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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Study period:
14 June 2010 - 29 July 2010
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP. The study is considered to be reliability 1 (reliable without restrictions); the read across of the result is considered to be reliability 2 (reliable with restrictions).
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
ISO 8692 (Water Quality - Fresh Water Algal Growth Inhibition Test with Scenedesmus subspicatus and Selenastrum capricornutum)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
Samples for possible analysis were taken from all test concentrations and the control according to the schedule below.
Frequency at t=0 h, t=24 h and t=72 h
Volume 4.8 ml
Storage Samples were stored in a freezer until analysis.

At the end of the exposure period, the replicates with algae were not pooled at each concentration before sampling. Samples were taken from only one replicate vessel per concentration, unless differences in cell density between replicate vessels were observed.
Compliance with the Quality criteria regarding maintenance of actual concentrations was demonstrated by running a test vessel at the highest substance concentration but without algae and samples for analysis were taken at the start, after 24 hours of exposure and at the end of the test period.
Additionally, reserve samples of 4.8 ml were taken from all test solutions for possible analysis. If not already used, these samples were stored in a freezer for a maximum of three months after delivery of the draft report, pending on the decision of the sponsor for additional analysis.
Vehicle:
no
Details on test solutions:
The batch of 202028/A tested was a clear colourless liquid with an aluminium content of 4.4%. The substance was completely soluble in test medium at the concentrations tested.

Preparation of test solutions started with a loading rate of 100 mg/l applying 15 minutes of magnetic stirring to accelerate the dissolving of the test substance in the test medium. The lower test concentrations were prepared by subsequent dilutions of the 100 mg/l concentration in test medium. The final test solutions were all clear and colourless.

After preparation, volumes of 50 ml were added to each replicate of the respective test concentration. Subsequently, 1 ml of an algal suspension was added to each replicate providing a cell density of 1000 cells/ml.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata
- Strain: NIVA CHL 1.
- Source (laboratory, culture collection): In-house laboratory culture
- Age of inoculum (at test initiation): 3 days before the start of the test, cells from the algal stock culture were inoculated in culture medium at a cell density of 1 x 10E4 cells/ml.
- Method of cultivation: Algae stock cultures were started by inoculating growth medium with algal cells from a pure culture on agar. The suspensions were continuously aerated and exposed to light (60 to 120 µE/m2/s when measured in the photosynthetically effective wavelength range of 400 to 700 nm. in a climate room at a temperature of 21-24°C.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
0.24 mmol(24 mg CaCO3/L)
Test temperature:
between 22.1 and 23.4°C
pH:
between 7.1 and 8.4
Nominal and measured concentrations:
Nominal concentrations: control and 1.0, 3.2, 10, 32 and 100 mg/l
Measured concentrations: The initial concentrations of aluminium were generally in agreement with nominal (72-100%). These concentrations significantly decreased during the test period. This decrease could be related to the fact that part of the test substance came out of the solution during the exposure period, as was observed before during the combined limit/range-finding test. From 24 hours of exposure onwards undissolved material was observed in all test concentrations. At nominal 3.2 mg/l the presence of undissolved material caused an anomaly in the measured concentrations.
Based on these results, the effect parameters were expressed in terms of both the nominal concentrations of PAX-XL9 and the average dissolved aluminium concentrations that were calculated to be 0.02, 0.04, 0.23, 0.47 and 2.8 mg/l.
Details on test conditions:
TEST SYSTEM
- Type: open
- Material, size, headspace, fill volume: 100 ml, normal headspace, 50 ml
- Aeration: no
- Initial cells density: 10000 cells/ml
- Control end cells density: 1600000 cells/ml
Replicates:
3 replicates of each test concentration;
6 replicates of the control;
1 extra replicate of each test concentration and the control for sampling purposes;
1 or 2 extra replicates of each test concentration without algae.

GROWTH MEDIUM
- Standard medium used: yes
OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuous
- Light intensity and quality: Continuously using TLD-lamps of the type ‘Cool-white’ of 30 Watt, with a light intensity within the range of 81 to 89 µE.m-2.s-1

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
72 h NOErC, 72 h NOEyC, 72 h ErC10, 72 h EyC10 ,72 h ErC50, 72 h EyC50

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2
- Test concentrations: control and 1.0, 3.2, 10, 32 and 100 mg/l
Reference substance (positive control):
yes
Remarks:
potassium dichromate (K2Cr2O7,)
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
3.1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% CI:0.36-8.4 mg/l
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
14 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% CI:6.8-24 mg/l
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: Yield
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.88 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: Yield
Remarks on result:
other: 95% CI: 0.52-1.5 mg/l
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
4.4 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: Yield
Remarks on result:
other: 95% CI: 2.7-7.1 mg/l
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.02 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
element
Remarks:
Aluminium
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.051 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
element
Remarks:
Aluminium
Basis for effect:
growth rate
Remarks on result:
other: 95% CI:0.001-0.23 mg/l
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.24 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
element
Remarks:
Aluminium
Basis for effect:
growth rate
Remarks on result:
other: 95% CI: 0.058-0.54 mg/l
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 0.02 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
element
Remarks:
Aluminium
Basis for effect:
other: Yield
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.015 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
element
Remarks:
aluminium
Basis for effect:
other: Yield
Remarks on result:
other: 95% CI: 0.007-0.031 mg/l
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.075 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
element
Remarks:
aluminium
Basis for effect:
other: Yield
Remarks on result:
other: 95% CI: 0.039-0.14 mg/l
Details on results:
Microscopic observations at the end of the test revealed a normal and healthy appearance of the exposed cells when compared to the control.
Results with reference substance (positive control):
Potassium dichromate reduced growth rate of this fresh water algae species at nominal concentrations of 0.56 mg/l and higher.
The EC50 for growth rate reduction (ERC50: 0-72h) was 1.1 mg/l with a 95% confidence interval ranging from 1.0 to 1.3 mg/l.
The EC50 for yield inhibition (EYC50: 0-72h) was 0.59 mg/l with a 95% confidence interval ranging from 0.51 to 0.68 mg/l.
Reported statistics and error estimates:
For determination of the NOEC and the EC50 the approaches recommended in the OECD guideline 201 were used. An effect was considered to be significant if statistical analysis of the data obtained for the test concentrations compared with those obtained in the negative control revealed significant reduction of growth rate or inhibition of yield (ANOVA, Tukey test, Bonferroni t-test, TOXSTAT Release 3.5, 1996, D.D. Gulley, A.M. Boelter, H.L. Bergman). Additionally, the EC10 was determined to meet the recommendations as put down in "A Review of Statistical Data Analysis and Experimental Design in OECD Aquatic Toxicology Test Guidelines" by S. Pack, August 1993. Calculation of the EC50 and EC10 values was based on log-linear regression analysis of the percentages of growth rate reduction and the percentages of yield inhibition versus the square root (growth rate) or the logarithms (yield) of the corresponding concentrations of the test substance.
Statistically significant reduction of growth rate was found at nominal test concentrations of 3.2 mg/l and higher (Bonferroni t and Tukey test, α = 0.05).
Statistically significant inhibition of yield was found at all nominal concentrations tested (Bonferroni t and Tukey test, α = 0.05).
Validity criteria fulfilled:
yes
Conclusions:
The EC50 for growth rate reduction (ERC50: 0-72h) was 14 mg/l based on nominal concentrations of 202028/A. The average concentration of dissolved aluminium originating from 202028/A was 0.24 mg/l.

The NOEC for growth rate reduction was nominally 1.0 mg/l (0.02 mg/l when based on aluminium).

The EC50 for yield inhibition (EYC50: 0-72h) was 4.4 mg/l based on nominal concentrations of PAX-XL9. The average concentration of dissolved aluminium originating from PAX-XL9 was 0.075 mg/l.

The NOEC for yield inhibition was nominally <1.0 mg/l (<0.02 mg/l when based on aluminium).
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:
other: Acceptable, well documented publication which meets basic scientific principles.
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
yes
Remarks:
additional microplates were used
Qualifier:
according to guideline
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
yes
Remarks:
additional microplates were used
Qualifier:
according to guideline
Guideline:
ISO 8692 (Water Quality - Fresh Water Algal Growth Inhibition Test with Scenedesmus subspicatus and Selenastrum capricornutum)
Deviations:
yes
Remarks:
additional microplates were used
GLP compliance:
no
Vehicle:
no
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Common name: green algae
- Strain: 86.81 SAG
- Source: Institute of Plant Physiology, University of Göttingen, Germany
Test type:
static
Water media type:
freshwater
Total exposure duration:
72 h
Test temperature:
23 ± °C
Details on test conditions:
EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: Fluorescene Spectrophotometer
Reference substance (positive control):
yes
Remarks:
several reference substances to avaluate the test conditions
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
10.9 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: (CI: 95% = 9.40-12.70) Erlenmeyer flask assay
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
14.3 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: (CI: 95% = 9.00-22.70) Erlenmeyer flask assay
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
14 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: (CI: 95% = 11.60-17.00) 24 well microplate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
16.5 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: (CI: 95% = 11.60-24.20) 24 well microplate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
13.7 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: (CI: 95% = 11.80-15.90) 96 well microplate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
14.4 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: (CI: 95% = 10.70-19.40) 96 well microplate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
12.87 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
other: endpoint measurement
Remarks on result:
other: (CI: 95% = 9.32-17.89) Erlenmeyer flask assay
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
12.19 mg/L
Nominal / measured:
not specified
Conc. based on:
not specified
Basis for effect:
other: endpoint measurement
Remarks on result:
other: (CI: 95% = 11.53-12.89) Erlenmeyer flask assay
Reported statistics and error estimates:
The inhibition values were calculated from three parallels according to standard ISO 8692. EC values were calculated from sigmoidal concentration-inhibition curves by probit analysis using the maximum-likelihood solution. Confidence limits were calculated using the equation from Fieller.
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Study period:
1993
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Very detailed article, non GLP, complete however applicability of endpoints in riskassessment might be restricted due to no complete substance identity data and the fact that only EC30 values are presented in the article, the reviewer has himself determniend EC10 values. Therefore it is reliable with restrictions
Guideline:
other: Rogeberg, E.J.S. and A. Henriksen. 1985. An automated method for fractionation and determination of aluminum species in fresh-waters. Vatten 41:48-53.
Guideline:
other: Allison, J.D., D.S. Brown and K.J. Novo-Gradac. 1991. MINTEQA2/PRODEFA2, User's Manual, Version 3.0. EPA 600/3-91-021. U.S. Environmental Protection Agency, Washington, DC.
Guideline:
other: Wehr, J.D., L.M. Brown and I.E. Vanderelst. 1986. Hydrogen ion buffering of culture media for algae from moderately acidic, oligotrophic waters. J. Phycol. 22:88-94.
Guideline:
other: Stainton, M.P., M.J. Capel and F.A.J. Armstrong. 1974. The chemical analysis of fresh water. Miscellaneous Special Publication 25. Canadian Department of Environment, Ottawa. Ontario.
Principles of method if other than guideline:
analyses was performed according to Rogeberg and Henriksen 1985
GLP compliance:
no
Analytical monitoring:
yes
Details on sampling:
Al speciation Concentrations of total, dissolved, and monomeric Al
were determined daily in the exposure media. The Al speciation
measurements involved an initial filtration step (0.4 um
Nuclepore® polycarbonate filters; Nuclepore Corp., Pleasanton,
CA) to distinguish operationally between particulate and
dissolved AI. Aliquots of both the original sample and the
filtrate were acidified (2 uI HN03 per ml; Ultrex grade, J.T.
Baker Chem. Co., Phillipsburg, NJ),
Vehicle:
no
Details on test solutions:
The Al was added as a concentrated
solution of AICI3 (3.7.10-4 M, pH <2; prepared by dilution
of an AA standard, Fisher Scientific, Montreal, QC)
and allowed to equilibrate in the exposure media for 24 h.
Two buffers were used for pH control: 2-(N-morpholino)ethanesulfonic
acid (MES; pH 5.0, 5.5, and 6.0); 3,3-dimethylglutaric
acid (DMGA; pH 4.3 and 4.6); in both cases
buffer concentrations of 0.01 M were needed to maintain a
reasonably constant pH over the growth period. In choosing
the maximum Al concentrations for these experiments,
we took particular care to avoid the formation of hydroxyAl
colloids or polynuclear species (i.e., initial concentrations
of inorganic Al were chosen to lie below the solubility limit
for microcrystalline gibbsite, AI(OHh(s)).
Test organisms (species):
Chlorella pyrenoidosa
Details on test organisms:
Stock cultures of C. pyrenoidosa (University of Toronto
Culture Collection UTCC 89) were maintained in a semicontinuous
culture system under controlled and constant
temperature (22°C) and light conditions (115 JLE m-2 S-I).
Stock cultures were grown in algal assay procedure (AAP)
growth medium, as modified by Chiaudani and Vighi [8],
under constant bubbling with filtered air in Teflon® containers
(1-2 L). Cell densities in these cultures were monitored
daily with an electronic particle counter (Coulter Electronics,
Toronto, Ontario; model TA-II, 70-JLm orifice). The particle
counter was calibrated with C. pyrenoidosa suspensions
for which the cell dimenSIons had been measured by optical
micrometry. Cultures were diluted to maintain a cell concentration
of approximately 105 cells ml-1
, which corresponded
to the early exponential growth phase. Axenicity of the stock
culture was monitored regularly by plating the culture onto
BHI nutrient broth 1/10 (Difco, Detroit, MI).
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
96 h
pH:
4.3-6.0
Nominal and measured concentrations:
nominal: 25, 50, 100, 150 ug/L
Details on test conditions:
Although the test algae were maintained in complete AAP
growth medium, the subsequent bioassays were carried out
in solutions based on the AAP medium but contained no
added trace metals, EDTA, or phosphorus (referred to as
AAP-). By simplifying the exposure medium in this manner,
we sought to avoid possible experimental artifacts attributable
to AI-P interactions in solution [6], or to competition
between Al and other trace metals at the algal surface [9].
Bioassays designed to test the effects of mononuclear
inorganic Al were performed at nominal pH values of 4.3,
4.6,5.0,5.5, and 6.0.
Reference substance (positive control):
no
Duration:
96 h
Dose descriptor:
other: EC30
Effect conc.:
70 other: nmol/L
Nominal / measured:
meas. (initial)
Conc. based on:
dissolved
Remarks:
monomeric Al3+
Basis for effect:
growth rate
Remarks:
pH 6
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
172.8 µg/L
Nominal / measured:
nominal
Conc. based on:
dissolved
Remarks:
monomeric Al3+
Basis for effect:
growth rate
Remarks:
determined by reviewer at pH 5
Duration:
96 h
Dose descriptor:
EC10
Effect conc.:
84 µg/L
Nominal / measured:
nominal
Conc. based on:
dissolved
Remarks:
monomeric Al3+
Basis for effect:
growth rate
Remarks:
determined by reviewer at pH5
Duration:
96 h
Dose descriptor:
other: EC30
Effect conc.:
1.8 µmol/L
Nominal / measured:
meas. (not specified)
Conc. based on:
dissolved
Remarks:
monomeric Al3+
Basis for effect:
growth rate
Remarks:
pH 5
Details on results:
The sensitivity of algal growth to inorganic monomeric
Al (Al-mono) was determined over the pH range 4.3 to 6.0
in buffered media. Inhibition of algal growth by
Almono was slight at pH 4.3 or 4.6 but increased markedly
at pH >=5. Plots of area under
the growth curve as a function of [Al]mono showed the
expected concentration dependence. EC30 values extracted
from such plots, expressed in terms of the free AI3+
ion, showed a marked pH dependence
Reported statistics and error estimates:
The effects of Al on algal growth were determined by comparing
the areas under the growth curves for the various
cultures (cell numbers vs. time over 4 d; cf. Nyholm [11]),
and EC30 values were determined for different pH values
(EC30 = the concentration of inorganic monomeric Al that inhibited
algal growth by 30070 compared to an AI-free control).
In one series of experiments designed to explore links between
Al toxicity and phosphate metabolism, particulate
phosphorus was determined on day 4 of the Al exposure,
according to the automated ascorbic acid/molybdenum blue
method described by Stainton et al. 1974. The EC10 and EC50 were determniend by lineair regression by the reviewer based on nominal contrations, available in the article. These values are, 84 and 172.8 ug/L respectively
Validity criteria fulfilled:
not applicable
Conclusions:
The EC30 was determined by the authors to be 70 nmol/L (at pH 6) and 1.8 umol/L at pH 5 (measured concentrations). The EC10 and EC50 (at pH 5) were determined by lineair regression by the reviewer based on nominal contrations, available in the article. These values are, 84 and 172.8 ug/L respectively. Study is valied and scientific sound but not performed under GLP.
Executive summary:

A unicellular green alga, Chiarella pyrenaidasa, was exposed to inorganic Al under controlled experimental conditions to determine whether the biological response elicited by the dissolved metal could be predicted from the free-metal ion concentration, [AI3+]. The experimental approach involved concurrent measurement of both AI speciation and AI bioavailability (bioaccumulation/growth inhibition) in buffered synthetic solutions of defined composition. The bioassay exposure media, containing neither phosphate nor trace metals, covered the pH range 4.3 to 6. For systems at a given pH, containing only inorganic monomeric AI, aluminum bioavailability varies predictably as a function of the free AP+ concentration. However, the effect of A13+ on algal growth is highly pH dependent; [AJ3+] needed to inhibit growth by 30010 (EC30) increases markedly from

3 ug/L (0.1 uM) to 50 ug/L (1.8 uM) as the pH is decreased from 6 to 5. This decreased toxicity of AI at low pH is partly explained by an effective competition between the H+ ion and Al3+ for binding sites at the algal surface; the effects of acidification at the biological surface are much more important than are its. effects on Al speciation in solution.

For systems containing both monomeric and polynuclear Al (the AI04AJdOH);r polycation), polymeric aluminum also contributes to aluminum toxicity. The EC10 and EC50 (at pH 5) were determined by lineair regression by the reviewer based on nominal contrations, available in the article. These values are, 84 and 172.8 ug/L respectively

Description of key information

Key value for chemical safety assessment

Additional information

No reliable studies on the acute toxicity of reaction mass of aluminium hydroxide and aluminium nitrate and aluminium sulphate to long term fish are available.Therefore, a weight of evidence approach is applied and data are read-across to various aluminium compounds based on an analogue approach.

Bouwman (2010) exposed Pseudokirchneriella subcapitata to aluminum chloride hydroxide sulfate. The EC50 for growth rate reduction (ERC50: 0-72h) was 14 mg/l based on nominal concentrations of the test substance. The average concentration of dissolved aluminium originating from aluminum chloride hydroxide sulfate was 0.24 mg/l.

A unicellular green alga,Chiarella pyrenaidasa, was exposed to inorganic Al (Parent and Campell, 1994) under controlled experimental conditions to determine whether the biological response elicited by the dissolved metal could be predicted from the free-metal ion concentration, [AI3+]. The experimental approach involved concurrent measurement of both AI speciation and AI bioavailability (bioaccumulation/growth inhibition) in buffered synthetic solutions of defined composition. The bioassay exposure media, containing neither phosphate nor trace metals, covered the pH range 4.3 to 6. For systems at a given pH, containing only inorganic monomeric AI, aluminum bioavailability varies predictably as a function of the free AP+ concentration. However, the effect of AI3+ on algal growth is highly pH dependent. This decreased toxicity of AI at low pH is partly explained by an effective competition between the H+ ion and Al3+ for binding sites at the algal surface; the effects of acidification at the biological surface are much more important than are its effects on Al speciation in solution. For systems containing both monomeric and polynuclear Al, polymeric aluminum also contributes to aluminum toxicity. The EC10 and EC50 (at pH 5) were determined by linear regression by the reviewer based on nominal concentrations, available in the article. These values are 84 and 172.8 µg/L respectively

Eisentraeger, A. et al. (2002) present results of a comparative studies on algal toxicity testing using fluorometric microplate and Erlenmeyer flask growth-inhibition assays. The EC50 values are between 10.9 mg/L and 14.4 mg/L for aluminium chloride.