A Physico-chemical and Toxicological Evaluation of Fracking Sand Dusts

Posted on by Jeffrey S. Fedan, PhD


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.


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



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.

Posted on by Jeffrey S. Fedan, PhD

6 comments on “A Physico-chemical and Toxicological Evaluation of Fracking Sand Dusts”

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    The ‘main findingst well constructed sentences…are awkward. For example: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.

    Would be more digestable as:
    “Nine FSD samples from diverse locations were introduced to laboratory rats.Their post-intertracheal adminstration indicated milder effects than mirrored experiments using crystalline silica.”

    Unfortunately the sample sizes and constituent material and ratios are not given. Silicosis experiments have only recently taken-on serious review. Reality-gaps are several.

    One I pursued throughout Australia’s universities and OHS, being a combination of silicon and diesel dust has no experimental data. It was commented upon as suggesting an interesting study. I could not then purse further that commonplace exposure for my MD postgrad. submission

    Another is that there is no certainty in what chemicals and in what quantity are being inhibited through OEL of 0.05mg/m3 (previously) 0.1mg/m3. The focus is on silica not other harmful dusts which alone or as catalysts might be influential. Experiment V111 may be a result of that.

    Air monitoring is only made on some construction sites and some silicon sawing and drilling premises. The recent Queensland ‘blitz’ of them (well advertised in advance ) nevertheless saw over 500 fines issued, some ‘stop works’ and no publicised ‘follow up.’

    Silicosis is not confined to influencing cancer , as may appear from the article, to cancer and silicosis…there are numerous others.

    Myself suffering asbestosis, with silicosis yet undetermined I have formed very circumspect views on the law’s view of asbestos duration required to produce asbestosis and the view concerning silicon and silicosis.

    Meanwhile relevance to reality has to be intrinsic in dealing with what we inhale in our particular atmosphere…what are the commonalities? , what catalyst effects occur? amongst various dusts.

    When people are being poisoned by other chemicals such (for only one example) as diesel dust how does it facilitate dust disease, with or without the mixture of the two in the one inhalation which we probably all experience in everyday life?

    Typically interest in the adverse effects on humans (also animals and plant-life) wax and wane with media interest and disinterest (‘moving on from there’) or some high profile party being affected. That is a failure caused by propaganda and stimulus orientated media. It’s not good enough.Unfortunately I cannot afford to buy the reports.

    Thank you for your interest. Much remains unknown about the potential health hazards associated with hydraulic fracturing due to inhalation of generated dust. As we note in the blog (and in the nine articles on which it is based), these are initial animal studies and there are still gaps in the research that require further studies. The purpose of this research was to better understand the physico-chemical characteristics of fracking sand dusts (FSDs) and to compare the biological effects of FSDs to pure crystalline silica in an animal model.

    This study did not examine diesel exhaust or asbestos nor are we familiar with problems associated with these materials that are specific to Australia. The second phase of the larger animal studies investigation will be to examine the effects of inhalation of exhaust from a type II diesel engine to assess the potential toxicity of the fumes; these engines are used at drilling sites. In the last phase of the overall investigation, animals will be exposed to FSD and diesel exhaust together to determine whether the combined exposure accentuates toxicity compared to the individual agents alone. When completed, these findings also will be published and posted in a blog.

    The literature on silica, silicosis, and lung cancer is broad and deep. There is quite a bit of information available on the NIOSH Silicosis Topic Page, https://www.cdc.gov/niosh/topics/silica/, and using the NIOSHTIC link there will point to 1,745 items. Additionally, the OSHA rulemaking docket from their 2016 Silica Rulemaking process includes copies of many scientific papers and commentaries that can be freely accessed at http://www.regulations.gov by searching for “OSHA-2010-0034.” There are 2,465 items posted under “Supporting and Related Material.”

    You metiond that personal breathing zone samples were collected in 2013 of dust collected at wells in six geographical areas. Were these locations associated with fracking operations? And if not, is the fracking operations consistent enough that a direct correlation between the two activities is acceptable? in other words are the two operations similar with respect to dust generation and worker exposures?

    Yes, the personal breathing zone samples described in the 2013 paper (Esswein et al) were all collected at well locations while hydraulic fracturing operations were being performed. The FSDs used in the animal studies were collected at different well locations during hydraulic fracturing operations.

    You stated that 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. How was FSD 8 different physically and/or chemically than the other FSD samples?

    The investigations did not attempt to characterize differences in the bioactivities of all the FSDs. Rather, comparisons were made, when possible, between the bioactivities of FSDs and crystalline silica. Differences in the physico-chemical characteristics of FSDs and crystalline silica were observed with regard to mineral composition. The full characterization of each of the FSDs tested was presented in one of the papers (Fedan, J. S., Hubbs, A.F., Barger, M., Schwegler-Berry, D., Friend, S., Leonard, S. S., Thompson, J. A., Jackson, M.C., Snawder, J.E., M. C., Dozier, A. K., Coyle, J., Kashon, M. L., Park, J-.H., McKinney, W., and Roberts, J. R.: Biological effects of inhaled hydraulic fracturing sand dust. II. Inhalation exposure system, particle characterization, and pulmonary effects 30 d following intratracheal instillation. Toxicol. Appl. Pharmacol. 409:115282, 2020), which can be accessed through the link in this blog.

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Page last reviewed: December 9, 2020
Page last updated: December 9, 2020