Occupational Exposure Assessment of Nanomaterials using Control Banding Tools

Nanotechnology can be termed as the “new industrial revolution”. A broad range of potential benefits in various applications for the environment and everyday life of humans can be related to the use of nanotechnology. Nanomaterials are used in a large variety of products already in the market, and because of their novel physical and chemical characteristics, the application of nanomaterials is projected to increase further. This will inevitably increase the production of nanomaterials with potential increase of exposure for the workers which are the first in line expected to become exposed to potentially hazardous nanomaterials.
Exposure assessment of nanomaterials is more difficult to define and conduct than that of traditional chemicals. This thesis provides an analysis of the field of occupational exposure assessment and a number of challenges are identified. The analysis showed that there are in general two approaches to assess the exposure of nanomaterials at the workplace: they can be measured or they can be estimated by modelling. It was pointed out that measurements are the standard approach used for the assessment of workplace exposure. However, as highlighted throughout the analysis, the assessment of conventional chemicals is well established with clear definition of which metric to use (generally mass concentration). For nanoparticles the assessment procedures are not defined yet and there is debate on which metric should be used (e.g., mass, surface, size-number distribution).
Similarly to measurements, it was found that models in general can be used successfully and effectively in assessing the exposure to conventional chemicals. Several models are suggested also by the European Chemicals Agency (ECHA) in the technical guidance document R.14 for the assessment of occupational exposure and some of them are under a validation process. However, difficulties arise when the existing models for chemicals are applied to nanoparticles, because of the rapid changes of the nanoparticles in aerosols, which is mainly due to different processes of transformation (agglomeration and aggregation, deposition, chemical reactions, and potential mixing and interaction between the nanomaterial and the background aerosol). Moreover, there are no extensive historical data for comparison and model calibration.
Nevertheless, as it is illustrated throughout this thesis, application of modelling for occupational exposure assessment to nanomaterials is still a promising route.
A few years ago a new conceptual model for the assessment of inhalation exposure to nanomaterials was developed. As illustrated in this thesis, this new model includes considerations on nanoparticles behaviour and physical and chemical properties. In addition, several Control Banding (CB) tools for estimating the exposure to nanomaterials have been developed. An evaluation of current CB tools showed that they are all meant for a qualitative or semi-quantitative exposure assessment of nanomaterials. Two of these tools, NanoSafer and Stoffenmanager Nano, are relatively advanced, and they are good foundations for an advanced exposure assessment. Considering the tiered approach for workplace assessment proposed by the OECD, these two tools could be situated, between Tier 1 (Information gathering) and Tier 2 (Basic exposure assessment).
Moreover, the thesis and the included scientific papers provide an in-depth analysis and a case study of CB tools. A set of parameters were identified which should always be taken into account for occupational assessment of inhalation exposure to nanoparticles. Harmonization considering a set of parameters was encouraged in order to pursue the development of an advanced CB tool for occupational exposure assessment to nanomaterials.
Such as model could be a suitable strategic component for a first exposure assessment and may also improve the risk communication between stakeholders involved in risk assessment of nanomaterials at the workplace.