Sodium chlorate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study generated according to generally valid and internationally accepted testing guideline and performed under GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Preparation of the stock solution: The test item was dissolved at 2 g/L in dechlorinated water. The stock solution was agitated during 5 minutes.
Test solutions were prepared by further dilution of the stock solution with water to provide a geometric series of concentrations.

Test organisms (species):

activated sludge, domestic

Details on inoculum:

Innoculum: Activated sludge
- Source: the water treatment plant of Evreux, France treating predominantly domestic wastewater.
- Pretreatment: the inoculum was left to settle and the supernatant rejected. It was then filtered (to remove the biggest particles) and washed with
dechlorinated water. Four samples of 50 mL were taken to determine the content in suspended matter (dry weight).
The concentration of sludge (4.98 g/L) was then adjusted to 4 g/L by addition of the appropriate volume of dechlorinated water.
Clean air was passed through the inoculum at the rate of 0.5 to 1 L/min until use.
- Concentration: 4 g/l
- Feeding: 50 mL of sewage feed were added, per liter prior to the test.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

Temperature of incubation: 21-23°C.

pH:

The pH of the test solution at 1000 mg/L was 7.83.

Dissolved oxygen:

Aeration: Air was bubbled through each solution at the rate of 0.5 to 1 L/min until the start of oxygen concentration measurements.

Nominal and measured concentrations:

Nominal test concentrations: 10, 31.6,100, 316 and 1000 mg/L and inoculum at 1.6 g/L.

Details on test conditions:

Type: aquatic
Controls: without test substance prepared at the beginning and at the end of the test
Measurements: Measurement of oxygen concentration was determined using an oxygen probe placed into an opaque BOD (Biological Oxygen Demand) flask filled with the test or reference solution which was agitated with a magnetic stirrer.
The oxygen probe was connected to a meter equipped with a chart recorder.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: respiration rate

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: respiration rate

Details on results:

- The respiration rate of the test solution of highest concentration (1000 mg/L) was equivalent to the respiration rate of the first control
(i.e. these rates were within 15% of each other).
Therefore, the oxygen consumption rate of the four other test solutions (10 to 316 mg/L) was not determined.
- Was control response satisfactory: yes

Results with reference substance (positive control):

Concentrations: 4, 12 and 36 mg/L and inoculum at 1.6 g/L.
Results: EC50 = 14.3 mg/l (95% c.l. 12.4-16.5 mg/l)

Oxygen consumption after incubation

Conc (mg/l)	respiration rate (mg O2/l*h)	% inhibition
Control 1	44.0
Control 2	40.5
1000	40.0	5

Comment from the reviewer:

As the respiration rate at 1000 mg/l did not differ from the controls it can be said that the NOEC is equal to or greater than 1000 mg/l.

Validity criteria fulfilled:

yes

Conclusions:

Test conducted under GLP with,analysis certificate and to relevant guideline. This study can be considered reliable without restrictions.
The EC50 based on respiration rate is greater than 1000 mg/l.
Because no efffects were seen at 100 mg/l it can be said that the NOEC is greater than or equal to 1000 mg/l.

Executive summary:

At the request of Cefic Sodium Chlorate Herbicide Registration Group, Brussels, Belgium, the effect of the test item, SODIUM CHLORATE, on the respiration of activated sewage sludge was evaluated using a 3-hour static test according to OECD guideline (No. 209, 4th April 1984).

Methods

The test solutions were prepared as follows:

• two control solutions: activated sludge in dechlorinated water to obtain a final sludge concentration of 1.6 g/L,

• five test item solutions: activated sludge in dechlorinated water (at 1.6 g/L) and test item (to obtain final concentrations of 10, 31.6, 100, 316 and 1000 mg/L),

• three reference item (3,5-dichlorophenol) solutions: activated sludge in dechlorinated water (at 1.6 g/L) and reference item (to obtain final concentrations of 4, 12 and 36 mg/L).

The oxygen consumption of test solutions was measured for approximately 10 minutes, with a chart recorder, after an aeration of 3 hours. The EC50 (concentration expected to cause 50% inhibition of the respiration rate) of the test item and the reference item was determined considering the oxygen consumption of the controls as 100%.

Results

As the validity criteria were met (the difference between the two controls was below 15% and the EC50 of 3,5-dichlorophenol was between 5 and 30 mg/L), the test was considered valid.

The respiration rate of the test solution of highest concentration (1000 mg/L) was equivalent to the respiration rate of the first control (i.e. these rates were within 15% of each other). Therefore, the oxygen consumption rate of the four other test solutions

(10 to 316 mg/L) was not determined.

EC50s, based on nominal concentrations, were as follows:

Substance	3 -hour EC50 (mg/L)	95% confidence limits (mg/L)
Test item	> 1000
Reference item	14.3	12.4 - 16.5

Conclusion

Under our experimental conditions, the 3-hour EC50 of the test item SODIUM CHLORATE is > 1000 mg/L for activated sludge.

The test item should be considered as non-toxic for the micro-organisms of a water treatment plant.

Description of key information

The NOEC is equal to or greater than 1000 mg/l.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

One test with activated sludge was considered to be valid.

The respiration rate of the microorganisms in the test solution of 1000 mg/l was equivalent to that of the controls. The EC50 for aquatic microorganisms is greater than 1000 mg/l and the NOEC is equal to or greater than 1000 mg/l.