Workers may be exposed to nanoparticles (NPs) by inhalation, cutaneous contact and gastroenteric pathways, but today there is no standardized method for either assessing or monitoring the occupational exposure. Moreover, there is no all-in-one assessment strategy, so it is preferable to consider different perspectives. Every assessment should be preceded by a preliminary analysis of the workplace in order to gather useful data on the potential exposure sources, which will help in outlining the assessment strategy. The purpose of air monitoring should be to characterize NP emissions and assess, as a minimum, the mass, particle number concentration, granulometric distribution, specific surface and chemical composition. There are several techniques which may assess these characteristics: the most used in real occupational contexts are mobility particle sizers, particle counters (optical, condensation, etc.), surface area monitors, while personal samplers are promising tools which still have been used almost only in research or controlled contexts. Skin and surfaces may be sampled according to the nature of substances and the circumstances of exposure. Sampling methods can be divided in three main categories: interception (e.g. carbon tabs), removal (e.g. adhesive tape stripping, wiping), in situ methods (e.g. UV fluorescence). Chemical analysis methods (e.g. spectroscopy) and electron microscopy techniques may enhance available data. Considering the available information, we suggest a stepwise approach for risk assessment composed of three steps, starting from a quick and relatively cheap screening method to assess exposure, followed by 2 gradually more accurate but costly approaches to perform whether a significant exposure is detected.
