Titanium dioxide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-11-04 to 2016-03-29

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

The deviations from the guideline do not effect the results.: Constant titanium concentrations (i.e. concentrations do not differ by more than 15 %), could not be reached. - Two vessels will be set up in a parallel design at 20 ± 1.0 °C, each vessel will be sampled several times instead of sampling one vessel every time. - Samples were filtered (i) only through 0.2 µm membranes, (ii) only by centrifugal filtration and (iii) through a 0.2 µm membrane followed by centrifugal filtration

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

1995

Deviations:

yes

Remarks:

Please refer to the field "Rationale for reliability incl. deficiences" above.

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

2008

Deviations:

yes

Remarks:

Please refer to the field "Rationale for reliability incl. deficiences" above

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Key result

Water solubility:

>= 0.024 - <= 0.172 other: µg Ti/L

Conc. based on:

element

Loading of aqueous phase:

500.6 µg/L

Incubation duration:

>= 1 - <= 17 d

Temp.:

20 °C

pH:

>= 6.1 - <= 6.3

Remarks on result:

other: Filtration through a 0.2 µm membrane and centrifugal filtration

Water solubility:

>= 0.07 - <= 0.283 other: µg Ti/L

Conc. based on:

element

Loading of aqueous phase:

500.6 mg/L

Incubation duration:

>= 1 - <= 17 d

Temp.:

20 °C

pH:

>= 6.1 - <= 6.3

Remarks on result:

other: Centrifugal filtration

Water solubility:

>= 7.94 - <= 15.58 other: µg Ti/L

Conc. based on:

element

Loading of aqueous phase:

500.6 mg/L

Incubation duration:

>= 1 - <= 17 d

Temp.:

20.3 °C

pH:

>= 6.1 - <= 6.3

Remarks on result:

other: Filtration through a 0.2 µm membrane, reanalysed after 1.5 months of storage

Details on results:

Observations: During the study, a whitish (milky) suspension and a white precipitate were observed in vessels containing the test item. After filtration, regardless of the filtration method (i.e. (i) through a 0.2 µm membrane, (ii) centrifugal filtration, or (iii) through a 0.2 µm membrane with subsequent centrifugal filtration), the solution was clear. In order to verify this, the turbidity of filtered samples was measured.

Temperature: The mean temperature was 20.3 ± 0.2 °C

Solution pH: The pH of solutions containing the test item and method blanks ranged from 6.0 to 6.7.

Turbidity: The turbidity of a sample from a solution containing the test item after filtration through a 0.2 µm membrane was measured with 0.04 NTU. This sample was further applied to centrifugal filtration. The turbidity in the respective filtrate was 0.06 NTU. In contrast, turbidity of drinking water should not be > 5 NTU and should ideally be < 0.1 NTU for an effective disinfection. Thus, based on the turbidity measurement, the solution samples were clear.

Titanium concentrations of method blanks: The titanium concentrations of method blanks (i) after filtration trough a 0.2 µm membrane (ii) after centrifugal filtration (iii) after filtration trough a 0.2 µm membrane and centrifugal filtration) were in the majority of cases below the respective LOQ.

Titanium concentrations of solutions containing the test item: The titanium concentrations of samples filtered only through a 0.2 µm membrane were above the calibration range in all measurement series, i.e. the concentration is at least above 50 µg Ti/L, whereas the Ti concentrations in method blanks were at least below 0.205 µg Ti/L. This may indicate that smaller particles (i.e. < 0.2 µm but > 3 kDa) are present in filtered solution samples, which however were not recorded by the turbidity measurement (presumably due to their size). Dissolved Ti concentrations in samples filtered only through 0.2 µm filters were remeasured after approx. 1.5 months of storage and seem to have decreased to concentrations in the range of 7.9 to 15.6 µg Ti/L but are at least 10-times above concentrations measured in samples after centrifugal filtration. The observed decrease in dissolved Ti may indicate that particulate material deposited on the bottom of the sample during storage. If samples containing particles are stored for a certain amount of time, formation of agglomerates and an inhomogeneous distribution of dissolved Ti in the sample cannot be excluded. The fluctuation of Ti concentrations of individual samples might also be due to an inhomogeneous distribution caused by a formation of colloids, agglomerates and precipitates in combination with very low dissolved Ti concentrations.

Mean background-corrected dissolved Ti concentrations of test solutions in samples (after filtration through a 0.2 µm membrane and centrifugal filtration) range from 0.024 µg Ti/L on day 1 to 0.149 µg Ti/L on Day 17 with the highest mean concentration of 0.172 µg Ti/L measured on day 3 and the lowest mean concentration of 0.024 µg Ti/L as measured on day 1.

Method validation summary

validation parameter	results	comment
selectivity	Titanium detected and evaluated at a wavelength of 334.941 nm	no matrix effects observed
linearity	applied calibration functions were linear	correlation coefficient at least 0.999872
limits of detection (LOD)	0.018 – 0.080 µg Ti/L
limits of quantification (LOQ)	0.054 – 0.240 µg Ti/L
method blanks	at least < LOQ except for samples from day 9 and 10 that are > LOQ.
accuracy and precision, reproducibility	mean recovery for quality control standard – 19 elements: 101.3 ± 1.5 % (n = 12)	diluted to 25 µg Ti/L
accuracy and precision, reproducibility	mean recovery for multi-element standard XVII: 96.7 ± 1.4 % (n = 12)	diluted to 10 µg Ti/L
accuracy and precision, reproducibility	mean recovery for recalibration samples: 102.2 ± 0.9 % (n = 12)	diluted to 5 µg Ti/L
trueness	recovery from fortification of samples: 96.0 – 111.3 % (n = 5)

Conclusions:

Under the conditions of this test (flask method; mean loading of 500.6 mg/L), a solubility equilibrium was not observed during the testing. Mean background-corrected dissolved Ti concentrations of test solutions in samples (after filtration through a 0.2 µm membrane and centrifugal filtration) ranged from 0.024 µg Ti/L to 0.172 µg Ti/L, which corresponds to 0.04 to 0.287 µg TiO2/L.

Reference 2

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-09-20 to 2017-02-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

no

Principles of method if other than guideline:

First a screening test was performed to determine the dissolution of titanium dioxide after 24 h in environmentally relevant test medium at pH 6 and 8. Additionally in a full transformation dissolution test, dissolution of titanium dioxide after 7 and 28 d was investigated.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.51 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6: centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.17/0.51 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.51 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.17/0.51 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.297 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6: centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.099/0.297

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.099 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8: centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.099

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0.024 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6: centrifugal filtration (~2.1 nm)

Remarks on result:

other: SD 0.019

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.007 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8: centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD (0.007)

Details on results:

Solution pH, oxygen concentrations, temperature:
Mean temperature was 20.8 ± 0.2 °C during the test over 1-d and 21.5 ± 0.2 °C during the test over 28-d.
In the 1-d test, the solution pH remained in the respective target pH range from 5.9 to 6.1 and from 7.8 to 8.0 in solutions containing the test item and in method blanks. In the 28-d test, the solution pH ranged from 6.0 to 6.6 and from 7.5 to 8.0 in solutions containing the test item and in method blanks. Oxygen levels of all test solutions were in the range recommended by the OECD Test Guidance 29 during the test (> 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L).

Analytical measurements: Within and between vessel variations in Titanium concentrations
Within and between vessel variations are not always in compliance with the guidance for the tests (<10% within-vessel variation, <20% between-vessel varition). The observed variations may be explained in parts with the ultrafine particle size of the test material, a low dispersion potential, low dissolution and resulting low titanium levels.

Analytical measurements - Screening test:
- Mean Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 (pH 8) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C were at least below LOQ of the quantification method (LOD: 0.17 µg/L, LOQ: 0.51 µg/L).
- Dispersed/Dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C amounted to 0.40 ± 0.12 µg/L.
Analytical measurements - Full test:
- Dispersed/dissolved titanium concentrations of 0.2 µm filtered samples in 28-d test at pH 8 shaking at 100 rpm under dark conditions at 21°C were below the respective LOD (0.022 – 0.297 µg Ti/L) for all sampled timepoints (7d, 14d, 28d).
- Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) shaking at 100 rpm under dark conditions at 21°C amount to 0.42 ± 0.16 µg Ti/L after 7 d, below LOQ (<0.36 µg Ti/L) after 14 d and
Validation experiments regarding applicability of filtration method:
Validation experiments were performed to show that dissolved nanosized TiO2 was not retained by the 0.2 µm filters or the ultrafiltration procedure. The applicability of the centrifugal filtration was investigated in a pre-test. The respective recoveries of dissolved titanium of three sequential filtrations of Ti ICP standard (1 mg / L) were as follows: 1st filtrate: 106.4 % 2nd filtrate: 89.2 % 3rd filtrate: 98.8 %.

Method validation summary (ICP-OES)

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.007 -0.171 µg Ti/ L.

Limits of quantification (LOQ) within all measurement series: 0.022 -0.512 µg Ti / L.

Correlation coefficients (r) within all measurement series: > 0.999521

Method validation summary

Mean recovery of fortified samples (n = 7): 87.2 -107.7 %

Mean recoveries for certified reference material CRM TM-26.4 and TMDA-54.5 (concentration range 3.35 - 6.15 µg Ti / L, n = 23): 93.3 -102.7 %

Mean recoveries for quality control standard (concentration range 0.5 -25 µg / L, n = 40): 99.7 - 109.2 %

Mean recoveries for internal standard (concentration 1 µg / L, n = 15): 104.0 - 110.1 %

Conclusions:

The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of titanium dioxide at a loading of 1 mg/L at pH 6 and 8 resulted after 1 and 28 days in dissolved titanium concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) that were at least below the limit of quantification (LOQ: 0.297-0.51 µg/L). Dissolved/dispersed Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) at a loading of 1 mg/L at pH 8 after 1, 7 and 28 days were also below the LOD/LOQ, whereas mean Ti concentrations of 0.396 and 0,423 µg/L were measured at pH 6 after 1 and 7, respectively and values below LOQ (<0.297 µg/L) after 28 days. Thus, the extent to which TiO2-pg-2 can produce soluble available ionic and other metal-bearing species in aqueous media is limited.

Reference 3

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-09-20 to 2016-11-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

no

Principles of method if other than guideline:

First a screening test was performed to determine the dissolution of titanium dioxide after 24 h in environmentally relevant test medium at pH 6 and 8. Additionally in a full transformation dissolution test, dissolution of titanium dioxide after 7 and 28 d was investigated.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.34 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6; centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.11/0.34 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.11 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.11 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.34 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.11/0.34 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.11 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.11 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.51 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOQ: 0.51 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.51 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.17/0.51 µg/L

Details on results:

Solution pH, oxygen concentrations, temperature:
Mean temperature was 20.8 ± 0.2 °C during the test over 1-d and 21.5 ± 0.2 °C during the test over 28-d.
In the 1-d test, the solution pH remained in the respective target pH range from 5.9 to 6.1 and from 7.8 to 8.0 in solutions containing the test item and in method blanks. In the 28-d test, the solution pH ranged from 5.9 to 6.2 and from 7.8 to 8.0 in solutions containing the test item and in method blanks. Oxygen levels of all test solutions were in the range recommended by the OECD Test Guidance 29 during the test (> 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L).

Analytical measurements: Within and between vessel variations in Titanium concentrations
Within and between vessel variations are not always in compliance with the guidance for the tests (<10% within-vessel variation, <20% between-vessel varition). The observed variations may be explained in parts with the ultrafine particle size of the test material, a low dispersion potential, low dissolution and resulting low titanium levels.

Analytical measurements - Screening test:
- Mean Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 (pH 8) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C were at least below LOQ of the quantification method (LOD: 0.17 µg/L, LOQ: 0.51 µg/L).
- Dispersed/Dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C amounted to 3.76 ± 0.52 µg/L.
Analytical measurements - Full test:
- Dispersed/dissolved titanium concentrations of 0.2 µm filtered samples in 28-d test at pH 8 shaking at 100 rpm under dark conditions at 21°C were below the respective LOD (0.105 – 0.114 µg Ti/L) for all sampled timepoints (7d, 14d, 28d).
- Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) shaking at 100 rpm under dark conditions at 21°C amount to 1.34 ± 0.93 µg Ti/L after 7 d, 0.42 ± 0.28 µg Ti/L after 14 d and 0.48 ± 0.18 µg Ti/L after 28 d of testing.

Validation experiments regarding applicability of filtration method:
Validation experiments were performed to show that dissolved nanosized TiO2 was not retained by the 0.2 µm filters or the ultrafiltration procedure. The applicability of the centrifugal filtration was investigated in a pre-test. The respective recoveries of dissolved titanium of three sequential filtrations of Ti ICP standard (1 mg / L) were as follows: 1st filtrate: 106.4 % 2nd filtrate: 89.2 % 3rd filtrate: 98.8 %.

Method validation summary (ICP-OES)

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.106 -0.221 µg Ti/ L.

Limits of quantification (LOQ) within all measurement series: 0.317 -0.664 µg Ti / L.

Correlation coefficients (r) within all measurement series: > 0.999521

Method validation summary

Mean recovery of fortified samples (n = 7): 97.4 -101.2 %

Mean recoveries for certified reference material TM-26.4 (concentration range 3.35 - 6.7 µg Ti / L, n = 26): 91.6 -105.6 %

Mean recoveries for quality control standard (concentration range 0.5 -500 µg / L, n = 34): 94.3 - 107.6 %

Mean recoveries for internal standard (concentration range 0.5 -100 µg / L, n = 24): 95.6 - 108.7 %

Conclusions:

The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of titanium dioxide at a loading of 1 mg/L at pH 6 and 8 resulted after 1, 7 and 28 days in dissolved titanium concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) that were below the limit of detection and/or quantification (LOD/LOQ: 0.11/0.34 µg/L). Dissolved/dispersed Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) at a loading of 1 mg/L at pH 8 after 1, 7 and 28 days were also below the LOD, whereas mean Ti concentrations of 3.76, 1.34 and 0.48 µg/L were measured at pH 6 after 1, 7 and 28 days, respectively. Thus, the extent to which TiO2-pg-1 can produce soluble available ionic and other metal-bearing species in aqueous media is limited.

Reference 4

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-09-20 to 2016-11-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

no

Principles of method if other than guideline:

First a screening test was performed to determine the dissolution of titanium dioxide after 24 h in environmentally relevant test medium at pH 6 and 8. Additionally in a full transformation dissolution test, dissolution of titanium dioxide after 7 and 28 d was investigated.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.34 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.11/0.34 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.11 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.11 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.34 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOQ: 0.34 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.34 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.11/0.34 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.51 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOQ: 0.51 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.51 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.17/0.51 µg/L

Details on results:

Solution pH, oxygen concentrations, temperature:
Mean temperature was 20.8 ± 0.2 °C during the test over 1-d and 21.5 ± 0.2 °C during the test over 28-d.
In the 1-d test, the solution pH remained in the respective target pH range from 5.9 to 6.1 and from 7.8 to 8.0 in solutions containing the test item and in method blanks. In the 28-d test, the solution pH ranged from 5.9 to 6.2 and from 7.8 to 8.0 in solutions containing the test item and in method blanks. Oxygen levels of all test solutions were in the range recommended by the OECD Test Guidance 29 during the test (> 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L).

Analytical measurements: Within and between vessel variations in Titanium concentrations
Within and between vessel variations are not always in compliance with the guidance for the tests (<10% within-vessel variation, <20% between-vessel varition). The observed variations may be explained in parts with the ultrafine particle size of the test material, a low dispersion potential, low dissolution and resulting low titanium levels.

Analytical measurements - Screening test:
- Mean Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 (pH 8) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C amounted to 0.378 ± 0.063 µ/L.
- Dispersed/Dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C amounted to 0.82 ± 0.22 µg/L.
Analytical measurements - Full test:
- Dispersed/dissolved titanium concentrations of 0.2 µm filtered samples in 28-d test at pH 8 shaking at 100 rpm under dark conditions at 21°C were at least below the respective LOQs (0.32-0.34 µg Ti/L) for all sampled timepoints (7d, 14d, 28d).
- Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) shaking at 100 rpm under dark conditions at 21°C amount to 0.51 ± 0.31 µg Ti/L after 7 d, 0.19 ± 0.21 µg Ti/L after 14 d and below LOQ (<0.341 µg/L) after 28 d of testing.


Validation experiments regarding applicability of filtration method:
Validation experiments were performed to show that dissolved nanosized TiO2 was not retained by the 0.2 µm filters or the ultrafiltration procedure. The applicability of the centrifugal filtration was investigated in a pre-test. The respective recoveries of dissolved titanium of three sequential filtrations of Ti ICP standard (1 mg / L) were as follows: 1st filtrate: 106.4 % 2nd filtrate: 89.2 % 3rd filtrate: 98.8 %.

 

Method validation summary (ICP-OES)

 

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.105 -0.221 µg Ti/ L.

Limits of quantification (LOQ) within all measurement series: 0.315 -0.664 µg Ti / L.

Correlation coefficients (r) within all measurement series: > 0.999521

 

Method validation summary

Mean recovery of fortified samples (n = 7): 95.9 -104.4 %

Mean recoveries for certified reference material TM-26.4 and TMDA-54.5 (concentration range 3.35 - 6.7 µg Ti / L, n = 26): 91.6 -105.6 %

Mean recoveries for quality control standard (concentration range 0.5 -500 µg / L, n = 36): 94.3 - 107.6 %

Mean recoveries for internal standard (concentration range 0.5 -100 µg / L, n = 24): 95.6 - 108.7 %

Conclusions:

The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of titanium dioxide at a loading of 1 mg/L at pH 6 and 8 resulted after 1 and 28 days in dissolved titanium concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) that were at least below the limit of quantification (LOQ: 0.30-0.51 µg/L). Dissolved/dispersed Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) at a loading of 1 mg/L at pH 8 after 1, 7 and 28 days were also below the LOD/LOQ, whereas mean Ti concentrations of 0.82 and 0.51 µg/L were measured at pH 6 after 1 and 7, respectively and values below LOQ (<0.34 µg/L) after 28 days. Thus, the extent to which TiO2-pg-3 can produce soluble available ionic and other metal-bearing species in aqueous media is limited.

Reference 5

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-09-07 to 2017-02-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

no

Principles of method if other than guideline:

First a screening test was performed to determine the dissolution of titanium dioxide after 24 h in environmentally relevant test medium at pH 6 and 8. Additionally in a full transformation dissolution test, dissolution of titanium dioxide after 7 and 28 d was investigated.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.14 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.14 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.14 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.14 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.007 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.007 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.007 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.007 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.099 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.099 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.099 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.099 µg/L

Details on results:

Solution pH, oxygen concentrations, temperature:
Mean temperature was 21.2 ± 0.2 °C during the test over 1-d and 21.5 ± 0.2 °C during the test over 28-d.
In the 1-d test, the solution pH remained in the respective target pH range from 6.0 to 6.2 and from 7.8 to 8.0 in solutions containing the test item and in method blanks. In the 28-d test, the solution pH ranged from 6.1 to 6.6 and from 7.6 to 8.0 in solutions containing the test item and in method blanks. Oxygen levels of all test solutions were in the range recommended by the OECD Test Guidance 29 during the test (> 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L).

Analytical measurements: Within and between vessel variations in Titanium concentrations
Within and between vessel variations are not always in compliance with the guidance for the tests (<10% within-vessel variation, <20% between-vessel varition). The observed variations may be explained in parts with the ultrafine particle size of the test material, a low dispersion potential, low dissolution and resulting low titanium levels.

Analytical measurements - Screening test:
- Mean Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 (pH 8) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C were at least below LOQ of the quantification method (LOQ: 0.42 µg/L).
- Dispersed/Dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C were at least below LOQ of the quantification method (LOQ: 0.42 µg/L).
Analytical measurements - Full test:
- Dispersed/dissolved titanium concentrations of 0.2 µm filtered samples in 28-d test at pH 8 shaking at 100 rpm under dark conditions at 21°C were at least below the respective LOQs (0.02-0.36 µg Ti/L) for all sampled timepoints (7d, 14d, 28d).
- Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) shaking at 100 rpm under dark conditions at 21°C amount to 1.02 ± 0.43 µg Ti/L after 7 d and 1.13 ± 0.71 µg/L) for 28 d testing.

Validation experiments regarding applicability of filtration method:
Validation experiments were performed to show that dissolved nanosized TiO2 was not retained by the 0.2 µm filters or the ultrafiltration procedure. The applicability of the centrifugal filtration was investigated in a pre-test. The respective recoveries of dissolved titanium of three sequential filtrations of Ti ICP standard (1 mg / L) were as follows: 1st filtrate: 106.4 % 2nd filtrate: 89.2 % 3rd filtrate: 98.8 %.

Method validation summary (ICP-OES)

 

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.007 -0.138 µg Ti/ L.

Limits of quantification (LOQ) within all measurement series: 0.022 -0.415 µg Ti / L.

Correlation coefficients (r) within all measurement series: > 0.999521

 

Method validation summary

Mean recovery of fortified samples (n = 7): 91.6 -112.3 %

Mean recoveries for certified reference material TM-26.4 and TMDA-54.5 (concentration range 3.35 - 6.15 µg Ti / L, n = 28): 96.4 -102.7 %

Mean recoveries for quality control standard (concentration range 0.5 -25 µg / L, n = 36): 98.3 - 109.2 %

Mean recoveries for internal standard (concentration range 0.5 -100 µg / L, n = 24): 99.6 - 110.1 %

Conclusions:

The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of titanium dioxide at a loading of 1 mg/L at pH 6 and 8 resulted after 1 and 28 days in dissolved titanium concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) that were at least below the limit of quantification (LOQ: 0.30-0.42 µg/L). Dissolved/dispersed Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) at a loading of 1 mg/L at pH 8 after 1, 7 and 28 days were also below the LOD/LOQ, whereas mean Ti concentrations of below LOQ (<0.42 µg/L), 1.02 ± 0.44 µg/L and 1.13 ± 0.71 µg/L were measured at pH 6 after 1, 7 and 28 days, respectively. Thus, the extent to which TiO2-uf-2 can produce soluble available ionic and other metal-bearing species in aqueous media is limited.

Reference 6

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-09-07 to 2017-02-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

no

Principles of method if other than guideline:

First a screening test was performed to determine the dissolution of titanium dioxide after 24 h in environmentally relevant test medium at pH 6 and 8. Additionally in a full transformation dissolution test, dissolution of titanium dioxide after 7 and 28 d was investigated.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.14 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.14 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.14 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.14 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0.03 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.022 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOQ: 0.022 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.297 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOQ: 0.297 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.099 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.099 µg/L

Details on results:

Solution pH, oxygen concentrations, temperature:
Mean temperature was 21.2 ± 0.2 °C during the test over 1-d and 21.5 ± 0.2 °C during the test over 28-d.
In the 1-d test, the solution pH remained in the respective target pH range from 6.0 to 6.2 and from 7.8 to 7.9 in solutions containing the test item and in method blanks. In the 28-d test, the solution pH ranged from 5.9 to 6.6 and from 7.5 to 8.0 in solutions containing the test item and in method blanks. Oxygen levels of all test solutions were in the range recommended by the OECD Test Guidance 29 during the test (> 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L).

Analytical measurements: Within and between vessel variations in Titanium concentrations
Within and between vessel variations are not always in compliance with the guidance for the tests (<10% within-vessel variation, <20% between-vessel varition). The observed variations may be explained in parts with the ultrafine particle size of the test material, a low dispersion potential, low dissolution and resulting low titanium levels.

Analytical measurements - Screening test:
- Mean Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 (pH 8) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C were at least below LOQ of the quantification method (LOQ: 0.42 µg/L).
- Mean Dispersed/Dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C were 0.94 ± 0.70 µg/L.
Analytical measurements - Full test:
- Dispersed/dissolved titanium concentrations of 0.2 µm filtered samples in 28-d test at pH 8 shaking at 100 rpm under dark conditions at 21°C were at least below the respective LOQs (0.02-0.36 µg Ti/L) for all sampled timepoints (7d, 14d, 28d).
- Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) shaking at 100 rpm under dark conditions at 21°C amount to 0.76 ± 0.62 µg Ti/L after 7 d and 0.225 ± 0.1 µg/L for 28 d testing.


Validation experiments regarding applicability of filtration method:
Validation experiments were performed to show that dissolved nanosized TiO2 was not retained by the 0.2 µm filters or the ultrafiltration procedure. The applicability of the centrifugal filtration was investigated in a pre-test. The respective recoveries of dissolved titanium of three sequential filtrations of Ti ICP standard (1 mg / L) were as follows: 1st filtrate: 106.4 % 2nd filtrate: 89.2 % 3rd filtrate: 98.8 %.

Method validation summary (ICP-OES)

 Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.007 -0.138 µg Ti/ L.

Limits of quantification (LOQ) within all measurement series: 0.022 -0.415 µg Ti / L.

Correlation coefficients (r) within all measurement series: > 0.999521

Method validation summary

Mean recovery of fortified samples (n = 7): 92.4 -109.5 %

Mean recoveries for certified reference material TM-26.4 and TMDA-54.5 (concentration range 3.35 - 6.15 µg Ti / L, n = 28): 96.4 -102.7 %

Mean recoveries for quality control standard (concentration range 0.5 -25 µg / L, n = 36): 98.3 - 109.2 %

Mean recoveries for internal standard (concentration range 0.5 -100 µg / L, n = 24): 99.6 - 110.1 %

Conclusions:

The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of titanium dioxide at a loading of 1 mg/L at pH 6 and 8 resulted after 1 and 28 days in dissolved titanium concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) that were at least below the limit of quantification (LOQ: 0.30-0.42 µg/L). Dissolved/dispersed Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) at a loading of 1 mg/L at pH 8 after 1, 7 and 28 days were also below the LOD/LOQ, whereas mean Ti concentrations of 0.94 ± 0.70 µg/L, 0.76 ± 0.62 µg/L and 0.23 ± 0.1 µg/L were measured at pH 6 after 1, 7 and 28 days, respectively. Thus, the extent to which TiO2-uf-3 can produce soluble available ionic and other metal-bearing species in aqueous media is limited.

Reference 7

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-09-07 to 2017-11-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

no

Principles of method if other than guideline:

First a screening test was performed to determine the dissolution of titanium dioxide after 24 h in environmentally relevant test medium at pH 6 and 8. Additionally in a full transformation dissolution test, dissolution of titanium dioxide after 7 and 28 d was investigated.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.34 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.11/0.34 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.11 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.11 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.34 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.11/0.34 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

< 0.11 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD: 0.11 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.14 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD 0.14 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.42 µg/L

Element analysed:

Ti

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, centrifugal filtration (~2.1 nm)

Remarks on result:

other: conc. of all replicates < LOD/LOQ: 0.14/0.42 µg/L

Details on results:

Solution pH, oxygen concentrations, temperature:
Mean temperature was 21.2 ± 0.2 °C during the test over 1-d and 21.5 ± 0.2 °C during the test over 28-d.
In the 1-d test, the solution pH remained in the respective target pH range from 6.0 to 6.3 and from 7.8 to 7.9 in solutions containing the test item and in method blanks. In the 28-d test, the solution pH ranged from 5.8 to 6.2 and from 7.8 to 8.1 in solutions containing the test item and in method blanks. Oxygen levels of all test solutions were in the range recommended by the OECD Test Guidance 29 during the test (> 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L).

Analytical measurements: Within and between vessel variations in Titanium concentrations
Within and between vessel variations are not always in compliance with the guidance for the tests (<10% within-vessel variation, <20% between-vessel varition). The observed variations may be explained in parts with the ultrafine particle size of the test material, a low dispersion potential, low dissolution and resulting low titanium levels.

Analytical measurements - Screening test:
- Mean Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 (pH 8) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C were at least below LOQ of the quantification method (LOQ: 0.42 µg/L).
- Dispersed/Dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) medium after 24 h of shaking at 100 rpm under dark conditions at 21°C amounted to 5.72 ± 2.06 µg/L.
Analytical measurements - Full test:
- Dispersed/dissolved titanium concentrations of 0.2 µm filtered samples in 28-d test at pH 8 shaking at 100 rpm under dark conditions at 21°C were at least below the respective LOQs (0.32-0.34 µg Ti/L) for all sampled timepoints (7d, 14d, 28d).
- Dispersed/dissolved concentrations of titanium after 0.2 µm filtration of the TM1 1:20 (pH 6) shaking at 100 rpm under dark conditions at 21°C amount to 0.16 ± 0.08 Ti/L after 7 d and below the respective LOQ (<0.34 µg/L) for28 d testing.


Validation experiments regarding applicability of filtration method:
Validation experiments were performed to show that dissolved nanosized TiO2 was not retained by the 0.2 µm filters or the ultrafiltration procedure. The applicability of the centrifugal filtration was investigated in a pre-test. The respective recoveries of dissolved titanium of three sequential filtrations of Ti ICP standard (1 mg / L) were as follows: 1st filtrate: 106.4 % 2nd filtrate: 89.2 % 3rd filtrate: 98.8 %.

Method validation summary (ICP-OES)

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.105 -0.221 µg Ti/ L.

Limits of quantification (LOQ) within all measurement series: 0.315 -0.664 µg Ti / L.

Correlation coefficients (r) within all measurement series: > 0.999521

Method validation summary

Mean recovery of fortified samples (n = 7): 91.5 -114.7 %

Mean recoveries for certified reference material TM-26.4 and TMDA-54.5 (concentration range 3.35 - 6.7 µg Ti / L, n = 26): 91.6 -105.6 %

Mean recoveries for quality control standard (concentration range 0.5 -500 µg / L, n = 34): 94.3 - 107.6 %

Mean recoveries for internal standard (concentration range 0.5 -100 µg / L, n = 24): 95.6 - 108.7 %

Conclusions:

The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of titanium dioxide at a loading of 1 mg/L at pH 6 and 8 resulted after 1 and 28 days in dissolved titanium concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) that were at least below the limit of quantification (LOQ: 0.32-0.42 µg/L). Dissolved/dispersed Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) at a loading of 1 mg/L at pH 8 after 1, 7 and 28 days were also below the LOD/LOQ, whereas mean Ti concentrations of 5.72 and 0.16 µg/L were measured at pH 6 after 1 and 7 days, respectively and values below LOQ (<0.34 µg/L) after 28 days. Thus, the extent to which TiO2-uf-1 can produce soluble available ionic and other metal-bearing species in aqueous media is limited.

Description of key information

The micro- and nanoforms of TiO2 do not dissolve to any relevant extent under regular environmental conditions. Thus, dissolution is not important for the environmental fate and behavior of nano-and microsized TiO2 in environmental compartments.

Additional information

Microsized TiO2

Klawonn et al. (2016) determined the water solubility of microsized TiO2 according to OECD TG 105 in ultrapure water. Under the conditions of this test (flask method, mean loading of 500.6 mg/L), a solubility equilibrium was not observed during the test. Mean background-corrected dissolved Ti concentrations of test solutions in samples (operationally defined as fraction < 2.1 nm, i.e. after filtration through a 0.2 µm membrane and centrifugal filtration) ranged from 0.024 µg Ti/L to 0.172 µg Ti/L, which corresponds to 0.04 to 0.287 µg TiO2/L.

The solubility of microsized TiO2 in environmental media is low based on results of transformation / dissolution (T/D) testing of three TiO2 materials (Klawonn et al. 2017a-c). The T/D of three microsized TiO2 materials, ranging in particle size from 120 to 165 nm and specific surface area from 7.1 to 17.1 m²/g, was tested according to OECD Series No. 29. Measured dissolved Ti concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) after 28 d at a loading of 1 mg/L at pH 6 and pH 8 were below the limit of detection / quantification (<0.11 / <0.34 µg Ti/L). After 28 d and at a loading of 1 mg/L, suspended Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) were below the LOD/LOQ (<0.11/<0.34 µg Ti/L) at pH 8, whereas at pH 6 they ranged from below the LOQ (<0.34 µg Ti/L) to 3.76 µg/L during the 28-day test. These findings indicate that microsized TiO2 materials do not dissolve to any relevant extent under regular environmental conditions. Further, measured Ti concentrations in the water phase decreased with decreasing filter size fraction (0.2 µm vs 2.1 nm), suggesting that Ti is associated with particles or colloids (Table 1, 2 and 3).

In sum, microsized TiO2 does not dissolve to any relevant extent under regular environmental conditions. Thus, dissolution is not an important process for the environmental fate and behavior of microsizedTiO2 in environmental compartments.

Nanosized TiO2

The solubility of nanosized TiO2 in environmental media is low based on results of transformation/dissolution (T/D) testing of three TiO2 materials (Klawonn et al. 2017d-f). The T/D of three TiO2 materials ranging in their particle size from 19 to 23 nm and specific surface area from 50.4 to 82.0 m²/g was tested according to OECD Series No. 29. Measured dissolved Ti concentrations (operationally defined as the dissolved Ti fraction after centrifugal filtration (~2.1 nm)) after 28 d at a loading of 1 mg/L at pH 6 and pH 8 were below the limit of detection / quantification (<0.11 / <0.34 µg Ti/L). After 28 d and at a loading of 1 mg/L, suspended Ti concentrations (operationally defined as the Ti fraction after 0.2 µm filtration) were below the LOD/LOQ (<0.11/<0.34 µg Ti/L) at pH 8, whereas at pH 6 they ranged from below the LOQ (<0.34 µg Ti/L) to 5.72 µg/L during the 28-day test. These findings indicate that nanosized TiO2 materials do not dissolve to any relevant extent under regular environmental conditions. Further, measured Ti concentrations in the water phase decreased with decreasing filter size fraction (0.2 µm vs 2.1 nm), suggesting that Ti is associated with particles or colloids (Table 1, 2 and 3).

In sum, nanosized TiO2 does not dissolve to any relevant extent under regular environmental conditions. Thus, dissolution is not an important process for the environmental fate and behavior of nanosized TiO2 in environmental compartments.

 

 Table 1 Measured Ti concentrations in T/D media at 1 mg/L loading after 24h at pH 8 and 6

pH 8	0.2-µm filtration		centrifugal filtration (~ 2.1 nm)
	Ti	Ti	Ti		Ti	Ti
	mean	SD	mean		LOD	LOQ
Material	µg/L	µg/L	µg/L		µg/L	µg/L
UF1	<LOQ		<LOQ		0,14	0,42
UF2	<LOQ		<LOD		0,14	0,42
UF3	<LOQ		<LOD		0,14	0,42
PG1	<LOQ		<LOQ		0,17	0,51
PG2	<LOQ		<LOQ		0,17	0,51
PG3	0.378	0.063	<LOQ		0,17	0,51
pH 6	0.2-µm filtration		centrifugal filtration (~ 2.1 nm)
	Ti	Ti	Ti		Ti	Ti
	mean	SD	mean		LOD	LOQ
	µg/L	µg/L	µg/L		µg/L	µg/L
UF1	5.720	2.057	<LOD		0.14	0.42
UF2	<LOQ		<LOD		0.14	0.42
UF3	0.938	0.704	<LOD		0.14	0.42
PG1	3.756	0.516	<LOQ		0.17	0.51
PG2	0.396	0.121	<LOQ/LOD		0.17	0.51
PG3	0.824	0.224	<LOQ		0.17	0.51

 

Table 2 Measured Ti concentrations in T/D media at 1 mg/L loading after 7 d at pH 8 and 6

(LOD/LOQ: 0.11 and 0.34 µg/L) 

pH 8	0.2-µm filtration		centrifugal filtration (~2.1 nm)
	Ti	Ti	Ti	Ti
	mean	SD	mean	SD
Material	µg/L	µg/L	µg/L	µg/L
UF1	< LOQ		< LOD
UF2	< LOQ		< LOD
UF3	< LOQ		< LOD
PG1	< LOD		< LOD
PG2	< LOQ		< LOD
PG3	< LOQ		< LOQ
pH 6	0.2-µm filtration		centrifugal filtration (~2.1 nm)
	Ti	Ti	Ti	Ti
	mean	SD	mean	SD
Material	µg/L	µg/L	µg/L	µg/L
UF1	0.164	0.075	< LOQ
UF2	1.016	0.435	< LOD
UF3	0.756	0.624	0.030	0.01
PG1	1.336	0.931	< LOQ
PG2	0.423	0.159	0.024	0.019
PG3	0.506	0.306	< LOQ

Table 3 Measured Ti concentrations in T/D media at 1 mg/L loading after 28 d at pH 8 and 6

(LOD/LOQ: 0.11 and 0.34 µg/L)

pH 8	0.2-µm filtration		centrifugal filtration (~2.1 nm)
	Ti	Ti	Ti	Ti
	mean	SD	mean	SD
Material	µg/L	µg/L	µg/L	µg/L
UF1	< LOD		< LOD
UF2	< LOD		< LOD
UF3	< LOD		< LOD
PG1	< LOD		< LOD
PG2	< LOD		< LOD
PG3	< LOD		< LOD
pH 6	0.2-µm filtration		centrifugal filtration (~2.1 nm)
	Ti	Ti	Ti	Ti
	mean	SD	mean	SD
Material	µg/L	µg/L	µg/L	µg/L
UF1	< LOQ		< LOQ
UF2	1.131	0.706	< LOD
UF3	0.225	0.107	< LOQ
PG1	0.481	0.176	< LOQ
PG2	< LOQ		< LOQ
PG3	< LOQ		< LOQ

In sum, the micro- and nanoforms of TiO2 do not dissolve to any relevant extent under regular environmental conditions. Thus, dissolution is not important for the environmental fate and behavior of nano-and microsized TiO2 in environmental compartments.