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Toxicity to aquatic plants other than algae

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Endpoint:
toxicity to aquatic plants other than algae
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
Not reported
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Meets generally accepted scientific standards, well documented and acceptable for assessment
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
other: ASTM, Proposed New Standard Practice for Conducting Static Toxicity Tests with Duckweed
Deviations:
not specified
Principles of method if other than guideline:
Not applicable
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material: anhydrous AlCl3
- Analytical purity: 99.7%
- Source: MCB Manufacturing Chemists, Inc.
- Lot/batch No.: B7N14
Analytical monitoring:
yes
Details on sampling:
- Concentrations: all exposures including control
- Sampling method: samples were collected before, at the beginning of, and at the end of the 96 hr exposure. Samples (15-20 mL) were collected midway between the surface and bottom of the water column in the center of each exposure chamber. A 30 mL adjustable-volume glass-teflon syringe was rinsed three times with the exposure water prior to collecting a sample.
- Sample storage conditions before analysis: All samples were immediately acidified to 1% (v/v) with concentrated nitric acid (Baker Instra analyzed Lot No: 340040). Two mL of potassium chloride solution (95 g KCl/L) was added per 100 mL sample, as suggested in method 202.1. Methods for Chemical Analysis of Water and Wastewater (U.S. EPA, 1979).
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Exposure and control tanks were prepared a minimum of 48 hr in advance of organism introduction to the tanks. The water volume was measured, then added to each exposure tank, and aluminum introduced from a 50,000 mg/l stock solution. Daily adjustments of pH were necessary in many of the exposures. Tests run at pH values above neutrality declined in pH in proportion to the total aluminum present. Controls dropped the least or not at all. Tests run at a pH below neutrality (6.5 nominal) rose in pH in all test chambers.
- Evidence of undissolved material: a precipitate was readily apparent at concentrations of 3.12 mg/L or above
- All other template details: Not reported
Test organisms (species):
Lemna minor
Details on test organisms:
TEST ORGANISM
- Common name: duckweed
- Source: A stock culture of Lemna minor was obtained from Dr. W. Wang, Water Quality Section, Illinois State Water Survey, Peoria, Illinois.
- All other template details: Not reported

ACCLIMATION
- Acclimation period: 7 days
- Culturing media and conditions: maintained in dilution water
- Any deformed or abnormal cells observed: not reported
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
Post exposure observation period:
Not reported
Hardness:
47.4 mg/L as CaCO3
Test temperature:
24 ± 2 degrees C
pH:
two pH levels: 7.6 ± 0.05 and 8.2 ± 0.05
Dissolved oxygen:
Not reported
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal test concentrations (mg/L): 0 (control), 3.12, 6.25, 12.5, 25.0, 50.0
Measured concentrations (mg/L): <0.3, 2.8, 5.9, 11.4, 23.2, 45.7
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 mL beaker
- Material, size, headspace, fill volume: 200 mL of test solution in each beaker
- Aeration: no
- Type of flow-through (e.g. peristaltic or proportional diluter):
- No. of colonies per replicate: 10
- No. of fronds per colony: 2
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
- All other template details: Not reported

GROWTH MEDIUM: Not reported

SEDIMENT USED: Not applicable

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Lake Superior water collected from a tap on the City of Cloquet, MN raw water intake in the City of Superior, WI. The source of the water was from approximately 3200 meters offshore on the lake bottom.
- Total solids: 61 ± 5 mg/L
- Particulate matter (total suspended solids): <1.0 mg/L
- Chloride: 1.5 ± 0.42 mg/L
- Alkalinity: 41.6 ± 1.27 mg/L as CaCO3
- Culture medium different from test medium: no
- Intervals of water quality measurement: measured on each batch of water used
- All other template details: Not reported

OTHER TEST CONDITIONS
- Sterile test conditions: not reported
- Adjustment of pH: Exposure solutions were pH adjusted using either NaOH or HCl of ACS grade purity if the pH differed from the desired test pH by more than 0.2 units.
- Photoperiod: not reported
- Light intensity and quality: 400 ± 40 ft. candles

EFFECT PARAMETERS MEASURED : total number of fronds
- Determination of frond number: nor reported, assumed manual counting

RANGE-FINDING STUDY: Not reported
Reference substance (positive control):
no
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
> 45.7 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
frond number
Remarks on result:
other: Unbounded NOEC for both pH levels
Details on results:
- Other: pH dropped during the test from 0.2 to 1.0 pH units. The 96 hr water column concentrations of Al were all at or below the detection limit with the exception of two questionable values.
- All other template details: Not reported
Results with reference substance (positive control):
Not applicable
Reported statistics and error estimates:
Not reported

TABLE 3. Frond Production by Duckweed (Lemna minor) Exposed for 96 Hr to A13+ in Lake Superior Water at Initial pH Values of 7.6 and 8.2.

Al3+ Concentration (mg/L)

 

Nominal

0

3.12

6.25

12.5

25

50

 

Total Measured 1

<0.3

2.8

5.9

11.4

23.2

45.7

pH 7.6

Mean Number of Fronds (± SD)

39.0 ± 3.5

37.0 ± 2.0

38.0 ± 1.7

38.7 ± 1.2

36.7 ± 2.5

38.3 ± 1.2

 

Percent Effect

-

10.5

5.3

1.6

12.1

3.7

pH 8.2

Mean Number of Fronds (± SD)

42.7 ± 0.6

36.3 ± 3.8

37.0 ± 2.6

38.7 ± 2.9

39.3 ± 3.2

40.7 ± 1.2

 

Percent Effect

-

28.2

25.1

17.6

15

8.8

 

1- Total measured Al is the initial amount present in the water column prior to pH adjustment and the start of the test. No precipitate was observed.

Conclusions:
96 hr exposure of Lemna minor to aluminium chloride concentrations up to 45.7 mg/L resulted in no significant effects on frond number compared to controls at a pH of 7.6 or 8.2.
Endpoint:
toxicity to aquatic plants other than algae
Type of information:
experimental study
Adequacy of study:
disregarded due to major methodological deficiencies
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
unsuitable test system
Principles of method if other than guideline:
Testing procedure is outlined in the publication
GLP compliance:
not specified
Test organisms (species):
other: Isoetes lacustris
Details on test organisms:
15 rooted sporelings of I. lacustris were carefully collected from the upper sediment using a syringe sampler (200 mL) in August 2008, 2010, 2011, 2013, and 2017. These sporelings were examined for biometry and Al uptake.
Mature spores of I. lacustris were obtained from opened sporangia of 50 macro-trophosporophylls and 50 micro-trophosporophylls harvested from the lake plants in October 2008. In the laboratory, the spores were released and debris rinsed off with distilled water. The spores were then kept in distilled water for six months in a growth box at 4 °C in the dark, simulating conditions at the surface sediment layer during winter, when spore germination is inhibited by low tempera- tures of 1–10 °C
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
52 wk
Remarks on exposure duration:
May 2009-April 2010
pH:
5.0
Nominal and measured concentrations:
Nominal: 0 (control), 100, 200, 300, 500 and 1000 μg/L
Details on test conditions:
The experiments lasted for two consecutive growing seasons (May–October; 17 °C; photoperiod, 14 h:10 h, light:- dark, ≤50 μmol m2/s PAR) and an interposed winter season (November–April, 4 °C, dark), thus providing enough time for spores of I. lacustris to germinate, and macrogametophytes and sporelings to develop
Details on results:
Combined effect of pH and Al, with an EC50 of 100 µg/L at pH5
Reported statistics and error estimates:
For each variable, the fits of commonly accepted nonthreshold (linear) and threshold (nonlinear, S- shaped) regression models to the data were compared in order to determine whether the dose–response relationship shows a risk at all exposures (linear model), or whether there is a threshold below which no adverse effects would be expected (S-shaped model). The variables not-fitting either regression model were further tested with ANOVA for a hormetic effect to assess whether adaptive mechanisms might be induced (i.e., stimu- lated) by low doses.
The best-fit values of model para- meters, ANOVA, and all respective tests were calculated using PRISM v. 6

Macrogametophyte rhizoids were the primary target organs that consistently indicated acidity or Al toxicity stress.

The acidity and Al toxicity EC50values of pH = 5 and CAl= 100 μg/L, respectively, as deduced for macrogametophyte rhizoids in our laboratory experiments, could be used as thresholds for the modelling of sporeling survival and recruitment success ofI. lacustrisin Černé Lake.

Though both hydrogen and aluminium ions are root toxicants with expected inhibitory effects on quillwort absorptive organs, our findings show the capability of the sporophyte root system to compensate for stressor-induced damage (inhibition) by stimulating growth.

Conclusions:
Acidic, Al-toxic lake water is primarily detrimental to the shallow- rooted early ontogenetic stages of I. lacustris, rather than to the deep- rooted adult plants. The sensitive responsiveness of the plant macro- gametophyte makes this spore-producing lycopod a suitable indicator taxon for the identification of acidification stress in oligotrophic soft- water lakes. On the contrary, the adults are highly resistant to the direct phytotoxic and acidifying effects of the lake water, and their long life span allowed for long-term population survival. The recruitment success of I. lacustris quillwort is hindered by the synergistic effects of its long germination phenology and consequent long exposure to low pH and elevated Al concentrations. Our study provides compelling evidence on the stage-specific responses of an isoetid species to changes at the water–sediment interface, helping to distinguish primary (high acidity and aluminium ion toxicity) from secondary (competition of acidotolerant species) effects of lake water acidification on the original flora in softwater lakes.
Executive summary:

The aquatic quillwort Isoëtes lacustris L. survived five decades of severe acidification in Černé Lake (Bohemian Forest, central Europe), but failed to reproduce. To detect which ontogenetic stage is more affected by water acidification and to identify water chemistry thresholds for successful recruitment, experiments were carried out on quillwort sporelings grown in the laboratory, using different pH (4–8) and aluminium (Al) concentrations (0–1000 μg/L). Growth-related symptoms and Al accumulations in tissues were compared with those observed in sporelings collected in the lake. In the laboratory, the threshold Al concentrations ≥100 μg/L and pH ≤ 5.0 reduced absorptive organs (macrogametophyte rhizoids, roots, and root hairs), so that the ratio of below-ground to above-ground sporeling biomass decreased to <1. Nonetheless, stimulatory growth was demonstrated that affected the dose-response relationships of both absorptive and assimilative organs as well as sporeling growth restoration. The sporelings exposed to Al concentrations ≥100 μg/L accumulated high amounts of Al in their macrogametophytes and roots, but not in leaves. The lake sporelings had markedly longer roots, lower Al ac- cumulations, but more reduced rhizoids and root hairs than those at 100 μg/L of Al in the laboratory. Even though water acidification was harmful to the shallow-rooted early ontogenetic stages, the in situ population survived due to the resistance and long life span of the deep-rooted adults. The effects of water acidification on sympatric congeneric quillworts as well as the other isoetids and competitive macrophytes in acid-sensitive softwater lakes are discussed, taking into account the influence of exposure to threshold acidity and Al toxicity and also the likelihood of such exposure.

Endpoint:
toxicity to aquatic plants other than algae
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
11/2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP comparable to guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 221 (Lemna sp. Growth Inhibition Test)
Qualifier:
according to guideline
Guideline:
other: Environment Canada (EC). 2007. Biological Test Method: Test for measuring the inhibition of growth using the freshwater macrophyte, Lemna minor. Conservation and protection, Environmental Protection, Ottawa, ON, Report EPS 1/RM/37.
Principles of method if other than guideline:
/
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material (as cited in study report): Aluminum nitrate nonahydrate
- Molecular formula (if other than submission substance): Al(NO3))3.9H2O
-Source: J.T. Baker, Philipsburg, NJ, USA
- Analytical purity:100.6%
- Impurities (identity and concentrations): Ca = 0.001%, Cl = 0.001%, Mg = 0.0002%, K = 0.0005%, Na = 0.003%, Pb = 0.0006%, Fe = 0.001%
- Purity test date: 20/10/2009
- Lot/batch No.:H43606
- Storage condition of test material:stored and sealed in its original container at room temperature
Analytical monitoring:
yes
Details on sampling:
- Analytical samples were taken from each treatment
- Sampling method:

TOTAL ALUMINUM
Approximately 5 mL was drawn into the syringe to rinse the inside of the syringe and then expunged. Then 15 mL of sample was drawn into the syringe and injected into a 15 mL polypropylene conical tube. Samples of old waters were taken from a composite of each replicate from each concentration. Old water was poured off from the top half/layer of the water column within each beaker.

DISSOLVED ALUMINUM
Approximately 20 mL was drawn into the syringe of which 5 mL was pushed through the filter to waste and the remaining 15 mL was collected into a 15-mL polypropylene conical test tube.

MONOMERIC ALUMINUM
Following collection of a sample for dissolved aluminum analysis, the same filter was used to filter approximately 15 mL aliquots for monomeric aluminum analysis. Monomeric samples were immediately analyzed.
- Sample storage conditions before analysis: Samples were preserved with trace metal grade nitric acid (AR-ACS grade, Mallinckrodt Chemical, Hazelwood, MO, USA) to pH < 2 and refrigerated (0 - 4 °C) prior to analysis.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method:A stock solution of 10 g Al/L was prepared by addition of 69.51 grams of Al(NO3)3·9H2O to 500 mL of Milli-Q water in a volumetric flask. The stock solution was then stored in a plastic container in the dark at 0 - 4°C. All concentrations within this report are expressed as micrograms Al per liter (μg/L Al).
Test organisms (species):
Lemna minor
Details on test organisms:
TEST ORGANISM
- Common name:Common Duckweed
- Source (laboratory, culture collection):OSU AquaTox (An initial stock of L. minor fronds was obtained from the Canadian Phycological Culture Centre (Waterloo, Ontario, Canada))
- Age of inoculum (at test initiation):10 days
- Method of cultivation:in Swedish Standard (SIS) Growth Media (OECD 2006)
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
7 d
Post exposure observation period:
/
Hardness:
32 mg/L as CaCO3
Test temperature:
25 +/- 2°C
pH:
5.8-6.3
Dissolved oxygen:
/
Salinity:
/
Nominal and measured concentrations:
Nominal concentration: 0, 625, 1250, 2500, 5000 and 10000μg/L
Average measured total Al concentration: <15.1; 666.8; 1116.2; 2760.3; 5313.8; 10482.3 μg/L
Details on test conditions:
TEST SYSTEM
- Incubation chamber used: yes
- Test vessel:250ml glass beaker
- Material, size, headspace, fill volume: glass beaker filled with 200ml of test solution
- Renewal rate of test solution (frequency/flow rate): water changes were performed on day 2 and 5
- Control end cells density:
- No. of colonies per vessel: 9-12
- No. of fronds per colony:2-4
- No. of vessels per concentration (replicates):3
- No. of vessels per control (replicates):1

GROWTH MEDIUM
- Detailed composition if non-standard medium was used: Swedish Standard Growth Media with the addition of MOPS (4-morpholinepropane sulphonic acid). The media was prepared as detailed in standard OECD methods (OECD 2006). The water was pH adjusted to 6.0 using dilute HCl and NaOH.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: The dilution/control water used in the toxicity test was Swedish Standard Growth Media with the addition of MOPS (4-morpholinepropane sulphonic acid). The media was prepared as detailed in standard OECD methods (OECD 2006). The water was pH adjusted to 6.0 using dilute HCl and NaOH. A new batch of media was prepared on the day prior to test initiation and each water renewal. At test initiation, the dilution/control water was characterized for hardness, alkalinity, and ammonia (NH3). The water was warmed to test temperature (25 ± 2°C) prior to use in the toxicity tests.
- Ca/mg ratio:1.17
- Alkalinity: 16 mg/L as CaCO3
- DOC: 208 mg/L
- Total residual chlorine: N/A
- Ammonia: <1.0 mg/L
- Calcium: 8.65 mg/L
- Magnesium: 7.42 mg/L
- Sodium: 28.2 mg/L
- Potassium: 3.34 mg/L
- Chloride: 19.9 mg/L
- Sulfate: 25.6 mg/L
- Culture medium different from test medium:no
- Intervals of water quality measurement: at test initiation, at renewal, (in both freshly prepared renewal waters and discarded waters), and at test termination. Hardness, alkalinity, and total ammonia were measured in the dilution water at test initiation.

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Photoperiod:under a continuous light cycle
- Light intensity and quality: cool-white fluorescent lights at 600-930 foot candles

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of frond number:[manual counting
- Determination of biomass:dry weight

Reference substance (positive control):
no
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
2 760.3 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
2 760.3 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
other: dry weight
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
2 760.3 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
growth rate
Duration:
7 d
Dose descriptor:
LOEC
Effect conc.:
5 313.8 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
LOEC
Effect conc.:
5 313.8 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
other: dry weight
Duration:
7 d
Dose descriptor:
LOEC
Effect conc.:
5 313.8 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
growth rate
Duration:
7 d
Dose descriptor:
EC10
Effect conc.:
2 694 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
frond number
Remarks on result:
other: CL: 1308-5550 μg/L
Duration:
7 d
Dose descriptor:
EC10
Effect conc.:
2 175 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
other: dry weight
Remarks on result:
other: CL: 417-11352 μg/L
Duration:
7 d
Dose descriptor:
EC10
Effect conc.:
4 545 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
growth rate
Remarks on result:
other: CL: 3348-6170 μg/L
Duration:
7 d
Dose descriptor:
EC20
Effect conc.:
3 982 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
frond number
Remarks on result:
other: CL: 2346-6757 μg/L
Duration:
7 d
Dose descriptor:
EC20
Effect conc.:
4 093 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
other: dry weight
Remarks on result:
other: CL: 1350 - 12413 μg/L
Duration:
7 d
Dose descriptor:
EC20
Effect conc.:
6 924 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
growth rate
Remarks on result:
other: CL: 5683-8437 μg/L
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
8 643 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
frond number
Remarks on result:
other: CL: 6800-10985 μg/L
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
14 537 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
other: dry weight
Remarks on result:
other: CL: 7063-29185 μg/L
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
15 966 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
: total Al
Basis for effect:
growth rate
Remarks on result:
other: CL: 13012 - 19590 μg/L
Details on results:
/
Results with reference substance (positive control):
/
Reported statistics and error estimates:
STATISTICAL ANALYSIS
Statistical analysis was performed using measured average total Al concentrations of newly prepared solutions. Differences in the number of fronds, dry weight, and growth rate at test termination were evaluated using a statistical computer package (Comprehensive Environmental Toxicity Information System [CETIS], Tidepool Scientific Software, McKinleyville, CA, USA and Toxicity Relationship Analysis Program [TRAP], Duluth, MN, USA). If the data met the assumptions of normality and homogeneity, the NOEC and LOEC were estimated using an analysis of variance to compare (p = 0.05) organism performance in the experimental treatments with that observed in the control. The effective concentrations to reduce growth by 10%, 20%, or 50% relative to control performance (EC10/EC20/EC50) were estimated using threshold sigmoid regression analysis. Exposure concentrations were log-transformed before determination of the EC10, EC20, and EC50 values.

Table: Biological results

 Average measured total concentration Al (μg/L)  Frond Count  Total dry weight (mg)  Growth rate (units)
 2.0  137.0 ± 13.9  14.58 ± 2.22  0.3885 ± 0.014
 666.8  137.7 ± 21.0  14.23 ± 1.68  0.3885 ± 0.022
 1116.2  118.3 ± 11.0  13.79 ± 1.67  0.3676 ± 0.013
 2760.3  125.0 ± 11.8  13.20 ± 0.98  0.3755 ± 0.013
 5313.8  89.7 ± 3.8 10.29 ± 0.80   0.3283 ± 0.006
 10482.3  53.3 ± 2.5  8.95 ± 1.15  0.2541 ± 0.007
Conclusions:
Total measured exposure concentrations ranged from 2 to 10,482.3 μg Al/L and resulted in a significant effect on plant growth at the highest two treatments. The study resulted in a no observable effect concentration [NOEC] of 2760.3 μg/L total Al and a lowest observable effect concentration [LOEC] of 5313.8 μg/L total Al for growth. Total dry weight was determined to be the most sensitive growth endpoint. The effective concentrations to reduce growth (as total dry weight) by 10% and 20% relative to control performance (EC10 and EC20 with 95% confidence intervals) were 2175 (417 – 11352) and 4093 (1350 – 12413) μg/L total Al, respectively.
Executive summary:

As part of an environmental program designed to provide data for the setting of water quality standards, data describing the chronic toxicity of aluminum to a variety of aquatic organisms are needed. Aluminum toxicity is a function of the chemical species of aluminum present in the water and this speciation is a function of the physico/chemical properties (e.g., pH) of the water. To this end, efforts are underway to develop data describing the chronic toxicity of aluminum to aquatic life at hydrogen ion concentrations (i.e., pH) typical of natural environmental conditions (i.e., pH of 6.0). The study reported herein determines the chronic toxicity of aluminum, at a pH of 6.0, to the freshwater duckweed, Lemna minor. Use of this test organism qualifies as a level of organization (Phylum) that is not currently represented as part of the minimum taxonomic requirements for calculation of a predicted no effect concentration (PNEC) for the freshwater aquatic compartment, within the context of a species sensitivity distribution approach (European Commission 2003). In this study, L. minor was exposed to a series of aluminum concentrations for seven days, starting as 10 day old plants. To allow for possible changes in aluminum speciation, exposure solutions were aged for a 3- hour equilibration period prior to plant exposure. Nominal test concentrations ranged from 0 to 10,000 μg Al/L and total, dissolved, and monomeric aluminum were measured throughout the test. As the formation of insoluble chemical species was apparent through low dissolved measurements (all concentrations measuring below 15.1 μg Al/L, with two exceptions [21.8 and 25.8 μg Al/L]), total Al was used to interpret the biological data in this study. Measured pH values in the test averaged a pH of 6.1. Total measured exposure concentrations ranged from 2 to 10,482.3 μg Al/L and resulted in a significant effect on plant growth at the highest two treatments. The study resulted in a no observable effect concentration [NOEC] of 2760.3 μg/L total Al and a lowest observable effect concentration [LOEC] of 5313.8 μg/L total Al for growth. Total dry weight was determined to be the most sensitive growth endpoint. The effective concentrations to reduce growth (as total dry weight) by 10% and 20% relative to control performance (EC10 and EC20 with 95% confidence intervals) were 2175 (417 – 11352) and 4093 (1350 – 12413) μg/L total Al, respectively.

Endpoint:
toxicity to aquatic plants other than algae
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Remarks:
Summary of available data used for the endpoint assessment of the target substance
Adequacy of study:
weight of evidence
Justification for type of information:
Refer to analogue justification provided in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
> 45.7 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Remarks:
Al
Basis for effect:
frond number
Remarks on result:
other:
Remarks:
unbounded NOEC for both pHlevels (7.6 ± 0.05 and 8.2 ± 0.05)
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
>= 8.643 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
element
Remarks:
total Al
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
EC10
Effect conc.:
>= 2 283 - <= 44 360 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: dry weight
Remarks on result:
other:
Remarks:
Range is based on normalised data from BLM; lower limit presents Ecoregion #7; upper limit presents Ecoregion #5

Description of key information

Two guideline studies with the aquatic plant L. minor (duckweed) were identified. Only in the OECD 221 tests that were reported in Stubblefield et al (2012) the testing period was sufficiently long. Effect concentrations were expressed as total aluminium, and assessed parameters were frond number, dry weight and growth rate. No adverse effects were noted, and consequently both NOEC and EC10 values are > 45.7 mg Al/L.

Key value for chemical safety assessment

Additional information