Chlorine dioxide

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)

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

OECD-GLP compliance 1996-09-09

Deviations:

no

Principles of method if other than guideline:

not applicable

GLP compliance:

yes (incl. QA statement)

Remarks:

1996-09-09

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
no data

Analytical monitoring:

no

Details on sampling:

After 3 h aeration, the first sample was taken for oxygen measurement over a period of up to 10 minutes. Thereafter, in 15 minute intervals, the rest of the samples were submitted to measurement of oxygen concentration. Sampling was started with control 1, continued with the reference substance samples, the positive controls and the test article samples. Finally the oxygen consumption of control 2 was determined.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Test solutions of shlorine dioxide were prepared by dissolving volumes of test article stock solution directly to the study beakers in order to obtain the requested concentrations taking into account the strength of the stock solution that was checked weekly, following the analytical method supplied by the sponsor.
- Eluate:
- Differential loading:
- Controls:
- Chemical name of vehicle (organic solvent, emulsifier or dispersant):
- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)):
- Evidence of undissolved material (e.g. precipitate, surface film, etc):

Test organisms (species):

activated sludge

Details on inoculum:

A synthetic sewage feed was made by dissolving the following in 1 L of water:
16 g peptone
11 g meat extract
3 g urea
0.7 g NaCl
0.4 g CaCl2.2H2O2O
0.2 g MgSO4.7H2O
2.8 g K2HPO4

Test type:

not specified

Water media type:

not specified

Limit test:

no

Total exposure duration:

3 h

Post exposure observation period:

no data

Hardness:

no data

Test temperature:

20 °C

pH:

6.24 - 7.13

Dissolved oxygen:

no data

Salinity:

not applicable

Nominal and measured concentrations:

Nominal concentrations: 100, 32, 10, 3.2, 1 mg/L

Actual test concentrations were not measured.

Details on test conditions:

TEST SYSTEM
- Test vessel: beakers
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: 500 ml of final volume
- Aeration: yes until use, with an air-flow using compressed air
- Type of flow-through (e.g. peristaltic or proportional diluter): not applicable
- Renewal rate of test solution (frequency/flow rate): not applicable
- No. of organisms per vessel: 200 ml of activated sludge
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- No. of vessels per vehicle control (replicates): not applicable
- Biomass loading rate: no data

OTHER TEST CONDITIONS
- Adjustment of pH: no data
- Photoperiod: no data
- Light intensity: no data

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol (batch 6300410, 99% purity)

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

10.7 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

100 %

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: The EC50 was a calculated value. 95 % confidence limit: 10.5 – 10.9 mg/L

Details on results:

The study was performed taking into account the actual content of the stock solution of chlorine dioxide. The toxicity values can therefore be expressed as referring to 100% ClO2 and to the solution at the nominal concentration of 0.2%. The calculated EC50 value of 100% ClO2 was 10.7 mg/L corresponding to 5.35 g/L of 0.2% solution being 1 g/L its density. The EC50 of the reference compound 3,5-dichlorophenol tested under the same conditions was 10.2 mg/L which is in the guideline accepted range.

Results with reference substance (positive control):

Nominal concentrations of the reference substance: 50, 32, 10 3.2, 1.0 mg/L

The EC50 of the reference substance compound 3,5-dichlorophenol was 10.2 mg/L which is in the guideline accepted range.

Reported statistics and error estimates:

No data

Table 1:          Effect data of chlorine dioxide

Concentration of Chlorine Dioxide (mg/L)	Oxygen Consumption (mgO2/Lmin)	Inhibition (%)	Starting pH
100	0	100	6.24
32	0.27	55.4	6.81
10	0.44	27.3	7.02
3.2	0.53	12.4	7.10
1	0.57	5.8	7.13

Table 2:          Effect data of the reference substance

Concentration of Reference (mg/L)	Oxygen Consumption (mgO2/Lmin)	Inhibition (%)	Starting pH
50	0.10	83.5	7.19
32	0.15	75.2	7.18
10	0.19	68.6	7.13
3.2	0.51	15.7	7.13
1.0	0.59	2.5	7.13

Validity criteria fulfilled:

yes

Remarks:

2 contro respiration rates within 15% of each other, and EC50 (3h) of reference substance is in the accepted range of 5-30 mg/L

Conclusions:

The calculated E50 value of 100% ClO2 was 10.7 mg/L with 95 % confidence limit of 10.5 – 10.9 mg/L.

Executive summary:

Inhibitory effect of chlorine dioxide on activated sludge was realized in a respiration inhibition test. Test article was tested with 5 different concentrations: 1, 3.2, 10, 32, and 100 mg/L of chlorine dioxide. Calculated EC50 = 10.7 mg/L (for 100% of ClO2), i.e. to 5.35 g/L of 0.2% solution being 1 g/L its density. All criteria were fulfilled.

Description of key information

Based on results from Gnemi (1996), EC50(3h) was 10.7 mg/L of chlorine dioxide on activated sludge. Chlorine dioxide reacts rapidly degrading to chlorite (which also degrades rapidly) and chlorate as dominant species. For chlorite the 3h EC50 for activated sludge was >75 mg/L, the highest concentration tested (as the sodium salt). For chlorate the 3h EC50 was >1000 mg/L, the highest concentration tested (as sodium salt).

Key value for chemical safety assessment

EC50 for microorganisms:

10.7 mg/L

Additional information

Three toxicity studies valid were found in chlorine dioxide, sodium chlorite, and sodium chlorate for activated sludge, according to OECD guideline 209 (Gnemi 1996; L'Haridon 2002; L'Haridon 2003).

Based on results from Gnemi (1996), EC50(3h) = 10.7 mg/L of 100% chlorine dioxide on activated sludge. Chlorine dioxide react easily and rapidly generating chlorite and chlorate as dominant species. In the absence of oxidisable substances, and in the presence of pH > 9, chlorine dioxide dissolves in water and decomposes with the slow formation of chlorite and chlorate ions.

Valid studies on both transformation products demonstrated an EC50(3h) > 75 mg/L for sodium chlorite (L'Haridon 2002), and an EC50(3h) >1000 mg/L for sodium chlorate (L'Haridon 2003), which corresponds to levels 7 to 90 times higher than that of chlorine dioxide.