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Posted: August 5, 2010

Safe Work Australia publishes reports on methods to reduce the risk of exposure to nanomaterials

(Nanowerk News) Safe Work Australia commissioned RMIT to undertake a survey of the current substitution/modification practices used in Australian nanotechnology-related activities and a literature review in order to determine the potential substitution/modification options that may reduce the toxicity of engineered nanomaterials used in Australia.
The document "Engineered Nanomaterials: Investigating substitution and modification options to reduce potential hazards" (pdf; 240 KB) can be downloaded from the Safe Work Australia website.
Summary from the survey
a) There were 38 respondents to the survey, who reported working on a range of different types of nanomaterials. The respondents' organisations were primarily universities, commercial/industry and government research groups. The most common nanomaterials handled are metal oxides, metals and carbon nanotubes and the most common areas of application are into energy, medical, surface coating and textile uses.
b) Many organisations (27/35), and notably universities (20/21), manufacture their own engineered nanomaterials, and a significant number also purchase them from overseas or from within Australia.
c) A number of respondents obtained work health and safety information about the nanomaterials that they are using from an MSDS. The main work health and safety issues examined for engineered nanomaterials are handling and storage, physical and chemical properties, toxicological data and exposure controls/personal protective equipment (PPE). The available information on these topics is limited.
d) Most respondents indicated that substitution/modification is used to change the functional properties of the product. A work sector analysis indicates that substitution/modification occurs more in university research and less in commercial/industry research which is as expected in product development.
e) The five properties that are manipulated by modifying or substituting engineered nanomaterials by the highest number of organisations are particle size, physical properties, agglomeration properties, chemical properties and conductive properties. A small number of respondents indicated that they use substitution/modification to change the health or toxicological properties.
f) Adding functional groups (17 responses) and modifying surface characteristics (16 responses) are the two most popular methods for the substitution/modification of engineered nanomaterials. Others include changing the form of the material, the particle size and shape, and the crystalline structure.
g) Australia's nanotechnology activities are generally at the early stage of nanomaterial development, i.e. more focussed on de novo research than later stages of product development/production. However substitution/modification methodologies are well known and used in Australia and thus there is an existing capability that might be applied more broadly to work health and safety related purposes.
Summary of the literature review
a) The mechanisms by which nanoparticles enter biological systems and subsequently cause toxicity are dependent on factors such as nanoparticle or aggregate size, physicochemical characteristics of particle surfaces (e.g. surface charge), biocompatibility and cell-specific effects on nanoparticle uptake. Various substitution and modification strategies for a range of nanomaterials have been described in the scientific literature.
b) Carbon nanotubes (CNTs) can be functionalised and surface-modified to increase their solubility and biocompatibility. It is also possible to reduce their chronic toxicity potential by using short CNTs and keeping their length to less than 5µm. Further investigation of the toxicity of these modified CNTs needs to be made to assess the extent of the reduction in potential workplace hazard.
c) When formulating a new product or use, the toxicity of fullerenes can be controlled by attaching functional groups to the fullerene moiety. Specifically, attaching water solubilising groups such as carboxyl or alcohol groups, will increase the solubility and lead to reduced toxicity of the prepared fullerene. This modification will also alter particle aggregation behaviour in water and its potential bioavailability and reactivity in aquatic systems, and this area requires further investigation.
d) It can be concluded that when formulating a new nano titanium dioxide (TiO2) product or use, its potential toxicity can be controlled by varying the crystalline form used, i.e. use the less reactive rutile form rather than the more reactive and photocatalyitc anatase form where functionally possible.
e) It can be ascertained that nano ceria under specific conditions exhibits antioxidant and biocompatible properties. However, outside this range of conditions antioxidant behaviour is not exhibited, and its redox cycling ability may be pro-oxidant. In an aquatic system, nano ceria has been found to be more toxic than the micron sized particles. It is not possible at this stage to suggest modifications that can be made to nano ceria until more data are obtained.
f) It can be concluded that nano zinc oxide (ZnO) used in sunscreen type products and for other similar applications exhibits a low level of toxicity and dermal penetration into the human body. There are surface modification options available for ZnO which have the potential to reduce toxicity further, in addition to structural modifications that help retain functionality, such as doping the ZnO crystalline lattice.
g) Nano gold particles can be surface-coated, e.g. with phosphatidylcholine, or encapsulated with biocompatible biopolymers, e.g. chitosan or polyethylene glycol, to reduce toxicity, whilst retaining functionality and useability. Alkanethiol-capping may be used to increase biocompatibility and also functionalise the nano gold for a range of biomedical applications.
h) Nano silver can be surface modified with hydrophilic groups, such as phosphorylcholine or phosphorylethanolamine, to increase biocompatibility. Such modifications would also decrease its antibacterial activity and potential usefulness in many current applications. However, further functionalisation of biocompatible forms of nano silver may provide potential new applications, such as in biomedical diagnostics and biosensors.
i) It is possible to modify the surface of nano silica with alkylsilylation, polymers or proteins to increase its hydrophobic character, causing increased particle aggregation and reduced direct membrane effects, and thereby improving its biocompatibility. Due to potential toxicity of silica nanomaterials with high aspect ratios, consideration should also be made as to whether nanowires may be substituted with nanospheres, while retaining functionality for a particular application.
j) It is possible to encapsulate quantum dot cores with stable shell coatings made from biocompatible polymers, e.g. chitosan or polyethylene glycol, to significantly reduce their cellular uptake and degradation, and consequently their cytotoxicity, whilst retaining functionality and useability.
Implications for work health and safety
There are known methods that can be used to substitute/modify engineered nanomaterials that are used, or researched, in Australia. The methods of surface modification, encapsulation, particle size control, functional group addition and crystalline phase type control can each be employed for different engineered nanomaterials to decrease their potential toxicity. However in some cases, such modifications may affect the functionality of nanomaterials in relation to intended end-uses.
If the researchers, developers and manufacturers of engineered nanomaterials adopt these methods then it is possible to re-engineer nanomaterials in the early stages of development to reduce the potential toxicity of manufactured nanomaterials. The downstream effect of this will be to reduce the risk posed by the use of these nanomaterials not only in the workplace but also in the general community.
Source: Safe Work Australia
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