6. How well can we assess the risks from nanomaterials?
- 6.1 What physicochemical properties are relevant?
- 6.2 What are relevant comparisons for manufactured nanomaterials?
- 6.3 How might the risk assessment framework be developed?
6.1 What physicochemical properties are relevant?
The most important properties of a nanomaterial to characterise, from a risk assessment viewpoint, are:
- Size and size distribution of free particles and fibres/rods/tubes. These may be produced during the manufacture, use (including wear) and/or disposal/recycling of the nanoproduct
- Specific surface area
- Stability in relevant media (including the ability to aggregate and disaggregate)
- Surface adsorption properties
- Water solubility
Chemical reactivity, including photoactivation and potential to generate active oxygen.
6.2 What are relevant comparisons for manufactured nanomaterials?
If nanomaterials are made in the form of fibres, rods or tubes that are rigid, long and thin, and persistent, they may pose similar hazards to asbestos.
Airborne fine particles from fires and combustion engines can cause respiratory and cardiovascular troubles. Manufactured nanoparticles or fibres with reactive surfaces are suspected to cause similar effects.
Some nanomaterials may be similar to existing materials with comparable dimensions and surface properties, but the database for comparisons is limited.
Comparisons with the same material in other, bulkier physical forms may also be relevant.
6.3 How might the risk assessment framework be developed?
An earlier report from the SCENIHR, in 2007, proposed a four stage risk assessment, beginning with potential for exposure for people and the environment. That recommendation is substantially unaltered, and provides for case by case treatment of potential risks. As knowledge improves, it may be possible to classify nanomaterials into specific risk categories, but this cannot be done yet.
The third stage of the proposed risk assessment, hazard identification and characterisation, can now be developed in the light of recent results. It should include:
- Cell and tissue uptake tests
- Bioaccumulation tests during prolonged exposure
- Use of a test system for asbestos-like nanofibres or tubes
- Tests for the ability of nanomaterials to trigger possible mechanisms of toxicity such as generation of reactive oxygen species
Aside from this framework from the SCENIHR, a wide range of other suggestions have been made for beginning to assess risks of nanomaterials while detailed information remains scarce. They include variants of life-cycle assessments, looking at each stage in the production, use and disposal of nanomaterials for potential hazards, multi-criteria decision analysis and structured scoring systems. However, development of a widely accepted and robust methodology for risk assessment depends on developing a data bank of case histories to assess its validity.