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Ecotoxicological information

Toxicity to soil microorganisms

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Administrative data

Endpoint:
toxicity to soil microorganisms
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: One concentration tested. No exposure in soil

Data source

Reference
Reference Type:
publication
Title:
Aquatic ecotoxicity tests of some nanomaterials
Author:
Velzeboer I, Hendriks AJ, Ragas AM, Van de Meent D
Year:
2008
Bibliographic source:
PMID: 19086210, Environmental Toxicology and Chemistry 27(9):1942-7

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Soil micro-organisms
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
- 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
- TiO2 (Sigma Aldrich, Zwijndrecht, The Netherlands), ordered as 10% (w/w) dispersion in water.
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
JUSTIFICATION FOR READ ACROSS
In the present study the water was spiked with the analogue material titanium dioxide and thus with exactly the substance formed by hydrolysis of the target chemical. As the additionally released hydrogen chloride fully dissociates in ions the substance self will not reach the sediment/terrestrial environment except via direct exposure, which is not expected in quantities exceeding the soil buffering capacity. The additional chlorine is nontoxic and with regard to the high natural background concentrations irrelevant. Thus additionally released hydrogen chloride should be disregarded.
In conclusion the test was conducted with the relevant transformation product.
Recalculation of the measured threshold values is required on an isomolar basis as the analogue material results from isomolar transformation of the target chemical.

Sampling and analysis

Analytical monitoring:
yes

Test substrate

Vehicle:
no

Test organisms

Test organisms (inoculum):
soil

Study design

Total exposure duration:
7 d

Test conditions

Details on test conditions:
Soil bacteria were sampled at Demmerik (The Netherlands) and added to 10M sterile Bis-tris(2-(bis(2-hydroxyethyl)amino)-2-(hydroxymethyl)propane-1,3-diol at pH 7. After 24h of incubation, the samples were transferred into multiwell, gram-positive plates.
These plates contained one organic substrate in each well together with a tetrazolium violet redox dye.
During one week, the color development was measured every day with a plate reader.
Nominal and measured concentrations:
100 mg TiO2/L nominal
Reference substance (positive control):
no

Results and discussion

Effect concentrationsopen allclose all
Duration:
7 d
Dose descriptor:
other: NOELR
Effect conc.:
>= 100 other: mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
respiration rate
Remarks:
detected colorimetrically using tetrazolium violet redox dye (Microtox® photometer )
Remarks on result:
other: Corresponds to 1.25 mmol/L
Duration:
7 d
Dose descriptor:
other: NOELR
Effect conc.:
>= 237 other: mg/L
Nominal / measured:
estimated
Conc. based on:
other: target chemical titanium tetrachloride
Basis for effect:
respiration rate
Remarks:
detected colorimetrically using tetrazolium violet redox dye (Microtox® photometer )
Remarks on result:
other: Converted from 1.25 mmol/L on the basis of MW TiCl4 = 189.712 g/mol

Applicant's summary and conclusion

Validity criteria fulfilled:
not applicable
Conclusions:
The test article exhibited no subacute toxic effects to soil micro-organisms in saturated solution together with undissolved microdisperse matter in excess
Executive summary:

The subacute toxicity of nanoscaled titanium dioxide (CAS 13463-67-7) to soil micro-organisms was studied using bacteria sampled at Demmerik (The Netherlands). The limit test was conducted during 7 days. However no guideline protocol was followed, the experiment is well documented and meets generally accepted scientific standards. Thus the study is considered valid and conclusive.

The test organisms were exposed in aqueous solution to the analogue material titanium dioxide and thus to exactly the substance formed by hydrolysis of the target chemical titanium tetrachloride (CAS 7550-45-0). Recalculation of the measured value was made on an isomolar basis as the analogue material results from isomolar transformation of the target chemical.

The insoluble test item was applied in a nominal loading rate of 100 mg/L. The loading is far above the water solubility of the test article, which is about 1 µg/L. No analytical dose verification was performed. Due to the multiwell plate exposure no separation of the test organisms and the test article, e.g. by precipitation is suggested. The respiration of the test organisms was detected colorimetrically using tetrazolium violet redox dye.

In the sole loading the test article exhibited no effect and a NOELR of = 100 mg/L was derived. Thus the applied loading is considered a NOELR with no corresponding LOELR. On the basis of the molar test article loading the level for the target chemical, titanium tetrachloride, was assessed to be = 237 mg/L. No threshold concentration can be derived.

In conclusion the test article exhibited no subacute toxic effects to soil micro-organisms in saturated solution together with undissolved microdisperse matter in excess.