Titanium carbide

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Meets generally accepted scientific standards, well documented and acceptable for assessement. Justification for read-across: No data on the behavior of titanium carbide in the environment are available. Concentration data for titanium metal are appropriate for read-across for this endpoint as the soluble species released are expected to be similar for each of the compounds, and are thus expected to behave similarly in the environment. For more details refer to the attached description of the read across approach.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Fish were exposed to TiO2 nanoparticles in concentrations of 0 (control), 0.1, 0.5 and 1.0 mg/L for 14 days. Concentrations of Ti in different tissues were measured after 0, 7 and 14 days.

GLP compliance:

not specified

Radiolabelling:

not specified

Vehicle:

no

Details on preparation of test solutions, spiked fish food or sediment:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: a 10 g TiO2/L stock solution was prepared by dispering the substance in ultrapure water by sonication; stock solution was again sonicated immediately prior to dosing each day.
- Dispersion was confirmed by analytical measurements (transmission electron microscopy, optical methods)
- fish tanks were dosed with 0.2, 1.0 or 2.0 ml of the 10 g/L stock solution to achive test substance concentrations of 0.1, 0.5 and 1.0 mg/L respectively

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM
- Common name: Rainbow trout
- Source: Hatchlands Trout Farm, Rattery, Devon
- Age at study initiation (mean and range, SD): juvenile
- Weight at study initiation: 28.1 ± 0.4 g (n = 189)
- Feeding during test: No, except for day 10 (in order to reduce hunger and aggressive behaviour of fish; fish were fed after water change and prior to re-dosing with TiO2)


ACCLIMATION
- Acclimation period: 4 weeks
- Acclimation conditions (same as test or not): flowing, aerated, dechlorinated tap water
- Type and amount of food: commercial trout food ad libitum
- Feeding frequency: not reported.
- Health during acclimation (any mortality observed): no data

Route of exposure:

aqueous

Test type:

semi-static

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

14 d

Hardness:

50 mg CaCO3/L

Test temperature:

14 ± 1 °C

pH:

7.11 ± 0.01

Dissolved oxygen:

Oxygen saturation: 87.0 ± 0.25%

TOC:

No data.

Salinity:

Not applicable.

Details on test conditions:

TEST SYSTEM
- Test vessel: glass aquaria
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: no data
- Aeration: yes
- Renewal rate of test solution: 80 % water change every 12 h; re-dosing after water change
- No. of organisms per vessel: 14
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated Plymouth tap water
- Na+ = 0.5 mmol/L
- K+ = 0.1 mmol/L
- Ca2+ = 0.4 mmol/L
- Mg2+ = 0.1 mmol/L

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 12h:12h light:dark
- Light intensity: no data

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
Different biochemical parameters (haematology, blood plasma ion concentrations, gill injury, liver, skinned muscle and brains etc.) as well as mortality and behaviour were measured after 0, 7 and 14 days (fish were randomly sampled).

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 TiO2/L treatments, respectively. Nominal values are used for calculation of BCF values.

Reference substance (positive control):

no

Key result

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: ca. 12.0-15.3 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/L

Key result

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: ca. 11.5-12.9 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/L

Key result

Type:

BCF

Value:

26 - 271 L/kg

Basis:

organ d.w.

Remarks:

muscle

Calculation basis:

other: after 14 d

Remarks on result:

other: Ti concentration in muscle: ca. 15.8-17.2 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/L

Key result

Type:

BCF

Value:

34 - 351 L/kg

Basis:

organ d.w.

Remarks:

brain

Calculation basis:

other: after 14 d

Remarks on result:

other: Ti concentration in brains: ca. 20.1-21.1 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/l

Details on kinetic parameters:

No information on kinetics.

Metabolites:

Not applicable.

Details on results:

- Tissue Ti concentrations in control media (no TiO2) 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.
- Compared to control, fish did not bioaccumulate TiO2 in the inner organs during exposure (see Table 1).
- TiO2 powder has been used as a digestibility marker in fish nutrition due to its non-significant absorption into the inner organs of fish (ca. 1% of ingested dose, Vandenberg and De La Noue, 2001; Richter et al., 2003 cited by Frederici et al., 2007).
- The authors compare the measured Ti tissues concetrations to other values reported in the literature. Reported Ti tissue concentrations (0.1–0.5 mol/g dw, see Table 1) by Frederici et al. (2007) are - as stated by the authors - similar to background levels in shellfish (0.04–1.34 mol/L dw , Bustamante and Miramand, 2005) and laboratory mice (1–4 mol/g ww, Wang et al., 2007).

Reported statistics:

- Pooled data were analysed with StatGraphics Plus (v5.1).
- Data were checked for kurtosis, skewness and unequal variance (Bartlett’s test)
- Subsequent ANOVA test for treatment or time effects by ANOVA followed by Fisher’s 95 % least-squares difference (95 % confidence limits)
- Kruskal–Wallis test (non-parametric data)
- Identification of differences by notched box and whisker plots
- Student’s t-test for determination of differences between pairs of data sets at the end of the experiment

Table 1: Tissue titanium concentrations [µmol Ti/g dry weight of tissue] in rainbow trout exposed to control (no TiO2), 0.1, 0.5, or 1.0 mg/L TiO2 NPs for up to 14 days

Tissue	Time (days)	Treatment
		Control	0.1 mg/L TiO2	0.5 mg/L TiO2	1.0 mg/L TiO2
Gill	0	0.28 ± 0.01 (7)
	7	0.37 ± 0.02 (6)	0.35 ± 0.02 (6)	0.32 ± 0.02 (6)	0.34 ± 0.02 (6)
	14	0.29 ± 0.02 (6)	0.25 ± 0.05 (6)	0.32 ± 0.03 (6)	0.25 ± 0.02 (6)
Liver	0	0.20 ± 0.01 (7)
	7	0.18 ± 0.01 (6)	0.18 ± 0.01 (6)	0.19 ± 0.01 (6)	0.19 ± 0.01 (6)
	14	0.26 ± 0.01 (6)^#,*	0.26 ± 0.01 (6)^#,*	0.27 ± 0.01 (6)^#,*	0.24 ± 0.01 (6)^#,*,D
Muscle	0	0.20 ± 0.01 (7)
	7	0.40 ± 0.05 (6)	0.34 ± 0.08 (6)	0.36 ± 0.05 (6)	0.30 ± 0.03 (6)
	14	0.39 ± 0.06 (6)	0.34 ± 0.05 (6)	0.36 ± 0.06 (6)	0.33 ± 0.05 (6)
Brain	0	0.36 ± 0.02 (7)
	7	0.14 ± 0.03 (6)^#	0.20 ± 0.03 (6)^#	0.29 ± 0.10 (6)^#	0.17 ± 0.03 (6)^#
	14	0.47 ± 0.09 (6)^*	0.44 ± 0.08 (6)^*	0.42 ± 0.01 (6)^*	0.42 ± 0.04 (6)^*

Data are mean ± S.E.M. (n fish/treatment) expressed as µmol Ti metal/g dry weight of tissue.

# Significantly different from initial fish (ANOVA or Kruskal–Wallis, P < 0.05).

* Significantly different between day 7 and 14 within treatment (ANOVA or Kruskal–Wallis, P < 0.05).

D Significantly different from the previous TiO2 concentration within row (ANOVA or Kruskal–Wallis, P < 0.05).

Table 2: Tissue titanium concentrations [mg Ti/kg dw] after 14 days

Tissue [mgTi/kg dw] after 14 d	Treatment
	Control	0.1 mg/L TiO2	0.5 mg/L TiO2	1.0 mg/L TiO2
Gill	13,891	11,975	15,328	11,975
Liver	12,454	12,454	12,933	11,496
Muscle	18,681	16,286	17,244	15,807
Brain	22,513	21,076	20,118	20,118

Table 3: BCF values for different tissues and Ti aqueous concentrations after 14 d

	BCF = cf/cw after 14 d
Ti [mg/L]:	0,06	0,3	0,6
Gill	200	51	20
Liver	208	43	19
Muscle	271	57	26
Brain	351	67	34

Validity criteria fulfilled:

not applicable

Conclusions:

Fish did not bioaccumulate TiO2 particles in the inner organs during the 14-d exposure.

Executive summary:

Oncorhynchus mykiss were exposed to the test substance TiO₂ for a total duration of 14 days to at aqueous concentrations of 0 (control), 0.1, 0.5, and 1.0 mg/L under semi-static conditions. Concentrations of Ti in gills, liver, muscle and brain were measured after 0, 7 and 14 days. Based on the results reported in the publication it is possible to calculate BCF values by following equation:

BCF = cf / cw

with cf = Ti concentration in fish and cw = Ti concentration in water.

The following BCF values could be determined for aqueous TiO2 concentrations ranging from 0.1 to 1 mg/L :

- Gills: 20‒200 L/kg

- Liver: 19‒208 L/kg

- Muscle: 29‒271 L/kg

- Brain: 34‒351 L/kg

It has to be noted that Ti tissues of control fish were in the same range as tissue concentrations of fish exposed to TiO₂ concentrations ranging from 0.1 to 1 mg/L. Thus, it can be concluded that fish did not bioaccumulate TiO₂ particles in the inner organs during the 14-d exposure.

Reference 2

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

For justification of read-across please refer to the attached read-across report (see IUCLID section 13).

Reason / purpose for cross-reference:

read-across source

Key result

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: ca. 12.0-15.3 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/L

Key result

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: ca. 11.5-12.9 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/L

Key result

Type:

BCF

Value:

26 - 271 L/kg

Basis:

organ d.w.

Remarks:

muscle

Calculation basis:

other: after 14 d

Remarks on result:

other: Ti concentration in muscle: ca. 15.8-17.2 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/L

Key result

Type:

BCF

Value:

34 - 351 L/kg

Basis:

organ d.w.

Remarks:

brain

Calculation basis:

other: after 14 d

Remarks on result:

other: Ti concentration in brains: ca. 20.1-21.1 mg Ti/kg dw. For details see "Any other information on results incl. tables".

Remarks:

Conc.in environment / dose:0.1-1.0 mg TiO2/l

Details on kinetic parameters:

No information on kinetics.

Metabolites:

Not applicable.

Details on results:

- Tissue Ti concentrations in control media (no TiO2) 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.
- Compared to control, fish did not bioaccumulate TiO2 in the inner organs during exposure (see Table 1).
- TiO2 powder has been used as a digestibility marker in fish nutrition due to its non-significant absorption into the inner organs of fish (ca. 1% of ingested dose, Vandenberg and De La Noue, 2001; Richter et al., 2003 cited by Frederici et al., 2007).
- The authors compare the measured Ti tissues concetrations to other values reported in the literature. Reported Ti tissue concentrations (0.1–0.5 mol/g dw, see Table 1) by Frederici et al. (2007) are - as stated by the authors - similar to background levels in shellfish (0.04–1.34 mol/L dw , Bustamante and Miramand, 2005) and laboratory mice (1–4 mol/g ww, Wang et al., 2007).

Reported statistics:

- Pooled data were analysed with StatGraphics Plus (v5.1).
- Data were checked for kurtosis, skewness and unequal variance (Bartlett’s test)
- Subsequent ANOVA test for treatment or time effects by ANOVA followed by Fisher’s 95 % least-squares difference (95 % confidence limits)
- Kruskal–Wallis test (non-parametric data)
- Identification of differences by notched box and whisker plots
- Student’s t-test for determination of differences between pairs of data sets at the end of the experiment

Table 1: Tissue titanium concentrations [µmol Ti/g dry weight of tissue] in rainbow trout exposed to control (no TiO2), 0.1, 0.5, or 1.0 mg/L TiO2 NPs for up to 14 days

Tissue	Time (days)	Treatment
		Control	0.1 mg/L TiO2	0.5 mg/L TiO2	1.0 mg/L TiO2
Gill	0	0.28 ± 0.01 (7)
	7	0.37 ± 0.02 (6)	0.35 ± 0.02 (6)	0.32 ± 0.02 (6)	0.34 ± 0.02 (6)
	14	0.29 ± 0.02 (6)	0.25 ± 0.05 (6)	0.32 ± 0.03 (6)	0.25 ± 0.02 (6)
Liver	0	0.20 ± 0.01 (7)
	7	0.18 ± 0.01 (6)	0.18 ± 0.01 (6)	0.19 ± 0.01 (6)	0.19 ± 0.01 (6)
	14	0.26 ± 0.01 (6)^#,*	0.26 ± 0.01 (6)^#,*	0.27 ± 0.01 (6)^#,*	0.24 ± 0.01 (6)^#,*,D
Muscle	0	0.20 ± 0.01 (7)
	7	0.40 ± 0.05 (6)	0.34 ± 0.08 (6)	0.36 ± 0.05 (6)	0.30 ± 0.03 (6)
	14	0.39 ± 0.06 (6)	0.34 ± 0.05 (6)	0.36 ± 0.06 (6)	0.33 ± 0.05 (6)
Brain	0	0.36 ± 0.02 (7)
	7	0.14 ± 0.03 (6)^#	0.20 ± 0.03 (6)^#	0.29 ± 0.10 (6)^#	0.17 ± 0.03 (6)^#
	14	0.47 ± 0.09 (6)^*	0.44 ± 0.08 (6)^*	0.42 ± 0.01 (6)^*	0.42 ± 0.04 (6)^*

Data are mean ± S.E.M. (n fish/treatment) expressed as µmol Ti metal/g dry weight of tissue.

# Significantly different from initial fish (ANOVA or Kruskal–Wallis, P < 0.05).

* Significantly different between day 7 and 14 within treatment (ANOVA or Kruskal–Wallis, P < 0.05).

D Significantly different from the previous TiO2 concentration within row (ANOVA or Kruskal–Wallis, P < 0.05).

Table 2: Tissue titanium concentrations [mg Ti/kg dw] after 14 days

Tissue [mgTi/kg dw] after 14 d	Treatment
	Control	0.1 mg/L TiO2	0.5 mg/L TiO2	1.0 mg/L TiO2
Gill	13,891	11,975	15,328	11,975
Liver	12,454	12,454	12,933	11,496
Muscle	18,681	16,286	17,244	15,807
Brain	22,513	21,076	20,118	20,118

Table 3: BCF values for different tissues and Ti aqueous concentrations after 14 d

	BCF = cf/cw after 14 d
Ti [mg/L]:	0,06	0,3	0,6
Gill	200	51	20
Liver	208	43	19
Muscle	271	57	26
Brain	351	67	34

Validity criteria fulfilled:

not applicable

Conclusions:

Fish did not bioaccumulate TiO2 particles in the inner organs during the 14-d exposure.

Executive summary:

Oncorhynchus mykiss were exposed to the test substance TiO₂ for a total duration of 14 days to at aqueous concentrations of 0 (control), 0.1, 0.5, and 1.0 mg/L under semi-static conditions. Concentrations of Ti in gills, liver, muscle and brain were measured after 0, 7 and 14 days. Based on the results reported in the publication it is possible to calculate BCF values by following equation:

 

BCF = cf / cw

with cf = Ti concentration in fish and cw = Ti concentration in water.

 

The following BCF values could be determined for aqueous TiO2 concentrations ranging from 0.1 to 1 mg/L :

- Gills: 20‒200 L/kg

- Liver: 19‒208 L/kg

- Muscle: 29‒271 L/kg

- Brain: 34‒351 L/kg

 

It has to be noted that Ti tissues of control fish were in the same range as tissue concentrations of fish exposed to TiO₂ concentrations ranging from 0.1 to 1 mg/L. Thus, it can be concluded that fish did not bioaccumulate TiO₂ particles in the inner organs during the 14-d exposure.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the attached read-across report (see IUCLID section 13).

Description of key information

Oncorhynchus mykiss did not bioaccumulate TiO2 particles in the inner organs during the 14-d exposure at concentrations up to 1 mg/L. 
These data are used in a read-across approach for TiC. For details please refer to the read-across report. 

Additional information

No data on bioaccumulation or levels of titanium carbide in aquatic organisms are available. However, bioaccumulation/bioconcentration data of titanium dioxide are available (Frederici et al., 2007). 14-day exposure of Oncorhynchus mykiss to TiO₂ at aqueous concentrations of 0 (control), 0.1, 0.5, and 1.0 mg/L did not lead to significant accumulation in tissues (gills, liver, muscle, and brain) compared to the control. Thus, it can be concluded that fish did not bioaccumulate TiO₂ particles in the inner organs during the 14-d exposure.