Titanium carbide

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil microorganisms

Data waiving:

other justification

Justification for data waiving:

other:

Reference 2

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Documentation insufficient for assessment. Artificial exposure conditions in multiwell plates instead of incubation in soil. 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:

TiO2 toxicity to soil bacteria was determined in the Biolog test via multivariate analysis. This test is conducted by means of specific multiwell plates which contain an organic substrate in each well together with a tetrazolium violet redox dye. Toxic effects of the test chemical can be quantified via reduction in the colour development.
The Biolog test contains a positive control in the multiwell plates. Thus, an additional positive control was not conducted.
For this Biolog test soil bacteria were sampled at Demmerik (The Netherlands; 52°12'0''N, 4°56'0'E; May 19, 2005) and were added to 10M sterile Bis-tris (2-(bis(2-hydroxyethyl)amino)-2-(hydroxy-methyl)propane-1,3-diol at pH 7. The samples were incubated for 24 h and then transferred into the multiwell, gram-positive plates (Biolog).
The color development was measured for 7 consecutive days with the plate reader (except for the weekend).

GLP compliance:

not specified

Analytical monitoring:

no

Vehicle:

no

Test organisms (inoculum):

soil

Total exposure duration:

1 wk

Test temperature:

No data.

Moisture:

Not applicable.

Details on test conditions:

TiO2 toxicity to soil bacteria was determined in the Biolog test via multivariate analysis. This test is conducted by means of specific multiwell plates which contain an organic substrate in each well together with a tetrazolium violet redox dye. Toxic effects of the test chemical can be quantified via reduction in the colour development.
The Biolog test contains a positive control in the multiwell plates. Thus, an additional positive control was not conducted.
For this Biolog test soil bacteria were sampled at Demmerik (The Netherlands; 52°12'0''N, 4°56'0'E; May 19, 2005) and were added to 10M sterile Bis-tris (2-(bis(2-hydroxyethyl)amino)-2-(hydroxy-methyl)propane-1,3-diol at pH 7. The samples were incubated for 24 h and then transferred into the multiwell, gram-positive plates (Biolog).
The color development was measured for 7 consecutive days with the plate reader (except for the weekend).

Nominal and measured concentrations:

Nominal concetrations: 100 mg TiO2/L

Reference substance (positive control):

no

Key result

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

> 100 other: mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: reduction of colour development

Remarks on result:

other: 100 mg TiO2/L did not induce quantifiable toxic effects on soil microorganisms

Duration:

7 d

Dose descriptor:

EC0

Effect conc.:

100 other: mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: reduction of colour development

Validity criteria fulfilled:

not applicable

Conclusions:

7-d exposure of soil bacteria at a concentration of 100 mg TiO2/L did not cause adverse effects on the microorganisms.

Executive summary:

TiO2 toxicity to soil bacteria was determined in the Biolog test via multivariate analysis. This test is conducted by means of specific multiwell plates which contain an organic substrate in each well together with a tetrazolium violet redox dye. Toxic effects of the test chemical can be quantified via reduction in the colour development. The Biolog test contains a positive control in the multiwell plates. Thus, an additional positive control was not conducted. For this Biolog test soil bacteria were sampled at Demmerik (The Netherlands; 52°12'0''N, 4°56'0'E; May 19, 2005) and were added to 10M sterile Bis-tris (2-(bis(2-hydroxyethyl)amino)-2-(hydroxy-methyl)propane-1,3-diol at pH 7. The samples were incubated for 24 h and then transferred into the multiwell, gram-positive plates (Biolog). The color development was measured for 7 consecutive days with the plate reader (except for the weekend).

Under the conditions of the test colour development was not affected. Thus the authors report the EC50 (7 -d) to be > 100 mg TiO2/L.

Reference 3

Endpoint:

toxicity to soil microorganisms

Type of information:

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

Adequacy of study:

supporting study

Key result

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

> 100 other: mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: reduction of colour development

Remarks on result:

other: 100 mg TiO2/L did not induce quantifiable toxic effects on soil microorganisms

Duration:

7 d

Dose descriptor:

EC0

Effect conc.:

100 other: mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: reduction of colour development

Validity criteria fulfilled:

not applicable

Conclusions:

7-d exposure of soil bacteria at a concentration of 100 mg TiO2/L did not cause adverse effects on the microorganisms.

Executive summary:

 

TiO2 toxicity to soil bacteria was determined in the Biolog test via multivariate analysis. This test is conducted by means of specific multiwell plates which contain an organic substrate in each well together with a tetrazolium violet redox dye. Toxic effects of the test chemical can be quantified via reduction in the colour development. The Biolog test contains a positive control in the multiwell plates. Thus, an additional positive control was not conducted. For this Biolog test soil bacteria were sampled at Demmerik (The Netherlands; 52°12'0''N, 4°56'0'E; May 19, 2005) and were added to 10M sterile Bis-tris (2-(bis(2-hydroxyethyl)amino)-2-(hydroxy-methyl)propane-1,3-diol at pH 7. The samples were incubated for 24 h and then transferred into the multiwell, gram-positive plates (Biolog). The color development was measured for 7 consecutive days with the plate reader (except for the weekend).

 

Under the conditions of the test colour development was not affected. Thus the authors report the EC50 (7 -d) to be > 100 mg TiO2/L.

This information is used in a read-across apprach 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 micro-organisms and read-across to titanium dioxide (TiO2) was used for this endpoint. Due to lower transformation/dissolution results for titanium carbide (the target substance) than for 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 substances and read-across to the source chemical is adequately protective. A hazard for soil microorganisms is not identified.

Additional information

In the available supporting (yet unreliable) study regarding the REACH endpoint “toxicity to soil microorganisms”, toxicity o f TiO₂ to soil bacteria was determined in the Biolog test over 7 consecutive days. No effects could be observed. The authors report the EC₅₀ (7 d) to be > 100 mg TiO₂/L. This result may in principle be used in a read-across approach to cover the endpoint requirements for the REACH registration of TiC. Toxic effects to soil microorganisms arise from exposure via soil pore water. Due to lower transformation/dissolution results for titanium carbide (the target substance) than titanium dioxide (the source substance), the resulting toxicity potential of TiC is also 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. Thus, TiC in considered to be practically insoluble. Release of Ti ions to any ecotoxicologically relevant extent (and potential subsequent formation of soluble and/or insoluble Ti compounds) is not expected. Therefore, any toxic effects to soil microorganisms are not expected to arise from TiC.

A corresponding key study regarding toxicity to soil microorganisms is not available. However, additional testing is not required as in accordance with REACH Annex IX, 9.4, column 2, the equilibrium partitioning method (EPM) based on aquatic data may be applied to assess the hazard to soil organisms in the absence of reliable toxicity data for soil microorganisms. However, a hazard for aquatic organisms was not identified. Consequently, no hazard is identified for soil microorganisms via the EPM. In addition, the available supporting study does not indicate toxic effects to soil microorganisms when exposed to Ti. Besides, experiments with soil macroorganisms and terrestrial plants do not indicate a hazard for the soil compartment.