Biological effects of inhaled hydraulic fracturing sand dust. II. Particle characterization and pulmonary effects 30 d following intratracheal instillation

Hydraulic fracturing ("fracking") is used in unconventional gas drilling to allow for the free flow of natural gas from rock. Sand in fracking fluid is pumped into the well bore under high pressure to enter and stabilize fissures in the rock. In the process of manipulating the sand on site, respirable dust (fracking sand dust, FSD) is generated. Inhalation of FSD is a potential hazard to workers inasmuch as respirable crystalline silica causes silicosis, and levels of FSD at drilling work sites have exceeded occupational exposure limits set by OSHA. In the absence of any information about its potential toxicity, a comprehensive rat animal model was designed to investigate the bioactivities of several FSDs in comparison to MIN-U-SIL (R) 5, a respirable alpha-quartz reference dust used in previous animal models of silicosis, in several organ systems (Fedan, J.S., Toxicol Appl Pharmacol. 00, 000-000, 2020). The present report, part of the larger investigation, describes: 1) a comparison of the physico-chemical properties of nine FSDs, collected at drilling sites, and MIN-U-SIL (R) 5, a reference silica dust, and 2) a comparison of the pulmonary inflammatory responses to intratracheal instillation of the nine FSDs and MIN-U-SIL (R) 5. Our findings indicate that, in many respects, the physico-chemical characteristics, and the biological effects of the FSDs and MIN-U-SIL (R) 5 after intratracheal instillation, have distinct differences.