The International Life Sciences Institute Research Foundation/Risk Science Institute convened an expert working group to develop a screening strategy for the hazard identification of engineered nanomaterials. The working group report presents the elements of a screening strategy rather than a detailed testing protocol. Based on an evaluation of the limited data currently available, the report presents a broad data gathering strategy applicable to this early stage in the development of a risk assessment process for nanomaterials. Oral, dermal, inhalation, and injection routes of exposure are included recognizing that, depending on use patterns, and exposure to nanomaterials may occur by any of these routes. The three key elements of the toxicity screening strategy are physicochemical characteristics, in vitro
assays (cellular and non-cellular), and in vivo
assays. There is a strong likelihood that biological activity of NPs will depend on physicochemical parameters not routinely considered in toxicity screening studies. Physicochemical properties that may be important in understanding the toxic effects of test materials include particle size and size distribution, agglomeration state, shape, crystal structure, chemical composition, surface area, surface chemistry, surface charge, and porosity. Numerous epidemiological studies have associated exposure to small particles such as combustion-generated fine particles with lung cancer, heart disease, asthma and/or increased mortality.[11
] Both Donalson et al
, and Oberdorster concluded in their reviews that ultra-fine particles of low solubility and low toxicity materials are more inflammogenic in the rat lung than larger particles of the same material.[11
] Additionally, NPs are able to penetrate deeply into the respiratory tract. Once deposited in the alveolar region, they may translocate to blood and to sites distant from their portal of entry such as the liver, spleen, kidney and brain. Their migration to distant sites is an important issue with regard to their toxicity. The kidney is particularly susceptible to xenobiotics owing to its high blood supply and ability to concentrate toxins. Few studies have examined the impact of NPs in kidney, while both glomerular structures during plasma ultra-filtration and tubular epithelial cells may be exposed to NPs.
There are two types of NPs to be considered in hygiene science; one is the environmental NP emitted from automobiles and the other is the manufactured NP. In general NPs (less than 100 nm) are reported to be permeable through the cell membrane and tissues and their large surface area is responsible for the greater toxicity compared to larger particles. However, there are contradictory reports on the health effects of NPs. Recent reports suggest that carbon nanotubes, fiber-shaped biopersistent NPs, resemble asbestos in the pathogenesis of granuloma and mesothelioma. Literature search describes a limited number of toxicological studies, but that all conclude that there are some health risks following exposure to NPs. For a given substance, the toxicity is much greater when the substance is of nanometric dimensions than when it is of micrometric dimensions. Since these particles are very small, they could have significant toxic effects on workers' health. Due to the many unknowns related to NPs and their potential health effects, caution and stringent prevention procedures are required for exposed people. There are no accepted standards for assessment of exposure to NPs. All the techniques to assess NPs are in a nascent and experimental state. The biggest hurdle is the practical impossibility of measuring NPs' exposure on mass basis. All the exposures are so small on mass basis that they are negligible.