A Physico-chemical and Toxicological Evaluation of Fracking Sand Dusts

 

During hydraulic fracturing, or “fracking,” a fluid is pumped under high pressure into a well bore to create fissures in the rock to facilitate the removal of gas. This fracking fluid contains a large number of ingredients, including water, chemical agents, and sand. The manipulation of sand at the well site creates respirable dust [fracking sand dust (FSD)] to which workers are exposed.

A series of nine papers was recently published as a special issue in Toxicology and Applied Pharmacology to help better understand the physico-chemical characteristics of FSDs and compare the biological effects of FSDs to pure crystalline silica in an animal model. Fracking sand dust samples were collected from a variety of drilling locations. While these papers are a thorough collection of work that help to delineate the toxicity of FSDs, these are initial animal studies and there are still gaps in the research that require further studies.

Background

Currently, there is no registry to help determine if lung disease occurs in workers at gas and oil drilling sites due to FSD inhalation. Also, it is currently unknown whether inhalation of FSD is associated with clinical symptoms of crystalline silica-induced diseases.

However, in many types of workplaces, inhalation of crystalline silica dust, which is also found in FSDs, is well known to cause silicosis, kidney disease, autoimmune disease, lung cancer and increased susceptibility to tuberculosis. From 2010 to 2011, NIOSH collected 111 air samples at 11 different hydraulic fracturing sites in five different states to evaluate worker exposure to crystalline silica. Many of the samples collected at these sites, exceeded the calculated Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit; the NIOSH Recommended Exposure Limit and the American Conference of Governmental Industrial Hygienists Threshold Limit Value (see Esswein et al., 2013).

There is concern that sand moving/transport operations surrounding hydraulic fracturing might give rise to a new cohort of workers who develop silicosis (Quail, 2017). In addition, there are also concerns about risks to workers associated with the mining and processing of sand for fracking (Walters et al., 2015). Because workplace exposures to FSD, which has crystalline silica in it, have exceeded the above-mentioned respirable crystalline silica exposure limits set by OSHA, studies to better understand the characteristics of FSDs, their potential effect on organ function, and to compare the effects of FSDs to pure crystalline silica were needed.*

The new special issue of Toxicology and Applied Pharmacology, Biological Effects of Inhaled Hydraulic Fracturing Sand Dust, is an initial step in this direction.

 

The Study

Because there is little to no information about FSD potential toxicity, NIOSH researchers designed a comprehensive hazard identification study using a rat animal model study to investigate the early adverse effects of several FSDs on organ functions (looking at respiratory, cardiovascular, immune systems, kidneys, and brain), in comparison to MIN-U-SIL^® 5, a respirable α-quartz dust (crystalline silica) that was used as a reference. The study explored the degree to which the health effects of inhaled FSD resemble those previously observed after pure crystalline silica dust inhalation and if the biological effects of FSD are restricted to the lungs.

Nine FSDs, taken from different drilling sites, were introduced into the tracheas of rats, and one FSD (FSD 8) was given to rats by inhalation exposure using a special exposure system. FSD 8 was examined more thoroughly, in other parts of the body, including the respiratory, cardiovascular and immune systems, brain and kidney.

The studies resulted in nine papers published in Toxicology and Applied Pharmacology:

I. Scope of Investigation

II. Particle characterization and pulmonary effects 30 d following intratracheal instillation

III. Cytotoxicity and pro-inflammatory responses in cultured murine macrophage cells

IV. Pulmonary effects

V. Pulmonary inflammatory, cytotoxic and oxidant effects

VI. Cardiovascular effects

VII. Neuroinflammation and altered synaptic protein expression

VIII. Immunotoxicity

IX. Summary and significance

 

Main Findings

Following short-term testing in rats, there were two major findings:

• Nine FSDs from different geographical locations have a milder effect on the lungs as compared with crystalline silica, at the post-exposure time points investigated after administering the dusts intratracheally to rats. Compared to crystalline silica, the FSDs that were studied contain crystalline silica and minerals in varying amounts depending on the geographical source. These minerals are currently hypothesized to blunt the biological response to the FSDs.
• The toxicities of one of the samples, inhaled FSD 8, were generally greater in the cardiovascular and immune systems, kidneys, and brain, than in the lungs. This was an unexpected finding as the typical effects of inhaled crystalline silica dust are thought to primarily cause lung diseases such as silicosis and cancer.

A summary of the findings can be found in article IX in the special issue.

These findings do not negate or replace current recommended standards to protect the health and safety of workers exposed to crystalline silica dust. These experiments were short-term exposures for hazard identification, and longer exposures might reveal greater similarities with crystalline silica’s toxicological effects. It is important that precautions continue to be taken at worksites when it comes to permissible exposure limits (PELs) and recommended exposure limits (RELs) to crystalline silica. It cannot be concluded from these studies that inhalation of FSD is without risk; repeated exposures of workers to the dust may eventually bring about the well-known diseases cause by crystalline silica inhalation.

This study was the first of a three-part NIOSH investigation to examine the toxicological response of a combination of inhaled FSD and diesel exhaust. The second phase is underway.

Jeffrey S. Fedan, PhD, is Chief of the Pathology and Physiology Research Branch in the NIOSH Health Effects Laboratory Division

 

References

E.J. Esswein, M. Breitenstein, J. Snawder, M. Kiefer, W.K. Sieber. Occupational exposures to respirable crystalline silica during hydraulic fracturing. J. Occup. Environ. Hyg., 10 (7) (2013), pp. 347-356.

M. Quail. Overview of silica-related clusters in the United States: Will fracking operations become the next cluster? J. Environ. Health, 79 (2017), pp. 20-27.

K. Walters, J. Jacobson, Z. Kroening, C. Pierce. PM2.5 airborne particulates near frac sand operations. J. Environ. Health, 78 (2015), pp. 8-12.

 

* Minor edits were made to the background section on 12/9/20 to provide greater clarity regarding the 2013 paper.