Exposure assessment to engineered nanoparticles handled in industrial workplaces: The case of alloying nano-TiO2 in new steel formulations

This experimental study addresses the occupational exposure assessment to nano-TiO2 (AEROXIDE ® TiO2 P 25, EVONIK GmbH) along the processing steps of ingot steelmaking at three sites, whose characteristics range from conditioned room to multi-source industrial environments (MSIS). In Site A, which is a MSIS of multiproduct flexible production, the alloying tablets are manufactured through compression of bulk nano-powder at room temperature. Tablets are then assembled in Site B, which is a lab room equipped with local exhaust ventilation (LEV). The alloying of steel takes place in Site C, which is a full-scale casting hall where substantial amounts of material per batch (3000 kg steel/batch) are processed in open-face molds and severe working conditions prevail. A comprehensive experimental strategy based on simultaneous measurements using direct reading instruments (DRI) and time integrated filter-based sampling has been set up. The main goal of this unusual campaign at an industrial site was to determine the suitability of the various options within the decision frame of the current methodological approaches, mainly chemical- and site-dependent. In Site A the DRI were of limited applicability for the quantification of exposure, because of a high-variability of the background and a characteristic low but unstable counting in the coarse size range where agglomerates of nano-TiO2 are present. In Site B, under controlled environmental conditions no interferences were relevant. Therefore, real-time devices showed no change in the total particle concentration suggesting that tasks performed did not result in any detectable release of the nano-powder. Readings in the size range>0.3 µm showed low-signals, in the order of the device accuracy, that could not be linked to any potential release. However, the mass concentration of TiO2, as obtained by the off-line analysis of personal breathing zone (PBZ) samples, spans from 0.021 to 0.296 mg/m3 in both Sites, which seems to be due to big agglomerates observed by scanning electron microcopy (SEM). In Site C (steel foundry) the on-line instruments could not be used due to access restrictions and severe working conditions. Therefore, only personal sampling approach was used, including the comparative study with and without nanomaterial, which indicates no additional or TiO2 specific workers exposure. This work highlights how, in this particular case, occupational exposure to engineered nanoparticles (ENP) is better assessed through off-line analysis of personal filter samples. The DRI, however, are of unquestionable applicability as real-time monitors to quantify engineering controls efficiency and, thus, for risk management activities and decision making. The need for a scientific consensus in performing such an exposure assessment in industrial contexts is stressed