SOURCES OF ARSENIC IN DUST-GENERATING SOILS FROM THE NELLIS DUNES OFF-ROAD VEHICLES RECREATIONAL AREA, NEVADA, USA

Dust from the Nellis Dunes Recreational Area in Nevada has been found to contain up to 312 µg g^-1 of total arsenic and up to 14.7 µg g^-1 of soluble arsenic (Soukup et al, 2012). This presents a potential health hazard not only to the over 300,000 annual visitors but also possibly to residents of nearby Las Vegas. In this study, soils that generate dust were examined with a scanning electron microscope (SEM) equipped with energy-dispersive and wavelength-dispersive spectrometers (EDS and WDS). Many grains are coated by several µm thick layers of microcrystalline alumino-silicates, most likely clays. Some of these coatings also contain thin (typically <1µm) layers and masses of iron-oxyhydroxides intermixed with the clays. SEM-EDS showed measurable concentrations of arsenic in the iron-oxyhydroxide layers. SEM-WDS shows significant arsenic concentrations of up to 3% weight percent associated with the iron-oxyhydroxides, but actual arsenic levels in oxyhydroxides are likely higher because the ~10µm electron-beam spot size resulted in a significant volume of silicates being included in the analyses. Our identification of the actual arsenic carrier will be useful for developing strategies to manage this hazard.