Titanium carbide

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil macroorganisms except arthropods: long-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:

OECD 222 guideline study without detailed documentation. 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 high 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:

according to guideline

Guideline:

OECD Guideline 222 (Earthworm Reproduction Test (Eisenia fetida/Eisenia andrei))

GLP compliance:

not specified

Analytical monitoring:

no

Vehicle:

no

Details on preparation and application of test substrate:

- Preparation of 100 ml stock solutions of TiO2 NP and bulk metal oxide in deionised water by ultra-sonication (Ultrasonic Cleaner 5510E-MT, Branson, Danbury, CT, USA) for 30 min
- Mixing of stock silutions into soil: manually

Test organisms (species):

Eisenia fetida

Animal group:

annelids

Details on test organisms:

TEST ORGANISM
- Common name: Eisenia fetida
- Source: Skandinavisk Miljøgødning (Grindsted, Denmark)
- Age at test initiation: adult
- Weight at test initiation: 2-600 mg (similar mean for all exposure replicates)

ACCLIMATION
- Acclimation period: 1 week
- Acclimation conditions: same as test
- Health during acclimation (any mortality observed):

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

yes

Total exposure duration:

28 d

Post exposure observation period:

28 days for assesment of production of juveniles and hatchability

Test temperature:

20 °C

pH:

8.5

Moisture:

50-60% of water holding capacity

Details on test conditions:

TEST SYSTEM
- Test container (material, size): plastic containers with perforated lids (height: 13 cm; diameter: 10.5 bottom and 12.5 cm top)
- Amount of soil or substrate: 500 g dry soil + 100 ml stock solution (controls: deionised water)
- No. of organisms per container (treatment): 10
- No. of replicates per treatment group: 4
- No. of replicates per control: 4
- Observation of produces cocoons:
* on moist filter paper at 20 °C in the dark; )
* hatching was monitored during the following 28 days

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Source: Askov experimental station, Aarhus University, Faculty of Agricultural Sciences, Denmark (batch no. 2-031207).
- Soil texture (if natural soil): sandy loam
- pH: 5.8
- % sand: 64.7
- % silt: 21.4
- % clay: 11.6
- Organic carbon (%): 1.36
- Pretreatment of soil:
* dried in oven at 80 °C for 24h
* sol was then grounded and sieved (2 mm)
- Storage (condition, duration): at room temperature until use

OTHER TEST CONDITIONS
- Photoperiod: 12 h: 12 h
- Light intensity: 295 Lux : 25 Lux
- Feeding: weekly (5 g dw cow-dung, pH 8.5, non-medicated animals; dung was dried at 100 °C and rewetted for feeding: 1g cow dung + 3.3 ml deinoised water)
- Evaporation > 1 % was was replenished to start weight if necessary

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): adult survival, reproduction, biomass

Nominal and measured concentrations:

Nominal: 1000 mg/kg soil dw (TiO2 nanoparticles as well as bulk form were tested at this concentration)

Reference substance (positive control):

no

Duration:

8 wk

Dose descriptor:

LC50

Effect conc.:

1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

other: TiO2 nanoparticles

Basis for effect:

reproduction

Key result

Duration:

8 wk

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

other: TiO2 bulk material

Basis for effect:

reproduction

Details on results:

No clear correlation could be drawn between particle characteristics and toxicity.

Results with reference substance (positive control):

Not applicable.

Reported statistics and error estimates:

Student’s t-test (assumption: appropriate equal variance where appropriate); significance level of 5 %

Table: Toxicity of TiO₂ nanoparticles and TiO₂ bulk material to Eisenia fetida; test substances were applied at a single concentration of 1000 mg/kg soil dw.

Endpoint	TiO2 nanoparticles	TiO2 bulk material
Survival [%]	97.5 ± 2.5	90.0 ± 4.1
Cocoon production [%]	80.7 ± 7.3	124 ± 12.3
Reproduction hatchability [%]	74.6 ± 5.7*	117 ± 22.2
Juvenile production [%]	50.7 ± 7.7*	159 ± 30.8
Biomass^a[%]	169 ± 64.0	160 ± 9.6

Results are mean values of 4 samples (control: n = 12)

* Result significantly different from control (p < 0.05, Student’s t-test)

^aBiomass: wet weight

Validity criteria fulfilled:

not specified

Conclusions:

The exposure of Eisenia fetida to TiO2 nanoparticles caused a clear reduction (about 50 %) of reproductive effects, whereas the reproduction of Eisneia fetida exposed to the same concentration of TiO2 bulk material did not cause any adverse effects on reproduction.

Executive summary:

A study according to OECD 222 was conducted to assess the effects of TiO₂ nanoparticles as well as TiO₂ bulk material on the reproduction of the earthworm Eisenia fetida. Animals were exposed in soil at a limit concentration of 1000 mg/kg soil dw for 28 days. The produced cocoons were placed on moist filter paper in order to asses production of juveniles and hatchability.

The exposure of Eisenia fetida to TiO₂ nanoparticles caused a clear reduction (about 50 %) of reproductive success, whereas the reproduction of Eisenia fetida exposed to the same concentration of TiO₂ bulk material did not cause any adverse effects on reproduction.

Reference 2

Endpoint:

toxicity to soil macroorganisms except arthropods: long-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

Duration:

8 wk

Dose descriptor:

LC50

Effect conc.:

1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

other: TiO2 nanoparticles

Basis for effect:

reproduction

Key result

Duration:

8 wk

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

other: TiO2 bulk material

Basis for effect:

reproduction

Details on results:

No clear correlation could be drawn between particle characteristics and toxicity.

Results with reference substance (positive control):

Not applicable.

Reported statistics and error estimates:

Student’s t-test (assumption: appropriate equal variance where appropriate); significance level of 5 %

Table: Toxicity of TiO₂ nanoparticles and TiO₂ bulk material to Eisenia fetida; test substances were applied at a single concentration of 1000 mg/kg soil dw.

Endpoint	TiO2 nanoparticles	TiO2 bulk material
Survival [%]	97.5 ± 2.5	90.0 ± 4.1
Cocoon production [%]	80.7 ± 7.3	124 ± 12.3
Reproduction hatchability [%]	74.6 ± 5.7*	117 ± 22.2
Juvenile production [%]	50.7 ± 7.7*	159 ± 30.8
Biomass^a[%]	169 ± 64.0	160 ± 9.6

Results are mean values of 4 samples (control: n = 12)

* Result significantly different from control (p < 0.05, Student’s t-test)

^aBiomass: wet weight

Validity criteria fulfilled:

not specified

Conclusions:

The exposure of Eisenia fetida to TiO2 nanoparticles caused a clear reduction (about 50 %) of reproductive effects, whereas the reproduction of Eisneia fetida exposed to the same concentration of TiO2 bulk material did not cause any adverse effects on reproduction.

Executive summary:

A study according to OECD 222 was conducted to assess the effects of TiO₂ nanoparticles as well as TiO₂ bulk material on the reproduction of the earthworm Eisenia fetida. Animals were exposed in soil at a limit concentration of 1000 mg/kg soil dw for 28 days. The produced cocoons were placed on moist filter paper in order to asses production of juveniles and hatchability.

The exposure of Eisenia fetida to TiO₂ nanoparticles caused a clear reduction (about 50 %) of reproductive success, whereas the reproduction of Eisenia fetida exposed to the same concentration of TiO₂ bulk material did not cause any adverse effects on reproduction.

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

Titanium carbide was not tested for toxicity to soil macro-organisms and read-across to titanium dioxide (TiO2) was used for this endpoint. In an earthworm reproduction test with Eisenia fetida the NOEC of bulk TiO2 was found to be greater than or equal to the highest concentration tested (≥1000 mg TiO2/kg dry soil).

Additional information

A study according to OECD 222 was conducted to assess the effects of TiO₂ nanoparticles as well as TiO₂ bulk material on the reproduction of the earthworm Eisenia fetida in soil at limit a concentration of 1000 mg/kg. The exposure of Eisenia fetida to TiO₂ nanoparticles caused a clear reduction (about 50 %) of reproductive success, whereas the reproduction of Eisenia fetida exposed to the same concentration of TiO₂ bulk material did not cause any adverse effects on reproduction.

 

Due to lower transformation/dissolution results for titanium carbide (the target substance) than the other titanium compounds referenced above (the source substances), the resulting toxicity potential would also be expected to be lower. Therefore, the dose descriptors are expected to be sufficiently higher for the target substances 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. Thus, TiC in considered to be practically insoluble, hence release of Ti ions to any ecotoxicologically relevant extent (and potential subsequent formation of soluble and/or insoluble Ti compounds) is not expected. (Bioelution results (KMHC, 2012) are in this case of minor relevance as earthworms digest food by enzymatic degradation during gut passage without influence of gastric fluids.)

Therefore, any toxic effects to terrestrial earthworms via soil pore water and/or TiC incorporated with food/soil are not expected to arise from TiC.

Besides, TiC is not manufactured in the nano form. Therefore, toxic effects attributable to nano-sized TiO₂ are considered not relevant for the assessment of bulk TiC. Therefore, toxic effects for soil macroorganisms are not expected to arise from TiC.