**Exposure to Tungsten in Three Nevada Communities**

Report Submitted to the Nevada State Health Division

June 2003

# 

# INTRODUCTION

In March and April 2002, the Health Studies Branch (HSB), Division of
Environmental Hazards and Health Effects, National Center for
Environmental Health (NCEH), Centers for Disease Control and Prevention
(CDC), assisted the Nevada State Health Division (NSHD) in conducting a
cross-sectional exposure assessment of selected environmental
contaminants in Churchill County, Nevada^1^. NSHD and CDC undertook the
assessment because of a statistically significant increase in the number
of cases of childhood acute lymphocytic and myelocytic leukemia. A key
finding of this exposure assessment was that approximately 68% of the
study participants had urine levels of tungsten above the 95^th^
percentile of the National Health and Nutrition Examination Survey
(NHANES) reference population. However, there was no difference in
tungsten levels between families with children with leukemia and
families without children with leukemia. This finding raised the
question of whether these higher levels are unique to the Churchill
County community, or if tungsten exposures similar to those of Churchill
County occur in other communities in Nevada.

Churchill County is an agricultural area irrigated by water from the
Carson River. Groundwater in the Churchill County area also principally
derives from Carson River water. Tungsten concentrations in Carson River
water reportedly range from 1.5 to 23 μg/L.^2^ The Carson River
watershed contains numerous tungsten mines and prospects.^3^
Geologically, tungsten is associated with intrusive granitic rocks. ^3^
Extensive outcrops of these rocks are in the headwaters of the Carson
River. Drinking water in Churchill County is supplied by domestic and
public supply wells.

Because research on tungsten is limited, especially regarding health
effects and urinary levels of concern, the NSHD requested assistance
from CDC in conducting a cross-sectional exposure assessment of tungsten
in three other Nevada communities.

## 

## Objectives 

The objective of this investigation was to assist state and local health
officials in assessing the level of exposure to tungsten in three
communities of Nevada, to determine whether the high levels of tungsten
are unique to residents of Churchill County, Nevada.

**METHODS**

**Study Design**

This investigation employed a cross-sectional survey design to assess
human exposure to tungsten. We administered questionnaires and collected
urine, water, dust, and soil samples to test for tungsten.

**Study Location**

The NSHD chose the communities of Lovelock, Yerington, and Pahrump,
Nevada, on the basis of these cities' hydrogeology and history of
tungsten mining. None of our sample locations have any tungsten
processing plants.

Lovelock is hydrologically similar to Churchill County. It is an
agricultural area irrigated by water from the Humboldt River.
Groundwater in the Lovelock area principally derives from Humboldt River
water. Tungsten concentrations in Humboldt River water are unknown. The
Humboldt River watershed contains numerous tungsten mines and prospects.
^3^ Like the Churchill County area, outcrops of granitic rocks are in
the Humboldt River basin. The potential for tungsten to be found in
Lovelock groundwater was considered high. However, all drinking water in
the Lovelock area is supplied by a few adjacent wells located north of
Lovelock near Oreana. Collecting numerous samples of tap water derived
from these wells would not have provided evidence about the range of
tungsten concentrations in Lovelock-area groundwater.

Yerington is hydrologically similar to Churchill County. It is an
agricultural area irrigated by water from the Walker River. Groundwater
in the Yerington area derives from Walker River water. Tungsten
concentrations in the Walker River water and its tributaries reportedly
range from 0.15 to 15 μg/L. ^2,4^ Tungsten concentrations in water from
nine wells in the Walker River basin ranged from 8 to 128 μg/L and a
spring in the basin contained over 300 μg/L. ^4^ No tungsten mines are
in the Yerington area. ^3^ Like the Churchill County area, outcrops of
granitic rocks are in the Walker River basin upstream of Yerington. The
potential for tungsten to be found in Yerington groundwater was
considered high, and like Churchill County, Yerington drinking water is
supplied by domestic and public supply wells.

Pahrump is not hydrologically similar to Churchill County. No perennial
streams flow through the basin. Pahrump is a rapidly growing suburban
area and is not presently an agricultural area. During the 1960s,
however, cotton was cultivated using groundwater supply for irrigation.
No tungsten mines are in the Pahrump area, ^3^ nor are there outcrops of
granitic rocks. The potential for tungsten in Pahrump groundwater was
considered low. Like Churchill County, Pahrump drinking water is
supplied by domestic and public supply wells.

**Sampling and Data Collection**

We collected data during February 13-21 and March 3-7, 2003. We selected
a geographically random sample from each study region. We recruited 30
households from Yerington and Pahrump, and 11 households from Lovelock.
The eligibility criteria for household enrollment were residence in the
city for at least 1 month before the interview and presence of one adult
and one child under 18 years of age who consented to participate in the
study. We recruited a total of 141 participants (Table 1). Each
consenting study participant submitted a spot urine sample for the
analysis of tungsten metabolites and responded to a questionnaire
detailing demographics and relevant exposures.

**Table 1: Sample Location Sites and Number of Participants for**

**Nevada Tungsten Assessment, 2003**

  ------------------------ ---------------------------- ------------------
  **Location**             **Households Recruited**     **Participants**

  Lovelock                 11                           21

  Pahrump                  30                           60

  Yerington                30                           60

  **Totals**               **71**                       **141**
  ------------------------ ---------------------------- ------------------

We collected a tap-water sample, a floor-dust sample, and a yard-soil
sample from each household. These samples were analyzed for their
tungsten content. The water samples were analyzed by the United States
Geological Survey (USGS), National Water Quality Laboratory, Lakewood,
Colorado, and the soil and dust samples were analyzed by DataChem
Laboratories, an Environmental Protection Agency (EPA)-certified
laboratory in Salt Lake City, Utah. The types of samples, their
collection procedures, and their analytical parameters were determined
on the basis of recommendations by the Agency for Toxic Substances and
Disease Registry, the Nevada Division of Environmental Protection, the
USGS, and the EPA. To maximize comparability, the sampling protocol used
was identical to that used in the Churchill County study. ^5^ The exact
location of each participating household was determined using geographic
positioning systems.

**Results**

Our study participants ranged in age from 2 to 65 years. The average age
for children (\< 18 years) was 9.4 years and for adults (\>18 years),
38.9 years. Of our adult participants, 75% were female; 73% of
participating children were male.

We compared levels of urinary tungsten and environmental tungsten
between our study populations, the Churchill County study participants,
and national reference levels, where applicable. We determined the
geometric mean of tungsten levels in urine and water (Table 2).

**Table 2: Geometric mean tungsten levels for urine and water samples**

+-----------------+------------+------------+-----------+-------------+
| Location        | Geometric  |            |           |             |
|                 | mean       |            |           |             |
|                 | tungsten   |            |           |             |
|                 | level      |            |           |             |
|                 |            |            |           |             |
|                 | (95%       |            |           |             |
|                 | confidence |            |           |             |
|                 | interval)  |            |           |             |
+-----------------+------------+------------+-----------+-------------+
|                 | Urine      |            |           | Tap Water   |
|                 | (µg/L)     |            |           | (µg/L)      |
+-----------------+------------+------------+-----------+-------------+
|                 | Adults     | Children   | Total     |             |
+-----------------+------------+------------+-----------+-------------+
| Lovelock        | 0.38       | 0.62       | 0.48      | 0.11        |
|                 |            |            |           |             |
|                 | (          | (          | (0        | (0.07-0.19) |
|                 | 0.33-0.45) | 0.50-0.76) | .34-0.68) |             |
+-----------------+------------+------------+-----------+-------------+
| Pahrump         | 0.4        | 0.56       | 0.51      | 0.04        |
|                 |            |            |           |             |
|                 | (0.38 -    | (0.48 --   | (0        | (0.02-0.06) |
|                 | 0.53)      | 0.66)      | .37-0.69) |             |
+-----------------+------------+------------+-----------+-------------+
| Yerington       | 1.04       | 1.18       | 1.11      | 3.32        |
|                 |            |            |           |             |
|                 | (          | (          | (0        | (1.82-6.04) |
|                 | 0.84-1.30) | 1.00-1.39) | .97-1.27) |             |
+-----------------+------------+------------+-----------+-------------+
| Churchill       | 0.81       | 2.31       | 1.19      | 4.66        |
| County          |            |            |           |             |
|                 | (0.56 -    | (1.66 -    | (0        | (2.98-7.30) |
|                 | 1.16)      | 3.22)      | .89-1.59) |             |
+-----------------+------------+------------+-----------+-------------+
| National        | [\>20      | [6--11     | 0.08      | N/A         |
| average\*       | yrs]{.     | yrs]{.     |           |             |
|                 | underline} | underline} | (0        |             |
|                 |            |            | .07-0.09) |             |
|                 | 0.07       | 0.15       |           |             |
|                 |            |            |           |             |
|                 | (          | (          |           |             |
|                 | 0.07-0.08) | 0.12-0.18) |           |             |
|                 |            |            |           |             |
|                 |            | [12-19     |           |             |
|                 |            | yrs]{.     |           |             |
|                 |            | underline} |           |             |
|                 |            |            |           |             |
|                 |            | 0.10       |           |             |
|                 |            |            |           |             |
|                 |            | (          |           |             |
|                 |            | 0.09-0.12) |           |             |
+-----------------+------------+------------+-----------+-------------+

\* From the *Second National Report on Human Exposure to Environmental
Chemicals*^6^, based on an NHANES reference population.

**Tungsten Levels in Urine**

All three of our study locations had geometric mean levels of urinary
tungsten at or above the 95^th^ percentile of the level established by
the NHANES reference population (0.48 µg/L). ^6^ Pahrump and Lovelock
had statistically identical levels, at 0.51 µg/L and 0.48 µg/L, while
Yerington had levels significantly higher than both Lovelock and Pahrump
(1.11 µg/L, p = .0001). Yerington's overall urinary tungsten levels were
similar to those in Churchill County.

Children had consistently higher urinary tungsten levels than adults
across all study populations.

**Tungsten Levels in Water**

Tap water samples were collected in each study household because water
is the most likely source of tungsten exposure in these communities.
Tungsten levels in water samples collected at study participants' homes
differed significantly by city. Pahrump had the lowest average level
(0.04 µg/L, range \<0.01-1.0 µg/L), followed by Lovelock (0.11 µg/L,
range 0.02-0.2 µg/L), and Yerington (3.32 µg/L, range 0.01-40 µg/L). For
comparison, the mean for Churchill County was 4.66 µg/L (range
\<0.25-336.0 µg/L). Each city's water tungsten level differed
significantly (p \< 0.0001) from that of the other cities probably
because of hydrogeologic differences between the water sources of each
city. The geometric mean for both Lovelock and Pahrump's tungsten levels
in water were significantly lower than Churchill County's (p \< 0.0001),
and Yerington's level did not differ significantly from Churchill
County's.

Analysis of the relation between urine tungsten and water tungsten
levels revealed a mixed picture. In Lovelock and Pahrump, we found no
significant relation between the two levels, although we did find a
correlation between urine and water tungsten levels in Yerington
(Pearson correlation = 0.54; p \<0.0001). This finding is difficult to
interpret because we did not collect detailed information about
individual water consumption patterns.

**Soil and Dust Tungsten Levels**

Soil and dust samples were collected at each participant's house to
further investigate other potential routes of exposure to tungsten.
Analysis of the first 60 samples identified only six samples with
detectable levels of tungsten. Because of the high limit of detection of
this analytic method (50 µg/g) and the low number of samples with
detectable levels of tungsten (\<10%), no other samples were analyzed.

**Conclusions**

The primary objective of the study was to assess the level of exposure
to tungsten in three Nevada communities, for the purpose of determining
whether Churchill County, Nevada, is unique in the high levels of
tungsten among its residents.

Our findings demonstrate that, like Churchill County, tungsten
concentrations in urine of residents of all three of the study
communities were at or above the 95^th^ percentile of the level
established by the NHANES reference population. One city, Yerington, had
levels of tungsten in urine and water samples that were statistically
similar to Churchill County's samples. These findings are likely the
result of Nevada's geology, which is rich in tungsten. The NSHD has not
identified any excess leukemia in the three communities we studied.

Exposure to tungsten in Churchill County does not appear to be unique
when compared to other communities in Nevada. People living in
communities having similar water sources and geologic formations to
Churchill County may be expected to have tungsten exposures well above
those reported as national reference levels from the NHANES survey.

Tungsten has been nominated to the National Toxicology Program (NTP) for
additional toxicologic testing.

[For further information please contact:]{.underline}

[General Information:]{.underline} [Water Sampling and Analysis
Questions:]{.underline}

George Luber, PhD, or Ralph Seiler, Ph.D.

Carol Rubin DVM, MPH U.S. Geological Survey

Health Studies Branch 333 W. Nye Lane

Division of Environmental Hazard and Carson City, NV 89706

Health Effects Tel: (775)887-7674

National Center for Environmental Health Fax: (775)887-7629

Centers for Disease Control and Prevention

1600 Clifton Rd., MS E-23

Atlanta, GA 30333

Tel: (404) 498-1340

Fax: (404) 498-1355

[References Cited]{.underline}

1.  CDC. Churchill County (Fallon), Nevada Exposure Assessment, 2003.
    Available at: <http://www.cdc.gov/nceh/clusters/Fallon/study.htm>
    \[cited June 12, 2003\].

2.  Johannesson KH, Lyons WB, Graham EY, and Welch KA. Oxyanion
    concentrations in eastern Sierra Nevada Rivers---3 Boron,
    molybdenum, vanadium, and tungsten: Aquatic Geochemistry
    2000;6:19-46.

3.  Stager H.K, Tingley JV. Tungsten deposits in Nevada. Nevada Bureau
    of Mines and Geology Bulletin 1988;105:256.

4.  Benson LV, Spencer RJ. A hydrochemical reconnaissance study of the
    Walker River Basin, California and Nevada. U.S. Geological Survey
    Open-File Report 1983; 83-740:53

5.  Biaggi A J, Rosse HL, Johnson JA. Environmental Sampling Plan,
    Churchill County, Nevada. 2001. Nevada Division of Environmental
    Protection, 2001.

6.  CDC. Second National Report on Human Exposure to Environmental
    Chemicals. Atlanta; USDHHS, CDC, National Center for Environmental
    Health; 2003.