquatic microorganisms and acute toxicity to daphnia and gave similar results. Furthermore, the 48-h EC50 daphnia results for both substances, the algae 72h ErC50 for the source and the fish 96h LC50 for the target substance are in the same classification band (1-10mg/L).
• Based on the above, the read-across is considered adequate for the purpose of classification and labelling and/or risk assessment.

4. DATA MATRIX
See Table 2 in attached "Algal Inhibition Read-Across justification for Decanal (RAAF 2017 version)".
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
4.5 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: read-across
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.759 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: read-across
Conclusions:
In a guideline study, conducted according to GLP, the closely-related substance nonanal was found to have an ErC50 (72 hr) (based on the initial measured test concentrations) of 4.5 mg/L and a NOEC (72 hr) of 0.759 mg/L - see source study summary for details.

The preferred observational end point in the algal growth inhibition test is growth rate because it is not dependent on the test design (ECHA guidance Chapter R.7b v1.1). The EU CLP regulation (No 1272/2008 and its adaption 286/2011) also states that classification should be based on the ErC50. Thus the 72-h EC50 and NOEC based on growth rate are used for classification purposes.

The detailed information provided in the read-across justification document indicates that the aquatic ecotoxicity of decanal (target substance) and nonanal (source substance) are expected to be similar as a result of structural similarity, similar mechanistic profiles and similar physicochemical properties. Therefore, direct read-across from the source substance is considered to give a reliable estimate of the algal inhibition 72-hr ErC50 and NOEC for decanal, which are respectively 4.5 and 0.759 mg/L.

Description of key information

A valid algal inhibition study is available for the analogue substance, nonanal. The 72h ErC50 was determined to be 4.50 mg/L and considered a reliable estimate for the target substance, decanal.

Key value for chemical safety assessment

EC50 for freshwater algae:
4.5 mg/L
EC10 or NOEC for freshwater algae:
0.759 mg/L

Additional information

A valid study is available for the analogue substance, nonanal. It is a GLP compliant study conducted in compliance with agreed protocols, with no or minor deviations from the standard test. Important considerations for the use of read-across are:

i) Decanal (the target chemical) is structurally similar to nonanal (the source substance). Both are linear aliphatic mono-aldehydes. The only structural difference is the chain length, C10 and C9 respectively.

ii) Both substances are expected to act via the same mode of action for aquatic toxicity. Characterization using the OECD QSAR Toolbox shows that the 5 primary profilers relevant to acute aquatic toxicity are identical

iii) There are no impurities that are expected to affect the ecotoxicological properties of the source and target substance

iv) Uptake / lipophilicity (as modelled by log Kow) is a known determinant of the toxicity in aquatic organisms. Nonanal and decanal, which vary only by one carbon atom in chain length, have similar measured log Kow values of 3.4 and 3.8 respectively, and therefore the strength of aquatic toxicity for the two substances is expected to be similar.

v) Both chemicals have been tested for ready biodegradability, acute toxicity to daphnia, and toxicity to microorganisms. Both chemicals gave similar results.

Based on the above, read-across is justified. Furthermore, the 48-h EC50 daphnia results for both substances, the algae 72h ErC50 for the source and the fish 96h LC50 for the target substance are in the same classification band (1-10mg/L) and as such the read-across is considered adequate for the purpose of classification and labelling and/or risk assessment.