&EPA
United States
Environmental Protection
Agency
Technical Fact Sheet -
Tungsten
January 2014
TECHNICAL FACT SHEET- TUNGSTEN
At a Glance
* Hard, steel-gray to white solid.
* Highest melting point among
metals and is a good conductor
of electricity.
* Typically used in welding, oil-
drilling, electrical and aerospace
industries.
* Low solubility in water and high
sorption (soil/water distribution)
coefficients at low to neutral pH
levels.
* Questions are being raised
about tungsten's environmental
stability.
* Exposure may cause eye and
skin irritation, cough, nausea,
diffuse interstitial pulmonary
fibrosis and changes in blood.
* No federal drinking water
standard established.
* Exposure limits set by the
National Institute for
Occupational Safety and Health
(NIOSH), Occupational Safety
and Health Administration
(OSHA) and the American
Conference of Governmental
lndustrialHygienists(ACGIH).
»»» Treatment methods for tungsten
in environmental media are
currently under development.
Methods under investigation
include electrokinetic soil
remediation and
phytoremediation.
Introduction
This fact sheet, developed by the U. S. Environmental Protection Agency
(EPA) Federal Facilities Restoration and Reuse Office (FFRRO), provides a
summary for tungsten, including physical and chemical properties;
environmental and health impacts; existing federal and state guidelines;
detection and treatment methods; and additional sources of information. This
fact sheet provides basic information on tungsten to site managers and other
field personnel who may address tungsten contamination at cleanup sites.
Tungsten was originally considered a stable metal in soil that does not
dissolve easily in water. However, tungsten-contaminated environmental
media are now a growing concern to the EPA and the U.S. Department of
Defense (DoD) because recent research indicates that tungsten may not be
as stable as was indicated in earlier studies. Furthermore, varying soil
properties such as pH may cause tungsten to dissolve and leach from soil into
underlying aquifers (ATSDR2005). Currently, little information is available
about the fate and transport of tungsten in the environment and its effects on
human health. Research about tungsten is ongoing and includes health
effects and risks, degradation processes and an inventory of its use in the
defense industry as a substitute for lead-based munitions.
What is tungsten?
Tungsten (also known as Wolfram and represented by the letter W in the
periodic table) is a naturally occurring element that exists in the form of
minerals, but typically not as a pure metal (ATSDR 2005; NIOSH 2010).
There are more than 20 known tungsten-bearing minerals. Wolframite
([FeMn]WO4) and Scheelite (CaWO4) are two common minerals that
contain tungsten and that are mined commercially (ATSDR 2005;
Koutsospyros and others 2006).
Based on its purity, the color of tungsten may range from white for the
pure metal to steel-gray for the metal with impurities. It is commercially
available in a powdered or solid form (ATSDR 2005; NIEHS 2003; NIOSH
2010).
The melting point of tungsten is the highest among metals and it resists
corrosion. It is a good conductor of electricity and acts as a catalyst in
chemical reactions (ATSDR 2005; Gbaruko and Igwe 2007; Koutsospyros
and others 2006).
Disclaimer: The U.S. EPA prepared this fact sheet from publically-available sources;
additional information can be obtained from the source documents. This fact sheet is not
intended to be used as a primary source of information and is not intended, nor can it be
relied upon, to create any rights enforceable by any party in litigation with the United
States. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
United States
Environmental Protection Agency
Office of Solid Waste and
Emergency Response (5106P)
1
EPA 505-F-14-004
January 2014
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Technical Fact Sheet - Tungsten
What is tungsten (continued)?
Tungsten in the form of finely divided powder is
highly flammable and may ignite spontaneously on
contact with air. Powdered tungsten may also
cause fire or explosion on contact with oxidants
(HSDB 2009a; NIOSH 2010).
Tungsten ore is used primarily to produce
tungsten carbide and tungsten alloys, which are
used in many general welding and metal-cutting
applications, for operations within the aerospace
industry and in sporting good products such as
golf clubs. Tungsten metal is also used to produce
lamp filaments, X-ray tubes, dyes and paints for
fabrics (Koutsospyros and others 2006; NIEHS
2003).
Tungsten/nylon "green" bullets were introduced as
a replacement to lead bullets and other
ammunition in the United States and other
countries. DoD began using tungsten as a
replacement for lead in bullets in 1999 for training.
In early 2003, the production of tungsten/nylon
bullets was discontinued based on flight instability
issues (ATSDR 2005; USAGE 2007).
Recent reports of tungsten contamination in
groundwater and soil at military sites have raised
concerns about tungsten's stability in the
environment and resulted in the suspension of
tungsten/nylon bullets in some military
applications. For example, the use of
tungsten/nylon bullets at the Massachusetts
Military Reservation was suspended in February
2006 based on concerns about tungsten's mobility
in the environment (Kennedy and others 2012;
USAGE 2007).
Under the U.S. Army's Green Ammunition
program, at least 85 million rounds of
tungsten/nylon bullets were produced. Currently,
the Army Environmental Center evaluating the fate
and transport properties of tungsten at training
ranges (USAGE 2007).
Exhibit 1: Physical and Chemical Properties of Elemental Tungsten
(ATSDR 2005; HSDB 2009a; NIEHS 2003; NIOSH 2010)
Property
Chemical Abstracts Service (CAS) Number
Physical Description (physical state at room temperature)
Molecular weight (g/mol)
Water solubility
Boiling point (°C at 760 mm Hg)
Melting point (°C)
Vapor pressure at 2,327°C (mm Hg)
Specific gravity/Density at 20/4 °C
7440-33-7
Hard, steel-gray to tin-white solid
183.85
Insoluble
5,900
3,410
1.97x10"'
18.7 to 19.3
Abbreviations: g/mol - grams per mole; °C - degrees Celsius; mm Hg - millimeters of mercury.
What are the environmental impacts of tungsten?
Tungsten is a common contaminant at mining
sites, industrial sites that use the metal and at DoD
sites involved in the manufacture, storage and use
of tungsten-based ammunition. It is also found in
detectable amounts in municipal solid waste and
landfill leachate because of its use in common
household products such as filaments in
incandescent light bulbs (Koutsospyros and others
2006).
Tungsten particles may be present in the
environment as a result of mining, weathering of
rocks, burning of coal and municipal solid waste,
land application of fertilizers or industrial
applications that involve tungsten (ATSDR 2005).
In the ambient atmosphere, tungsten compounds
exist in the particulate phase because of their low
vapor pressures. These particles may settle on
soil, water or other surfaces and can be deposited
through rain or other forms of precipitation (ATSDR
2005; NIEHS 2003).
Tungsten is considered a "lithophilic" element
(preferring terrestrial over atmospheric or aquatic
environments) based on its low vapor pressure and
atmospheric interference factor. Tungsten
compounds are expected to exist as ions or
insoluble solids in the environment; therefore,
volatilization from soil surfaces is not considered
an important fate and transport process
(Koutsospyros and others 2006; NIEHS 2003).
The sorption coefficients for tungsten increase as
pH decreases, indicating low to moderate mobility
of tungsten in soil under low to neutral
environmental conditions. Sorption coefficients for
the tungstate ion range from 100 to 50,000 at
about pH 5, 10 to 6,000 at about pH 6.5 and 5 to
90 at pH 8 to 9 (Meijer and others 1998).
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Technical Fact Sheet - Tungsten
What are the environmental impacts of tungsten? (continued)
Studies indicate that an elevated pH in soil may
increase the solubility of tungsten by decreasing
its sorption coefficient, which may cause it to leach
more readily into the groundwater table (ATSDR
2005; ASTSWMO 2011).
Increased acidification and oxygen depletion of
soils from dissolution of tungsten powder have
been shown to trigger changes in the soil microbial
community, causing an increase in fungal biomass
and a decrease in the bacterial component
(Dermatas and others 2004; Strigul and others
2005). In water, tungsten compounds are
expected to adsorb to suspended solids and
sediment based on their sorption coefficients
(HSDB 2009b).
In 2006, the assumed stability of tungsten in the
environment was questioned when tungsten was
detected in groundwater and in soil above
baseline levels at a small arms range at the
Massachusetts Military Reservation, where
tungsten/nylon bullets were being used. The use
of these bullets was then suspended in
Massachusetts per a Governor's Office Cease and
Desist Order (ASTSWMO 2011; EPA Region 1
2013; USAGE 2007).
Studies suggest that the tungsten powder used in
the Army's tungsten/nylon bullets forms oxide
coatings on the bullets that are soluble in water
(Dermatas and others 2004; USAGE 2007).
Tungsten has been shown to accumulate in plants
in substantial amounts. The extent of
accumulation appears to be related to the
tungsten content in soil and varies widely,
depending on the plant genotype (Koutsospyros
and others 2006).
Results from an aged soil bioassay indicated that
sodium tungstate-spiked soil impaired cabbage
growth (Kennedy and others 2012).
As of 2005, tungsten had been identified at more
than six sites on the EPA National Priorities List
(NPL) (HazDat 2005).
What are the routes of exposure and the health effects of tungsten?
Toxicological information on tungsten and its
compounds is limited (Koutsospyros and others
2006).
Occupational exposure is considered the most
common scenario for human exposure to tungsten
and its compounds. Inhalation, ingestion and
dermal and eye contact are the possible exposure
pathways (ATSDR 2005).
Occupational exposure to tungsten is known to
affect the eyes, skin, respiratory system and
blood. Tungsten may cause irritation to eyes and
skin; diffuse interstitial pulmonary fibrosis; loss of
appetite; nausea; cough; and changes in the blood
(Gbaruko and Igwe 2007; NIOSH 2010).
Studies on female rats have shown that oral
exposure to tungsten caused post-implantation
deaths and developmental abnormalities in the
musculoskeletal system. Exposure of pregnant
rats to sodium tungstate resulted in fetal death
(NIEHS 2003).
Studies on rats also found that tungsten primarily
accumulated in bones and in the spleen after oral
exposure (NIEHS 2003).
Tungsten has not been classified for carcinogenic
effects by the Department of Health and Human
Services, the International Agency for Research
on Cancer or the EPA.
The EPA's Toxic Substances Control Act (TSCA)
Interagency Testing Committee has included
tungsten compounds in the Priority Testing List,
which is a list of chemicals regulated by TSCA for
which there are suspicions of toxicity or exposure
and for which there are few, if any, ecological
effects, environmental fate or health effects testing
data (EPA 2006).
Are there any federal and state guidelines and health standards for
tungsten?
A federal drinking water standard has not been
established for tungsten. In addition, the EPA has
not derived a chronic inhalation reference
concentration (RfC) or a chronic oral reference
dose (RfD) for tungsten or tungsten compounds
(EPA 2013).
»«» The American Council of Governmental Industrial
Hygienists (ACGIH) has established a threshold
limit value of 5 milligrams per cubic meter (mg/m3)
as the time-weighted average (TWA) over an 8-
hour work exposure and 10 mg/m3 as the 15-
minute short-term exposure limit (STEL) for
airborne exposure to tungsten metal and for
insoluble tungsten compounds (ACGIH 2008).
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Technical Fact Sheet - Tungsten
Are there any federal and state guidelines and health standards for
tungsten? (continued)
Tungsten and related compounds were included
as part of EPA's 2012 Integrated Risk Information
System (IRIS) agenda. The current projected start
date for conducting the literature search for the
chemical is fiscal year 2014 (EPA 2012).
The National Institute for Occupational Safety and
Health (NIOSH) has established a recommended
exposure limit of 5 mg/m3 as the time-weighted
average (TWA) over a 10-hour work exposure and
10 mg/m as the 15-minute short-term exposure
limit (STEL) for airborne exposure to tungsten and
insoluble tungsten compounds (NIOSH 2010).
The Occupational Safety and Health
Administration (OSHA) recommends a permissible
exposure limit of 5 mg/m3 for insoluble compounds
of tungsten and a PEL of 1 mg/m3 limit for soluble
compounds in the construction and shipyard
industries as a TWA over an 8-hour work
exposure. OSHA also established a PEL of 10
mg/m3 as the 15-minute STEL for airborne
exposure to insoluble compounds of tungsten and
3 mg/m3 as the 15-minute STEL for airborne
exposure to soluble tungsten compounds (OSHA
2013).
What detection and site characterization methods are available for
tungsten?
Tungsten is commonly deposited in the
environment as discrete particles with strongly
heterogeneous spatial distributions. Unless
precautions are taken, this distribution causes
highly variable soil data that can lead to confusing
or contradictory conclusions about the location
and degree of contamination. Proper sample
collection (using an incremental field sampling
approach), sample processing (which includes
grinding) and incremental subsampling are
required to obtain reliable soil data (EPA 2003).
NIOSH Method 7074 uses flame atomic
absorption to detect tungsten in air. It has a
detection limit of 0.125 mg/m3 for insoluble forms
of tungsten and 0.05 mg/m3 for soluble forms of
tungsten (NIOSH 1994).
Other NIOSH methods for the detection of
tungsten in air are Methods 7300 and 7301,
involving inductively coupled argon plasma-atomic
emission spectroscopy. The working range for
these methods is 0.005 to 2.0 mg/m3 for each
element in a 500-liter sample. Special sample
treatment may be required for some tungsten
compounds (NIOSH 2003a, b).
OSHA Method ID-213 is also used for the
detection of tungsten in air. The method uses
inductively coupled plasma (ICP)-atomic emission
spectroscopy (AES) and has a quantitative
detection limit of 0.34 mg/m3 (OSHA 2013).
Tungsten in soil and water can be measured using
the ICP-AES, ICP-mass spectrometry (ICP-MS)
and ultraviolet/visible spectroscopy (UV/VIS)
methods (ATSDR 2005).
Tungsten is not currently included on the list of
analytes under EPA SW-846 Methods 6010, ICP-
AES, and 6020, ICP-MS; however, these methods
may be modified for the detection of tungsten in
soil and water (ASTSWMO 2011; EPA 2007b, c).
Tungsten is also not currently included on the list
of recoverable metals using SW-846 Method
3051 A, a microwave-assisted acid digestion
method. Therefore, the digestion method is being
modified to enhance tungsten recovery from soils
(EPA 2007a; Griggs and others 2009).
Trace concentrations of tungsten in water and air
can also be estimated by instrumental neutron
activation analysis (Gbaruko and Igwe 2007;
NIEHS2003).
What technologies are being used to treat tungsten?
Treatment technologies to address tungsten
contamination in environmental media are
currently under development.
Preliminary studies indicate that phytoremediation
may be a potential treatment method for tungsten
contaminated sites based on the reported
accumulation of tungsten in plant tissue (Strigul
and others 2005; Tuna and others 2012).
Electrokinetic soil remediation is an emerging in
situ technology for removal of tungsten from low-
permeability soils in the presence of heavy metals
such as copper and lead. A direct current is
applied to contaminated soils using electrodes
inserted into the ground (Braida and others 2007).
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Technical Fact Sheet - Tungsten
What technologies are being used to treat tungsten? (continued)
Studies have reported the efficient removal (98 to
99 percent) of tungsten from industrial wastewater
by precipitation, coagulation and flocculation
processes using ferric chloride under acidic
conditions (pH below 6) (Plattes and others 2007).
A recent study demonstrated the efficient recovery
of tungsten (over 90 percent) in aqueous solutions
using a water-soluble polymer (polyquaternium-6)
for complexing anion forms of tungsten prior to
ultrafiltration (Zeng and others 2012).
Where can I find more information about tungsten?
Agency for Toxic Substances and Disease
Registry (ATSDR). 2005. "lexicological Profile for
Tungsten."
www.atsdr.cdc.gov/toxprofiles/tp186.pdf
American Conference of Governmental Industrial
Hygienists (ACGIH). 2008. Tungsten. "Threshold
Limit Values for Chemical Substances and
Physical Agents and Biological Exposure Indices."
Cincinnati, Ohio.
Association of State and Territorial Solid Waste
Management Officials (ASTSWMO). 2011.
"Tungsten Issues Paper." www.astswmo.org/
Files/Policies and Publications/Federal Facilities/
2011-02 FINAL Tungsten Issues 2-O.pdf
Braida, W., Christodoulatos, C., Ogundipe, A.,
Dermatas, D., and G. O'Connor. 2007.
"Electrokinetic Treatment of Firing Ranges
Containing Tungsten-Contaminated Soils." Journal
of Hazardous Materials. Volume 149. Pages 562
to 567.
Dermatas, D., Braida, W., Christodoulatos, C.,
Strigul, N., Panikov, N., Los, M., and S. Larson.
2004. "Solubility, Sorption, and Soil Respiration
Effects of Tungsten and Tungsten Alloys."
Environmental Forensic. Volume 5. Pages 5 to 13.
Gbaruko, B.C. and J.C. Igwe. 2007. "Tungsten:
Occurrence, Chemistry, Environmental and Health
Exposure Issues." Global Journal of
Environmental Research. Volume 1 (1). Pages 27
to 32.
Griggs C., Larson, S., Nestler, C., and M.
Thompson. 2009. "Coupling of Oxygen and pH
Requirements for Effective Microwave-Assisted
Digestion of Soils for Tungsten Analysis." Land
Contamination & Reclamation. Volume 17. Pages
121 to 128.
Hazardous Substances Data Bank (HSDB).
2009a. Elemental Tungsten, http://toxnet.nlm.nih.
gov/cgi-bin/sis/htmlgen?HSDB
HSDB. 2009b. Tungsten Compounds.
http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?
HSDB
HazDat. 2005. HazDat Database: ATSDR's
Hazardous Substance Release and Health Effects
Database. Atlanta, GA.
Kennedy, A.J., Johnson, D.R., Seiter, J.M,
Lindsay, J.H., Boyd, R.E., Bednar, A.J., and P.G.
Allison. 2012. "Tungsten Toxicity,
Bioaccumulation, and Compartmentalization into
Organisms Representing Two Trophic Levels."
Environmental Science and Technology. Volume
46 (17). Pages 9646 to 9652.
Koutsospyros, A., Braida, W., Christodoulatos, C.,
Dermatas, D., and N. Strigul. 2006. "A Review of
Tungsten: From Environmental Obscurity to
Scrutiny." Journal of Hazardous Materials. Volume
136. Pages 1 to 19.
Meijer, A., Wroblicky, G., Thuring, S., and M.W.
Marcell. 1998. "Environmental Effects of Tungsten
and Tantalum Alloys." Elgin Air Force Base,
Florida: Air Force Research Laboratory. AFRL-
MN-EG-TR-2000-7017.
National Institute of Environmental Health
Sciences (NIEHS). 2003. "Tungsten and Selected
Tungsten Compounds - Review of Toxicological
Literature." http://ntp.niehs.nih.gov/ntp/htdocs/
Chem Background/ExSumPdf/tungsten 508.pdf
National Institute for Occupational Safety and
Health (NIOSH). 1994. "Tungsten (Soluble and
Insoluble) - Method 7074." NIOSH Manual of
Analytical Methods (NMAM), Fourth Edition.
www.cdc.gov/niosh/docs/2003-154/pdfs/7074.pdf
NIOSH. 2003a. "Elements by ICP (Nitric/Perchloric
Acid Ashing) - Method 7300." NIOSH Manual of
Analytical Methods (NMAM), Fourth Edition.
www.cdc.gov/niosh/docs/2003-154/pdfs/7300.pdf
NIOSH. 2003b. "Elements by ICP (Aqua Regia
Ashing) - Method 7301." NIOSH Manual of
Analytical Methods (NMAM), Fourth Edition.
www.cdc.gov/niosh/docs/2003-154/pdfs/7301 .pdf
NIOSH. 2010. NIOSH Pocket Guide to Chemical
Hazards: Tungsten.
www.cdc.gov/niosh/npg/npgd0645.html
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Technical Fact Sheet - Tungsten
Where can I find more information about tungsten? (continued)
Occupational Safety and Health Administration
(OSHA). 2013. "Tungsten and Cobalt in
Workplace Atmospheres (ICP Analysis)."
www.osha.gov/dts/sltc/methods/inorganic/id213/id
213.html
Plattes, M., Bertrand, A., Schmitt, B., Sinner, J.,
Verstraeten, F., and J. Welfring. 2007. "Removal
of Tungsten Oxyanions from Industrial Wastewater
by Precipitation, Coagulation and Flocculation
Processes." Journal of Hazardous Materials.
Volume 148 (3). Pages 613 to 615.
Strigul, N., Koutsospyros, A., Arienti, P.,
Christodoulatos, C., Dermatas, D., and W. Braida.
2005. "Effects of Tungsten on Environmental
Systems." Chemosphere. Volume 61. Pages 248
to 258.
Tuna, G.S., Braida, W., Ogundipe, A., and D.
Strickland. 2012. "Assessing Tungsten Transport
in the Vadose Zone: From Dissolution Studies to
Soil Columns." Chemosphere. Volume 86 (12).
Pages 1001 to 1007.
U.S. Army Corps of Engineers (USAGE). 2007.
"Fate and Transport of Tungsten at Camp
Edwards Small Arms Ranges." ERDC TR-07-5.
www.crrel.usace.army.mil/librarv/technicalreports/
TR-07-5.pdf
U. S. Environmental Protection Agency (EPA).
2003. "Guidance for Obtaining Representative
Laboratory Analytical Subsamples from Particulate
Laboratory Samples." EPA/600/R-03/027.
EPA. 2006. "Fifty-Eighth Report of the TSCA
Interagency Testing Committee to the
Administrator of the Environmental Protection
Agency; Receipt of Report and Request for
Comments; Notice." Federal Register. Volume 71
(132). Page 39187.
EPA. 2007a. "Method 3051 A. Microwave Assisted
Acid Digestion of Sediments, Sludges, Soils, and
Oils." SW-846 On-line, www.epa.gov/osw/
hazard/testmethods/sw846/pdfs/3051a.pdf
EPA. 2007b. "Method 601OC. Inductively Coupled
Plasma-Atomic Emission Spectrometry." SW-846
On-line, www.epa.gov/osw/hazard/testmethods/
sw846/pdfs/6010c.pdf
EPA. 2007c. "Method 6020A: Inductively Coupled
Plasma-Mass Spectrometry." SW-846 On-line.
www.epa.gov/osw/hazard/testmethods/sw846/pdfs
/6020a.pdf
EPA. 2012. Integrated Risk Information System
(IRIS); Announcement of 2012 Program. Federal
Register. Volume 77 (88). Pages 26751 to 26755.
www.gpo.gov/fdsys/pkg/FR-2012-05-07/html/
2012-10935.htm
EPA. 2013. Drinking Water Contaminants.
water.epa.gov/drink/contaminants/index. cfm#List
EPA. Region 1. 2013. Massachusetts Military
Reservation, www.epa.gov/region01/mmr/.
Zeng, J., Sun, X., Zheng, L, He, Q. and S. Li.
2012. "Recovery of Tungsten (VI) from Aqueous
Solutions by Complexation-Ultrafiltration Process
with the Help of Polyquaternium." Chinese Journal
of Chemical Engineering. Volume 20 (5). Pages
831 to 836.
Contact Information
If you have any questions or comments on this fact sheet, please contact: Mary Cooke, FFRRO, by phone at
(703) 603-8712 or by email at cooke.maryt@epa.gov.
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