Nanotoxicity of Occupational Dust Generated in Granite Stone Saw Mill

The risk of occupational exposure to particles of granite exists during quarrying, saw milling and construction work environment. These particles are known to have predominantly micro-size as well as nanosize. Moreover, toxicological profiles of these particles are not known. An attempt was therefore made to study size-dependent cytotoxicity of granite particles using lung epithelial cell line A549. Occupational dust settled around the saw mill was collected and analyzed for their particle size in microscale and found to be 49%, 31% and 20% of 30-50 μm, 10-30μm and 5-10 μm, respectively. With the help of ball mill occupational dust was grinded to particle size 5-8 μm observed under optical micrometry which was further nanotised to 80-130 nm as characterized by DLS. For experimentation occupational dust (OD), microdust 5-8 μm (MD) and nanodust 83±31nm (ND) were exposed to A549 for 72 hr to study cytotoxicity, oxidative stress and inflammatory bioactivity. Detailed cytotoxicity studies showed LC50 values as 326 μg/ml, 269 μg/ml and 127 μg/ml for OD, MD and ND, respectively. Effects of LC50 concentrations of OD, MD and ND on cellular release of LDH, content of GSH, LPO and ROS production were helpful to assess the differential toxicity caused by microand nanoparticles of granite. Granite particle mediated release of LDH in the incubation media , in comparison with control were 1.3-fold, 2.1 -fold and 3.2-fold in the case of OD, MD and ND, respectively. Exposure of these particles caused significant depletion in cellular GSH i.e. 19.8% and 33.9% due to MD and ND exposure, respectively. Particle mediated ROS production increased by 1.4-fold, 2.3-fold and 3.4- fold, by OD, MD and ND, respectively. These particles also enhanced LPO profiles significantly by 1.4-fold, 4.0-fold and 6.5- fold due to OD, MD and ND, respectively. Inflammatory bioactivities of these particles were explored acknowledging TNF-α, IL-1β and IL-6 as markers of inflammation. Expressions of these cytokines were significantly enhanced by ND in comparision with MD and OD. Present study suggests that nanosizing of granite particle from microsize enhances cytotoxic and inflammatory bioactivities of granite particle. Particle size- dependent toxicological profiles of granite would help extrapolating health effects of populations exposed to different work environment risk right from quarrying, stone saw milling and civil installation. It is concluded that different safety standards are required depending upon the work environment prevalent with microor nano-size granite particles.