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Posted: Jul 17, 2006

Nanohazards: Knowledge is our first defense

(Nanowerk Spotlight) Addressing the potential hazards associated with nanomaterials requires a comprehensive approach to gaining, collecting and publishing knowledge about individual nanomaterials. Expanding MSDS (Material Safety Data Sheets) into nMSDS for nanomaterials could be a way to accomplish this.
"Many articles call upon scientists to formulate a standardized framework for dealing with the ‘problem’, but unfortunately the great diversity of types of nanomaterials makes it impossible to generalize when it comes to both properties and hazards" says Dr. Amanda S. Barnard, a senior research fellow in the Materials Modeling Laboratory of the Department of Materials, University of Oxford in the UK.
"Using all the scientific c knowledge and intuition that we have gained, in all but a few cases we still cannot accurately predict how nanomaterials will react with living organisms; there are simply too many variables" she says.
Barnard published a recent commentary, titled "Nanohazards: Knowledge is our first defense" in the April, 2006 issue of Nature Materials.
A first step in a strategy to deal with nanorisks is to identify which nanomaterials are potentially hazardous. Since both the desirable and undesirable properties of nanomaterials are dependent on a wider range of parameters than the bulk material, it is necessary not only to understand these dependencies more fully, but also the linkage between many of these dependencies. Barnard gives two examples:
1) The relationship between reactivity and size. Many materials that are inert at the macroscale can be highly reactive as nanoparticles, as for instance is the case with silver. At the nanoscale silver becomes antimicrobial, that is, it becomes bioactive. This change in reactivity cannot be predicted based on knowledge of the properties of the bulk material.
2) The relationship between size and phase. Macroscopically the rutile phase of titanium dioxide is stable and the anatase phase is metastable, but when the particle size is under ∼20 nm this situation is reversed. Barnard explains the intrinsic relationship between the two dependencies, size and phase: "This is of critical importance, because rutile and anatase react very differently when exposed to light. Nanoparticles of rutile are used in sunscreens, whereas nanoparticles of anatase are used in self-cleaning windows. Both technologies are currently in use around the world without discernable risk, but a phase transition in either case would do more than reduce the efficiency of these respective products, it could also be damaging to the substrate which in the case of rutile-based sunscreen, is us. It is easy to see why there was a need for a detailed understanding of how the properties of titanium dioxide depend upon the physical structure before these products could be developed and commercialized."
A very important factor when assessing the potential risk of a nanomaterial is the relationship between this nanomaterial and the environment.
"There is a type of cyclic causality at work here, where environmental variations (such as changes in temperature, pressure, humidity or electrostatic charge) can alter the stability and properties of nanomaterials, thereby changing the way they interact with the environment" says Barnard. "This has the unfortunate consequence of adversely affecting our dynamic control over properties, and our ability to anticipate nanohazards in a given situation. Our only defense against the technological and environmental ambiguity introduced by this cyclic causality is to increase our knowledge of the various types of instabilities native to nanomaterials, along with their respective causes."
The question arises of how to improve or complement the current standards that are regulating how we work with biohazards and chemical hazards. Expanding the current system of MSDS, or their international equivalents, might be one way to go about it.
MSDS are forms containing data regarding the potentially hazardous properties of a particular chemical substance or product. In the U.S., the Occupational Safety and Health Administration requires that MSDS be available to employees for potentially harmful substances handled in the workplace under the Hazard Communication regulation. Other countries have similar systems. In the European Union, Risk and Safety Statements ( R- and S-phrases) and a symbol appear on each label and safety data sheet for hazardous chemicals.
Barnard makes a practical suggestion as to how the required data could be collected. It would require a more efficient reporting of a wider range of characteristics, and focusing more attention on how these characteristics depend on the physical, chemical and environmental parameters.
"Moreover" says Barnard, ", we need to give more attention to discovering how various dependencies moderate both properties and stability. This type of knowledge allows us to construct algorithms for assessing the likelihood of nanotoxicity, so that we can properly regulate exposure."
A first steps toward achieving this could be the widespread introduction of a new section or subsection in each scientific article, addressing potential instabilities and providing guidelines for storage and operating conditions applicable to the nanomaterials described in the rest of the paper.
Barnard concludes: "Nanomaterials may be reactive, but nanoscientists should be proactive."
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