Table 3.
Physico-chemical parameters for characterisation of nanomaterial inherent reactivity and suitability of associated analytical methods.
| Methods a | Available standards | Tested in OECD WPMN b | Suitable for testing nanomaterials? | Remarks |
|---|---|---|---|---|
|
Redox potential As the redox potential reflects reactivity of a substance, it is relevant for regulatory safety assessment. | ||||
| SDR (Oxo-Dish method) | – | TiO2, SiO2 | No | The test endpoint is oxygen level and not redox potential; although dissolved oxygen may correlate with redox potential, this is not always the case. |
| Potentiometric method |
– |
ZnO, CeO2 |
No |
Method is more sensitive to the ions in the test medium than to the added nanomaterials. |
|
Radical formation potential The formation of reactive oxygen species (ROS) induced by free radicals is a relevant factor in the toxicity of nanomaterials. | ||||
| EPR/ESR | ISO/TS 18827 | TiO2 | Yes | Suitable for a wide range of nanomaterials, provided that they have unpaired electrons. |
| Potassium Iodide test (KI) | – | ZnO, CeO2 | Yes, with restrictions | Suitable for nanomaterials that generate hydroxyl radicals. |
| Benzoic acid formation in phosphate buffer solution |
– |
SiO2 |
No |
|
|
Photocatalytic activity Photocatalytic materials generate ROS under irradiation of light. | ||||
| Rhodamine-B dye degradation | – | ZnO, CeO2 | Yes, with restrictions | Not suitable for nanomaterials that form coloured suspensions. |
| DPPH degradation | – | ZnO, CeO2 | Yes, with restrictions | Not suitable for nanomaterials that form coloured suspensions. |
| EPR | – | TiO2 | Yes, with restrictions | There was insufficient information in the dossier to evaluate the applicability of this method to other nanomaterials. |
| Orange-II degradation | – | TiO2 | Yes, with restrictions | There was insufficient information in the dossier to evaluate the applicability of this method to other nanomaterials. |
| Formaldehyde degradation | – | TiO2 | Yes, with restrictions | There was insufficient information in the dossier to evaluate the applicability of this method to other nanomaterials. |
| Acetaldehyde degradation | ISO 22197:2 | C60, SWCNT, MWCNT | Yes, with restrictions | Suitable for carbon nanomaterials and (metal)oxide forms of nanomaterials. Insufficient for quantitative measurements (may be improved by optimisation of the sample preparation). |
| Monitoring of photo-induced NADH | ISO (under development) | – | Not evaluated | |
a
For abbreviations and technical details of methods see Supplementary Information.
b
Analytical methods have been evaluated for measurement of physico-chemical properties of specific nanomaterials within the OECD WPMN Testing Programme of Manufactured Nanomaterials as indicated.