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Naturally Occurring Asbestos Research

UNLV researchers Brenda Buck, Dirk Goossens, Rodney Metcalf, Minghua Ren, UNLV student Fritz Freudenberger and Bloomsberg University scientist Brett McLaurin recently published an article in the Soil Science Society of America Journal related to naturally occurring asbestos in Boulder City, southeast Henderson, and surrounding regions.

Research Fund

Donations to this fund will support geological research activities into Naturally Occurring Asbestos in southern Nevada and adjacent areas. Donations in any amount are welcome, smaller gifts ($20) can support expendable lab supplies or can support analytical costs for a single soil or rock sample ($200); larger gifts can support a graduate student research project ($10,000-$20,000 in analytical costs), upgrades to UNLV analytical instruments (up to $100,000) or a major research project (>$100,000). Go to the UNLV College of Sciences website to make a donation.


Naturally occurring asbestos refers to asbestos found as a natural component of rocks and soils. It occurs in rocks and soils as a result of natural geological processes and is found in many states. Previous to this study the presence of naturally occurring asbestos in Clark County, NV, was not recognized.

Asbestos is the name given to six different, regulated, fibrous minerals that occur naturally in the environment. The six fibrous minerals are divided into two categories: amphibole and serpentine. Amphibole forms include riebeckite (commercial name crocidolite), grunerite-cummingtonite (commercial name amosite), anthophyllite, tremolite, and actinolite.. The serpentine form is called chrysotile. Amphibole asbestos minerals are more toxic than the serpentine form. One of these regulated amphibole asbestos minerals (actinolite) is the asbestos type in Southern Nevada.

Other fibrous amphibole minerals that are not regulated, but are known to cause disease include winchite, magnesioriebeckite and richterite. These minerals are found in northwestern Arizona and studied by Metcalf.

The source of the naturally occurring asbestos in Southern Nevada is granite bedrock, and sediments and soils that have eroded from these rocks.

Much of the asbestos is found in soils formed on alluvial fans (deposits of sediment eroded from the granite), and in sediment found in active washes (stream drainages) and dry lakebeds. Soils and sediments represent the most likely source for dust containing naturally occurring asbestos.


The primary route of exposure for people is through air. Any activity or natural wind that generates dust from soils that contain asbestos will put the fibers in the air and increase the risk that people will be exposed. Therefore, the Agency for Toxic Substances and Disease Registry (ATDSR) and the Environmental Protection Agency (EPA) recommend avoiding activities that generate dust in order to lessen your exposure. However, asbestos fibers cannot be seen by the naked eye and therefore they can be present even without visible dust. Links for more information about how to limit exposure are listed below.

Health Information

Asbestos is a known human carcinogen with no known safe levels of exposure. Other, non-regulated minerals are also hazardous and behave similarly to asbestos when inhaled. In particular, Erionite is a carcinogenic mineral, but is non-regulated. 

The risk for adverse health effects increases with increasing exposure over time because the amphibole fibers remain in the body. This is particularly worrisome for children, as early life exposures have more time to manifest in disease (latency period).

In Libby, Mont., and other sites in the U.S., and other nations, there is significantly increased risk for disease in areas where people are being exposed to sources of asbestos in the environment.

For example, researchers at the University of California, Davis, found increased risk of malignant mesothelioma with residential proximity to naturally occurring asbestos. That information was published in an American Journal of Respiratory and Critical Care Medicine article: Residential Proximity to Naturally Occurring Asbestos and Mesothelioma Risk in California

Recently, Dr. Francine Baumann from the University of Hawaii with co-authors from UNLV, Bloomsberg University, and the USDA/NRCS published the study, “The presence of asbestos in the natural environment is likely related to mesothelioma in young individuals and women from Southern Nevada.” This study hypothesizes that mesothelioma caused by environmental exposure to asbestos might be initially distinguishable from that caused by occupational exposure by looking at male-to-female ratios in younger people (< 55 yrs old). The hypothesis is that environmental exposure should occur at earlier ages than occupational (even since birth), therefore mesothelioma will occur in younger individuals (< 55 yrs old). Environmental exposures should also occur equally to both men and women, therefore male to female ratios in those < 55 yrs old is important to examine. In contrast, occupational exposure occurs at older ages, therefore mesothelioma tends to occur later in life (> 55 yrs old), and occurs primarily in men (male to female ratios that vary from 4:1 to 6:1) because it is usually men that do jobs where asbestos exposure occurs. Of course actually determining causes of mesothelioma must be done in a case-by-case basis. This paper uses the above hypothesis to indicate where environmentally-exposed mesothelioma might be occurring so that researchers can focus additional research in those locations.

This paper was published in the Journal of Thoracic Oncology and was singled out as “Editor’s Choice”:

“Baumann and colleagues present interesting data with public health implications in terms of environmental asbestos exposure and the development of mesothelioma in young women in Nevada, USA. The manuscript — The presence of asbestos in the natural environment is likely related to mesothelioma in young individuals and women from Southern Nevada Baumann et al - will undoubtedly generate debate in the public health community and is worthy of significant attention.” — quote from Editor.

The USEPA recently released an inhalation reference concentration (RfC) value for chronic exposure for non-cancer health effects. 

The RfC is defined as an estimate of exposure that is likely to be without an appreciable risk of adverse health effects over a lifetime (70 yrs). The RfC is expressed in terms of the lifetime exposure in units of fibers per cubic centimeter of air (fibers/cc) as measured by phase contrast microscopy (PCM). The chronic RfC value for non-cancer health effects is 0.00009 f/cc.  

Results for ambient air are presented in the Final Phase I Site Characterization Report for the Boulder City Bypass Naturally occurring Asbestos (NOA) Project Phase I (Railroad Pass to Silverline Road).

Ambient air was measured in the area of Railroad Pass, for Phase I of the Boulder City Bypass (see final report).  Reported values from May 8 to August 10, 2014 vary from non-detect to 0.0014 s/cc with an average of 0.00021 s/cc. 

Hazard Quotient HQ = Ambient air concentration/Reference concentration. Using the limited data available (3 months summer 2014): HQ = 0.0002/0.00009 = 2.33. If the Hazard Quotient is calculated to be less than 1, then no adverse health effects are expected as a result of exposure. 

Note that OSHA (Occupational Safety and Health Administration) has a Permissible Exposure Limit (PEL) for asbestos that is 0.1 f/cc as an 8 hr time-weighted average. As you can see this number is much higher than the 0.00009 f/cc listed above. OSHA admits that although these levels are permissible, they do involve significantly increased health risk. In addition, the OSHA PEL only counts the 6 regulated asbestos minerals, therefore the asbestos minerals that are similar to those in Libby Montana that are found in and around Wilson Ridge in Arizona, and erionite, do not count towards the permissible exposure limit. 

Exposure to asbestos is known to cause the following diseases:

  • Mesothelioma
  • Pleural Plaque
  • Pleural Effusion
  • Asbestosis
  • Lung Cancer
  • Ovarian Cancer
  • Pneumoconiosis
  • Interstitial Pulmonary Fibrosis
  • Laryngeal Cancer

There is evidence that asbestos may cause or contribute to other possible health effects including:

  • Gastrointestinal Cancer
  • Colorectal Cancer
  • Throat Cancer
  • Kidney Cancer
  • Esophagus Cancer
  • Gallbladder Cancer
  • Pharyngel Cancer
  • Stomach Cancer
  • Cardiovascular Disease 
  • Immuned Disorders (autoimmune diseases: lupus, rheumatoid arthritis, lupus, scleroderma)


Buck and her research team specialize in medical geology, a field that studies how Earth materials affect health. In particular, their research focuses on the health effects of exposure to mineral dusts. This research led them to find the naturally occurring asbestos in Southern Nevada.

For their most recent research, which was published in the Soil Science Society of America Journal, the team collected 43 samples. Seventeen rock samples were collected from exposed granitoid outcrops: seven from Boulder City, four from Black Hill, and six from the McCullough Range. Seventeen soil samples were collected, 11 of which were from desert surfaces and six from dirt roads. They also collected samples from Buck’s clothing after she walked her horse on dirt roads in Boulder City. The subsequent analysis showed that all 43 samples, including rock, soil, dust, car tire, and clothing, contained fibrous amphiboles.

The sites that were found to contain the fibrous amphiboles include areas in and around Boulder City, and BLM-managed land south of Henderson.

Next Steps

Researchers are aware that there is a hazard but that air sampling and epidemiological studies are needed to learn more before speaking affirmatively about risks to human populations. Buck and Metcalf are partnering with local, state and federal agencies, and the Universities of Hawaii and Cincinnati to pursue more research on this topic.

Buck and Metcalf are also continuing to locate other deposits of naturally occurring asbestos in the region. As new data becomes available, maps showing these new locations will be uploaded here.

Helpful Links

Peer-Reviewed Publications

Publications/News Stories

About the Researchers

Brenda Buck is a professor in UNLV’s Department of Geoscience. She is an elected Fellow in both the Geological Society of America and the Soil Science Society of America. She also was awarded the M.L. & C.M. Jackson Award, for Outstanding Contributions in Soil Mineralogy/Chemistry from the Soil Science Society of America.

Buck is the Founding Director of the Environmental Soil Analytical Laboratory. Her research focuses on medical geology, in particular how geological materials impact health. Currently her work focuses on dust and hazards associated with dust exposure including those from asbestiform minerals, arsenic, and other carcinogens.

Rodney Metcalf is an associate professor in UNLV’s Department of Geosciences. His research interests center on the origin and evolution of the earth’s crust. His research tools are drawn primarily from igneous and metamorphic petrology, mineral chemistry, trace element and isotope geochemistry, and geochronology. He has served as chair of the Department of Geosciences and as Associate Dean for the College of Sciences at UNLV. He is secretary of the Cordilleran Section of the Geological Society of America and served two terms as an Associate Editor for the Bulletin of the Geological Society of America.