Arsenic concentrations in dust emissions from wind erosion and …csub.edu/~dbaron/nellis.pdf · 2019-12-04 · to Las Vegas and the surrounding urban area, a study was under-taken

Arsenic concentrations in dust emissions from wind erosion and off-road vehiclesin the Nellis Dunes Recreational Area, Nevada, USA

Deborah Soukup a,⇑, Brenda Buck a, Dirk Goossens a,b, April Ulery c, Brett T. McLaurin d, Dirk Baron e,Yuanxin Teng a

aDepartment of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4010, USAb Physical and Regional Geography, Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200E, 3001 Heverlee, BelgiumcDepartment of Plant and Environmental Sciences, New Mexico State University, MSC3Q, P.O. Box 30003, Las Cruces, NM 88003-8003, USAdDepartment of Geography and Geosciences, Bloomsburg University of Pennsylvania, Bloomsburg, PA, USAeDepartment of Physics and Geology, California State University, 9001 Stockdale Highway, Bakersfield, CA 93311, USA

a r t i c l e i n f o

Article history:Received 5 June 2011Revised 15 November 2011Accepted 21 November 2011Available online xxxx

Keywords:ArsenicSoilDust emissionWind erosionOff-road vehicles (ORVs)

a b s t r a c t

Field and laboratory experiments were performed in the Nellis Dunes Recreational Area near Las Vegas,NV, USA to evaluate arsenic concentrations associated with dust emissions from wind erosion and off-road vehicles. Soil samples were collected from 17 types of desert surfaces and five unpaved parkinglot locations for analyses. The surface units are based on surficial characteristics that affect dust emis-sions. Arsenic concentrations were also measured in dust emitted from each surface unit using a PortableIn Situ Wind Erosion Laboratory (PI-SWERL). Emissions were measured from ORV trails and undisturbedterrain. Concentrations of As in the soil and parking lot samples ranged from 3.49 to 83.02 lg g�1 andfrom 16.13 to 312 lg g�1 in the PI-SWERL samples. The lower concentrations in the soil samples areexpected because of the larger particle sizes (<2 mm) as compared to the PI-SWERL samples (<10 and10–60 lm). Soluble As in the PI-SWERL samples was as high as 14.7 lg g�1. In the Nellis Dunes areathe emission rates for As for wind-induced emissions (wind erosion) are highest for the surfaces withsignificant amounts of sand. Surfaces rich in silt and clay, on the other hand, produce nearly no arsenicduring wind erosion but can emit substantial arsenic concentrations when driven on by off-road vehicles.The elevated arsenic emissions from the Nellis Dunes area are of great concern because the site is locatedin the immediate vicinity of the city of Las Vegas, and utilized by over 300,000 visitors annually.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

Exposure to arsenic (As) has been strongly linked to healthproblems such as heart disease, hypertension, peripheral vasculardisease, diabetes, immune suppression, acute respiratory infec-tions, intellectual impairment in children, and skin, lung, prostate,bladder, kidney, and other cancers (Chen et al., 1992; Abernathyet al., 1999; Järup, 2003; Tseng et al., 2003; Smith et al., 2006;von Ehrenstein et al., 2007; Kozul et al., 2009a). Additionally,arsenic has been found to be uniquely harmful to lung tissue byinhibiting wound repair and altering genes associated withimmune functions in lung tissue (Olsen et al., 2008; Kozul et al.,2009a,b).

Exposure to arsenic may occur through ingestion of contami-nated groundwater, food containing inorganic or organic arsenic,or by inhalation of airborne dust (Mandal and Suzuki, 2002). Themajority of atmospheric arsenic is highly respirable inorganic

arsenic particulate matter smaller than 2.5 lm (ARB, 1990). Com-bustion of fossil fuels, geothermal steam development, and arsen-ical pesticide/herbicide use are the largest sources of inorganicarsenic emissions to the atmosphere. Other sources of inorganic ar-senic emissions are mining and quarry operations, cement manu-facturing, glass manufacturing, agricultural burning, wasteincineration, and secondary lead smelting (ARB, 1990). Consideringthese sources, it is not surprising that most studies on arsenic con-centrations in air have been performed on or near polluted sites, orin cities.

Another source of airborne arsenic is windblown dust. Severalstudies have documented the dispersal of arsenic through airbornedust at the local, regional, or even continental scale. Morman(2010) described African dusts bringing arsenic to the Caribbeanand southeastern USA, and expressed potential concern regardingarsenic-laden dust in the southwestern USA. Reynolds et al.(2008), Reheis et al. (2009), and Breit et al. (2009) described the po-tential for naturally-derived dusts from playas in the southwesternUSA to contain high arsenic concentrations. Arsenic contaminationfrom dust is now being recognized in some of the most remote

1875-9637/$ - see front matter � 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.aeolia.2011.11.001

⇑ Corresponding author.E-mail address: [email protected] (D. Soukup).

Aeolian Research xxx (2011) xxx–xxx

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Please cite this article in press as: Soukup, D., et al. Arsenic concentrations in dust emissions from wind erosion and off-road vehicles in the Nellis DunesRecreational Area, Nevada, USA. Aeolian Research (2011), doi:10.1016/j.aeolia.2011.11.001

locations in the world: Yeo and Langley-Turnbaugh (2010) foundAs concentrations that are above US EPA drinking water guidelinesin snow samples on Mount Everest in the Himalayas.

Barren desert surfaces and dry lake beds have long been identi-fied as important dust sources (Gill and Gillette, 1991; Mulitzaet al., 2010). Natural wind erosion is the dominant mechanism fordust production in these areas. However, many desert surfacesare increasingly disturbed by human activity. One type of distur-bance that requires special attention is off-road vehicular (ORV)activity. ORV driving is one of the most prevalent and fastest grow-ing leisure activities on public lands worldwide (Cordell, 2004;

Cordell et al., 2008). In southern Nevada (USA) the number of off-road drivers has quadrupled in the last few years (Spivey, 2008).Dust emissions created by ORV activities require special attentionbecause ORV driving is a non-selective process. This means thatcomponents that normally stay fixed in the soil may be releasedand inhaled. This is a special concern if ORV-driven substrata con-tain potentially hazardous chemicals, minerals, or organisms.

The results of several recent investigations have documentedelevated concentrations of arsenic in dust and surface sedimentsin southern Nevada and California (Gill et al., 2002; Reynoldset al., 2008; Rojo et al., 2008; Reheis et al., 2009; Breit et al.,

Fig. 1. Study area location map.

2 D. Soukup et al. / Aeolian Research xxx (2011) xxx–xxx


2009). This study investigates the occurrence of arsenic in the NellisDunes Recreational Area (NDRA), one of the most popular destina-tions for ORV activity in this region. NDRA is visited by over 300,000people annually and located only 6 km from the northeastern por-tion of the conurbation of Las Vegas, north Las Vegas, and Hender-

son, Nevada. Research performed within the NDRA has shownthat large amounts of dust are emitted year round from this site,and that some of this dust blows into the city (Goossens andBuck, 2011a). Given the significant increase in ORV activity insouthern Nevada in recent years and the proximity of the NDRA

Fig. 2. Occurrence of the 17 surface units at the Nellis Dunes Recreation Area.

D. Soukup et al. / Aeolian Research xxx (2011) xxx–xxx 3


to Las Vegas and the surrounding urban area, a study was under-taken to characterize the chemical constituents in dust emissionsfrom the NDRA.

2. The study area

The NDRA is located approximately 6 km northeast of thenortheastern boundary of Las Vegas, Nevada, USA (Fig. 1). This37 km2 area is managed by the Bureau of Land Management(BLM) and is the only area in southern Nevada that is legally acces-sible to the public for off-road vehicular use. According to the BLM,over 300,000 people visit the area annually to drive their ORVs inthe dunes, washes, desert pavements, and rock-covered hills thatare characteristic of this part of the Mojave Desert (Goossens andBuck, 2009a).

The Las Vegas Valley is located within the Great Basin region ofthe Basin and Range physiographic province. It is an intermountainvalley, surrounded by generally N–S trending mountain ranges be-tween 450 and 2100 m above the valley floor in the N and E, and upto 3000 m above the valley floor in the west. The NDRA is locatedon the eastern side of the valley, between the Las Vegas and DryLake Ranges (to the N) and the Sunrise and Frenchman Mountains(to the S). It is primarily composed of incised fan remnants andexposed Neogene and Quaternary sediments, except for the moun-tains in the northeast, which are Paleozoic and composed predom-inantly of limestone (Goossens and Buck, 2009b). The Neogenedeposits within the field area are believed to be the Muddy CreekFormation (�10 to 5 Ma). They consist of a 2–50 m thick limestoneoverlying, and partially interbedded with, a marl succession up to10 m thick. The marl locally contains limestone rock fragments andthin layers of gypsite (Castor and Faulds, 2001). The limestone and

marl is underlain by a fine-grained sandy interval. Neogene toQuaternary fan remnants and inset fans occur throughout the fieldarea. These alluvial gravels are capped by extensive petrocalcichorizons and overlie the Muddy Creek Formation. Extensive inci-sion, particularly in the northern portion of the field area, has ex-posed the fine-grained Muddy Creek Formation. The middle ofthe southern portion of the field area is occupied by an extensivezone of dune sands, which cover the Neogene deposits. Althoughmuch of the sand is generally less than a meter thick, many highlyactive reversing dunes (oriented NW–SE) are present. These dunesmay be up to 250 m long and are among the most popular off-roaddriving zones within the area (Goossens and Buck, 2009b).

Soil development is negligible in the active sand dunes andareas where bedrock is exposed, including the badlands of the ex-posed Muddy Creek Formation. Surficial characteristics in these re-gions are controlled by the underlying bedrock geology or dunesand characteristics. In the remaining areas, primarily the fan rem-nants, the soils are characterized by thin (0–10 cm), platy, alkaline,Av (vesicular) horizons containing low amounts of organic matteroverlying calcic and/or petrocalcic horizons. Vesicular A (Av) hori-zons are generally associated with desert pavements. In manyareas, particularly in the western portion of the field area, the sur-face horizons are eroded and petrocalcic horizons are exposed atthe surface. Most of the surface gravels are composed of brokenfragments of the petrocalcic horizons in these areas. Soils in thestudy area are classified as Typic Haplocalcids, Calcic Petrocalcids,and Typic Torriorthents (Goossens and Buck, 2009b).

The climate within the study area is arid, and summers are long,hot, and dry with average daily maximum temperatures over 40 �C.In contrast, winters are mild, with an average daily maximum tem-perature in January around 13.5 �C. The average annual tempera-ture is 19.5 �C (Lazaro et al., 2004). Mean annual precipitation is

Table 1Overview and characteristics of the 17 surface units in the Nellis Dunes area.

Mapunit

Description Rock fragments Surface crust Vegetation

Sand and sand-affected areas1.1 Active dunes without vegetation. Decimeter to several meters thick. Sparse; may have exposed petrocalcic

horizonsAbsent Absent

1.2 Active dunes with vegetation. Coppice dunes <50 cm may bepresent.

Sparse; <5% rock cover Absent Isolated shrubs

1.3 Anthropogenic disturbed sand surfaces. Typically <2–3 cm thickloose sands overlying petrocalcic horizons or bedrock.

Common, mixed with 2–3 cm thickloose sand overlying bedrock

Absent Absent

1.4 Patchy, shallow (1–3 cm thick), loose sand overlying silty/rockysubsoil

Common, not interlocking, rocks insubsoil are exposed at surface

Absent Isolated shrubs

1.5 Very fine sand and coarse silt outcrops. Commonly badlands Absent Physical Mostly absent

Silt/clay areas2.1 Silt/clay outcrops with biological crust Sparse, <3–4% rock cover Biologic Isolated shrubs2.2 Silt/clay outcrops with gravel Common, <15%, not interlocking Physical Usually absent2.3 Aggregated silt deposits, commonly badlands, aggregates <5 mm

diameterAbsent Physical, patchy

distributionAbsent

2.4 Anthropogenic disturbed silt surfaces Variable, not interlocking Absent Absent

Rock-covered areas3.1 Well-developed desert pavements with underlying silty Av horizon Abundant: tightly interlocking rock

fragments, nearly 100% surface coverPhysical between rockfragments

Rare, isolatedshrubs

3.2 Rock-covered surface with silt/clay Many: 60–80%, poorly interlocking Physical and biologicalbetween rock fragments

Common, shrubs(10–15%)

3.3 Rock-covered surface with sandy loam Many: 60–80%, poorly interlocking Physical and biologicalbetween rock fragments

Common, shrubs(10–15%)

3.4 Rock-covered with encrusted sand and biological crusts Common: 20–30%, poorly interlocking Biological, continuous Common, shrubs(10%)

3.5 Bedrock and/or exposed petrocalcic horizons Continuous rock outcrop Absent Rare shrubs

Active drainages4.1 Gravelly drainages, without fine sediment Abundant: 90–100%, non-interlocking

gravel clastsAbsent Absent

4.2 Gravel and sand drainages Abundant: 70–80% with sand mixture Absent Absent4.3 Gravel and silt/clay drainages Common: 30–60%, poorly interlocking,

with silt mixturePhysical Common, shrubs

(10–30%)



105 mm, but may vary substantially. Monthly average precipita-tion ranges from 2 mm in June to 14 mm in February. Scatteredthunderstorms typically occur during July and August.

The average annual wind speed in the NDRA is about 3.3 m s�1

and gusts can be up to 25 m s�1 (Goossens and Buck, 2011a).Winds blow primarily from the northeast from November throughMarch and from the south from April through September. Duringstrong winds, blowing sand and dust are common in the NDRAalthough there is considerable variation over the area. The dunesand loose silty deposits in the west are much more active thanthe stabilized silt, gravel, and bedrock substrata in the east(Goossens and Buck, 2009b).

Previous studies of dust emissions in the NDRA (Goossens andBuck, 2009a,b; McLaurin et al., 2011) identified and mapped fourmajor surface classes within the study area comprising a total of17 types of surfaces (Fig. 2). A description of each unit is providedin Table 1. The major surface classes include:

1. Sands and sand-affected areas: active or stabilized sands, withor without rock fragments and/or vegetation.

2. Silt/clay areas: loose and slightly stabilized silt/clay deposits,with or without sparse rock fragments exposed at the surface.

3. Rock-covered areas: stabilized silty or sandy silty deposits withnumerous rock fragments on top, desert pavements over a siltysublayer, bedrock, and petrocalcic horizons.

4. Active drainages: active drainages in sand and silt areas, andgravelly drainages.

3. Methods and procedure

3.1. Field procedure

During previous studies at NDRA, field measurements were per-formed at 68 locations (four for each surface unit) within the areato measure natural dust emission by wind erosion (Goossens andBuck, 2011b). Soil samples were also collected from the upper 2–3 cm of all surface units (minimum of four samples per surfaceunit) and from five unpaved areas used for parking.

Additional dust samples were collected for the current studyfrom16 of the 17 surface types and from the five parking areas usinga Portable In Situ Wind Erosion Laboratory (PI-SWERL). This instru-ment creates an increased wind shear near the ground producingwind erosion under controlled conditions, and allows collection ofthe emitted particles. It was developed by the Division of Atmo-spheric Sciences, Desert Research Institute, Las Vegas, Nevada; de-tailed descriptions are provided in Etyemezian et al. (2007) andSweeney et al. (2008). For this study, the mini-SWERL version,which samples 0.26 m2 of the soil surface, was utilized. Six to 20samplings were performed for each surface type until a minimumof 10 g of airborne dust was collected. The rotational speed of theinternal ring was set at 6000 round min�1 which corresponds to ashear velocity of 0.91 m s�1. PI-SWERL dust samples were collectedboth onORV trails and on undisturbed terrain. No sampleswere col-lected fromareas of outcropping bedrock or outcropping petrocalcichorizons, which contain negligible emittable dust.

Field experiments were also performed in the NDRA during aprevious study to measure anthropogenic dust emissions causedby off-road vehicular activity (Goossens and Buck, 2009b). Dustemissions from off-road vehicular use were measured using threedifferent types of ORVs including a four-wheeler (quad), dunebuggy, and dirt bike (motorcycle). These vehicles account for over99% of all ORV activity in the NDRA. The purpose of these experi-ments was to compare dust emission from ORVs with natural winderosion. In the current study, the dust emission data was combinedwith soil chemical data to determine the emission rates for As foreach of the ORV types.

3.2. Laboratory procedures

3.2.1. Total elemental analysesThe soil samples collected from each of the surface units were air

dried and sieved to remove coarse fragments (>2 mm). The <2 mmfraction was then digested in accordance with EPA Method 3052(USEPA, 1996). The digested samples were initially scanned for 66different elements using inductively coupled plasma mass spec-troscopy (ICP-MS). The purpose of the initial semi-quantitative scanwas to identify elements that might be present at concentrationsexceeding naturally occurring background concentrations reportedin soils in the area. Based on the results of the semi-quantitativescan, 17 elements were identified as potentially exceeding reportedbackground concentrations andwere re-analyzed quantitatively forthese elements using ICP-MS. This manuscript focuses exclusivelyon the As concentrations. The remaining elements will be ad-dressed in a separate manuscript.

To ensure quality control for the ICP-MS analyses, samples ofBuffalo River Sediment Reference Material 8704 were digested inaccordance with EPA Method 3052 and analyzed along with theNDRA samples. Satisfactory recoveries (±10% of known values)were found for the trace elements analyzed.

Analyses for the 17 elements were also made on dust samplescollected using the PI-SWERL. The <10 lm (PM10) and 10–60 lmsize fractions were separated by sedimentation (Jackson, 1985)

Table 2Total arsenic concentrations in surface unit soil samples (<2 mm).a

Surface unit description As(lg g�1)

USEPA Regional Screening Levelsb

Residential soil 0.39Groundwater protection 0.0013

Sand and sand-affected areas1.1: Dunes with no vegetation 4.371.2: Dunes with vegetation 3.491.3: Disturbed sand surfaces 6.741.4: Patchy layers of sand over silty/rocky subsoil 4.921.5: Outcrops of very fine sand and coarse silt 46.06

Silt/clay areas2.1: Silt/clay with crust 19.712.2: Silt/clay with gravel 83.022.3: Aggregated silt deposits 11.012.4: Disturbed silt surfaces 11.79

Rock-covered areas3.1: Desert pavements 13.563.2: Rock-covered surfaces with silt/clay zones 7.893.3: Rock-covered surfaces with sandy loam 6.853.4: Rock-covered surfaces with encrusted sand 7.283.5: Bedrock and/or petrocalcic horizons 9.03

Drainage areas4.1: Gravelly drainages 32.364.2: Gravel and sand drainages 23.394.3: Gravel and silt/clay drainages 31.45

Parking lot areasNorth Parking Lot #1 5.98South Parking Lot #1 4.88South Parking Lot #2 6.86Southeast Parking Lot #1 17.62

Standard samplesBuffalo River Standardc 14.64Buffalo River Reference Material 8704 reported As

concentration17

a Soil samples were acid digested prior to analysis using EPA Method 3052.b The screening levels (SLs) are developed using risk assessment guidance from

the EPA Superfund program and are used for site ‘‘screening’’ and as initial cleanupgoals, if applicable. The groundwater protection concentrations shown are soilconcentrations considered to be protective of groundwater resources.

c Buffalo River Reference Material 8704 sample that was digested in accordancewith EPA Method 3052 and analyzed with the NDRA samples.



and wet sieving and acid-digested in accordance with EPA Meth-od 3052 prior to analysis. The 60 lm limit was used as a cut-offfor total suspendable particles (TSP) because it represents themaximum size of grains that will still be transported in short-term suspension during average wind speed and turbulence(Pye and Tsoar, 1990). It also nearly coincides with the maximumdiameter of silt (52 or 63 lm, depending on which criterion isused; Goossens and Buck, 2009b). Additionally, 1:10 soil:waterextracts were prepared to determine the water soluble constitu-ents in the <60 lm fraction of the PI-SWERL dust samples. Thesesamples were allowed to sit overnight and were then filtered toobtain the supernatant. The supernatant solution was also ana-lyzed by ICP-MS using similar instrument settings and qualitycontrol measures.

3.2.2. X-ray diffraction (XRD) analysesX-ray diffraction (XRD) analyses were made on all soil samples

to determine the mineralogical composition. Two size fractionswere investigated, <2 lm, and 2–20 lm, because these grain sizesmay have implications for arsenic occurrence and mobility. These

Table 3Non-water-soluble arsenic concentrations (EPA method 3052) in PI-SWERL samples.

Surface unit description Particle size(lm)

As(lg g�1)

USEPA Regional Screening Levelsa

Residential soil 0.39Groundwater protection 0.0013

Sand and sand-affected areas1.1Rb: Dunes with no vegetation <10 43.31

10–60 30.40

1.1: NRc <10 46.5610–60 28.37

1.2R: Dunes with vegetation <10 52.4510–60 42.14

1.2NR <10 48.7810–60 36.55

1.3R: Disturbed sand surfaces <10 54.1410–60 46.34

1.3NR <10 37.9610–60 30.37

1.4R: Patchy layers of sand over silty/rockysubsoil

<10 26.3210–60 20.46

1.4NR <10 27.2110–60 19.76

1.5R: Outcrops of very fine sand and coarse silt <10 279.0310–60 248.31

1.5NR <10 290.0110–60 312.42

Silt/clay areas2.1R: Silt/clay with crust <10 87.95

10–60 79.68

2.1NR <10 83.0310–60 79.30

2.2R: Silt/clay with gravel <10 145.3910–60 130.61

2.2NR <10 161.3210–60 138.50

2.3R: Aggregated silt deposits <10 18.5610–60 24.87

2.3NR <10 27.4410–60 33.46

2.4R: Disturbed silt surfaces <10 25.1010–60 24.40

2.4NR <10 23.5410–60 26.02

Rock-covered areasd

3.1R: Desert pavements <10 28.1110–60 26.46

3.1NR <10 24.8610–60 22.34

Rock-covered areas3.2R: Rock-covered surfaces with silt/clay

zones<10 27.8810–60 21.85

3.2NR <10 18.8510–60 16.13

3.3R: Rock-covered surfaces with sandy loam <10 32.9310–60 25.84

3.3NR <10 30.9810–60 70.64

3.4R: Rock-covered surfaces with encrustedsand

<10 44.0310–60 49.54

3.4NR <10 41.7410–60 41.43

Table 3 (continued)

Surface unit description Particle size(lm)

As(lg g�1)

Drainage areas4.1R: Gravelly drainages <10 64.33

10–60 70.59

4.1NR <10 78.1410–60 70.24

4.2R: Gravel and sand drainages <10 54.1610–60 45.35

4.2NR <10 44.1510–60 41.27

4.3R: Gravel and silt/clay drainages <10 65.1310–60 66.00

4.3NR <10 94.0910–60 72.20

Parking lot areasNorth Parking Lot #1 <10 28.09

10–60 20.03

North Parking Lot #2 <10 27.7610–60 23.99

South Parking Lot #1 <10 34.3410–60 19.25

South Parking Lot #2 <10 23.5610–60 17.10

Southeast Parking Lot #1 <10 45.2410–60 39.89

Standard samplesBRS1e 21.08BRS2 19.16BRS3 20.33BRS4 18.46BRS5 18.64

Buffalo River Reference Material 8704 reported As concentration 17

a The screening levels (SLs) are developed using risk assessment guidance fromthe EPA Superfund program and are used for site ‘‘screening’’ and as initial cleanupgoals, if applicable. The groundwater protection concentrations shown are soilconcentrations considered to be protective of groundwater.

b R samples collected within ORV trailsc NR samples collected in undisturbed areas.d Surface unit 3.5 (bedrock) was not sampled.e Buffalo River Reference Material 8704 samples that were digested in accor-

dance with EPA Method 3052 and analyzed with the NDRA samples.



fractions were separated by centrifugation and sedimentation fol-lowing rinsing with distilled water. The distilled water rinses werenecessary to remove soluble salts from the soils in order to dis-perse the samples prior to fractionation.

Pastes of K- and Mg-saturated clay (<2 lm) and silt (2–20 lm)were smeared on glass slides (Theisen and Harward, 1962). TheK-saturated sample slides were examined by XRD at 25 �C andafter heating at 350 and 550 �C for 2 h. The Mg-saturated sampleswere also analyzed at 25 �C and after being placed in a desiccatorcontaining a pool of ethylene glycol and heated at 65 �C for 2 h.The desiccator vent was closed upon removal from the ovenand the slides stored in the desiccator at least 12 h prior toXRD analysis. All samples were examined by XRD (CuKa radia-tion) using a PANalytical X’PERT Pro diffractometer, equippedwith an X’Celerator detector. Additional descriptions of these

methods can be found in Reid-Soukup and Ulery (2002) andSoukup et al. (2008).

4. Results

The concentrations of As in the surface unit and parking lot soilsamples ranged from 3.49 to 83.02 lg g�1 or parts per million(ppm; Table 2). The highest concentrations of As in the soil samplesoccurred within the silt/clay areas (surface units 2.1–2.4), thedrainages (surface units 4.1–4.3), and surface unit 1.5 (very finesand and coarse silt outcrop). The As concentration in the South-east Parking Lot #1 sample (17.62 lg g�1) was also elevated com-pared to the other soil samples collected from parking areas.

The As concentrations in the PM10 and 10–60 lm fractions in thePI-SWERL dust samples ranged from18.56 to 290.01 and from16.13to 312.4 lg g�1, respectively (Table 3). The highest As concentra-tions in both size fractions of dust were in the samples collectedfromundisturbed terrainof theveryfine sandand coarse silt outcrop(surfaceunit 1.5). ElevatedAs concentrations (41.13–161.32 lg g�1;Table 3) also occurred in theORV trails andundisturbed terrain sam-ples from silty/clay areas and active drainages (surface units 2.1, 2.2,4.1, 4.2, and 4.3). The lowest concentrations occurred in the undis-turbed terrain samples of rock-covered surfaces with silt/clay (sur-face unit 3.2).

Water-extractable or soluble As concentrations in the 0–60 lmfractions of the PI-SWERL dust samples ranged from 0.42 to14.71 lg g�1 (Table 4). Highest soluble As concentrations werefound in the undisturbed gravel and sand drainages (unit 4.2).Other areas with increased soluble As include the undisturbedgravel and silty drainages (unit 4.3), many of the silt/clay units(2.1, 2.2, 2.4), some of the sandy units (1.2, 1.4, 1.5), and some ofthe unpaved parking areas (Table 4). The pH values of the solublePI-SWERL extracts were near-neutral to alkaline, ranging from6.58 to 9.11 (Table 4). Electrical conductivity (EC) values of the ex-tracts ranged from 0.06 to 2.43 dS m�1 and document the salinityof most of the soils in the NDRA, particularly considering the dilu-tion factor of 10. Historically, a soil was classified as saline if the ECof the saturation extract exceeded 4 dS m�1 (United States SalinityLaboratory Staff, 1954). More recently, saline soils have been de-fined to indicate the types of crops capable of tolerating variouslevels of soil salinity. Saline soils are defined as EC > 1.5 dS m�1

for sensitive crops; EC > 3.0 dS m�1 for moderately sensitive crops;EC > 6 dS m�1 for moderately tolerant crops; and EC > 10 dS m�1

for tolerant crops (Essington, 2004).The mineralogical composition of the clay (<2 lm) and silt

(2–20 lm) fractions of the soil samples at NDRA is dominated bysmectite with lesser amounts of palygorskite, mica/illite, kaolinite,quartz, and calcite. Gypsum was also identified in several samples,although it should be noted that most of the gypsum presentwould have been removed during the distilled water rinses priorto fractionation.

5. Discussion

5.1. Occurrence of arsenic at NDRA

Geographically, the highest arsenic concentrations are found inthe northern portion of theNDRA in specific exposures of theMuddyCreek Formation: units 1.5 (fine sand and coarse silt), and 2.2 (silt/clay with gravel). Arsenic concentrations are also high in the drain-ages (4.1–4.3). The veryhigh arsenic contents in theunits 1.5 and 2.2(up to >80 ppm in the topsoil, and >300 ppm in the PI-SWERLsamples) suggests that the occurrence of arsenic in the NDRA is lar-gely controlled by one or more geologic processes. Arsenic enrich-ment is frequently caused by hydrothermal alteration (Boyle and

Table 4pH, electrical conductivity, and soluble arsenic concentrations in PI-SWERL 1:10soil:water extracts (<60 lm fraction).

Surface unit description pH Electricalconductivity(dS m�1)

As(lg g�1)

Sand and sand-affected areas1.1Ra: Dunes with no vegetation 8.23 2.43 1.781.1NRb 7.81 0.90 0.551.2R: Dunes with vegetation 7.83 0.76 4.361.2NR 8.18 0.18 2.231.3R: Disturbed sand surfaces 8.47 0.62 6.821.3NR 8.15 0.28 0.611.4R: Patchy layers of sand over silty/

rocky subsoil7.44 1.85 6.05

1.4NR 7.43 1.42 2.801.5R: Outcrops of very fine sand and

coarse silt7.86 2.87 8.04

1.5NR 7.55 2.31 4.13

Silt/clay areas2.1R: Silt/clay with crust 7.50 1.70 8.282.1NR 8.05 0.35 5.882.2R: Silt/clay with gravel 7.86 2.15 9.242.2NR 7.84 2.11 10.592.3R: Aggregated silt deposits 7.74 1.78 5.022.3NR 7.83 2.19 1.492.4R: Disturbed silt surfaces 7.63 2.08 9.582.4-NR 7.76 1.46 2.17

Rock-covered areasc

3.1R: Desert pavements 7.91 0.72 0.813.1NR 8.29 0.38 1.043.2R: Rock-covered surfaces with

silt/clay zones8.06 0.42 0.87

3.2NR 8.60 0.30 0.653.3R: Rock-covered surfaces with

sandy loam8.21 0.30 1.91

3.3NR 8.11 0.32 1.403.4R: Rock-covered surfaces with

encrusted sand8.13 0.07 2.20

3.4NR 6.58 0.06 0.42

Drainage Areas4.1R: Gravelly drainages 7.87 2.26 3.114.1NR 8.39 0.48 3.474.2R: Gravel and sand drainages 7.71 1.74 2.174.2NR 7.87 1.26 14.714.3R: Gravel and silt/clay drainages 8.07 0.40 3.934.3NR 8.56 0.12 9.15

Parking lot areasNorth Parking Lot #1 8.03 0.85 1.38North Parking Lot #2 7.93 1.03 1.04South Parking Lot #1 9.11 1.96 7.78South Parking Lot #2 8.31 0.50 1.32Southeast Parking Lot #1 8.28 0.44 5.57

a R samples collected within ORV trails.b NR samples collected in undisturbed areas.c Surface unit 3.5 (bedrock) was not sampled.



Jonasson, 1973), or can also occur via weathering and erosion ordepositional processes (Henke, 2009). Research is on-going to betterunderstand the geological processes that have concentrated arsenicin the northern NDRA.

Soluble arsenic concentrations are highest in the drainages(units 4.2, 4.3), and are also elevated in some of the silty units(2.1, 2.2, 2.4) and some of the sandy units (unit 1.2, 1.4, 1.5). Thesoluble arsenic at NDRA is likely explained by the overall lowpotential for leaching because of fine-grained texture (units2.1–2.4), or well-developed vesicular horizons (Av) associated withdesert pavements (units 3.1–3.4) (Young et al., 2004). Additionally,drainages in this area are commonly cemented with calcium car-bonate at shallow depths, inhibiting permeability (units 4.1–4.3).These features, combined with the arid regional climate allowsfor highly soluble arsenic minerals to be retained near the surfaceand subsequently remobilized later via dust deposition or duringbrief periods of runoff followed by evaporation.

Arsenic content at NDRA is greatest in the finer-grainedfractions. Some of the PI-SWERL dust samples (0–10 lg; PM10and 10–60 lm fractions) were as much as one order of magnitudehigher in arsenic than the soil samples (0–2 mm fraction) (Tables 2and 3). For most of the PI-SWERL samples the As concentrationswere higher in the 0–10 lm fraction than in the 10–60 lm frac-tion. Many other studies have shown that As is often preferentiallyconcentrated in finer size fractions. For example, Chen et al. (1999)reported that clay content and cation exchange capacity (CEC)

were highly correlated with As concentrations in Florida surfacesoils. Van Pelt and Zobeck (2007) quantified the chemical constit-uents of fugitive dust in the Southern High Plains of Texas and re-ported that the finer particles in the source soils contained higherconcentrations of As, although at significantly lower concentra-tions than in NDRA, ranging from 1.13 to 3.894 lg g�1.

The increased As concentrations in the finer-grain fractions sug-gests adsorption of As on clay complexes, hydrous metal oxides (Al,Mn, and Fe), carbonates, and/or concentration of As within clay orother fine grained mineral species. XRD analyses revealed that themineralogical composition of the clay (<2 lm) and silt (2–20 lm)fractions of the soil samples at NDRA is dominated by smectitewith lesser amounts of palygorskite, mica/illite, kaolinite, quartz,calcite, and gypsum. Previous studies have reported sorption ofAs onto the surface and isomorphic substitution within thestructures of both calcite (Roman-Ross et al., 2003; Di Benedettoet al., 2006) and gypsum (Roman-Ross et al., 2003; Fernández-Martínez et al., 2008). Another mechanism for concentrating Asin the fine-grained fractions of soils is As-rich clay minerals. Pascuaet al. (2005) described the occurrence of an As-rich smectite(1500–4000 ppm) in a geothermal field in Japan. These investiga-tors found minimal adsorption of As on smectite surfaces; instead,the As was predominantly dissolved within the smectite or oc-curred within mineral occlusions. As stated previously, additionalstudies are currently underway to determine the geological pro-cesses that lead to the concentration of As in the NDRA sediments.

Fig. 3. Arsenic concentrations in the Nellis Dunes Recreation Area. (a) Soil (0–2 mm); (b) emitted by PI-SWERL, 0–60 lm; (c) emitted by PI-SWERL, 0–10 lm (PM10);(d) emitted by PI-SWERL, 10–60 lm.



The differences in arsenic concentration with grain size also re-sult in different areal patterns of arsenic distribution at NDRA. TheAs concentrations in soil samples at NDRA are shown in Fig. 3a.This map was constructed by combining the soil As concentrationswith the surface unit map of NDRA presented in McLaurin et al.(2011). The As map is based on 51 data points, and the data is con-sidered representative because the size of the arsenic concentra-tion classes is very large compared to the variation in Asconcentrations within each surface unit. Evaluation of the NDRAdata shows that spatial variation of the As concentration within aunit falls within the width of the classes shown on the map (i.e.,they do not change the patterns shown on the maps). Comparisonof the soil map (0–2 mm, Fig. 3a) with the maps for airborne dust(0–60 lm, Fig. 3b; 0–10 lm, Fig. 3c; 10–60 lm, Fig. 3d) showssome differences in patterns. Arsenic concentrations in the air-borne fractions are highest in the sandy areas located in the north-west, southwest, and just north of the central sand dunes, and also,though somewhat less, in the sand dunes themselves (Fig. 3b). Acomparison between the finest (0–10 lm; PM10) and the some-what coarser dust fraction (10–60 lm) also shows differences,with the sand dunes being the most emissive areas for As in thePM10 fraction and the non-dune sand surfaces the most emissiveareas for As in the 10–60 lm fraction (Fig. 3c and d). The differ-ences between the distribution of As in the 0–10 lm and that inthe 10–60 lm fraction is significant, because PM10 is transportedin long-term suspension whereas much of the coarser dust is trans-ported in short-term suspension (Pye and Tsoar, 1990). Therefore,the PM10 fraction travels farther and may potentially affect popu-lations at greater distances from the source area compared to the10–60 lm fraction.

In NDRA there is no clear relationship between As concentra-tions and location of disturbed versus undisturbed surfaces. TheAs concentrations in associated disturbed and undisturbed samplesare the same order of magnitude for both the PM10 and 10–60 lmfractions. For the PM10 samples, As concentrations in 9 of the 16ORV trail samples were 1.56–16.18 lg g�1 higher than those mea-sured in the associated undisturbed terrain samples, and approxi-mately equal in one sample (Table 3). In the other six PM10samples, the As concentrations in the undisturbed terrain sampleswere 3.25–28.96 lg g�1 higher than those detected in the associ-ated ORV trail samples. Arsenic concentrations in the 10–60 lmfraction were 2.03–8.11 lg g�1 higher in seven of the 16 ORV trailsamples and approximately equal in three samples as comparedto the associated undisturbed terrain samples (Table 3). The As con-centrations in the other six ORV trail samples were from 1.62 to64.11 lg g�1 lower than those reported in the corresponding undis-turbed terrain samples.

5.2. Regional and national distribution of As in soils

The concentrations of As in some of the soil samples at NDRAare substantially higher (3.49–83.02 ppm) than in soils elsewherein the United States, where the average ranges from 3.6 to8.8 ppm; and throughout the world where averages range from2.2 to 25 ppm (McBride, 1994). In a 1975 study of 21 soil samplescollected in the western United States, As concentrations rangedfrom non-detectable to 97 ppm with an average concentration of6.1 ppm (Connor and Shacklette, 1975). In another study, As anal-yses were performed on 50 soils collected throughout California.Arsenic concentrations in these soils ranged from 0.6 to 11 ppm,

Fig. 4. Total As concentrations (mg kg�1) in soil samples from the United States (source: USDA-NRCS, 2010).



with an average concentration of 3.5 ppm (Bradford et al., 1996).Reheis et al., 2009 reported median As concentrations of 10 ppmin surface soil samples in southern Nevada and California. How-ever, the As concentration in five surface soil samples in that studyranged from approximately 30 to 50 ppm.

Arsenic concentration data for the entire United States is alsoavailable from a soil inventory prepared by the United StatesDepartment of Agriculture Natural Resources Conservation Service(USDA-NRCS, 2010). This database includes information on As con-centrations in more than 2800 soil samples collected at over 450different locations in the United States. Using this data, we con-structed a figure showing the reported soil As concentrations(Fig. 4). The legend of this map is the same as that shown in Fig. 3to allow for comparison between the two. Arsenic concentrationsin the USDA-NRCS database are nearly always less than 20 ppm,and rarely above 30 ppm. Comparing this data shows that As con-centrations for most surface units at NDRA are comparable withthose measured elsewhere in the United States. The exceptionsare the drainage units (4.1–4.3) and units 1.5 and 2.2, which haveanomalously high As concentrations (Table 2).

The As concentrations in soils for NDRA units 1.5 and 2.2 areamong the highest documented in the United States to date. Breitet al. (2009) reported As concentrations in the water soluble soilfraction at Franklin Lake Playa (approximately 100 km southwestof NDRA) over 400 ppm, but these values were measured at adepth of more than 50 cm below the playa surface. Arsenic concen-trations were much lower closer to the playa surface, <100 ppm ata depth of 20 cm and <50 ppm in the uppermost 10 cm. Reynoldset al. (2008) and Goldstein et al. (2007) reported water-solublesalts on the ground surface in Ash Meadows and Carson Slough,immediately north of Franklin Playa, had As concentrations as highas 600 ppm. The Reynolds et al. (2008) and Goldstein et al. (2007)

studies are the only studies performed on non-mining sites in thewestern United States that we are aware of with reported As con-centrations in soil higher than those of NDRA unit 2.2.

5.3. Arsenic in airborne dust

Few studies have analyzed As in airborne dust from natural sur-faces, and none have reported values as high as found in this study.Reheis et al. (2002) studied the contributions of different localsources to dust in the southwestern United States by comparing ele-mental analyses of samples collected from dust traps to analyses ofsamples from potential source sediments, such as alluvial and playadeposits. The average concentration of As in the <50 lm fraction ofdust samples in their study ranged from 5 to 25 ppm. The results ofthe Reheis et al., 2002 study also showed that all dust samples wereenriched in As relative to source samples, and that dusts in theOwens Valley (California) have higher concentrations of As thandust samples from other areas. The highest concentrations of As oc-curred in Owens Valley alluvium and lake-marginal deposits awayfrom the dry bed of Owens Lake. The average concentration of Asin the <50 lm fraction from the Owens Valley lake bed sampleswas reported to be 40 ppm, and 45 ppm in dust from elsewhere inOwens Valley (Reheis et al., 2002). More recently, Reheis et al.(2009) and Rojo et al. (2008) conducted a compositional study ofmodern dust and surface sediments in southernNevada and Califor-nia. These investigators reported median As concentrations of20 ppm in airborne dust (collected at a height of 2 m above the sur-face) and 10 ppm in surface soil samples. One outlier airborne dustsample had an As concentration of 50 ppm. These values contrastgreatly with those at NDRA, where, for PM10 alone, arsenic concen-tration is 290 ppm for unit 1.5 and over 160 ppm for unit 2.2(Table 3).

Fig. 5. Potential emission rate for arsenic during wind erosion. Data are for the PM10 (0–10 lm) fraction.



5.4. Arsenic hazards to health

Because arsenic has long been known to be extremely harmfulto health (Chen et al., 1992; Abernathy et al., 1999; Järup, 2003;Tseng et al., 2003; Smith et al., 2006; von Ehrenstein et al., 2007;Kozul et al., 2009b), the reported concentrations of As in the soiland PI-SWERL samples were initially compared with the USEPA Re-gion 3, 6, and 9 screening levels (SLs) for chemical contaminants inresidential soils and soil concentrations considered to be protectiveof groundwater resources (USEPA, 2010). The total As concentra-tions in all of the samples analyzed exceed the EPA’s SL of0.39 lg g�1 for As in residential soil by one to three orders of mag-nitude (Table 2).

The reported concentrations of As in all of the samples also ex-ceed the EPA SLs considered to be protective of groundwater.Although the reported As concentrations exceed the EPA SLs, thepotential risk to groundwater resources from leaching of As is con-sidered to be minimal in the Nellis Dunes area. This is becausegroundwater in the Nellis Dunes area is deep (>30 m below groundsurface), the arid climate and most soil characteristics minimizeleaching, and As is strongly sorbed to most soils (Matera and LeHécho, 2001). However, the high water-soluble concentrations ofAs are of concern because of the potential for downstream contam-ination from runoff. Lake Mead, a major drinking water source forLas Vegas, is located hydrogeologically downgradient of the NDRA.

The most important potential health hazard in this area is hu-man exposure to As through inhalation of dust. In order to betterunderstand potential risks of As in dust emissions we calculatedPM10 emission rates for As resulting from natural wind erosion inNDRA for each surface unit.Wemultiplied the emission rates for to-tal PM10 dust (Goossens and Buck, 2011b) with the As content ofthe PM10 PI-SWERL samples. PI-SWERL samples are used in the cal-culation because they represent the sediment fractions prone toemission during wind erosion. The As emission rates ranged froma low of <1 � 10�17 g cm�2 s�1 in surface unit 3.5 (bedrock and/oroutcropping petrocalcic horizons; classified as stable) to a maxi-mum of 3.67 � 10�14 g cm�2 s�1 in surface unit 1.5 (outcrops ofvery fine sand and coarse silt; classified as highly erosive). AlthoughAs concentration was not measured in dust from bedrock surfaces(unit 3.5; classified as stable), we could estimate it based on As con-centrations in dust derived from well-developed desert pavements(unit 3.1; classified as stable), which are a representation of localand regional background dust (McFadden et al., 1998; Reheiset al., 2009) and are a good proxy for dust deposited on the bedrocksurfaces. In addition to unit 1.5, emission rates for Aswere classifiedas being very erosive or erosive in the other units containing sand(1.1, 1.2, 1.3, 1.4, and 3.4) (Fig. 5). Note that these values representpotential emission rates; not actual emission rates. Nonetheless,they allow us to rank the 17 NDRA surface units according to theircapacity to emit arsenic during wind erosion (Fig. 5).

Similarly, we calculated PM10 emission rates for As resultingfrom ORV activities (Fig. 6a–c). These rates were calculated by mul-tiplying the ORV emission rates (g cm�1) for total PM10 dust (Goos-sens and Buck, 2009b) with the As concentration in the PM10 PI-SWERL samples.Here too, thenumbers represent potential emissionrates; not actual emission rates. The emission rates for each ORVactivity were highest in surface units 2.2 (silt/clay with gravel; clas-sified as highly erosive) and3.1 (desert pavements; classified as veryerosive). The lowest emission rates occur in surfaceunits 1.1 (unveg-etated dunes; classified as stable) and 3.5 (bedrock; classified as sta-ble). The As emission rates ranged from <1 � 10�9 g cm�1 to1.89 � 10�6 for dirt bikes, <1 � 10�9 to 3.71 � 10�7 g cm�1 for dunebuggies, and <1 � 10�9 to 2.12 � 10�6 g cm�1 for four-wheelers.These rates are calculated for a driving speed of 30 km h�1, whichis a conservative, but representative average for the NDRA. Theaverage emission rate for a dirt bike, dune buggy, and four-wheeler

at 30 km h�1 is 1.24 � 10�7 g cm�1. At higher driving speeds,emission rates are considerably higher. For example, for an average

Fig. 6. Potential emission rate for arsenic during ORV activity: (a) Dirt bike; (b)dune buggy; (c) four-wheeler. Data are for the PM10 (0–10 lm) fraction and for anaverage driving speed of 30 km h�1.



vehicle (average of a dirt bike, dune buggy, and four-wheeler), theemission rate is 1.89 times greater at 40 km h�1, and at 50 km h�1

more than triples (3.27 times greater).The results of this study present an interesting dilemma for

development of a management plan for the NDRA. Dust emissionsat NDRA occur from both ORV activity and wind erosion. Previ-ously, McLaurin et al. (2011) used dust emission data alone to sug-gest a management plan that directed ORV activity to stay withinthe sandy surface units (1.1–1.5) and avoid the silt/clay areas withgravel, desert pavements and the gravel silt/clay drainages (surfaceunits 2.2, 3.1, and 4.3). This suggestion was based on dust emissiondata that showed that ORV-generated dust emission is lowest inthe sandy surfaces and highest in the fine silt and clay areas, thedesert pavements and the silty drainages. However, the As datapresented here indicate that in this case, dust emission data aloneare not enough to make a sound management plan. When includ-ing arsenic with both wind and ORV-generated dust emissions, wefind that the sandy areas emit the highest amounts of As annuallybecause they comprise the zones that are most susceptible to winderosion (Goossens and Buck, 2011b). When driving in these zonesduring wind erosion, riders are exposed to increased amounts of Asthat could potentially be inhaled. Therefore, until more is knownabout actual human exposure and health risk at NDRA, peopleshould consider avoiding these sandy areas and areas downwindduring windy conditions. These conclusions are also supportedby the maps in Fig. 3, which show that for the fractions most sub-ject to inhalation (especially PM10), the sand areas have the high-est concentrations of As in emitted dust. People should consideravoiding dust emitted from ORV driving on units 2.2 and 3.1 be-cause this activity also generates high As emissions.

The potential health effects of the dust generated during ORVuse at the NDRA are not known because emissions vary greatlydepending on what type of vehicle is used, how intensely an areais driven, and whether riders drive closely behind one another.Information regarding the exact number of drivers, the length ofeach drive and the specific routes followed is also unknown (Goos-sens and Buck, 2009b). It is also important to note that the grainsize distribution of the PI-SWERL released dust does not necessar-ily correspond to that of ambient dust. The PI-SWERL dust is locallyeroded dust whereas ambient dust also contains particles thatwere eroded elsewhere and are in transport. Archived ambientdust samples that were previously collected at NDRA using BigSpring Number Eight (BSNE) passive samplers will be analyzed inthe future to evaluate whether As concentrations are similar tothose in the PI-SWERL samples. In order to determine the actualexposures, monitoring of personal dust exposure must be per-formed on ORV users under different driving conditions, and onother visitors at the site.

6. Conclusions

Elevated arsenic concentrations were measured in soil (up to>80 ppm) and airborne dust samples (up to >300 ppm) from theNellis Dunes Recreation Area. To date, we are not aware of anyother studies that have reported As concentrations in dust fromnatural surfaces as high as those found in the NDRA. The highestconcentrations are associated with two deposits of the MuddyCreek Formation (surface units 1.5 and 2.2) in the northern portionof NDRA, and in the drainages. Significant water-soluble As is pres-ent in several surface units, and runoff is likely concentrating As inthe drainages. The highest concentrations of arsenic occur in theairborne dust, especially in the PM10 fraction, and may be as muchas one order of magnitude higher than the soil samples. The arealdistribution of As varies according to grain size, but the highest Asconcentrations occur mostly in the western portions of NDRA. In

the PM10 fraction As is greatest in the sandy units (1.2, 1.3, 1.5),two of silty units (2.1, 2.2) and all of the drainages (4.1–4.3).

The most important potential health hazard in this area is hu-man exposure to As through inhalation of dust. Emission ratesfor As resulting from both natural wind erosion and ORV activitywere calculated for all 17 surface unit in the NDRA. For PM10, dur-ing windy conditions, the sandy surfaces (units 1.1–1.5, and 3.4)have the highest emission rates for As. In contrast, ORV-generatedemission rates for As are highest on unit 2.2 (silt/clay with gravel)and desert pavements (unit 3.1). Arsenic emission rates vary withtype and speed of ORV: four-wheelers have the highest emissionrates, followed by dune buggies and dirt bikes. Emission rates forAs nearly double when comparing driving speeds of 30 km h�1,to 40 km h�1 and at 50 km h�1 more than triple.

Currently, there are no EPA regulations in the United States forAs in recreational settings. To accurately evaluate the potentialhealth effects, monitoring of personal dust exposure must be per-formed on ORV users and other site visitors. The actual concentra-tion of As in the air must be quantified, since that is what existingstandards for As exposure in the workplace are based upon. A site-specific human health risk assessment must also be performed tomodel the biological responses to all of the constituents in NDRAdust. However, until the potential risk to human health is betterdefined, site visitors should consider avoiding the sandy areasand downwind areas during windy conditions, and avoid exposureto ORV-generated dust on units 2.2 and 3.1. Finally, this researchindicates that a better understanding of the geochemical complex-ity of natural desert surfaces and their response to natural andanthropogenic disturbances is needed.

Acknowledgements

The U.S. Bureau of Land Management (BLM) funded this projectthrough a Southern Nevada Public Land Management Act(SNPLMA) Conservation Initiative, and granted permission for allfieldwork in the Nellis Dunes Recreation Area. Lisa Christianson(BLM) provided administrative assistance throughout the project.The authors thank Rebecca Burt and Mike Wilson with the NaturalResources Conservation Service for providing the NRCS arsenicdata. The authors also thank Tom Gill for sharing his expertise inchemical analyses, and G. Breit for discussions on arsenic behavior.

The views and conclusions contained in this document arethose of the authors and should not be interpreted as representingthe opinions or policies of the U.S. Government. Mention of tradenames or commercial products does not constitute their endorse-ment by the U.S. Government.

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Arsenic concentrations in dust emissions from wind erosion and …csub.edu/~dbaron/nellis.pdf · 2019-12-04 · to Las Vegas and the surrounding urban area, a study was under-taken