A team of geologists led by Dr Brenda Buck from the University of Nevada-Las Vegas has discovered naturally occurring asbestos minerals in Clark County in southern Nevada and across the border in northwestern Arizona.
Amphibole asbestos minerals – riebeckite, grunerite-cummingtonite, anthophyllite, tremolite and actinolite – are known human carcinogens.
Exposure to fibrous and asbestiform amphiboles can cause asbestosis; lung, ovarian, and larynx cancer; mesothelioma; pleural fibrosis; and possibly other health effects.
In 2012, an epidemiologist analyzing cancer data from Clark County, Nevada, found a higher incidence than expected of mesothelioma, a fatal cancer of the lining of the chest cavity that is caused by inhalation of asbestos.
In response, Dr Buck and her colleagues have discovered geologically unexpected deposits of an amphibole asbestos mineral that might be the source.
They found fibrous amphibole mineral known as actinolite in the Miocene plutons (bodies of intrusive igneous rocks) in the McCullough Range, Black Hill, and Boulder City areas.
“In the arid climate of Nevada, populations may be exposed to these fibers through dust emissions that can occur from both natural wind erosion and anthropogenic activities. The evidence of fibrous amphiboles on car tires and on clothing after recreational activities shows that they can be brought back to family members and thus increase the risk of exposure for other populations besides those directly exposed through outdoor dust emissions,” the scientists said.
“Because health effects may occur even at low levels of exposure to fibrous amphiboles, our data indicate a potential public health threat in southern Nevada.”
They added: “because Boulder City, Henderson, and Las Vegas are located only a few kilometers, sometimes even only a few tens of meters, downwind from the sources, potentially large populations in the cities could be exposed.”
In 2014, Dr Buck and her colleagues, Dr Rodney Metcalf of the University of Nevada-Las Vegas, found deposits of asbestos minerals in Mohave County, northwestern Arizona.
“As with all naturally occurring asbestos, natural erosion processes have released the fibrous amphiboles from bedrock outcrops and redistributed them. Human exposures are primarily from both natural wind erosion and anthropogenic disturbances that release fibers from soil into the air. These processes are enhanced by the arid climate of the region (Nevada and Arizona).”
“Fibrous amphibole sources include public lands with popular hiking and off-road-vehicle trails, and fibrous actinolite sources overlap a portion of the greater Las Vegas metropolitan area.”
The discoveries, described in two papers in the journal Geology and the Soil Science Society of America Journal, suggest that asbestos may be more widespread than previously thought.
They also raise questions about the potential health hazards of naturally occurring asbestos.
Rodney V. Metcalf & Brenda J. Buck. 2015. Genesis and health risk implications of an unusual occurrence of fibrous NaFe3+-amphibole. Geology, vol. 43, no. 1, pp. 63-66; doi: 10.1130/G36199.1
Brenda J. Buck et al. 2013. Naturally Occurring Asbestos: Potential for Human Exposure, Southern Nevada, USA. Soil Science Society of America Journal, vol. 77, no. 6, pp. 2192-2204; doi: 10.2136/sssaj2013.05.0183
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