Transportation issues in porous media (soils etc.) and surface waters have already been discussed. There is clearly further need for data and appropriate interpretative models on transportation rates and mechanisms. There is also a need for some means of tracking nanoparticles as they move in either lab or field scale. In simple systems (laboratory-scale cores), this can be performed relatively easily using light scattering or other spectroscopic methods. In more complex real systems, there is more difficulty. A possible means of overcoming this problem may be to customise nanoparticles by labelling with stable or radio-isotopes and detecting changes in the signal by inductively coupled plasma mass spectroscopy (ICP-MS) or g or a counting. Secondly, physico-chemical separation by means such as acid digestion, solvent extraction or chromatography may be required prior to analysis. Further analytical validation may be required.
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