Framework for human health characterization factor calculation of tio2 nanoparticles

The widespread use of engineered nanoparticles (ENPs) in various industrial applications is leading inevitably to releases of these materials into the environment, increasing like this human and environmental exposure to these substances, and is getting consequently more and more a concern regarding their potential adverse effects on both, the environment and the human health. In this context, Life Cycle Assessment (LCA) is recognized as one of the key methods for the assessment of the environmental performance of products containing such ENPs. However, so far, factors to assess releases of ENPs into the environment have been still completely missing, making all LCA studies of such materials incomplete. For this, a clear toxicological characterization of the effects is a prerequisite in order to establish trustworthy characterization factor (CFs) for release of nanoparticles into the environment. Humans could potentially be exposed to ENPs releases along the whole life cycle (i.e. during manufacture, handling, use and disposal treatment of ENPs). Therefore, this work aims to provide a methodological framework for establishing human health CFs for releases of ENPs, using titanium dioxide nanoparticles (TiO2-NPs) as an exemplary example. Starting point for this is USEtox, the internationally recognized consensus model for the assessment of toxicity within LCA studies. USEtox calculates the impact on human toxicity as product of emission, intake fractions (iF) and effect factors (EF). The intake fraction is originally defined as ratio of the mass intake by an individual over the mass released to the environment. The effect factor on the other hand contemplates the change in life time disease probability due to change in life time intake of a pollutant. Both effects, i.e. carcinogens and non-carcinogens, are taken into account in the calculation of the actual EF: • the EF for carcinogens effects is determined based on a benchmark dose used by the National Institute for Occupational Safety and Health (NIOSH) to determinate the recommended occupational exposure limit (REL) for TiO2-NPs; • the EF for non-carcinogens effects is calculated based on NOAEL (no-observed adverse effect level) and LOAEL (lowest observed adverse effect level) values. Limiting the examinations here on releases to air as only investigated compartment, a one-box model using steady-state conditions and direct human exposure can be applied for the calculation of the intake fractions. Here, intake fractions for indoor and outdoor conditions have been calculated for TiO2-NPs. While indoor iF, a complete mixing for the volume and the indoor volume per workers for the Chemical industry in Switzerland have been evaluated. For the outdoor iF, the fate factor matrix has been calculated by applying the SimpleBox4Nano (SB4N) multimedia modelling developed by Meesters and co-author. Thanks to this model it is possible to obtain transport and removal rates constants for ENPs in and across air, rain, surface water, soil and sediment compartments, taking into account various input parameters (i.e. radius, mass density, aggregation and attachement efficiency of TiO2-NPs) and systemic dimensions (area, height and volume for each compartments). Again, based on the study by Mueller and Nowack, the scenario is focusing on Switzerland as geographical area.