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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Link to relevant study record(s)

Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: No GLP and no standard test protocol, but test described in enough detail.
Guideline:
other: Standard 72h growth inhibition bioassay (Stauber etal., 1994)
Principles of method if other than guideline:
Toxicity of chlorate at 3 nitrate concentrations (<0.005, 1 and 15 mg/l NO3) was studies using a standard 72 hours growth inhibtion bioassay (Stauber et al., 1994). At a nitrate concentration of <0.005 mg/l the toxicity of chlorate at 5 concentrations (0.5, 1, 5, 10 and 20 mg/l) was determined. At higher nitrate concentration (1 and 15 mg/l), 5 concentrations of chlorate were tested ranging from 1-1000 mg/l depending on the alga and nitrate concentration in each experiment.
Cell densities were determined daily using a Coulter Multisizer IIE with 70 µm aperture.
GLP compliance:
no
Analytical monitoring:
yes
Details on sampling:
See details in analytical methods.
Vehicle:
no
Details on test solutions:
Three nitrate levels were used: <0.005, 1 and 15 mg/l NO3. At nitrate concentrations of <0.005 mg/l the toxicity of chlorate was tested at 0.5, 1, 5, 10 and 20 mg/l ClO3-. At nitrate concentrations of 1 and 15 mg/l the test concentrations were ranging from 1 to 1000 mg/l ClO3-, depending on the alga and nitrate concentration in each experiment.
Test organisms (species):
other: other algae: Nitzschia closterium
Details on test organisms:
Nitzschia closterium (Ehrenberg) W. Smith, originally isolated from Port Hacking, NSW, Strain CS-5c.
Culture medium: Medium f (Guillard and Ryther, 1962) with the iron and trace element concentrations halved.
Test type:
static
Water media type:
saltwater
Limit test:
no
Total exposure duration:
72 h
Nominal and measured concentrations:
At nitrate concentrations of <0.005 mg/l the toxicity of chlorate was tested at 0.5, 1, 5, 10 and 20 mg/l ClO3-.
At nitrate concentrations of 1 and 15 mg/l the test concentrations were ranging from 1 to 1000 mg/l ClO3-, depending on the alga and nitrate concentration in each experiment.

Chlorate was measured in each bioassay flask at the beginning and end of the test and was always within 10% of the nominal chlorate concentration.
Details on test conditions:
Seawater for the preparation of the test medium was collected 0-1 km offshore from Port Hacking, NSW. The seawater was filtered through a 0.45 µm membrane filter and stored at 4 °C.
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
1.9 mg/L
Nominal / measured:
nominal
Conc. based on:
other: chlorate ion
Basis for effect:
growth rate
Remarks on result:
other: 95% CL: 1.6 - 2.3 mg/l Nitrate conc: < 0.005 mg/l
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
10 mg/L
Nominal / measured:
nominal
Conc. based on:
other: chlorate ion
Basis for effect:
growth rate
Remarks on result:
other: Nitrate conc: 1 mg/l
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 500 mg/L
Nominal / measured:
nominal
Conc. based on:
other: chlorate ion
Basis for effect:
growth rate
Remarks on result:
other: Nitrate conc: 15 mg/l
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: chlorate ion
Basis for effect:
growth rate
Remarks on result:
other: Nitrate conc: 15 mg/l
Details on results:
- Analytical results: Chlorate was measured in each bioassay flask at the beginning and end of the test and was always within 10% of the nominal chlorate concentration. Chlorate concentrations remained stable over the 3 days and chlorate was not reduced to chlorite or chloride in the light either in the presence or absence of algal cells.
Reported statistics and error estimates:
Data analyses were performed using Toxcalc version 5.0 (Tidepool scientific software).
 Recalculation of the results from mg/l ClO3- to KClO3. EC50:
- <0.005 mg nitrate/l: 1.9 mg ClO3-/l (95% c.i. 1.6-2.3 mg/l) corresponds to 2.8 mg KClO3/l (95% c.i. 2.3-3.4 mg/l)
- 1 mg nitrate/l: 10 mg ClO3-/l corresponds to 15 mg KClO3/l - 15 mg nitrate/l: >500 mg ClO3-/l corresponds to >735 mg KClO3/l NOEC:- 15 mg nitrate/l: 100 mg ClO3-/l corresponds to 147 mg KClO3/l Control cell division rate (doublings/day) - <0.005 mg nitrate/l: 0.8 - 1 mg nitrate/l: 1.1 - 15 mg nitrate/l: 1.3 Remark from reviewer: According to OECD guideline 201 Freshwater Alga and Cyanobacteria, Growth Inhibition Test the
The biomass in the control cultures should have increased exponentially by a factor of at least 16 within the 72-hour test period. This corresponds to a specific growth rate of 0.92 day-1. For the test performed at <0.005 mg nitrate/l this was not the case and therefore this test result is not valid and can not be used.
Validity criteria fulfilled:
not specified
Conclusions:
EC50:
- 1 mg nitrate/l: 10 mg ClO3-/l corresponds to 15 mg KClO3/l
- 15 mg nitrate/l: >500 mg ClO3-/l corresponds to >734 mg KClO3/l

NOEC:- 15 mg nitrate/l: 100 mg ClO3-/l corresponds to 147 mg KClO3/l

The results obtained at a nitrate concentration of <0.005 mg/l were not considered to be valid due to a low doubling rate in the control vessels and can not be used, therefore.
Executive summary:

Toxicity of chlorate at 3 nitrate concentrations (<0.005, 1 and 15 mg/l NO3) was studies using a standard 72 hours growth inhibtion bioassay (Stauber et al., 1994). At a nitrate concentration of <0.005 mg/l the toxicity of chlorate at 5 concentrations (0.5, 1, 5, 10 and 20 mg/l) was determined. At higher nitrate concentration (1 and 15 mg/l), 5 concentrations of chlorate were tested ranging from 1-1000 mg/l depending on the alga and nitrate concentration in each experiment.

Cell densities were determined daily using a Coulter Multisizer IIE with 70 µm aperture.

Nitzschia closterium was used as test organism.

EC50:

- <0.005 mg nitrate/l: 1.9 mg ClO3-/l (95% c.i. 1.6-2.3 mg/l) corresponds to 2.8 mg KClO3/l (95% c.i. 2.3-3.4 mg/l)

- 1 mg nitrate/l: 10 mg ClO3-/l corresponds to 15 mg KClO3/l

- 15 mg nitrate/l: >500 mg ClO3-/l corresponds to >734 mg KClO3/l

NOEC:- 15 mg nitrate/l: 100 mg ClO3-/l corresponds to 147 mg KClO3/l

The results obtained at a nitrate concentration of <0.005 mg/l were not considered to be valid due to a low doubling rate in the control vessels and can not be used, therefore.

Description of key information

The lowest endpoint for freshwater algae and plants is determined for Lemna minor which is described in section 6.1.6.

The lowest endpoint for marine algae with a more standard nitrate concentration was found for Nitzschia closterium, with a NOEC of 100 mg ClO3-/l, which is equal to 147 mg KClO3/l.

Key value for chemical safety assessment

EC50 for marine water algae:
735 mg/L
EC10 or NOEC for marine water algae:
147 mg/L

Additional information

No studies with freshwater aquatic algae are available on potassium chlorate. The key study for the endpoint aquatic algae and plants is a study with Lemna minor described in section 6.1.6.

Two tests (valid with restriction) were found for marine algae performed with potassium chlorate (Stauber, 1998). The endpoints were expressed in mg chlorate/l. The endpoints were recalculated to mg potassium chlorate/l. Stauber performed the test at three different nitrate levels namely <0.005, 1 and 15 mg nitrate/l. At the lower nitrate concentrations cell growth in the controls was not according to the standard criteria and these results cannot be used therefore.

The original data for the EC50was for Dunaliella tertiolecta > 1000 mg chlorate/l (15 mg/l nitrate) and for Nitzschia closterium 10 mg chlorate/l and > 500 mg chlorate/l, 1 and 15 mg/l nitrate respectively. The NOEC values were 500 mg chlorate/l for Dunaliella tertiolecta and 100 mg chlorate/l for Nitzschia closterium.

The lowest short-term value for marine algae species was found for Nitzschia closterium, the EC50was 15 mg/l at 1 mg nitrate/l.

The difference in toxicity noted between marine and freshwater algae, appears to be related more to the relative difference in concentration of nitrate in freshwater and marine compartments than to different mechanisms of toxicity between species. The concentration of nitrate in the test water influences the effect concentration of chlorate (Stauber, 1998) indicating that competitive inhibition occurs between nitrate and chlorate with excess nitrate inhibiting chlorate toxicity. This is supported by the acute studies on marine species using chlorate performed by Stauber at several nitrate concentrations.

When comparing studies, comparison should be made of studies performed under the same standard conditions as much as possible. A more standard nitrate concentration is 15 mg/l, therefore this test result should be used. For Nitzschia closterium a NOEC of 100 mg ClO3-/l, which is 147 mg/ potassium chlorate was determined under more standard conditions.

One valid test with marine algae is available (Tobiesen, 2010a) for sodium chlorate. Tobiesen performed a standard test with Skeletonema costatum according to guideline and GLP. Chemical analyses were performed on the test concentrations. He found that S. Costatum was not sensitive to sodium chlorate, with a NOEC greater than or equal to 1000 mg/l. On a molecular weight basis this would be 1151 mg/l potassium chlorate.