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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Administrative data

Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Bioaccumulation study on target compound titanium oxide sulphate itself is technically not feasible as the substance is highly unstable in aqueous environment in the environmentally relevant pH range. Thus a read-across from supporting substance is being proposed by using the stable, final hydrolysis product titanium dioxide as test surrogate. No guideline followed, but well documented and well performed study; measured TiO2 concentrations during exposure period.

Data source

Reference
Reference Type:
publication
Title:
Toxicity of titanium dioxide nanoparticles to rainbow trout (Oncorhynchus mykiss): Gill injury, oxidative stress, and other physiological effects
Author:
Federici G, Shaw BJ, Handy RD
Year:
2007
Bibliographic source:
PMID: 17727975, Aquatic Toxicology 84(4):415-30

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
EPA OPPTS 850.1730 (Fish Bioconcentration Test)
Deviations:
yes
Remarks:
- No depuration phase, no kinetic determined
Principles of method if other than guideline:
A semi-static test system was used to expose rainbow trout to TiO2 nonoparticles in freshwater for up to 14 days. Deviating from the guideline sampling was restricted to two measurements at day 7 and 14 and thus no kinetic investigation was performed and no depuration phase included.
GLP compliance:
no

Test material

Constituent 1
Reference substance name:
Titanium dioxide
EC Number:
236-675-5
EC Name:
Titanium dioxide
Cas Number:
13463-67-7
IUPAC Name:
dioxotitanium
Constituent 2
Reference substance name:
Rutile (TiO2)
EC Number:
215-282-2
EC Name:
Rutile (TiO2)
Cas Number:
1317-80-2
IUPAC Name:
dioxotitanium
Details on test material:
- Name of test material (as cited in study report): Titanium dioxide
- Molecular formula (as other than submission substance): TiO2
- Molecular weight (as other than submission substance): 79.899 g/mol
- Smiles notation (as other than submission substance): [Ti](=O)=O
- InChl (as other than submission substance): InChI=1/2O.Ti/rO2Ti/c1-3-2
- Structural formula attached as image file (as other than submission substance): O=Ti=O
Powder form of ultrafine titanium dioxide nanoparticles from DeGussa AG (UK), P25 TiO2 type.
Manufacturer's information: crystal structure of 75% rutile and 25% anatase TiO2 purity was at least 99% TiO2 (maximum impurity was 1% Si) average particle size was 21 nm with a specific surface area of 50±15 m²/g
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
JUSTIFICATION FOR READ ACROSS
Bioaccumulation study on target compound titanium oxide sulphate itself is technically not feasible as the substance is highly unstable in aqueous environment in the environmentally relevant pH range. Thus a read-across from supporting substance is being proposed by using the stable, final hydrolysis product titanium dioxide as surrogate.
In the present study the water was spiked with the test surrogate titanium dioxide. In conclusion the test was conducted with the relevant transformation product. The other final hydrolysis product sulphuric acid is considered irrelevant, as pH effects should be excluded according to the relevant test guidelines, and sulphate is not bioaccumulating.
Radiolabelling:
no

Sampling and analysis

Details on sampling:
No data

Test solutions

Vehicle:
no
Details on preparation of test solutions, spiked fish food or sediment:
A stock solution of 10 g/L TiO2 was prepared by dispersing the nanoparticles in ultrapure water.

Test organisms

Test organisms (species):
Oncorhynchus mykiss (previous name: Salmo gairdneri)
Details on test organisms:
Juvenile rainbow trout (n=189) were obtained from Hatchlands Trout Farm, Rattery, Devon.
Fish weighing 28.1 ± 0.4 g.
Stock animals were fed to satiation on a commercial trout food before the test.

Study design

Route of exposure:
aqueous
Test type:
semi-static
Water / sediment media type:
natural water: freshwater
Total exposure / uptake duration:
14 d

Test conditions

Hardness:
50 mg CaCO3/L
Test temperature:
14 ± 1 °C
pH:
7.11 ± 0.01
Dissolved oxygen:
Oxygen saturation: 87.0 ± 0.25 %
Details on test conditions:
12 experimental glass aquaria: 3 tanks/treatment, 14 fish/tank.
Semi-static exposure regime: 80 % water change every 12h with re-dosing after each change.
Photoperiod was 12 h light: 12 h dark.
Fish were not fed 24 h prior to or during the experiment. Except for day 10, just after water change and prior to re-dosing with TiO2, to minimise aggressive behaviour associated with hunger. The food was consumed by the fish immediately without leaving residues.
Nominal and measured concentrations:
In order to achieve working concentrations of 0 (control), 0.1, 0.5 and 1.0 mg/L TiO2 in the fish tanks, each tank was dosed with 0, 0.2, 1.0 or 2.0 ml of the 10 g stock solution, respectively. Measured TiO2 concentrations after dosing the tanks were 95, 98 and 97 % of the nominal target values for the 0.1, 0.5 and 1.0 mg TiO2/L treatments, respectively. Before the 12 h water change, measured concentrations were 89, 85 and 86 % of the nominal values for the 0.1, 0.5 and 1.0 mg/L TiO2 treatments, respectively. Nominal values are used for calculation of BCF values.
Reference substance (positive control):
not required
Details on estimation of bioconcentration:
No data

Results and discussion

Bioaccumulation factoropen allclose all
Type:
BCF
Value:
19 - 208 L/kg
Basis:
organ d.w.
Remarks:
liver
Calculation basis:
other: after 14 d
Remarks on result:
other: Ti concentration in liver: 11.5-13.0 mg Ti/kg dw. BCF decreases with increasing TiO2 dose in water.
Remarks:
Conc.in environment / dose:0.1-1.0 mg TiO2/L
Type:
BCF
Value:
26 - 272 L/kg
Basis:
organ d.w.
Remarks:
muscle
Calculation basis:
other: after 14 d
Remarks on result:
other: Ti concentration in muscle: 15.8-17.3 mg Ti/kg dw. BCF decreases with increasing TiO2 dose in water.
Remarks:
Conc.in environment / dose:0.1-1.0 mg TiO2/L
Type:
BCF
Value:
34 - 352 L/kg
Basis:
organ d.w.
Remarks:
brain
Calculation basis:
other: after 14 d
Remarks on result:
other: Ti concentration in brains: 20.2-21.1 mg Ti/kg dw. BCF decreases with increasing TiO2 dose in water.
Remarks:
Conc.in environment / dose:0.1-1.0 mg TiO2/L
Type:
BCF
Value:
20 - 200 L/kg
Basis:
organ d.w.
Remarks:
gills
Calculation basis:
other: after 14 d
Remarks on result:
other: Ti concentration in gills: 12.0-15.4 mg Ti/kg dw. BCF decreases with increasing TiO2 dose in water.
Remarks:
Conc.in environment / dose:0.1-1.0 mg TiO2/L
Details on kinetic parameters:
No dta
Metabolites:
Not applicable
Results with reference substance (positive control):
Not applicable
Details on results:
Tissue Ti concentrations in control media after 14 days:
Gill: 13.9 mg Ti/kg d.w.
Liver: 12.5 mg Ti/kg d.w.
Muscle: 18.7 mg Ti/kg d.w.
Brain: 22.5 mg Ti/kg d.w.
Reported statistics:
No recalculation of the measured BCF is required as the test surrogate TiO2 results from isomolar transformation of the target chemical TiOSO4.

Any other information on results incl. tables

Conc. in environment / dose Type Value Basis Calculation basis Remarks
0.1 mg TiO2/L BCF 280 organ d.w. gill after 7 d Concentration organism: 16.8 mg Ti/kg dw
0.5 mg TiO2/L BCF 51 organ d.w. gill after 7 d Concentration organism: 15.4 mg Ti/kg dw
1.0 mg TiO2/L BCF 27 organ d.w. gill after 7 d Concentration organism: 16.3 mg Ti/kg dw
0.1 mg TiO2/L BCF 200 organ d.w. gill after 14 d Concentration organism: 12.0 mg Ti/kg dw
0.5 mg TiO2/L BCF 51 organ d.w. gill after 14 d Concentration organism: 15.4 mg Ti/kg dw
1.0 mg TiO2/L BCF 20 organ d.w. gill after 14 d Concentration organism: 12.0 mg Ti/kg dw
0.1 mg TiO2/L BCF 144 organ d.w. liver after 7 d Concentration organism: 8.6 mg Ti/kg dw
0.5 mg TiO2/L BCF 30 organ d.w. liver after 7 d Concentration organism: 9.1 mg Ti/kg dw
1.0 mg TiO2/L BCF 15 organ d.w. liver after 7 d Concentration organism: 9.1 mg Ti/kg dw
Conc. in environment / dose Type Value Basis Calculation basis Remarks
0.1 mg TiO2/L BCF 208 organ d.w. liver after 14 d Concentration organism: 12.5 mg Ti/kg dw
0.5 mg TiO2/L BCF 43 organ d.w. liver after 14 d Concentration organism: 13.0 mg Ti/kg dw
1.0 mg TiO2/L BCF 19 organ d.w. liver after14 d Concentration organism: 11.5 mg Ti/kg dw
0.1 mg TiO2/L BCF 272 organ d.w. muscle after 7 d Concentration organism: 16.3 mg Ti/kg dw
0.5 mg TiO2/L BCF 58 organ d.w. muscle after 7 d Concentration organism: 17.3 mg Ti/kg dw
1.0 mg TiO2/L BCF 24 organ d.w. muscle after 7 d Concentration organism: 14.4 mg Ti/kg dw
0.1 mg TiO2/L BCF 272 organ d.w. muscle after 14 d Concentration organism: 16.3 mg Ti/kg dw
0.5 mg TiO2/L BCF 58 organ d.w. muscle after 14 d Concentration organism: 17.3 mg Ti/kg dw
1.0 mg TiO2/L BCF 26 organ d.w. muscle after 14 d Concentration organism: 15.8 mg Ti/kg dw

Conc. in environment / dose Type Value Basis Calculation basis Remarks
0.1 mg TiO2/L BCF 160 organ d.w. brain after 7 d Concentration organism: 9.6 mg Ti/kg dw
0.5 mg TiO2/L BCF 46 organ d.w. brain after 7 d Concentration organism: 13.9 mg Ti/kg dw
1.0 mg TiO2/L BCF 14 organ d.w. brain after 7 d Concentration organism: 8.2 mg Ti/kg dw
0.1 mg TiO2/L BCF 352 organ d.w. brain after 14 d Concentration organism: 21.1 mg Ti/kg dw
0.5 mg TiO2/L BCF 67 organ d.w. brain after 14 d Concentration organism: 20.2 mg Ti/kg dw
1.0 mg TiO2/L BCF 34 organ d.w. brain after 14 d Concentration organism: 20.2 mg Ti/kg dw

Applicant's summary and conclusion

Validity criteria fulfilled:
not applicable
Conclusions:
Steady state BCF values of 200-272 at 0.1 mg/L and 20-26 at 1 mg/L were measured in gills and muscles respectively. BCF values of 208-352 at 0.1 mg/L and 19-34 at 1 mg/L were found in liver and brain. The BCF values are well below trigger levels for classification issues or the PBT discussion.
Executive summary:

Bioaccumulation study on target compound titanium oxide sulphate itself is technically not feasible as the substance is highly unstable in aqueous environment in the environmentally relevant pH range. Thus a read-across from supporting substance is being proposed by using the stable, final hydrolysis product titanium dioxide as test surrogate.

In the present study the water was spiked with the test surrogate titanium dioxide. In conclusion the test was conducted with the relevant transformation product. The other final hydrolysis product sulphuric acid is considered irrelevant, as pH effects should be excluded according to the relevant test guidelines, and sulphate is not bioaccumulating.

The study investigates the enrichment of titanium species in fish (Oncorhynchus mykiss). The test was not performed under GLP and no technical guidance protocol applied. Nonetheless the study is sufficiently documented and comparable to U.S. EPA OPPTS 850.1730 standards. The experiments are considered valid and conclusive.

The titanium concentrations in the various fish tissues were constant over the concentration range. The resulting BCFs were 200-20 (gills), 272-26 (muscle), 208-19 (liver), and 352-34 (brain). The data show clearly the decreasing BCF with increasing TiO2 concentrations in the aqueous medium. The effect mainly can be explained by the very limited water solubility of TiO2 at around neutral pH, which has been shown to be in the low µg/L range. Subsequently the effectively bioavailable, dissolved Ti concentration can safely be assumed to be largely the same for all TiO2 concentration levels tested in this study (i.e. 0.1, 0.5, and 1.0 mg/l TiO2). In all cases the determined BCF values were found such in an order of magnitude which poses no reason of concern (e.g. threshold value for BCF = 2000 L/kg for triggering PBT discussion or classification issues).