Titanium carbide

Toxicity to terrestrial arthropods

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to terrestrial arthropods: short-term

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 assessment. Justification for read-across: Due to lower transformation/dissolution results for titanium carbide (the target substance) than titanium dioxide (the source substance), the resulting toxicity potential would also be expected to be lower, so read-across is appropriate. Therefore, the dose descriptors are expected to be sufficiently higher for the target substance, and read-across to the source chemical is adequately protective. For more details refer to the attached description of the read-across approach.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The effects of nanosize titanium dioxide (TiO2; anatase, 15 nm) on the terrestrial isopod Porcellio scaber (Isopoda, Crustacea) was investigated after 3-d dietary exposure. TiO2 was applied at concentrations of 1, 10, 100, 1000, 2000, and 3000 µg/g food. Evaluated endpoints include weight change, feeding rate, food assimilation efficiency, and survival (=higher-level endpoints), as well as activities of antioxidant enzymes, such as catalase (CAT) and glutathione-S-transferase (GST) (= lower-level endpoints).

GLP compliance:

not specified

Application method:

oral

Analytical monitoring:

yes

Vehicle:

yes

Details on preparation and application of test substrate:

- Different concetrations of TiO2 were suspended in bidistilled water with pH 5.7 (pH of bidistilled water; pH independent of TiO2 concentrations)
- Sonication of the dispersion prepared in bidistilled water (0.7 g/L) for 30 min
- Determination of the TiO2 phase of sonicated and nonsonicated dispersions: dospersions were put on carbon-coated grids, dried at room temperature, examined with a 200-keV field emission transmission-electron microscope and analyzed by transmission-electron diffraction
- Inspections of sonicated and non-sonicated TiO2 dispersions by DLS technique: measurements were not possible (signal either too weak or too strong)

Test organisms (species):

Porcellus scaber

Animal group:

Crustacea (soil-dwelling woodlouse)

Details on test organisms:

TEST ORGANISM
- Common name: rough woodlouse (P. scaber Latreille 1804)
- Source: collected in the field (uncontaminated sites near Ljubljana)
- Weight at test initiation (mean and range, SD): 30 to 80 mg and of both sexes and all molt stages
- Date of collection: no data

ACCLIMATION
- Acclimation period: 1-11 days
- Acclimation conditions (same as test or not): terrarium (20x35x20 cm) filled with a 2- to 5-cm layer of moistened sand and soil as well as a thick layer of partly decomposed hazelnut tree leaves (Corylus avellana).
- Feeding: hazelnut tree leaves (Corylus avellana)

Study type:

laboratory study

Limit test:

no

Total exposure duration:

3 d

Post exposure observation period:

Not applicable.

Test temperature:

21±1 °C

Humidity:

very high (close to 100 %)

Photoperiod and lighting:

16:8 (light:dark, 15 lux:5 lux)

Details on test conditions:

TEST SYSTEM
- Test container / cage (material, size): Petri dish
- No. of organisms per container (treatment): 1
- No. of animals per replicate: 6-10
- No. of replicates per treatment group: 2-3
- No. of replicates per per control: 3

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
- Higher-level endpoints: weight change, feeding rate, food assimilation efficiency, and survival
- Lower-level endpoints: activities of antioxidant enzymes, such as catalase (CAT) and glutathione-S-transferase (GST)

VEHICLE CONTROL PERFORMED: yes (bidistilled water)

Nominal and measured concentrations:

Nominal: 0, 0.1, 0.5, 1, 10, 100, 1000, 2000 and 3000 µg/g leaf

Reference substance (positive control):

no

Key result

Duration:

3 d

Dose descriptor:

NOEC

Effect conc.:

>= 3 000 mg/kg diet

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

TiO2

Basis for effect:

other: mortality, weight change, feeding rate and defecation rate, food assimilation efficiency

Remarks on result:

other: No difference between nonsonicated and sonicated TiO2.

Details on results:

Results on enzyme activity are considered not relevant a population level. Thus no details are reported here.

Results with reference substance (positive control):

Not applicable.

Reported statistics and error estimates:

Significant differences determined by Kruskal-Wallis analysis and Mann-Whitney U-test.

- Animals and leaves were weighed after drying at room temperature

- Fecal pellets were counted and weighed after drying in the exsiccator for 48 h

- Animals were dissected, and the digestive glands (hepatopancreas) were isolated for measurements of CAT and GST activities. Animal mortality also was recorded.

Data analysis:

- Higher-level endpoints: only animals between the two molts and females without brood chambers were included in the analyses due to possible influence of molt and presence of broods on feeding and animal mass change

- Calculation of the feeding rate and a defecation rate as mass of consumed leaf and mass of fecal pellets per wet-

weight animal and per day, respectively.

- Food assimilation efficiency: calculated as difference between the feeding and defecation rates.

- Determination of the animal mass change: difference in animal mass at the beginning and at the end of the experiment.

- Amount of daily TiO₂ consumption: calculated from mass of consumed leaf and the corresponding concentration of TiO₂ applied.

Validity criteria fulfilled:

not applicable

Conclusions:

The 3-d NOEC for Porcellio scaber weight change, feeding rate, food assimilation efficiency, and survival is 3000 mg/kg food.

Executive summary:

The effects of nano-size titanium dioxide (TiO₂ ; anatase, 15 nm) on the terrestrial isopod Porcellio scaber (Isopoda, Crustacea) was investigated after 3-d dietary exposure. TiO₂ was applied at concentrations of 1, 10, 100, 1000, 2000, and 3000 µg/g food. Evaluated endpoints include weight change, feeding rate, food assimilation efficiency, and survival (= higher-level endpoints), as well as activities of antioxidant enzymes, such as catalase (CAT) and glutathione-S-transferase (GST) (= lower-level endpoints).

Exposure concentrations of 0.5, 2000, and 3000 µg non-sonicated TiO₂/g food led to a decrease in CAT and GST activities, but intermediate concentrations (1, 10, 100, and 1000 µg/g food) did not result in significant changes of enzyme activities.

Higher-level endpoints were not affected up to the highest tested concentration of TiO₂ in food (3000 µg/g).

Reference 2

Endpoint:

toxicity to terrestrial arthropods: short-term

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

For details and justification of read-across please refer to the report attached in section 13 of IUCLID.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

3 d

Dose descriptor:

NOEC

Effect conc.:

>= 3 000 mg/kg diet

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

TiO2

Basis for effect:

other: mortality, weight change, feeding rate and defecation rate, food assimilation efficiency

Remarks on result:

other: No difference between nonsonicated and sonicated TiO2.

Details on results:

Results on enzyme activity are considered not relevant a population level. Thus no details are reported here.

Results with reference substance (positive control):

Not applicable.

Reported statistics and error estimates:

Significant differences determined by Kruskal-Wallis analysis and Mann-Whitney U-test.

- Animals and leaves were weighed after drying at room temperature

- Fecal pellets were counted and weighed after drying in the exsiccator for 48 h

- Animals were dissected, and the digestive glands (hepatopancreas) were isolated for measurements of CAT and GST activities. Animal mortality also was recorded.

Data analysis:

- Higher-level endpoints: only animals between the two molts and females without brood chambers were included in the analyses due to possible influence of molt and presence of broods on feeding and animal mass change

- Calculation of the feeding rate and a defecation rate as mass of consumed leaf and mass of fecal pellets per wet-

weight animal and per day, respectively.

- Food assimilation efficiency: calculated as difference between the feeding and defecation rates.

- Determination of the animal mass change: difference in animal mass at the beginning and at the end of the experiment.

- Amount of daily TiO₂ consumption: calculated from mass of consumed leaf and the corresponding concentration of TiO₂ applied.

Validity criteria fulfilled:

not applicable

Conclusions:

The 3-d NOEC for Porcellio scaber weight change, feeding rate, food assimilation efficiency, and survival is 3000 mg/kg food.

Executive summary:

The effects of nano-size titanium dioxide (TiO₂ ; anatase, 15 nm) on the terrestrial isopod Porcellio scaber (Isopoda, Crustacea) was investigated after 3-d dietary exposure. TiO₂ was applied at concentrations of 1, 10, 100, 1000, 2000, and 3000 µg/g food. Evaluated endpoints include weight change, feeding rate, food assimilation efficiency, and survival (= higher-level endpoints), as well as activities of antioxidant enzymes, such as catalase (CAT) and glutathione-S-transferase (GST) (= lower-level endpoints).

Exposure concentrations of 0.5, 2000, and 3000 µg non-sonicated TiO₂/g food led to a decrease in CAT and GST activities, but intermediate concentrations (1, 10, 100, and 1000 µg/g food) did not result in significant changes of enzyme activities.

Higher-level endpoints were not affected up to the highest tested concentration of TiO₂ in food (3000 µg/g).

This information is used in a read-across 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

Titanium carbide was not tested for toxicity to soil macro-organisms and read-across to titanium dioxide (TiO2) was used for this endpoint. In a feeding study with Porcellio scaber TiO2 applied at concentrations up to 3000 mg/kg food did not increase mortality compared to control.

Additional information

The effects of nano-size titanium dioxide (TiO₂; anatase, 15 nm) on the terrestrial isopod Porcellio scaber (Isopoda, Crustacea) was investigated after 3-d dietary exposure. TiO₂ was applied at concentrations of 1, 10, 100, 1000, 2000, and 3000 mg/kg food. Evaluated endpoints included weight change, feeding rate, food assimilation efficiency, and survival (= higher-level endpoints), as well as activities of antioxidant enzymes, such as catalase (CAT) and glutathione-S-transferase (GST) (= lower-level endpoints).

Exposure concentrations of 0.5, 2,000, and 3,000 mg non-sonicated TiO₂ /kg food led to a decrease in CAT and GST activities, but intermediate concentrations (1, 10, 100, and 1,000 mg/kg food) did not result in significant changes of enzyme activities.

Higher-level endpoints (e.g. mortality) were not affected up to the highest tested concentration of TiO2 in food (3000 mg/kg).

Due to lower transformation/dissolution results for titanium carbide (the target substance) than titanium dioxide, the resulting toxicity potential of TiC is also be expected to be lower. Therefore, the dose descriptors are expected to be sufficiently high for the target substance, and read-across to the source chemical is adequately protective. In fact, (eco-) toxicologically relevant release of Ti ions from titanium carbide is not expected as the concentration of soluble Ti ions was below the method detection limit (< 0.4 µg/L) in the T/D test. (Bioelution results (KMHC, 2012) are in this case of minor relevance as woodlice digest food by enzymatic degradation during gut passage without influence of gastric fluids.)

Thus, TiC in considered to be practically insoluble and thus non-bioavailable in the gut. Therefore, any toxic effects to terrestrial woodlice via food are not expected to arise from TiC.