ORIGINAL PAPER
Spatial patterns of tungsten and cobalt in surface
dust of Fallon, Nevada
Paul R. Sheppard Æ Robert J. Speakman Æ
Gary Ridenour Æ Michael D. Glascock Æ
Calvin Farris Æ Mark L. Witten
Received: 28 March 2006 / Accepted: 26 January 2007

 Springer Science+Business Media B.V. 2007
Abstract Spatial patterns of tungsten and cobalt
are described for surface dust of Fallon, Nevada,
where a cluster of childhood leukemia has been
ongoing since 1997. In earlier research, airborne
tungsten and cobalt was shown to be elevated in
total suspended particulates in Fallon. To fine-
tune the spatial patterns of tungsten and cobalt
deposition in Fallon, surface dust was collected in
a grid pattern within as well as outside of Fallon
to establish background concentrations of metals.
In surface dust, tungsten and cobalt show sharp
peaks (934 ppm and 98 ppm, respectively) within
Fallon just north of highway 50 and west of
highway 95. These two peaks overlap spatially,
and given the grid pattern used for collecting
surface dust, the source area of these two
airborne metals can be pinpointed to the vicinity
of hard-metal industry located north of highway
50 and west of highway 95. Fallon is distinctive in
west central Nevada because of high airborne
tungsten and cobalt particulates, and given its
cluster of childhood leukemia, it stands to reason
that additional biomedical research is in order to
test directly the leukogenicity of combined air-
borne tungsten and cobalt particulates.
Keywords Fallon 
 Nevada 
 Childhood
leukemia 
 Tungsten 
 Cobalt 
 Surface dust
chemistry
Introduction
Spatial patterns of tungsten and cobalt are
described for surface dust of Fallon, Nevada
(Fig. 1), where a cluster of childhood leukemia
has been ongoing since 1997. Officially, 16 cases
of childhood leukemia were diagnosed from 1997
to 2002 inclusive (Expert Panel 2004), and one
additional case was reported in December 2004
(Nevada State Health Division 2004). Given
Fallon’s pediatric population of ~2,500 children
up to 19 years in age (U.S. Census 2000) and a
national expected rate of childhood leukemia of
P. R. Sheppard (&) 
 C. Farris
Laboratory of Tree-Ring Research, University of
Arizona, Tucson, AZ 85721, USA
e-mail: sheppard@ltrr.arizona.edu
R. J. Speakman
Museum Conservation Institute, Smithsonian
Institution, Suitland, MD 20746, USA
G. Ridenour
625 W. Williams Ave., Suite B, Fallon,
NV 89406, USA
M. D. Glascock
Research Reactor Center, University of Missouri,
Columbia, MO 65211, USA
M. L. Witten
Department of Pediatrics, University of Arizona,
Tucson, AZ 85721, USA
123
Environ Geochem Health
DOI 10.1007/s10653-007-9085-1
4.1 cases per 100,000 children up to 19 years in
age per year (US NCI 2003), the expected rate of
childhood leukemia for Fallon should be only one
case every 10 years.
This cluster, deemed ‘‘one of the most unique
ever reported’’ (Steinmaus et al. 2004), has
prompted extensive research in an effort to
determine if an environmental cause might be
responsible. Prior research has included drinking
water (Moore et al. 2002), jet fuel (US ATSDR
2002), pesticides (US CDC 2003a), surface water
(U.S. ATSDR 2003a), outdoor air (US ATSDR
2003b), surface soil and indoor dust (US ATSDR
2003c), potential lingering effects of underground
nuclear bomb testing in the area (Seiler 2004),
and groundwater (Seiler et al. 2005). Although
few definitive conclusions have been made, sig-
nificantly elevated airborne tungsten and cobalt
levels have been identified in airborne particu-
lates within Fallon relative to comparison towns
(Sheppard et al. 2006) and in lichens within
Fallon compared to outlying desert areas (Shepp-
ard et al., 2007). Toxicological research on effects
of tungsten and cobalt on leukemia has been
recommended, as has additional environmental
research in Fallon to improve understanding of its
airborne tungsten and cobalt.
An additional environmental monitoring tech-
nique that is applicable to Fallon is surface dust
chemistry, the measurement and interpretation of
element concentrations in fine sediments that
accumulate on outdoor surfaces. Surface dust is
an ideal indicator of atmospheric deposition,
especially for heavy metals. Surface dust is easy
to collect, so large spatial arrays of samples can be
obtained quickly. Surface dust reflects the chem-
ical composition of recent deposition, on the
order of days to weeks depending on precipitation
frequency. By collecting surface dust in a grid
pattern, it is possible to map differing concentra-
tions of atmospheric deposition of heavy metals
and thereby pinpoint sources of unusual airborne
metals (Mielke et al. 1999; Lee et al. 2006).
Paired studies of surface dust and total suspended
particulates can be particularly fruitful for con-
firming airborne chemistry and identifying spatial
patterns of metals (Muskett and Jones 1980;
Boudissa et al. 2006). Many case studies exist
worldwide of using surface dust chemistry to
quantify atmospheric loading of heavy metals
and/or identify spatial patterns of deposition
(Harrison 1979; Duggan 1984; Fergusson and
Ryan 1984; Thornton et al. 1985; Rapsomanikis
and Donard 1985; Davies et al. 1987; Tam et al.
1987; Wong and Mak 1997; Benin et al. 1999;
Reid et al. 2003; Clark et al. 2005). Accordingly,
surface dust chemistry in and around Fallon was
used to establish the spatial patterns of tungsten
and cobalt deposition, with the objective of
pinpointing the source or sources of elevated
airborne tungsten and cobalt particulates within
Fallon.
Methods
Fallon is a small, rural farming community
(Greater Fallon Area Chamber of Commerce
2005) located in west central Nevada (Fig. 1). Its
climate is cool to mild and dry, with a mean
annual temperature and precipitation of 10.7C
and 127 mm, respectively, as typified from mete-
orological data from Fallon (monthly data from
1931 to 2004 obtained online from the National
Climatic Data Center, NOAA 2006). Along with
service industries and small businesses, Fallon has
Fallon
Carson City
NEVADA
100 km
Fig. 1 Map of Nevada showing the location of Fallon
Environ Geochem Health
123
an industrial facility that carries out hard-metal
metallurgy, including tungsten carbide and cobalt
(Harris and Humphreys 1983). This hard-metal
facility has been suggested as a candidate source
of tungsten within Fallon generally (Reno Gaz-
ette-Journal, 5 February 2003) and more specif-
ically for elevated airborne tungsten and cobalt in
total suspended particulates of Fallon (Sheppard
et al. 2006).
The strategy for surface dust chemistry was to
map concentrations of elements in outdoor dust
deposits within and around Fallon. Fieldwork
took place in March, 2005, at which time Fallon
had not experienced a substantial rain storm for
three weeks (daily data obtained online from the
National Climatic Data Center, NOAA 2006),
allowing surface dust to accumulate for that
length of time. In total, 125 surface dust samples
were collected along a grid pattern within Fallon
as well as outside of Fallon to establish back-
ground concentrations of metals (Amini et al.
2005; Rimmer et al. 2006; Biasioli et al. 2006).
Within Fallon, the grid cell length was 0.5 km,
which maximized the sampling density inside the
town. Outside of Fallon, the grid cell length was
relatively coarser (2.0–5.0 km), which maximized
the spatial extent of sampling away from Fallon.
The high density of sampling points and large
overall spatial coverage throughout Fallon and
outside of the town was intended to account for
variation in surface dust chemistry that might
be due to wind and/or unusual distribution of
the population. Geographic coordinates were
recorded for each sample to facilitate spatial
analysis of metal concentrations across Fallon and
the surrounding area and to map distributions of
metals.
Surface dust samples were collected mostly
from paved surfaces using a clean brush and clean
paper as a dustpan (Harrison 1979; Duggan 1984;
Thornton et al. 1985; Harrop et al. 1990). Sam-
ples were stored in clean polyethylene vials.
Outside of Fallon, where surfaces are not paved,
samples were collected from undisturbed desert
and therefore contained some coarse sand. In all
cases, samples were sieved to isolate the fine
fraction (<0.150 mm) for analysis to make them
comparable. Sieved samples were transferred to
clean, glass, screw-cap vials and oven-dried at
100C for 24 h. Coarse and fine fractions from
each sample are archived in the event that future
analyses are necessary.
Two aliquots of each sample were prepared
for analysis by instrumental neutron activation
analysis (INAA). Approximately 150 mg of
powder was weighed into clean high-density
polyethylene vials used for short irradiations. At
the same time, 200 mg of each sample was
weighed into clean high-purity quartz vials used
for long irradiations. Individual sample weights
were recorded to ±0.01 mg. Both vials were
sealed prior to irradiation. Certified standard
reference materials of SRM-1633a (coal fly ash),
SRM-1648 (urban particulate matter), and
SRM-688 (basalt rock) were similarly prepared,
as were quality-control samples (e.g., standards
treated as unknowns) of SRM-1648 (urban
particulate matter), SRM-278 (obsidian rock)
and Ohio Red Clay (a standard developed for
in-house applications).
INAA of sediments, which consists of two
irradiations and a total of three gamma counts,
constitutes a superset of procedures used at most
INAA laboratories (Glascock 1992; Neff 1992,
2000). A short irradiation was carried out through
a pneumatic tube irradiation system (Glascock
1992). Samples in polyvials were sequentially
irradiated, two at a time, for 5 s by a neutron
flux of 8 · 1013 n cm–2 s–1. The 720-s count
yielded gamma spectra containing peaks for nine
short-lived elements: aluminum, barium, calcium,
dysprosium, potassium, manganese, sodium, tita-
nium, and vanadium. For the second irradiation,
samples were encapsulated in high-purity quartz
vials and were subjected to a 12-h irradiation at a
neutron flux of 5 · 1013 n cm–2 s–1. This long
irradiation is analogous to the single irradiation
utilized at most other laboratories. After the long
irradiation, samples decayed for five days and
were then counted for 1,800 s (the middle count)
on a high-resolution germanium detector coupled
to an automatic sample changer. The middle
count yielded determinations of eight medium-
half-life elements: arsenic, lanthanum, lutetium,
neodymium, samarium, tungsten, uranium, and
ytterbium. After an additional three-week decay,
a final count of 10,000 s was carried out on
each sample. The latter measurement yielded 17
Environ Geochem Health
123
long-half-life elements: cerium, cobalt, chromium,
cesium, europium, iron, hafnium, nickel, rubid-
ium, antimony, scandium, strontium, tantalum,
terbium, thorium, zinc, and zirconium. Data were
standardized using the standard-comparator
method in which the concentrations of the
unknown samples (i.e., dust samples) were deter-
mined by ratioing the measured activities per unit
weight of the unknown sample to those for a
reference standard (SRM-1633a, SRM-1648, and
SRM-688) with known concentrations. The med-
ian recovery from the urban particulate matter
SRM for all measured elements with a certified
value was 96%, indicating excellent performance
of INAA on surface dust. Based on the analyses
of thousands of separate quality control measure-
ments made during the past 15 years, the preci-
sion of INAA for this matrix is generally better
than 5% for most elements (with the exception of
As, Nd, Ni, Sr, Zn, and Zr).
Results
Most of the elements measured in surface dust
show little variability across sampling points
within and around Fallon, with coefficients of
variation (standard deviation standardized to the
mean, Sokal and Rohlf 1981) of less than 50%
(Fig. 2). This establishes a background pattern
with little spatial variability in atmospheric depo-
sition of metal particulates across the greater
Fallon area. In sharp contrast to this pattern of
little spatial variability, tungsten shows large
spatial variability, with a coefficient of variability
of 732%. After tungsten, cobalt has a coefficient
of variability of 77% followed by arsenic at 71%.
Tungsten and cobalt have several sampling points
with high values, but arsenic has only one high
value.
Tungsten and cobalt show sharp peaks
(934 ppm and 98 ppm, respectively) within Fallon
just north of highway 50 and west of highway 95
(Fig. 3). Spatially, these two peaks overlap
exactly, with the same sampling location having
the highest value for both metals. Adjacent
sampling locations in north-central downtown
Fallon also have notably high concentrations of
tungsten and cobalt. The other sampling locations
in and around Fallon have concentrations of
<10 ppm tungsten and <15 ppm cobalt, which
establishes natural background levels for these
two metals in the area. These background values
are roughly similar to typical crustal values of
1.2 ppm for W and 22 ppm for Co (Krauskopf
1995).
Discussion
Previous environmental research related to the
cluster of childhood leukemia in Fallon, Nevada,
has noted elevated tungsten. Tungsten has been
high in drinking water (US CDC 2003b), in
groundwater (Seiler et al. 2005), and in blood
and urine samples of residents (US CDC 2003b).
However, a consensus has been that tungsten is
not unusual enough in Fallon to merit additional
concern related to the cluster of childhood
leukemia there. Tungsten is ubiquitous through-
out northern Nevada (Stager and Tingley 1988),
and elevated tungsten in and around Fallon has
been suggested to be a result of the natural
geology of the region (Expert Panel 2004; Pardus
et al. 2005).
However, the high peak values of tungsten and
cobalt in the surface dust of central Fallon are not
likely to be a result of tungsten and cobalt found
in rocks and/or soils of the area. Rocks collected
within Fallon as well as from desert sites around
Fallon show normal concentrations of tungsten
and cobalt (Sheppard et al., 2007). Soils of
residential Fallon and nonresidential outlying
0
200
400
600
800
E
u
S
r
R
b
S
m
C
e
L
a
S
c
N
d
T
b
Y
b
F
e
C
r
L
u
C
s
Z
r
H
f
U Z
n
T
h
T
a
S
b
A
s
C
o
W
Element
)
%(
 
n
oit
air
aV
 f
o
 t
n
eici ff
e
oC
Fig. 2 Coefficients of variation (standard deviation stan-
dardized to the mean, Sokal and Rohlf 1981) of elements
measured in surface dust of Fallon. For all elements,
n = 125. Bromine, molybdenum, and nickel are not
included here because they had many values below the
detection limits
Environ Geochem Health
123
desert areas are also not notable for high levels of
any metals, presumably including tungsten and
cobalt (US ATSDR 2003c). Alternatively, the
peak sampling location coincides spatially with
the hard-metal facility located within Fallon,
which supports the suggestion that the hard-
metal facility in Fallon be considered as a
candidate source of Fallon’s elevated airborne
tungsten and cobalt particulates (Sheppard et al.
2006, 2007).
Fig. 3 Surface dust
concentrations of (a)
tungsten and (b) cobalt
Environ Geochem Health
123
Conclusions
Fallon is distinctive from nearby comparison
towns in Nevada as well as from outlying desert
areas because of significantly elevated tungsten
and cobalt in total suspended particulates and in
lichens (Sheppard et al. 2006, 2007). This present
study fine-tunes the spatial patterns of tungsten
and cobalt using surface dust within Fallon. Ele-
vated levels of these two metals, which are
otherwise unrelated geologically in Nevada, sug-
gest a local point source instead of widespread co-
occurrence. Given the grid pattern used for
collecting surface dust, the source area of these
two metals can be pinpointed to the area of
the hard-metal facility that is located just north
of highway 50 and west of highway 95. This
area merits direct monitoring to determine the
exact source of airborne tungsten and cobalt
particulates.
It cannot be concluded from only environmen-
tal data that elevated airborne tungsten and/or
cobalt cause childhood leukemia. Such a connec-
tion requires biomedical research. Nonetheless,
given that childhood leukemia in Fallon is the
‘‘most unique cluster ever reported’’ (Steinmaus
et al. 2004) and that Fallon is distinctive because
of elevated airborne tungsten and cobalt partic-
ulates, it stands to reason that additional biomed-
ical research is in order to test directly the
leukogenicity of airborne tungsten and cobalt.
Acknowledgements Angelika Clemens assisted with
fieldwork, and Nicole Little, Tessa Schut, and Jon Dake
assisted with sample preparation and analysis of surface
dust samples. INAA measurements were conducted at the
University of Missouri Research Reactor Center. This
project was supported in part by the Gerber Foundation
and the Cancer Research and Prevention Foundation,
neither of which is otherwise responsible for any content of
this paper.
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