Trititanium pentaoxide

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

key study

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across: supporting information

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

in filtrate (0.1 µm filtered after 48 h of stirring)

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

in filtrate (0.1 µm filtered after 48 h of stirring)

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

filtrate, 0.1 µm filtered after 48 h of stirring

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

filtrate, 0.1 µm filtered after 48 h of stirring

Basis for effect:

biomass

Details on results:

For the measurement parameters growth rate and yield (biomass), the EC50, EC20 and EC10 were not calculated, since no concentration dependent effect was observed and the strongest inhibition was 6.2 % compared to controls for yield at a loading rate of 32.0 mg/L at test end.
Therefore, the EC50 values were set to be > 100 mg/L, the highest loading rate. The algal growth inhibition test revealed a NOEC for titanium dioxide of ≥ 100 mg/L.

Results with reference substance (positive control):

- EC50: The most recent nominal ErC50 value of 3.78 mg/L (95 % confidence limits 3.64 - 3.92 mg/L) is in good agreement with the results of an international ring test with ErC50 of 3.38 ± 1.30 mg/L.

Reported statistics and error estimates:

The evaluation of the concentration-effect-relationships and the calculations of effect concentrations were based on the nominal loading of the test medium. The mean value of the cell counts for each concentration plot was used for plotting growth curves. Calculation of the percent inhibition of growth rate [r] and yield [y] was performed according to the guideline OECD 201. The percent inhibition values were plotted as a function of the test item concentration. The test results were statistically analyzed to determine EC10 and EC50 values with 95 % confidence intervals using Probit-analysis [9] assuming log-normal distribution of the values by using the computer program ToxRat®. The NOEC and LOEC values were determined by the Williams Multiple Sequential t-test or the Dunnett’s multiple t-test. The computer program ToxRat Professional was used for statistical evaluations.

Table: Chemical analysis of test item, results [µg/L].

	Ti concentration [µg/L]
Treatment [mg/L]	Control	10.0	18.0	32.0	56.0	100	LOD	LOQ
Test start	<LOQ (0.6151)	0.9095	<LOQ (0.7653)	0.9571	<LOQ (0.6009)	0.9116	0.2870	0.8610
Test end	<LOD	<LOD	<LOD	<LOQ (0.5445)	<LOD	<LOQ (0.5722)	0.4736	1.4209
	TiO2* concentration [µg/L]
Treatment [mg/L]	Control	10.0	18.0	32.0	56.0	100	LOD	LOQ
Test start	<LOQ (1.026)	1.518	<LOQ (1.277)	1.597	<LOQ (1.003)	1.521	0.4789	1.437
Test end	<LOD	<LOD	<LOD	<LOQ (0.9086)	<LOD	<LOQ (0.9548)	0.7904	2.371

*The TiO₂concentration was calculated based on a purity of the test item of 98.72% as stated in the certificate of analysis.

Validity criteria fulfilled:

yes

Conclusions:

Dissolved/dispersed fractions of a pigment grade TiO2 material, which were prepared by stirring the test material in test medium for 48 h and by subsequently filtering this test dispersion through a 0.1 µm filter, did not significantly affect the growth rate and biomass yield of Pseudokirchneriella subcapitata in an algae growth inhibition test according to OECD 201 after 72 h of exposure (72 h-NOEC ≥ 100 mg/L; 72 h-LOEC > 100 mg/L, nominal). Measured TiO2 concentrations in the test medium (10-100 mg TiO2/L, nominal) at test start ranged from 1.52-1.60 µg TiO2/L or were smaller than the LOQ (1.437 µg TiO2/L), and did not depend on the TiO2 loading rate.
The same EC50 and NOEC values are predicted for the structural analogue titanium oxide (Ti3O5) based on its similar low water solubility and the fact that any free titanium released will react to TiO2 when in contact with oxygen.

Description of key information

No significant effect on growth rate and biomass was observed at 100 mg/L in a key study on the effects of TiO₂ powder on Pseudokirchneriella subcapitata (Wiensch et al., 2015). The same conclusions are taken forward for the structural analogue titanium oxide (Ti₃O₅) based on its similar low water solubility and the fact that any free titanium released will react to TiO₂ when in contact with oxygen in water or air.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L