Physico-chemical, mineralogical and toxicological assessment of inorganic dusts from tile-cutting operations

The literature indicates that jobs which involve cutting and rectifying or edge-grinding of ceramic tiles are potential sources of particulate matter (PM) and respirable crystalline silica (RCS) emissions. The European Union has recently included “jobs that involve exposure to respirable crystalline silica dust generated in a work process” as a carcinogen in the Directive that regulates exposure to carcinogens or mutagens at work (Directive 2004/37/EC and amendments). In general, ceramic tile production facilities have implemented different preventive and/or corrective measures (air extraction protocols, personal protective measures, etc.) to reduce workers exposure to PM. However, this activity may also be carried out in smaller-sized facilities, where sometimes the mitigation measures applied could have less efficiency, as well as by individuals applying tile floorings in residential areas, not always using the adequate personal protective equipment. The literature regarding this kind of exposures and their impact on the human health is scarce, a gap which this work aims to fill.

The objective of this work was to characterise the number and mass concentrations, RCS, chemical composition, morphology and in vitro toxicity of particles released during different ceramic tile-cutting operations. Experiments were carried out in a chamber with controlled ventilation and no infiltration from outside air, using on-line and offline aerosol instrumentation. Aerosol chemical composition was characterised using SKC PCIS impactors (PM0.25, PM0.5, PM1, PM2.5, PM10) and ELPI+ (0.006 μm to 10 μm). PM2 aerosols were sampled in liquid suspension using a Biosampler, and in vitro assessments were performed with a commercial A549 lung-cell line. Particle morphology was determined by SEM. The dust emitted during cutting operations was also analysed by ICP-OES and ICP-MS.

 

Release of coarse, fine and ultrafine particles, including nanoparticles, was evidenced during the experiments. Particle number concentrations were comparable during cutting of both types of materials, reaching on average 20.000-45.000/cm³ (1-min concentrations) of which 87% were smaller than 100nm. Peak respirable mass concentrations typically reached 30-50 mg/m³. The dust deposited during the cutting operations showed a similar baseline composition in terms of major components (e.g., SiO₂, Al₂O₃), while it differed regarding tracer elements (e.g., Zn) which could be due to the different body, glaze and decoration composition of the products studied. The chemical composition of aerosols released was consistent with that of the deposited dust. The content of crystalline silica in respirable dust was 10-20%, indicating that cutting operations may also produce high RCS levels. In vitro assessments (MTT assay) showed statistically significant differences between tiles, ranging between non-significant toxicity to moderate cytotoxicity for aerosols generated during the different cutting operations. Similar results were obtained for the generation of reactive-oxygen species (ROS).

Overall, it was concluded that tile cutting has potential to impact human health if exposures are not controlled. The experimental setup used in this work could be useful to characterise dust generation when different ceramic products are processed under controlled conditions.