Disodium hexatitanate

Toxicity to microorganisms

Administrative data

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20 December 2011 - 02 March 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))

Version / remarks:

adopted 22 July 2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Disodium hexatitanate

EC Number:

815-182-4

Cas Number:

12058-75-2

Molecular formula:

Na2Ti6O13

IUPAC Name:

Disodium hexatitanate

Test material form:

solid: particulate/powder

Sampling and analysis

Analytical monitoring:

no

Test solutions

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
A preliminary solubility assessment was carried out prior the main test. Test substance was not sufficiently soluble to prepare a stable solution, therefore at test initiation aliquots of the test substance were added to the required vessels to give nominal weights of 5, 50 and 500 mg/500 mL.

- Evidence of undissolved material (e.g. precipitate, surface film, etc.):Not recorded

Test organisms

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

On the day of collection, an aliquot (10 mL) of the activated sludge was filtered through a dried and preweighed Whatman GF/C filter paper, which was then dried again at approximately 105°C for at least one hour, allowed to cool in a desiccator and reweighed.
The mixed liquor suspended solids (MLSS) content of the activated sludge was then calculated. Synthetic sewage (50 mL/L) was added to the stock of activated sludge and this was aerated overnight.
On the day of the test, the MLSS content of the sludge was determined (in triplicate) and adjusted to 4 g/L by the addition of tap water. The pH and temperature of the sludge were also measured. Aliquots (200 mL) were then added to each mixture to give a final MLSS concentration of 1.6 g/L.

Study design

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test conditions

Test temperature:

19.7 - 20.4°C

pH:

7.22 - 7.81

Dissolved oxygen:

Initial nominally 6.5 mgO2/L

Nominal and measured concentrations:

Nominal 10, 100 and 1000 mg/L

Details on test conditions:

TEST SYSTEM
Mixtures were incubated in 500 mL bottles fitted with an oxygen probe, a sinter to deliver air and a nitrogen gas nozzle.
- No. of vessels per concentration (replicates): 5
- No. of vessels per control (replicates): 5
- Sludge concentration: Mixed Liquor Suspended Solids (MLSS) = 1.6 g/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Reverse osmosis water. 100 µL of an antifoam agent (silicone oil in water) were added to each vessel (100 µL / 500 mL bottle)

OTHER TEST CONDITIONS
- Adjustment of pH: No
- Photoperiod: Not applicable
- Light intensity: Not recorded
- Details on termination of incubation: Not applicable

EFFECT PARAMETERS MEASURED: Following the exposure period, the aeration was stopped and the headspace of each bottle was flushed with nitrogen during the oxygen measurement phase. The instrument measured the amount of oxygen in the mixtures at one minute intervals for at least 15 minutes.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10-fold

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol (3,5-DCP). Single replicates were tested at 3, 10 and 32 mg/L

Results and discussion

Effect concentrations

Effect concentrations 1

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:

inhibition of total respiration

Effect concentrations 2

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Results with reference substance (positive control):

- Results with reference substance valid: Yes
The three-hour 50% effect concentration (EC50) for 3,5-DCP was calculated to be 5.63 mg/L (95% confidence limits 1.57 to 19.6 mg/L).

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

Terracess DSR did not significantly inhibit the respiration rates of samples of activated sludge. Consequently the EC50 for inhibition could not be calculated but must be >1000 mg/L, the highest concentration tested in this study.

The no observed effect concentration (NOEC) for Terracess DSR was 1000 mg/L.