Questions on Nanomaterials
- What are nanomaterials?
- How can nanomaterials be characterised?
- How can exposure to nanomaterials be measured?
- What are the potential health effects of nanomaterials?
- What are the potential environmental effects of nanomaterials?
- How well can we assess the risks from nanomaterials?
- What do we still need to know?
The answers to these questions are a faithful summary of the scientific opinion produced in 2006 by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR):
"modified Opinion (after public consultation) on the appropriateness of existing methodologies to assess the potential risks associated with engineered and adventitious products of nanotechnologies" Learn more...
1. What are nanomaterials?
Nanotechnologies involve designing and producing objects or structures at a very small scale, on the level of 100 nanometres (100 millionth of a millimetre) or less. Nanomaterials are one of the main products of nanotechnologies – as nano-scale particles, tubes, rods, or fibres. Nanoparticles are normally defined as being smaller that 100 nanometres in at least one dimension.
2. How can nanomaterials be characterised?
Descriptions of nanomaterials ought to include the average particle size, allowing for clumping and the size of the individual particles and a description of the particle number size distribution (range from the smallest to the largest particle present in the preparation).
Detailed assessments may include the following:
1. Physical properties:
- Size, shape, specific surface area, and ratio of width and height
- Whether they stick together
- Number size distribution
- How smooth or bumpy their surface is
- Structure, including crystal structure and any crystal defects
- How well they dissolve
2. Chemical properties:
- Molecular structure
- Composition, including purity, and known impurities or additives
- Whether it is held in a solid, liquid or gas
- Surface chemistry
- Attraction to water molecules or oils and fats
A range of techniques for tracking nanoparticles exist, and new ones are under development. Realistic ways of preparing nanomaterials for test of their possible effects on biological systems are also being developed.
3. How can exposure to nanomaterials be measured?
The measurement methods to use depend on the kind of exposure. The most reliable methods are for particles in the air. Nanoparticles may also be in contact with solids and liquids, especially in consumer products.
Current techniques to assess nanoparticle exposure are suitable for personal or area-based monitoring, continuous or discontinuous use, and basic characterisation of samples. However, data on airborne exposures are scarce, and there have been few if any studies outside the workplace.
exposure estimates from food and consumer products also remain difficult. Information on the presence of manufactured nanomaterials comes from manufacturers. There is also limited information about product use.
4. What are the potential health effects of nanomaterials?
There is experimental evidence of a range of possible interactions with biological systems and health effects of manufactured nanoparticles. In experimental systems in the laboratory they can affect the formation of the fibrous protein tangles which are similar to those seen in some diseases, including brain diseases. Airborne particles might cause effects in the lungs but also on the heart and blood circulation similar to those already known for particulate air pollution. There is some evidence that nanoparticles might lead to genetic damage, either directly or by causing inflammation.
All these effects would depend on nanoparticles’ fate in the body. Only a minimal amount of nanoparticle doses escape the lungs or intestine, but long-term exposure could still mean a large number are distributed round the body. Most are held in the liver or the spleen, but some appear to reach all tissues and organs. There may also be entry into the brain via the membranes inside the nose.
Nanotubes or rods with similar characteristics to asbestos fibres pose a risk of the mesothelioma (a form of cancer of the pleura).
5. What are the potential environmental effects of nanomaterials?
Wider use of nanomaterials will lead to increases in environmental exposure. Little is known about how they may then behave in air, water or soil. They may be concentrated in particular “hot spots”, either by clumping together with minerals or by interaction with organic matter.
Like other pollutants, they may pass from organism to organism, and perhaps move up food chains.
As a result of their diversity, nanomaterials may have a wide range of effects. Some kill bacteria or viruses. Experiments so far have also shown possible harmful effects on invertebrates and fish, including effects on behaviour, reproduction and development. There is less research to date on soil systems and terrestrial species, and it is not clear whether laboratory results relate to what may happen out in the real world.
6. How well can we assess the risks from nanomaterials?
Existing risk assessment methods are generally applicable to nanomaterials but specific aspects related to nanomaterials need more development. They include methods for both estimating exposure and identifying hazards. The highest potential risks come from free, insoluble nanoparticles either dispersed in a liquid or as dust.
Risk assessment requires a detailed examination of properties, including:
- Particle size
- Surface area
- Surface properties
- Chemical reactivity
Comparisons with well-known existing hazards may help inform risk assessment. They include those from airborne fine particles, and asbestos fibres.
The recommended approach to assess the risks from nanomaterials is still the four stage risk assessment proposed by the SCENIHR in 2007. Today, additional details can be added to this approach in the light of recent work on evaluating possible harmful effects of nanomaterials, especially using controlled laboratory tests (in vitro assays). These tests are useful for screening and for investigating mechanisms of adverse effects. However, tests using living organisms (in vivo assays) are also needed to improve knowledge of possible risks to people and the environment. Improvements are sought in the determination of exposures, and there is an urgent need for long-term exposure studies.
Full evaluation of the potential hazards of most nanomaterials is still to come. It will include estimation of exposure in normal use, abuse, waste and recycling of products containing nanomaterials, and detailed measurement of physical and chemical properties.
An OECD programme is producing dossiers on hazard identification for 14 common nanomaterials. Each will include physical and chemical properties, environmental effects, toxicology in mammals and material safety. This will help assess whether current OECD guidelines on identifying hazards are suitable for nanomaterials.
As knowledge improves, a category-based system to classify new nanomaterials may be developed, but at present a case by case approach is needed, leading to a data bank of case histories.
7. What do we still need to know?
Research identified by SCENIHR in 2007 is still needed. Recent work has also identified new concerns around protein behaviour, nanotubes, and food chain transfers.
There are urgent needs for reference materials and methods for measuring manufactured nanomaterials against natural background occurrence.
For environmental assessment, the most important need is to establish methods to measure free nanomaterials after dispersal.
Tests using living organisms (in vivo assays) are also needed to improve knowledge of possible risks to people and the environment. Improvements are sought in refining exposure doses in biological testing, and there is an urgent need for long-term exposure studies.