titanyl (IV) diascrobate

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

Study period:

2019

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes (incl. QA statement)

Test organisms (species):

activated sludge of a predominantly domestic sewage

Total exposure duration:

3 h

Remarks on exposure duration:

contact time 3 hours, during which aeration takes place

Test temperature:

20 ± 2°C

Details on test conditions:

Duration: contact time 3 hours, during which aeration takes place
Air supply: clean, oil-free air. Air flow 0.5 to 1 litre/minute
Nutrient solution: synthetic sewage feed
Test item concentrations:: 0.10, 1.0, 10.0, 100.0 and 1000.0 mg/l
Reference item concentrations: 0.01 , 0.1, 1.0 , 10.0 and 100.0 mg/l
Blank controls: Inoculated sample without test substance
Temperature: 20 ± 2°C
Test item stock solutions 10 g/l (at pH = 7.0) (no undissolved particles were
observed)
Reference substance stock solutions 1 g/l
Synthetic medium stock solution: See p. 3.1.4
Activated sludge stock suspension: 3 g/l of suspended solids
Activated sludge suspension in test vessels 1.5 g/l of suspended solids
ATU stock solution 2.32 g/l

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

0.43 mg/L

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

0.19 mg/L

Basis for effect:

inhibition of heterotrophic respiration

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

0.68 mg/L

Basis for effect:

inhibition of nitrification rate

Duration:

3 h

Dose descriptor:

EC50

Remarks:

extrapolated

Effect conc.:

2 796 mg/L

Basis for effect:

inhibition of nitrification rate

Details on results:

The lowest tested concentration that causes the observed respiration inhibition is equal to 0.1 mg/l.
The test item – in the measured substance content range of 0.1-1000 mg/l - has a toxic effect on the oxidation of ammonium (nitrification) but only slight, with tendency to diminish for increasing test item concentration, on heterotrophic oxidation (biodegradation).
The heterotrophic respiration was stimulated (probably hormesis phenomenon), achieving about 0% (extrapolated) of inhibition for test item content greater than 1000 mg/l.

Validity criteria fulfilled:

yes

Conclusions:

calculated values of the end points EC10 for the test item were found to be:
1. Total respiration inhibition: 0.43 mg/l.
2. Heterotrophic respiration inhibition: 0.19 mg/l.
3. Nitrification inhibition: 0.68 mg/l .

The lowest tested concentration that causes the observed respiration inhibition is equal to 0.1 mg/l. The very low doses of test item did not influence heterotrophic respiration process (biodegradation, i.e. organic carbon oxidation) up to 1 mg/l. For higher concentrations heterotrophic respiration increased and instead of respiration inhibition we observed a stimulation of oxygen consumption. May be a hormesis phenomenon was revealed.
Hormesis is any process in a cell or organism that exhibits a biphasic response to exposure to increasing amounts of a substance. In toxicology, hormesis is a dose response phenomenon characterized by a low dose stimulation, high dose inhibition. This hormesis process did not influenced a nitrification process. The test substance has a toxic effect on the nitrifying bacteria, oxidising ammonium to nitrite and nitrate. Even very low doses (10 mg/l) influenced nitrification process and caused an inhibition of this process.
For higher substance content a nitrification inhibition increased up to 41.8 % for substance concentration equel to 1000 mg/l. The test item – in the measured content range - has a toxic effect on the oxidation of ammonium (nitrification) but no or slight one on heterotrophic oxidation (biodegradation). The test item – in the measured substance content range of 0.1-1000 mg/l - has a toxic effect on the oxidation of ammonium (nitrification) but only slight, with tendency to diminish for increasing test item concentration, on heterotrophic oxidation (biodegradation).
the heterotrophic respiration was stimulated (probably hormesis phenomenon), achieving about 0% (extrapolated) of inhibition for test item content greater than 1000 mg/l.

Key value for chemical safety assessment

EC50 for microorganisms:

2 796 mg/L

EC10 or NOEC for microorganisms:

0.19 mg/L

Additional information

calculated values of the end points EC10 for the test item were found to be:

1. Total respiration inhibition: 0.43 mg/l.

2. Heterotrophic respiration inhibition: 0.19 mg/l.

3. Nitrification inhibition: 0.68 mg/l .