Characterization of Engineered Stone Dust Reactive Oxygen Species Generation and Cytotoxicity In Vitro

Details

• Personal Author:
  Mandler, W. Kyle ; Knepp, Alycia K. ; Leonard, Stephen S. ; McKinney, Walter G. ; Keeley, Sarah ; Qian, Yong
• Description:
  ABSTRACT: Background and Purpose: Engineered stone (ES), a composite material composed primarily of crushed quartz and a polymer binder, is widely used for countertops and flooring due to its durability and aesthetic appeal. However, the fabrication processes of cutting, grinding, and polishing generate respirable engineered stone dust (ESD), posing a significant occupational health hazard. ESD contains high concentrations of respirable crystalline silica (CS), a well-established causative agent of silicosis, lung cancer, and other respiratory diseases. Furthermore, these processes release volatile organic compounds (VOCs), potentially exacerbating toxicity. Recent global outbreaks of accelerated silicosis among ES workers, often affecting young individuals with relatively short exposure durations, underscore the urgent need for comprehensive research and effective workplace safety regulations. The underlying mechanisms driving this accelerated form of silicosis remain incompletely understood. This study investigated ESD-induced cellular toxicity and the generation of reactive oxygen species (ROS) in vitro, comparing the effects of freshly generated and aged ESD particles. Methods: Particles were generated using a custom-built, automated system mimicking countertop fabrication. A circular saw with a stone-cutting disc cut ES slabs within a sealed stainless-steel chamber with HEPA-filtered air intake. Aerosols exited at 30 L/min, passing through a cyclone (5ìm cut size) to select respirable dust, and collected on Teflon filters. Collected particles were stored under nitrogen gas at -80 degrees C. A subset was aged in air at room temperature for two weeks. Three ES materials (A, B, C), natural granite, and Min-u-sil-5 (MS5, a CS positive control) were used. CS content varied: 60% (ES A), 20% (ES B), 0% (ES C), 30% (Granite), and 99.5% (MS5). Electron paramagnetic resonance (EPR) spin-trapping assessed free radical generation. Particles were exposed to hydrogen peroxide (H2O2) to evaluate hydroxyl radical (.OH) production via a Fenton-like reaction. RAW 264.7 macrophages were cultured and exposed to 10ìg/well of fresh or aged ESD, or MS5, for 24 hours. Cell viability, apoptosis (Caspase 3/7), necrosis (Propidium Iodide), and ROS production (CellRox Deep Red) were measured using high-content imaging. The antioxidant N-acetyl cysteine (NAC) was used to assess the contribution of ROS to cytotoxicity. Results: Fresh materials exhibited significantly higher EPR peak intensities (indicating greater radical generation) than aged counterparts. All materials generated more radicals than background and MS5. In the presence of cells, fresh materials still showed higher EPR intensities, but aging significantly reduced this effect. Live cell counts were significantly reduced in wells treated with fresh ES materials and granite compared to controls, while aged materials and MS5 showed no significant difference. The percentage of apoptotic cells increased for all materials compared to controls, with no significant differences between fresh and aged materials. Necrotic cells increased in samples treated with fresh granite, fresh and aged ES A, and fresh ES B, with fresh materials showing significantly higher levels than aged counterparts. Oxidative stress increased in cells exposed to fresh and aged ES A and C, and aged granite. Despite decreased cell counts, total cell area increased in wells containing fresh and aged granite, fresh and aged ES A, fresh ES C, and MS5. Adding NAC did not attenuate the cytotoxic effects of ES exposure. Conclusions: Freshly-generated ES dusts exhibit different radical generating capacity compared to their aged counterparts. This capacity was only partially silica-content dependent. Cell viability, apoptosis, necrosis, and total cell area were all altered differently by aged vs fresh ES materials. The addition of antioxidant to the culture media did not attenuate any cytotoxic effects of ES exposure, indicating that ROS may not be the main factor contributing to the observed effects. Granite and ES A exposure tended to elicit the largest changes in toxicity and ROS production, while ES B produced fewer changes. ES C, which contains no measurable CS, was still capable of inducing ROS generation and cytotoxicity. These findings suggest that material silica content is an important, but not the sole factor contributing to cytotoxicity. Additionally, particle aging plays a significant role in ESD toxicity and should be a consideration in any future studies with these materials. Description provided by NIOSH
• Subjects:
  • Dust
  • Occupational Health
  • Particulate Matter
  • Respiratory System
  • Safety
  • Silicon Dioxide
• Keywords:
  • Crystalline silica; Cytotoxicity; Reactive oxygen species; ROS; Toxicology; Respirable dust; Countertops; Stone products;
  • Author Keywords: Particulates; Safety Evaluation; Respiratory Toxicology; Reactive Oxygen Species; Silica
• Source:
  Toxicologist 2025 Mar; 204(S2):7-8
• ISSN:
  1096-6080
• Document Type:
  Text
• Genre:
  Abstract or Summary
• Place as Subject:
  Philadelphia Region OSHA ; West Virginia
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  HELD - Health Effects Laboratory Division
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  3 pdf pages
• Volume:
  204
• NIOSHTIC Number:
  nn:20071593
• CAS Registry Number:
  • Quartz (SiO2) (CAS RN 14808-60-7)
• Federal Fiscal Year:
  2025
• NORA Priority Area:
  Manufacturing
• Peer Reviewed:
  False
• Download URL:
  https://stacks.cdc.gov/view/cdc/259368/cdc_259368_DS1.pdf
• File Type:
  [PDF - 502.41 KB]
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:37daa8f405cec157667228bacc634299d44c68e6c02366dbb95230985f6bdfbb957b71b1be3c662dd042490b387c22d2db0598ae2070453b4cbb3ba6469a42e4