Pulmonary Toxicity of Nine Sand Dusts Generated at Hydraulic Fracturing Sites in Comparison to Respirable Crystalline Silica

Abstract

The levels of respirable crystalline silica (RCS) at gas wells employing hydraulic fracturing (fracking) sites have been reported to exceed regulatory standards. Inhalation of RCS in work places may cause silicosis and other diseases in workers. While the effects of inhalation of RCS in humans and animal models has been well‐characterized, the pulmonary hazards to worker associated with RCS inhaled at fracking sites has not been investigated. In this study, nine fracking sand dusts(FSDs) collected by vacuum dust controls from different fracking sites in the US were compared to MIN‐U‐SIL 5® (MIN) with respect to particle size, mineral composition, Si radicals and pulmonary toxicity. Chemical analysis revealed that total mineral content of the FSDs other than Si ranged widely from 9.9 g/kg to 32.5 g/kg when compared to 1.4 g/kg for MIN. This heterogeneity was confirmed by energy‐dispersive X‐ray spectroscopy (EDS). Hydrodynamic particle diameter of neat FSDs using dynamic light scattering (DLS) indicated non‐concordant, mono‐ orbi‐modal spectral distributions of particle sizes; the spectrum for MIN was mono‐modal. Electron paramagnetic resonance (EPR) analysis indicated the presence of the Si radical in MIN but not in neat FSDs. After incubating the FSDs in water the Si radical was revealed in some samples, indicating occlusion of the radical in neat FSDs. To examine pulmonary toxicity, rats were intratracheally instilled with a single dose of FSD or MIN (159 or 500 μg/rat), or vehicle. Thirty days later, bronchoalveolar lavage (BAL) was performed to assess the development of pulmonary inflammatory responses: changes in lactate dehydrogenase (LDH) and differential cell counts. This time point has been shown previously to be one at which pre‐silicotic responses to MIN are observed. As expected, MIN elicited a dose‐dependent increase in LDH levels, total BAL cells, and total alveolar macrophages, polymorphonuclear lymphocytes and eosinophils. As a group, the FSDs did not elicit these responses. These findings indicate that, in many respects, the chemical and biophysical characteristics, and the biological effects of the FSDs and MIN after intratracheal instillation, have distinct differences.Support or Funding InformationNIOSH 6927ZLDC