HRTEM characterization in environmental risk assessment of engineered nanoparticles

For the purpose of assessing the risk of nanoparticles or of the products incorporating them, it is important to specify clearly the physical and chemical properties of these nanoparticles or products. High resolution transmission electron microscopy (HRTEM) offers the unique ability to observe nanoparticles (or any solid material) directly in real space at or close to the atomic scale, i.e., the scale at which they are ultimately defined. With modern HRTEM instruments, lattice or structure images of very small crystals (crystallites) or very small regions in larger crystals can be obtained with 0.2-0.3 nm (2-3 angstroms) resolution (less than 0.2 nm with dedicated intermediate--or high-voltage HRTEM instruments). No general conclusions applicable to all nanoparticle-based products are possible regarding the risks. Therefore, each product and process involving nanoparticles must be considered separately.