8. Are current risk assessment methodologies for nanoparticles adequate?
- 8.1 What considerations should the risk assessment take into account?
- 8.2 What factors of exposure do risk assessment methodologies need to specify?
- 8.3 How should risks and hazards related to nanoparticles be addressed?
- 8.4 What should be done to improve the risk assessment of nanoparticles?
Chemicals in their nanoparticle form have properties that are completely different from their larger physical forms and may therefore interact differently with and in biological systems. As a result, it is necessary to assess the risks arising from any nanoparticle that will potentially come in contact with humans, other species or the environment, even if the toxicology of the chemicals that make up the nanoparticle is well known.
Because of the restricted range of nanoparticle types whose biological properties have been studied to date, it is uncertain whether or not the current limited evidence on the behaviour in biological systems is representative of nanoparticles in general.
The traditional risk assessment methodology – which consists of exposure assessment, hazard identification, hazard characterization and finally risk characterization – has not yet been applied to nanoparticles. At the moment, there are no official guidelines on what is an appropriate testing procedure. The commercial manufacture of nanoparticles is relatively new and there is very little data available on their effects on human populations or on the environment.
More specifically, risk assessment of nanoparticles may need to address:
- Worker safety during the manufacture of nanoparticles.
- Safety of consumers using products that contain nanoparticles.
- Safety of local human populations due to release of nanoparticles from manufacturing and /or processing facilities.
- The impact on the environment and on the potential for human re-exposure through the environment.
- The environmental and human health risks involved in the disposal or recycling of nanomaterials.
More safety requirements are expected for new or emerging technologies than for tried and tested technologies. If these expectations are not met, the public may come to fear or even reject products based in nanotechnology. More...
8.1 What considerations should the risk assessment take into account?
In terms of general exposure and health risks to humans, it is important for any risk assessment methodology to consider that:
- Humans can be exposed to nanoparticles not only through inhalation, but also through ingestion, dermal contact, and injection or implantation.
- Exposure dose should not only be measured in terms of mass, but also in terms of total surface area, number of particles, or their combination .
- Nanoparticles may be able to go through cell membranes and have the potential to reach the cells of several organs, including the brain. This ability of nanoparticles to get inside biological systems may cause unique adverse effects never previously observed for chemicals in larger physical forms.
- The toxicity of nanoparticles and their ability to pass through cell membranes may either increase gradually as particle size decreases, or increase suddenly below a certain particle size. Nanoparticles may have a greater toxicity or, perhaps, a different toxicity compared to larger particles of the same substance.
- Nanoparticles may have the potential for bioaccumulation in humans and possibly in other species and in the environment.
- Nanoparticles in ambient air will probably be widely dispersed – unless they react with other components in the air – but they may distribute and persist in the environment differently from larger particles. The potential problems associated with nanoparticles that persist in the environment may be considerable.
- Some individuals, including people with severe chronic respiratory and heart diseases, are much more sensitive to the adverse effects of certain nanoparticles from ambient air pollution than the general public and potentially to other types of airborne nanoparticles.
8.2 What factors of exposure do risk assessment methodologies need to specify?
Risk assessment can be applied either to a chemical in nanoparticle form or to the product in which these nanoparticles are incorporated.
It is important for the purpose of assessing the risk of a chemical in nanoparticle form or of the product where such nanoparticles are incorporated to specify clearly the following factors:
- The physical and chemical properties of these nanoparticles or products, the amount that will be produced, the expected uses, the proposed routes for their disposal or recycling at the end of their useful lives, as well as their solubility, bioaccumulation and biodegradability.
- The likely human or environmental exposure in different situations of use, including normal and intensive use, misuses, and accidents.
- The detailed examination of human exposure, including how the nanoparticle enters the body and moves inside it, as well as the potential for accumulation in the body after repeated exposure.
- The detailed examination of environmental exposure, including the amount, distribution, and persistence of nanoparticles in the environment, as well as the potential for bioaccumulation in different species. Attention should be given to those nanoparticles that are designed to be deliberately released into the environment (for example agents used to clean up chemical spillages) and the waste products of nanotechnology.
If the above processes and characteristics of the nanoparticle are similar to those of the chemical at larger, conventional scale, the risk assessment could require fewer data. More...
8.3 How should risks and hazards related to nanoparticles be addressed?
The ability of nanoparticles to cause hazards can be mainly due to:
- a) the toxicological properties of the chemical composing the core of the nanoparticle; or
- b) their greater reactivity caused by their relatively large surface area compared to their volume ; or
- c) their potential to adsorb other chemicals of concern onto their surfaces; or
- d) any combination of these three factors.
In the case of a), the nanoparticles are expected to have properties similar to those of the same chemicals in larger, conventional forms, unless the distribution of the nanoparticles in the body or in the environment is very different.
In the case of b) and c), nanoparticles will have toxic effects different from those of the same chemical in larger physical forms. In addition, in the case of c), the potential for the release of these adsorbed chemicals of concern will need to be addressed.
To identify the hazards related to nanoparticles made up of well known chemicals, a testing method to determine whether or not the nanoparticle form will cause significantly different adverse effects is needed.
No conclusions applicable to all nanoparticle-based products can be drawn at this stage regarding risks and hazards. Therefore, each product and process involving nanoparticles must be considered separately when assessing the safety of workers involved in its manufacture, the safety of consumers and of the public living near manufacturing or processing facilities, the environmental impact, and the human health and environmental risks involved in the disposal or recycling of the nanoparticle products.
When suitable hazard information is lacking, particular care is needed regarding nanoparticles which are likely to be highly persistent in humans and in environmental species.
At present there is no reliable information on the effect of the simultaneous exposure to multiple forms of nanoparticles, or on the interaction between nanoparticles and other agents. Therefore, risks should be assessed on a case-by-case basis. More...
8.4 What should be done to improve the risk assessment of nanoparticles?
In order to produce detailed guidelines for the risk assessment of nanoparticles, critical gaps in knowledge need to be filled. For instance, it would require:
- new techniques for the measurement of exposure levels in humans and in the environment from the routine use of nanoparticle-based products.
- protocols to assess the release of nanoparticles from various products and production processes.
- to determine whether it is possible to extrapolate from the toxicology of non-nanosize materials to nanoparticles of the same substance, and between nanoparticles of different size ranges.
- information on the health of workers involved in the manufacture and processing of nanoparticles.
- information on the behaviour of nanoparticles in the environment and their effects on various species.
- data on current and past exposure of humans and the environment to nanoparticles.
The confidential nature of much of the research on nanoparticles calls for international cooperation on identifying and resolving gaps in knowledge. Cooperation with industry is also necessary.
Regulations for chemicals are currently based on tonnage, which may have to be reviewed as there are many more nanoparticles to the tonne than is the case for larger particles. Also, for the purpose of hazard warning labels, the nanoparticle form of each chemical should have its own identification. In addition, new workplace exposure standards need to be developed for nanoparticles that are different from those for dusts. Similarly, classification and labeling for human health and the environment may need to be reconsidered
Other needed developments include a harmonized terminology for the physical characteristics of nanoparticles and their general properties, standardized testing methodologies, available reference materials for the measuring of adverse effects, and a clear and widely acceptable framework to weight up the benefits and risks of nanotechnology. More...