Sodium chlorate

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

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:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
[further information is included as attachment to Iuclid section 13]

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
This read-across is based on the hypothesis that the common compound ClO3- is solely responsible for the effects encountered, because the source and the target substance were transformed (by dissociation) into chlorate-ion (ClO3-).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Refer to the Test material section of the source and target records.

3. ANALOGUE APPROACH JUSTIFICATION
See attached document in Iuclid section 13

4. DATA MATRIX
See attached document in Iuclid section 13

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across: supporting information

Remarks:

Read-Across justification document

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

128 mg/L

Conc. based on:

other: sodium chlorate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 638 mg/L

Conc. based on:

other: sodium chlorate

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

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

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

Validity criteria fulfilled:

not specified

Conclusions:

According to the experimental study performed on the source substance, the E50 (Nitzschia closterium) of the target substance is determined to be :
- 1 mg nitrate/l: 10 mg ClO3-/l corresponds to 12.7 mg NaClO3/l
- 15 mg nitrate/l: >500 mg ClO3-/l corresponds to >638 mg NaClO3/l

NOEC:- 15 mg nitrate/l: 100 mg ClO3-/l corresponds to 128 mg NaClO3/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:

The experimental study on the source substance was used as a key study to asses the toxicity of the registered substance to algae.Therefore, good quality data for a related source substance have been read-across for this endpoint.

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)and to 2.42 mg NaClO3/L

- 1 mg nitrate/l: 10 mg ClO3-/l corresponds to 15 mg KClO3/l and to 12.7 mg NaClO3/l

- 15 mg nitrate/l: >500 mg ClO3-/l corresponds to >734 mg KClO3/l and to >638 mg NaClO3/l

NOEC:- 15 mg nitrate/l: 100 mg ClO3-/l corresponds to 147 mg KClO3/l and to 128 mg NaClO3/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.

Therefore, based on the considerations above, it can be concluded that the result of the algae study conducted with the source substance is likely to predict the properties of the target substance and is considered as adequate to fulfil the information requirement of Annex VII, 9.1.2 of the REACH regulation.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

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

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

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 acute value for freshwater algae was found for Selenastrum capricornutum. The EbC50 was 129 mg/l after 72 hours. The lowest NOEC for freshwater algae was found for Selenastrum capricornutum and was 62.5 mg/l.

The lowest valid short-term value for marine algae species was found for Nitzschia closterium,the EC­­₅₀was 500 mg chlorate/l (corresponds to 638 mg/L for sodium chlorate) at 15 mg nitrate/l.

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 128 mg NaClO3/l.

Key value for chemical safety assessment

EC50 for freshwater algae:

129 mg/L

EC50 for marine water algae:

638 mg/L

EC10 or NOEC for freshwater algae:

62.5 mg/L

EC10 or NOEC for marine water algae:

128 mg/L

Additional information

Three studies, one on Selenastrum capricornutum and two on Scenedesmus subspicatus were found. One was valid without restrictions (Ward and Boeri, 1991e) and two were valid with restrictions because not all details on the results were provided.

The lowest acute value for freshwater algae was found for Selenastrum capricornutum. The EbC50 was 129 mg/l after 72 hours. The lowest NOEC for freshwater algae was found for Selenastrum capricornutum and was 62.5 mg/l.

One valid test with marine algae is available (Tobiesen, 2010a) and one test (valid with restriction) performed by Hutchinson (1994b) (see table 7.6). 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. Hutchinson performed a test with Phaeodactylum tricornutum and found a NOEC of 64 mg sodium chlorate/l for biomass and a NOEC of 128 mg sodium chlorate/l for the growth rate.

Two tests (valid with restriction) were found for marine algae performed with potassium chlorate. Stauber performed the tests with potassium chlorate and expressed the endpoints in mg chlorate/l. The endpoints were recalculated to mg potassium chlorate/l for comparison with the studies on sodium chlorate and are provided in table 7.7. The original data for the EC₅₀was for Dunaliella tertiolecta > 1000 mg chlorate/l and for Nitzschia closterium 10 mg chlorate/l and > 500 mg chlorate/l, respectively. The NOEC values were 500 mg chlorate/l for Dunaliella tertiolecta and 100 mg chlorate/l for Nitzschia closterium.

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. Only valid results are given in the table above.

Tests performed with potassium chlorate can be used in this dossier, because the toxicity of the test substance is caused by the chlorate ion. In water sodium and potassium are naturally present and the amounts added with the test substance are not considered to have an impact on the total concentration and on the test result, therefore the counter ion present is not relevant for the test result.

The lowest valid short-term value for marine algae species was found forNitzschia closterium,the EC­­₅₀was 500 mg chlorate/l (corresponds to 638 mg/L for sodium chlorate) at 15 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 (1998) at several nitrate concentrations. Seawater has considerably lower concentrations of nitrate than freshwater systems so competitive inhibition of chlorate by nitrate will be reduced in marine environments. This is discussed in detail in the introduction of this chapter. 

When comparing studies, comparison should be made of studies performed under the same standard conditions as much as possible. Phaeodactylum tricornutum showed the same sensitivity under standard test conditions, with a NOEC for growth rate of 128 mg/l (100.4 mg ClO^3-/l). Stauber found exactly the same outcome with a more standard nitrate concentration for Nitzschia closterium, with a NOEC of 100 mg ClO^3-/l.