Cytotoxicity and genotoxicity of size-fractionated particulate matter collected in underground workplaces

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Road tunnel construction involves the use of explosives and diesel-powered machines in a very limited indoor space. Tunnel construction workers are thus exposed to a variety of toxic substances, including dust, asbestos, silica, concrete, diesel fumes, and oil mist. In this study, the low noise miniaturized Sioutas Cascade Impactor (SKC) has been used to collect PM samples as a function of particle size (i.e., aerodynamic diameter). Airborne particulates were sampled into a road tunnel (final length 2391 m) under construction near the village of Pale, Municipality of Foligno, Umbrian Apennines (State Highway 77 “Val di Chienti”). Three sampling sessions were performed: (i) in the West yard, during dislodging of rocks; (ii) in the East yard during drilling of rocks, and (iii) during scaling and grouting with quick-drying shotcrete. The aim of this study was to characterize size-fractionated PM samples for their cytotoxic/genotoxic potentials. Toxicological evaluation was carried out in vitro on A549 lung carcinoma cells: cytotoxicity was assessed by Trypan blue dye exclusion assay, whereas genotoxicity was assessed by comet assay (primary DNA damage) and cytokinesis-block micronucleus (CBMN) Cytome assay (cytogenetic effects). Primary DNA damage (i.e., strand breakage) was mainly caused by coarse fractions A (O > 2.5 μm) sampled in the West yard (sample i) and in the East yard (sample iii). Cytogenetic effects were mainly caused by the fine fractions AF (aerodynamic O < 0.25 μm) sampled in the East yard (sample ii). Results reported in this article show that particulate matter (PM) samples collected underground (i.e., during road tunnel construction) may trigger various cytotoxic/genotoxic effects. The recent classification of air pollution and PM itself as carcinogenic to humans (group 1) by the IARC makes indoor/outdoor air pollution a growing matter of concern. Our results highlight the need in this occupational setting for a reduction, if applicable, of PM emission (prevention), or an implementation of work practices by stressing the importance of proper use of protective equipment (protection).