MCHB-TS-TTE (40)

MEMORANDUM FOR Commander, U.S. Army Center Environmental Center, ATTN:

SFIM-AEC-ETP (Kelly Rigano), Aberdeen Proving Ground

MD 21010-5401

SUBJECT: Review of Tungsten

1\. Per request for information regarding Tungsten please find the
attached report.

2\. The U.S. Army Center for Health Promotion and Preventive Medicine
point of contact is Dr. Wilfred McCain at extension 5-3980.

FOR THE COMMANDER:

Atch LEROY W. METKER

Program Manager

Toxicity Evaluation

**TUNGSTEN:**

**A REVIEW**

**I. Historical Background**

[General]{.underline}:

The history of the development of tungsten and its alloys for practical
use is more than two centuries old. C.W. Scheele first discovered
tungsten in 1781. J.J. and F. de Elhuyer published the first account
regarding the isolation of tungsten from ore in 1783. It wasn't until
1847, however, when Oxiand patented processes describing the manufacture
of two chemicals used as starting materials in tungsten metallurgy
(tungstic acid and sodium tungstate) that industrialization of tungsten
began in earnest. In the mid-1800\'s efforts to produce tungsten steel
succeeded and the field developed rapidly from that point onward. The
importance of tungsten hardened steel was recognized immediately, the
manufacture of rails being the first practical application of that
product.

A number of other practical applications followed. The Bethlehem Steel
Co. exhibited tungsten high-speed steel tools at the Pads Exposition in
1900. The process for drawing tungsten filaments was patented in 1904,
and development of the tungsten filament itself began 5 years later. The
result of this invention is perhaps the single best known application
that there is of tungsten light bulbs.

Further developments and applications of tungsten came about with the
introduction of tungsten carbide, produced when tungsten is blended with
carbon and heated to about 1,550ºC. The carbide is extremely hard, but
it found few applications at first because of its brittleness. The
discovery in Germany in the late 1920\'s that the properties of tungsten
carbide were improved enormously upon addition of a cementing or bonding
agent led to a significant 25 year period of development-the so-called
\"carbide era\" (Li and Yu Wang, 1955).

[Military Applications]{.underline}:

The development of armor-piercing tungsten carbide penetrators by
Germany during World War II signaled the onset of an irreversible change
in modern tank warfare-both in armor and in antiarmor weaponry. The use
of high velocity tungsten carbide penetrators for the first time-by
Rommel\'s forces against British armors cited by Li as a major
contributor to Germany\'s near success in its North Africa campaign. Two
years later, American forces perfected similar antiarmor penetrators
that were highly effective against German armor.

The development of spaced array armor in the 1960\'s made tungsten
carbide penetrators obsolete. The tungsten carbide rods were susceptible
to breakage upon impact, even against a relatively thin plate.
Metallurgical advances in the manufacture of tungsten alloys and
adaptation of a new swaging process resulted in substantially improved
performance of penetrators against the new challenge posed by the
advanced armor systems (Davitt, 1980).

Tungsten alloy penetrators remained the mainstay of the Army\'s
antiarmor ammunition until the end of the 1970\'s when production of the
105-mm M735 tungsten kinetic energy (KE) penetrator round was phased
out, and depleted uranium (DU) KE penetrators were introduced, i.e., the
105-mm M774 (Coleman, 1995).

The U. S. Navy formerly used DU in Phalanx penetrator cartridges and
switched back to tungsten alloy in 1990 (Coleman, 1995). The reasons for
the changeover included the following: (1) for their purposes, a slight
improvement was found in tungsten performance over depleted uranium; (2)
transition to tungsten obviated the need for protective shielding, thus
lowering costs; and (3) there are lower demilitarization costs for
tungsten ammunition than for DU.

[Industrial and Other Applications]{.underline}:

The physical attributes of tungsten alloys' density, hardness, and
heat-resistance have led to a multitude of peacetime uses. Modern uses
of tungsten alloys are in aircraft, automotive and power components, in
light bulbs as filaments, for shielding and for arc welding. A further
attribute of the metal that it is relatively inert-has resulted in its
use as a Carrier of DNA for genetic engineering of plants and for
research on advanced immunological techniques.

> The use of tungsten or its alloys in our daily lives is becoming
> increasingly common: For instance, tungsten is used in the manufacture
> of some hand tools such as chisels and saw blades; in various types of
> sporting equipment, such as dart barrels and as weights in golf-club
> heads. It is also used for electrical lighting filaments, for
> automotive distributor points, as a flame-retardant for cellulose, and
> in x-ray and cathode ray tubes. In general, tungsten is used where
> metals with a high temperature tolerance and a low reactivity rate are
> needed.

A process for embedding tungsten in a polymeric matrix has recently been
patented (USEPA, 1994). Items fabricated from the composite have the
advantages of high density and absence of toxicity. The absence of
toxicity in tungsten composites is particularly important because the
new material provides environmental relief from the known toxicity of
lead to wildlife.

**II. Occurrence**

Naturally occurring tungsten is found, for the most part, in the base
ores wolframite ((Fe, Mn)WO~4~), scheelite (CaWO~4~), ferberite
(FeWO~4~), and hubnerite (MnWO~4~). Worldwide, wolframite is the most
important ore while sheelite is the principal domestic ore. The richest
deposits are in China, Alaska, and Mexico. Worldwide production is
around 50,000 metric tons per year. It has an abundance of 1 ppm in the
earth's crust. Tungsten has also been found in drinking water at levels
between 0.03 to 0.1 µg/l depending on sampling site. Atmospheric levels
of tungsten are in the "very low" category (less than 1.5 ng/m^3^) and
are generally related to industrial emissions. Tungsten is found in
rainwater at levels less than 0.1 µg/l. Nuclear explosions have produced
tungsten radioisotopes. These are widely distributed in the environment,
primarily as tungstic oxide.

**III. Properties**

Tungsten (Wolfram; W) metal is lustrous and silvery white in color and
does not occur naturally in the environment. Tungsten containing ore is
first converted to the trioxide and then reduced to the metal by
reduction in hydrogen (carbon cannot be used as the very stable carbide
would result). Tungsten metal is relatively inert, resisting attack by
oxygen, acids and alkalis, although it will react with fused oxidizing
alkali media. It has the highest melting point of all metals and, when
pure, it can be worked with relative ease; the presence of impurities
renders tungsten extremely brittle and, therefore, difficult to
fabricate. Tungsten is a transitional element in group VIa of the
periodic table and is therefore closely associated with the elements
molybdenum and chromium.

The high melting point of tungsten makes it suitable for use as electric
filaments (e.g. in light bulbs). It is also the basis of a range of
alloys containing tungsten, copper and nickel which are used for
radiation shielding as they provide a 50% increase in density compared
to lead. Tungsten and its alloys also find uses in military applications
as armor and ammunition. Tungsten carbide powder (with possible
additions of titanium or tantalum carbides) along with nickel or cobalt
powders, are compressed and sintered to produce cemented carbides. These
products are used in place of high-speed steel to form the tip of the
cutting and drilling tools, or for parts which will be subject to heavy
usage.

  ------------------------------------ ------------------ ----------------
  **Atomic Properties**                                   

  Atomic number                        74                 

  Atomic radius                        0.141 nm           

  Atomic weight                        183.85 amu         

  Crystal structure                    Body centered      
                                       cubic              

  Electronic structure                 Xe 4f^14^ 5d^4^    
                                       6s^2^              

  Photoelectric work structure         4.55 eV            

  Thermal neutron absorption           18.5 Barns         
  cross-section                                           

  Valences shown                       2, 3, 4, 5, 6      

  Natural Isotope distribution         Mass No.           \%

                                       180                0.1

                                       182                26.3

                                       183                14.3

                                       184                30.7

                                       186                28.6

  Ionization potential                 No.                EV

                                       1                  7.98

                                       2                  17.7
  ------------------------------------ ------------------ ----------------

  ----------------------------------------- -----------------------------
  **Physical Properties**                   

  Boiling point                             5660^o^C

  Density @ 20^o^C                          19.3 g cm^-3^

  Melting point                             3140^o^C
  ----------------------------------------- -----------------------------

  ----------------------------------------- -----------------------------
  **Electrical Properties**                 

  Electrical resistivity @ 20^o^C           5.4 µΩcm

  Temperature coefficient @ 0-100^o^C       0.0048 K^-1^

  Superconductivity critical temperature    0.0154 K

  Thermal emf against pt (cold 0^o^C -- hot \+ 1.12 mV
  100^o^C)                                  
  ----------------------------------------- -----------------------------

  ----------------------------------------- -----------------------------
  **Thermal Properties**                    

  Latent heat of evaporation                4009 J gm^-1^

  Latent heat of fusion                     192 J gm^-1^

  Linear expansion coefficient @ 0-100^o^C  4.5 x 10^-6^ K^-1^

  Specific heat @ 25^o^C                    133 J K^-1^ kg^-1^

  Thermal conductivity @ 0-100^o^C          173 W m-1K^-1^
  ----------------------------------------- -----------------------------

  ----------------- ----------------- ----------------- -----------------
  **Mechanical                                          
  Properties**                                          

  Material          Soft              Hard              Polycrystalline
  condition                                             

  Bulk modulus                                          311 Gpa

  Hardness          360               500               
  (Vicker's)                                            

  Poisson's ratio                                       0.28

  Tensile modulus                                       411 GPa

  Tensile strength  550-620           1920 MPa          

  Yield strength    550 Mpa                             
  ----------------- ----------------- ----------------- -----------------

**IV. Production**

This section is excerpted from Gold and Los (1966).

[Manufacturing]{.underline}:

Some physical and chemical properties of tungsten and the procedures
necessary to purify intermediates when producing metallic tungsten are
presented here as an aid to understanding tungsten metallurgy as it
applies to kinetic energy penetrators.

Tungsten has an extremely high melting temperature (3,410± 200°C), the
highest of all elements with the exception of carbon. \[Tantalum carbide
is one of the few carbides that has a higher melting point than tungsten
(Rieck, 1967)\] Because of tungsten\'s high melting point, methods
involving chemical decomposition and purification must be used instead
of ordinary processing techniques such as pyro-metallurgy. The purified
powder can then be used for manufacturing penetrators or other Army
materiel.

Ores containing tungsten are generally treated to obtain intermediates
such as sodium tungstate, which must then be purified. A practical
approach to purification is to first transform the sodium tungstate to
ammonium paratungstate. This is digested, washed, and then redissolved
in ammonia to reprecipitate ammonium paratungstate crystals. The process
is repeated several times to obtain pure ammonium paratungstate which,
after digestion with nitric and hydrochloric acids followed by drying,
yields pure tungsten trioxide. Reduction of tungsten trioxide in a
hydrogen atmosphere produces metallic tungsten powder. \[Reduction of
tungsten with carbon (e.g., lampblack or carbon black) in a hydrogen
atmosphere between 1,450°C and 1,550^o^C produces tungsten carbide (Li
and Yu Wang, 1955).

The manufacture of penetrators involves compaction of a blend of metal
powders in molds at high pressure (predominantly tungsten with lesser
amounts of alloying metals). After they are removed from the molds, the
compacts are sintered, annealed, swaged, and finally cut to a prescribed
shape. These operations are described in greater detail.

[General]{.underline}: Tungsten heavy alloys (WHA) are the materials of
choice for tungsten-based penetrators. Tungsten carbide was used during
WW II, but changes in target materials and design-as well as advances in
metallurgy and processing techniques-shifted attention to tungsten heavy
alloys. In addition to providing the hardness that was associated with
tungsten carbide, these alloys have other noteworthy characteristics
that affect penetrator performance and cost: (1) greater density, (2)
increased strength and ductility, (3), machinability, (4) reasonable
production costs, and (5) resistance to corrosion when stored, over long
periods of time (German, 1992).

Modern tungsten-based alloy penetrators are manufactured by a powder
metallurgy process that involves compaction of tungsten powder (the
primary phase) with alloying (binding or cementing) elements such as
nickel and iron and possibly cobalt (the secondary phase). In general,
tungsten particles with diameters in the nominal range less than 5 p are
used. Recent efforts have focused on smaller grain sizes, including
ultrafine dimensions, to improve tungsten alloys (Dowding, 1991).

The manufacturing process described here for large-diameter penetrators
was used by Teledyne Firth Sterling, LaVergne, Tennessee (Brooks, 1986).

[Powder blending and compaction]{.underline}: Tungsten Powder was
blended with sieved matrix elements such as nickel and iron (and
possibly cobalt) with the aid of a V-blender equipped with a central
high-speed intensifying bar to improve efficiency. The amount of
tungsten powder in the blend is high, up to 97%; nickel and iron powders
are widely used in the industry in an optimum ratio of 7:3 (Dowding,
1991), though other ratios are also used.

Approximately 15 lb. (7 kg) of blended powder was-fed to a rubber mold
which in turn was surrounded by a steel casing to ensure accurate
shaping during pressing. Each rubber mold was then sealed and the
compact cold-pressed isostatically. This involved sealing the molds
inside a chamber where they were exposed to water pressure up to 2,000
bar (30 ksi). The process was termed \"wet-bag\" inasmuch as the molds
were in direct contact with pressurized water. As many as 250
large-diameter penetrator compacts could be processed simultaneously in
the pressure chamber used by Teledyne, a converted 16-in. gun.

Small penetrator rods (⅛ in. to 1 in. diameter) were produced
automatically in a dry-bag pressing device. The process consisted of
compaction of powder in forms placed inside a bag within a bag. Only the
outside bag was exposed to the hydrostatic fluid (a water and soluble
oil mixture) at about 2,000 bar (30 ksi). Components could be loaded
into the dry-bag instrument and cold pressed, all within a 45-sec
interval.

[Sintering]{.underline}: Liquid phase sintering consisted of bringing
the compact to a temperature at which it would liquefy and then
maintaining the compact at that temperature so that the metallic
secondary phase elements remained liquid through­out all or most of the
process. As a consequence of this process: (1) a portion of the tungsten
was dissolved in the liquid fraction; (2) upon cooling, there was a
substantial increase in the diameter of the undissolved tungsten
particles. The compact was strengthened and densified by this operation.

Sintering at Teledyne was carried out in semi-automatic twin-muffle
electric furnaces which were equipped to provide three individually
controlled temperature zones in a hydrogen atmosphere. Penetrators were
sintered in alumna boats (to avoid contact with carbon) at temperatures
in the range of 1,350 to 1,560ºC and higher for alloys that contained
more than 97% tungsten.

Alloys with less than 95% tungsten required a shorter exposure interval
at lower temperatures and a maximum temperature of approximately
1,500ºC. Teledyne used other suitable furnaces for sintering such
alloys.

Heating in appropriate furnaces as performed by Teledyne is one kind of
sintering process used in the powder metallurgy industry. Resistive
heating is another. In resistive heating, a current is passed through a
compacted preformed item. At suitable electrical current and resistance
levels, a temperature greater than 2,500ºC is obtained and the powder is
fully sintered within minutes. The resulting product is suboptimum from
the viewpoint of ductility at room temperature, however, and requires
cold work such as rolling or swaging and elevated temperatures to
improve its properties (Dowding, 1991).

An experimental approach taken by other investigators to improve
properties of tungsten heavy alloys involved liquid phase sintering in a
vacuum. Alloys sintered in a vacuum were compared with alloys sintered
in a heated dry hydrogen atmosphere. Improvements attributable to vacuum
sintering included, production of an alloy with a density that
approached the theoretical value and strength and ductility values
comparable to the best reported. A disadvantage, however, was that
prolonged sintering in a vacuum resulted in loss of matrix phase metals
through vaporization (Bose et al, 1987).

[Annealing]{.underline}: Special vacuum furnaces capable of heating 9
tons of sintered rods at once were used at Teledyne. This post-sintering
operation was designed to remove residual hydrogen, which, if left
behind, could have resulted in penetrator embrittlement. Ductility was
improved by annealing. If impurities were present at the surface of the
penetrator they were redistributed back into the nickel-iron binder
during the annealing process.

[Swaging]{.underline}: Large penetrators were swaged in a fixed-die
600-ton swaging machine. Bars were held between centers and rotated
while passing through a set of four die segments that have a stroke of
approximately 2 mm. A single pass through the machine sufficed to obtain
the desired final diameter.

[Machining]{.underline}: The bars were cut to length and milling of the
ends was begun. Further machining was done on a lathe by securing a
large rod in a chuck at one end and a center at the other. As an example
of the extent of machining required to produce a finished penetrator, a
bar 25-in. long (650 mm) with a diameter of about 2 in. (50 mm) was
machined down to a diameter of 1.444 in. (36.7 mm). Additional metal
shaping involved machining buttress grooves on the penetrator. The
quantity of metal removed in this machining step was dependent on the
configuration of grooves on the penetrator, which varied according to
proprietary customer specifications.

**V. Environmental Levels and Exposures**

Standards and Regulations:

> MSHA STANDARD (air): TWA 1 mg/m^3^ (soluble)
>
> MSHA STANDARD (air): TWA 5 mg/m^3^ (insoluble)
>
> OEL-DENMARK TWA 5 mg/m^3^
>
> OEL-RUSSIA STEL 2 mg/m^3^
>
> OEL SWEEDEN TWA 5 mg/m^3^
>
> OEL-UNITED KINGDOM TWA 5 mg/m^3^
>
> STEL 10 mg/m^3^

NIOSH Documents:

> NIOSH REL to Tungsten: insoluble (air) TWA 5 mg(W)/m^3^
>
> STEL 10 mg(W)/m^3^
>
> Soluble (air) TWA 1 mg(W)/m3
>
> STEL 3 mg(W)/m3
>
> National Occupational Exposure Survey (1983): Hazard Code 74980
>
> National Occupational Exposure Survey (1983): Hazard Code X5928
>
> National Occupational Exposure Survey (1983): Hazard Code X7685
>
> National Occupational Hazard Survey (1974): Hazard Code 74980

Status in the United States:

> EPA TSCA Section 8(b) Chemical Inventory
>
> EPA TSCA Section 8(d) Unpublished Health / Safety Studies
>
> EPA TSCA Test Submission (TSCATS) Database, April 1997
>
> NIOSH Analytical Method, 1994: Tungsten (Soluble and Insoluble), 7074
>
> U.S. Army: Approved Health Hazard Assessment of the 120 mm Armor
> Piercing, Fin Stabilized, Detachable Sabot-Tracer, Kinetic
> Energy-Tungsten (APFSDS-T, KE-W) round.
>
> U.S. Fish and Wildlife Service has approved the use of tungsten-iron
> shot for waterfowl hunting. 1997
>
> USEPA has approved replacement of lead sinkers with tungsten for
> fishing 1997

**VI. Background Levels in Humans**

Webster and his colleagues (1973), using neutron activation analysis,
determined the serum concentration of tungsten in humans. The
concentration was 5.8 (±3.5) ng/ml in eight healthy subjects.

**VII. Potential Exposure (Forms of Tungsten and Route of Entry)**

Recent studies at Oak Ridge National Laboratories and Picatinny Arsenal
have indicated that only insoluble forms of tungsten are generated from
small caliber rounds. These forms include tungsten metal (W), oxides of
tungsten (tungsten trioxide, WO~3~; tungsten hemipentoxide, W~2~O~5~;
and tungsten dioxide, WO~2~), and tungstic (VI) acid (H~2~WO~4~). It is
unlikely that salts of tungsten (Na and Ca) will be formed either from
the manufacturing process or normal use of small caliber tungsten
rounds. Insoluble forms of tungsten are generally less toxic than are
the soluble forms.

Studies conducted by the Close Combat Arms Center (CCAC) indicated that
airborne levels of tungsten did not exceed the Threshold Limit Value
(TLV) set by the American Congress of Governmental Industrial Hygienists
(ACGIH) or Permissible Exposure Level (PEL) set by the Occupational
Safety and Health Administration. In fact, the airborne levels of
tungsten produced from firing 30 rounds of 5.56 mm tungsten ammunition
was two to three orders of magnitude lower than the 5.0 mg/m^3^ TLV or
PEL. Investigators from the CCAC have indicated that little or no
soluble forms of tungsten are produced during live fire exercises.

Several epidemiological studies measured airborn concentrations of
tungsten during the manufacturing process. Kaplum and Mezentseva (1959)
reported airborne concentrations of tungsten in various processing
operations between 8.6 and 107 mg/m^3^. Another study conducted in 1975
reported concentrations of tungsten in the grinding process between 0.2
and 12.8 mg/m^3^.

The most likely route of entry for tungsten from manufacturing or use of
the small caliber rounds is the pulmonary route. This route may be more
problematic in the manufacturing process than from firing small caliber
rounds. In both cases, however, areosols containing tungsten will be
produced. Because of the density of tungsten (19.3 g/cm^3^), only
particles 5 µm or less will remain airborne for extended periods of
time. Dusts containing smaller particles (0.5 to 1 µm) may be produced
around powdered metallurgy operations where mixing, milling, shaping,
and grinding of tungsten and its alloys occur.

The dermal or ocular routes of exposure are also relevant. Deposition of
tungsten on the exposed surfaces of the body is likely in manufacturing
operations. Deposition may also occur at indoor firing ranges where the
concentration of minute particles of tungsten may be concentrated.

Ingestion is another potential route of entry for tungsten, although it
is not considered to be of great importance. Inhaled tungsten particles
may be carried to the gastrointestinal tract by the mucociliary
escalator. This mechanism is important in both the removal of inhaled
tungsten particles from the respiratory system as well as providing a
secondary route of exposure for tungsten.

**VIII. Metabolism (Absorption, Distribution and Elimination)**

The disposition of tungsten in the body has been evaluated by several
investigators. In rats, 40 percent of ingested ^185^W was excreted in
the urine after 24 hours and 58 percent had either been eliminated in
the feces or remained unabsorbed in the gut. Only 2 percent remained in
the tissues (Ballou, 1960). The absorption in dogs of inhaled
^181^W-labeled tungstic oxide indicated that 60 percent of the activity
was deposited in the respiratory tract. One third of the activity was
cleared to systemic circulation within ten days and the remaining two
thirds was cleared to the gastrointestinal tract (Aamodt, 1975).

The distribution of ingested tungsten metal, tungstic oxide, sodium
tungstate and ammonium-*p*-tungstate was evaluated by Kinard and Aull
(1945). The principal sites of deposition were bone and spleen. With
less than 1 percent deposited in the kidney, liver, and, in some
animals, the blood lung muscle, and testes. These investigators
indicated that there was essentially no difference in distribution among
the compounds evaluated. The Aamodt study (1975), where labeled tungsten
was inhaled, indicated that the highest concentration of tungsten was
found in the lung and the kidney 165 days after exposure,.
Concentrations in bone, gall bladder, liver, and spleen were
approximately one order of magnitude less than that found in the lung
and kidney. When this data is examined as organ burden, the highest
activity levels were found in bone (37%) and lung (31%).

The primary route of elimination for both soluble and insoluble forms of
tungsten is the urine. This type of elimination is rapid for tungsten.
Following intravenous injection of ^185^W-labeled sodium tungstate, 91
percent was eliminated within 24 hours. The rate of decrease in blood
activity of inhaled ^181^W-labelled tungstic oxide was lower than that
for injected sodium tungstate. This phenomenon may have been due to the
extended rate of absorption of tungsten to blood from the lungs. The
daily excretion rate for ten workers exposed to tungsten carbide was 490
µg W/24 hours (Barborik, 1972). A study of urinary and fecal elimination
of tungsten was conducted on four healthy young adults. With only small
variations, tungsten elimination was equivalent to tungsten ingested
from the diet.

The biological half life of inhaled metallic tungsten has been
determined for dogs. More than 94 percent of the inhaled metal was
removed within nine hours. The longest half life was 139 days for the
final 1.6 percent.

**IX. Toxicity Information**

[Data]{.underline}:

Information evaluated on the toxicity of tungsten for this review falls
into two major categories. One type of data includes information on
human worker exposure. Toxicologists, industrial hygienists, and
occupational health physicians have reviewed historical data, coupled
with ambient workplace levels of tungsten and its alloys. The
interpretation of many of the studies, which focused on tungsten alloys,
is difficult due to the presence of other, more toxic, materials such as
cobalt and nickel. Severe adverse health effects have, for the most
part, have been attributed to the presence of cobalt and nickel in the
alloyed product. The National Institute of Occupational Safety and
Health (NIOSH), in order to develop workplace exposure criteria,
reviewed this type of information as well as pertinent information
obtained from animal studies. The second type of data includes studies
on the toxicity of tungsten in both humans and animals. This type of
specific information is scanty at best. Environmental studies are also
considered in this category. Other studies in which tungsten was used
but not evaluated as a toxicant were reviewed as well. Care was taken to
evaluate only studies that examined only the effects of insoluble forms
of tungsten and tungsten metal.

[General toxicity information]{.underline}:

The median intraperitoneal toxic dose (LD~50~) for tungsten in rats is
5000 mg/kg and the estimated LD~50~ for humans is between 500 and 5000
mg/kg. This range is between an ounce and a pound for a 70 kg (154 lb.)
individual. However, no ill effects were observed in a patient given
25-80 grams of tungsten metal orally as a substitute for barium in
radiological examinations. The LD~50~ for tungstic oxides and tungstic
acid are approximately 1000 mg/kg in the rat via the oral route.

Tungsten metal and insoluble forms of tungsten have not been shown to be
mutagenic or carcinogenic. Tungsten has a reproductive hazard rating of
B- (few reproductive effects in animals but no human data) and a general
toxicity hazard rating of 1 (may cause reversible effects that are not
life threatening) according to REPROTEXT®. The toxicity hazard rating of
1 for tungsten is due more to its effects as a mechanical irritant than
to the toxicity of the compound.

[Respiratory toxicology]{.underline}:

Almost all human studies are of tungsten carbide and its alloys in
connection with its use in the hard metal industry. Hard metal disease,
a form of debilitating pulmonary fibrosis, occurs in persons chronically
exposed to the mixed dust of cobalt-cemented metal carbides. However,
pure tungsten did not cause pneumoconiosis, and hard metal disease is
believed to be caused by cobalt (ACGIH, 1986; Friberg *et al*, 1986).

Respirable particles less than 10 µm Mean Mass Aerodynamic Diameter
(MMAD) pose the greatest danger to health. The deposition of particles
in the respiratory system is influenced by four mechanisms: impaction,
sedimentation, interception, and diffusion. The MMAD of a particle will
also influence where is deposited within the respiratory system and, to
some extent, the rate of its elimination. The respiratory
characteristics for humans and particle clearance phases are tabulated
below:

Respiratory Characteristics for Humans

+-----------------+-----------------+-----------------+-----------------+
| **Respiratory** | **Number**      | **Diameter**    | **Flow Speed**  |
|                 |                 |                 |                 |
| **Region**      |                 | **(mm)**        | **(cm/sec)**    |
+-----------------+-----------------+-----------------+-----------------+
| Trachea         | 1               | 18              | 390             |
+-----------------+-----------------+-----------------+-----------------+
| Main Bronchus   | 2               | 12              | 430             |
+-----------------+-----------------+-----------------+-----------------+
| Terminal        | 66,000          | 0.6             | 5               |
| Bronchioles     |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Alveoli         | 3 x 10^8^       | 0.3             | \~0             |
+-----------------+-----------------+-----------------+-----------------+

(Kennedy and Valentine, 1994)

Particle Clearance Phases:

+-----------------------+-----------------------+-----------------------+
| **Anatomic Region**   | **Clearance**         | **Approximate         |
|                       |                       | Clearance Half-time** |
|                       | **Mechanism**         |                       |
+-----------------------+-----------------------+-----------------------+
| Nasopharynx           | Mucociliary transport | Minutes               |
+-----------------------+-----------------------+-----------------------+
| Tracheobronchial      | Mucociliary transport | Minutes to hours      |
+-----------------------+-----------------------+-----------------------+
| Alveolar              | Macrophages           | Days to weeks         |
+-----------------------+-----------------------+-----------------------+
| Pulmonary             | Interstitial          | Months                |
|                       | migration             |                       |
+-----------------------+-----------------------+-----------------------+
| Pulmonary             | Dissolution           | Months to years       |
+-----------------------+-----------------------+-----------------------+

(Kennedy and Valentine, 1994)

The International Commission on Radiologic protection (ICRP) has
developed a model for the deposition of particles in humans. The
collective data indicates that deposition is at a minimum with particles
approximately 0.3-0.5 µm MMAD. Particles in this size range are affected
the least by deposition mechanisms and particles greater than 30 to 80
µm are not inhalable through the nose. As indicated in the particle
clearance chart, above, particle size greatly affects clearance of
material from the respiratory system and the clearance mechanism
utilized.

Studies in animals have indicated that morphological changes occur in
the respiratory system after exposure to tungsten. Four months after
intertracheal instillation of tungsten metal, rats displayed an increase
in macrophage infiltration in proximity to pulmonary blood vessels. At
six months, there was distinct cellular proliferation around the blood
vessels with overlying collagenous fibers. At this time, there was also
a swelling of the endothelium and a thickening of the walls of the small
blood vessels. Some lymph nodes contained free particles of tungsten
carbide (Mezentseva, 1967). Rats inhaling tungsten carbide dust (600
mg/m^3^) remained healthy and displayed no morphological changes at this
concentration (Mezentseva, 1967).

The effect of tungsten metal dust on the respiratory system was
evaluated in guinea pigs (Delahant, 1955). His findings one month after
intertracheal instillation were similar to those of Mezentsva and
included macrophage infiltration and focal cellular lesions around
capillary blood vessels of the lung. Guinea pigs examined one year after
intertracheal instillation of tungsten metal dust displayed focal,
interstitial cellular infiltration caused by retained particles.

[Reproductive and teratogenic toxicity]{.underline}:

No information exists at this time on the effects of tungsten on
reproductive performance in humans. One study currently in progress is
an evaluation of birth rates among women in the tungsten mining industry
in China. No data is available at this time.

A study conducted by Wide (1984) indicated that mice given intravenous
sodium tungstate on day eight resulted in increased fetal resorptions.
Sodium tungstate, however, is a soluble form of tungsten and not a
potential chemical of concern for this review. It is the results of this
study that classified tungsten as a B- reproductive toxicant.

Dulak and his colleagues (1984) found no treatment related effects in
female rats fed a high tungsten diet. The study was conducted to assess
the effect of a sulfite oxidase-deficient rat model rather than to
observe the effects of dietary tungsten. A developmental trend was was
observed in anophthalmia (complete absence of eyes) in tungsten treated
rats, however, the observation was not significantly different from
control animals.

[Dermal and ocular toxicity (acute exposure)]{.underline}:

The standard Draize test was conducted on New Zeland white rabbits.
There was a mild reaction to tungsten metal on shaved rabbit skin
following an exposure of 500 mg for 24 hours. There was also a mild
reaction 24 hours after placing 500 mg of tungsten in the rabbit's eyes.
A few (20 of 1200) workers at a cemented tungsten manufacturing plant
had erythemateous, papular dermatitis. Patch tests demonstrated that
these workers were not sensitive to tungsten metal or tungsten oxides
but positive reactions followed exposure to cobalt and cobalt chloride.

[Systemic toxicology]{.underline}:

There are certain properties of an element that determine its biological
behavior. These include the stable oxidation state of an element or
compound at body pH, the solubility of the stable state, the tendency to
be incorporated into organic molecules, and the tendency to associate
with specific proteins.

Tungsten is capable of replacing the molybdenum molecule in several
protein systems responsible for oxygen modification. These enzyme
systems include xanthine dehydrogenase, xanthine oxidase, sulfite
oxidase, aldehyde oxidase, and nitrate reductase. In a study conducted
by Matsubara and his colleagues, tungsten displayed a protective effect
against paraquat induced toxicity in rats by inhibiting xanthine
oxidase. This was determined by examining S-phase chromosomes from liver
and lung cells 1, 3, and 5 days after exposing the rats to paraquat.
Rats fed a standard diet displayed an increase in S-phase cell
populations in the lungs while rats given a tungsten-enriched diet
displayed no increase in S-phase cell populations. A tungsten enriched
diet fed to rats for 4 weeks diminished xanthine oxidase and lessened
the rise in intracellular hydrogen peroxide production after
lippopolysaccharide treatment. Liver damage, as assessed by serum
transaminase levels, was also ameliorated by the tungsten-enriched diet.

Although no studies have indicated that tungsten is mutagenic or
carcinogenic, it could potentially contribute to these effects. One
study (Kirsch-Volders *et al*, 1997) indicated that although tungsten
carbide did not cause single strand breaks in DNA, in cultured human
peripheral lymphocytes, it may allow some uncoiling of the chromatin.
This effect may lead to an increased DNA sensitivity to clastogenic
effects. In another study, tungsten carbide alone does not produce DNA
single strand breaks while tungsten carbide cobalt produced more ssb
than cobalt alone. One indication is that the WC, when mixed with Co,
increases the production of hydroxyl radicals. Furthermore, WC may
modify the structure of chromatin, leading to increased DNA sensitivity
to clastogenic effects (Anard,1997).This information concurs with
results of the comet assay (single cell gel electrophoresis) where
tungsten cobalt did not induce DNA strand breakage in human leukocytes.

Recently, a case study appeared in *The Lancet* (Marquet *et al*, Oct.,
1996) which implicated tungsten in the illness of a young soldier. This
soldier, and others, had ingested wine poured through the barrel of a
155 mm artillery piece after several shots had been fired. The soldier
was admitted unconscious and with seizures to the hospital. The soldier
suffered anuric renal failure after three days and was placed on
hemodialysis. Renal biopsy demonstrated extensive tubular necrosis. The
soldier was released completely recovered 35 days after being admitted
to the hospital. Inductively coupled plasma emission spectrometry
indicated that there was a high level of tungsten in the wine (1540
mg/l) and in all biological samples measured. Dr. Lison (*The Lancet*,
Jan., 1997), who suggested that there was no causal relationship between
tungsten and toxicity, questioned the validity of Dr. Marquet's
assessment. No animal or human data supports the nephrotoxic activity of
tungsten. Nephrotoxicity as well as neurotoxicity has, however been
associated with some nitroaromatics used as a propellants for large
caliber artillery rounds and could explain, in part, some of the effects
noted in this particular soldier. This argument was refuted by Dr.
Marquett (*The Lancet*, Jan., 1997).

Some neurotoxic effects have been associated with the use of tungsten.
Tungsten metal has been used as a research tool to produce epilepsy in
cats. A 0.02 ml gel placed on the surface of the cortex produced
abnormal electroencephalogram (EEG) activity within 20 to 30 minutes
which eventually produced ictal (acute epileptic seizures) activity.
This system is used currently to model epilepsy. An evaluation of memory
deficits was conducted in 12 former hard metal workers who had been
exposed primarily to tungsten carbide and cobalt. These workers obtained
lower verbal memory index scores and had lower attention span than did
non-exposed workers. Their visual-spatial memory was unaffected. The
contribution of cobalt to these memory defecits is unknown.

**X. Environmental Effects of Tungsten**

Tungsten has few noticable effects on plants. According to one study,
tungsten inhibited trace metal uptake in plants. Studies on tungsten
uptake by bean plants were conducted at Oak Ridge National Laboratory.
These studies indicated that bean plants are capable of accumulating
tungsten from the soil. The uptake of tungsten powder was greater than
that for tungsten trioxide. This phenomenon may be due more to particle
size than to chemical properties of the materials

Tungsten has been found to be a suitable replacement for lead and steel
shot for waterfowl hunting. Embedded tungsten/bismuth/tin shot, as
compared to steel resisted corrosion and induced comparatively mild
inflammatory responses in mallard muscle tissue according to Krabbel and
his colleagues at the Colorado Division of Wildlife.

A study was conducted for the U.S. Army to determine the effect of soil
type (dry vrs. moist) on deposition concentration of tungsten. The
authors concluded that in dry soil, the concentration would not be
greatly reduced in 100 years while a substantial reduction would occur
in moist soil. Studies are currently being conducted at Oak Ridge
National Laboratories to determine mobility and corrosion of tungsten
under various conditions (Louden, 1998). This information will add to
the existing database on environmental fate of tungsten.

The EPA does not list tungsten as an environmental contaminant and no
studies have indicated that it is environmentally unsafe. There is some
concern on the effect of tungsten on the spectacled eider and, for that
reason, tungsten shot is not currently allowed in the Yukon-Kuskokwim
Delta region of Alaska. Toxicity testing is in progress that will
determine tungsten's effect on this bird.

**XI. Environmental Assessments Involving Tungsten**

Environmental assessments have been conducted at two sites where
tungsten was thought to be a problem. An environmental assessment, which
focused on tungsten, was conducted at the Kerr Reservoir. Although lead
was found at unacceptable levels, tungsten was not found at levels high
enough to be considered problematic. The Li Tungsten Corporation site in
Glen Cove, NY was placed on the National Priority List (NPL) in 1992.
Tungsten was not found at levels that were of concern to the U.S.
Environmental Protection Agency (EPA). The Li Tungsten site was placed
on the NPL due to the presence of several other materials such as
arsenic, cadmium, chromium, lead, and mercury.

**XII. Data Gaps**

Although there are a vast number of papers exist on tungsten and its
alloys in the medical literature, no papers were found that specifically
examine tungsten/tin or tungsten/nylon, the materials selected for the
small caliber rounds. It is unlikely that these alloys would be any more
insidious than tungsten metal, its oxides or its acids.

It is unknown if the tungstate ion is formed from firing tungsten
bullets, although this is unlikely, due to the chemical properties of
tungsten metal and its low reactivity at low temperatures. If this ion
is formed, further assessment will have to be performed in order to
determine the amount of ion formed and potential exposure.

**XIV. Conclusions**

Exposure to tungsten dust is highly probable in both manufacturing and,
to a far less extent, firing of small caliber munitions. The most likely
route of exposure is through the respiratory system followed by dermal
contact and ingestion. Once in the body, tungsten is, for the most part,
rapidly eliminated by the urinary system. The small fraction remaining
is incorporated primarily in bone, lung, and kidney from which it is
released at a slower rate. The application of appropriate engineering
methodologies and the use of personal protective equipment will
significantly reduce exposure to tungsten aerosols.

The effects of insoluble tungsten on biological systems are minimal. It
displays some systemic toxicity in that it can inhibit the activity of
some molybdenum-containing enzymes. This capability has led to
tungsten's use in the treatment of paraquat toxicity and
ischemia-reperfusion injury induced from organ transplants. Although
insoluble tungsten has not been identified as being mutagenic or
carcinogenic, it may contribute to clastogenic damage of DNA by causing
partial uncoiling of chromatin. Tungsten is a mechanical irritant when
inhaled and produces a generalized response by the body to foreign
material. This effect, whether produced by tungsten or some other
compound, presents some cause for concern. Although adverse reproductive
effects have been noted for sodium tungstate, there is no information on
the adverse reproductive effects of tungsten metal or insoluble forms of
tungsten.

The acceptance of tungsten as a replacement for lead is indicated by
recent policy decisions of the U.S. Fish and Wildlife Service and the
U.S. Environmental Protection Agency. These decisions are based on the
relative safety of tungsten as an environmental toxicant when compared
to lead. Increased use of tungsten products by the public is indicated
by a wider range and increased sales of tungsten products.

Based on the evaluation of the available data, there appears to be
minimal risk associated with the use of tungsten bullets. On a
comparative basis, tungsten is far less toxic to humans and the
environment than the copper/lead currently used.

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     and Tungsten Complexes of I -Thioglucose,, *J Organometallic Chem.*
     479:217-220.

450. Zisa, T. 1997. Demonstration of lead-free projectile alternatives
     for 5.56 mm ammunition. Technical Report prepared for the U.S. Army
     Armament Research, Development and Engineering Center, Picatinny
     Arsenal, NJ

**APPENDIX II:**

**SOLUBILITY OF SELECTED TUNGSTEN COMPOUNDS**

Adapted from NIOSH Publication No. 77-127, *Criteria for a Recommended
Standard. Occupational Exposure to Tungsten and Cemented Tungsten
Carbide*, September 1977.

+------------------------+-------------------+-------------------------+
| **Compound Name**      | **Chemical        | **Solubility (g/100cc   |
|                        | Formula**         | H~2~O) \***             |
+------------------------+-------------------+-------------------------+
| Ammonium metatungstate | (NH~4~)           | Soluble                 |
|                        | ~6~H~2~W~12~O~40~ |                         |
+------------------------+-------------------+-------------------------+
| Ammonium paratungstate | (NH~4~)~10~       | Insoluble               |
|                        | (H~10~W~12~O~46~) |                         |
+------------------------+-------------------+-------------------------+
| Ammonium               | (NH~4~)~          | Soluble                 |
| phosphotungstate       | 3~P(W~3~O~10~)~4~ |                         |
+------------------------+-------------------+-------------------------+
| Cadmium tungstate      | CdWO~4~           | 0.05                    |
+------------------------+-------------------+-------------------------+
| Calcium tungstate      | CaWO~4~           | 0.00064 @ 15ºC 0.00323  |
|                        |                   | @ 25ºC                  |
+------------------------+-------------------+-------------------------+
| Calcium tungstate      | CaWO~4~           | 0.013 @ 20ºC 0.0002 @   |
| (Sheelite)             |                   | 90ºC                    |
+------------------------+-------------------+-------------------------+
| Calcium metatungstate  | Ca~3~H            | Decomposes in acid      |
|                        | ~4~\[H~2~(W~2~O~7 |                         |
|                        | ~)~6~\]·~27~H~2~O |                         |
+------------------------+-------------------+-------------------------+
| Cerium (III) tungstate | Ce~2~(WO~4~)~3~   | \-                      |
+------------------------+-------------------+-------------------------+
| Cesium tungstate       | CsWO~4~           | 85.6 @ 17ºC             |
+------------------------+-------------------+-------------------------+
| Cobalt tungstate       | CoWO~4~           | Insoluble               |
+------------------------+-------------------+-------------------------+
| Copper (III) tungstate | CuWO~4~·~4~H~2~O  | 0.1 @ 15ºC              |
+------------------------+-------------------+-------------------------+
| Cycl                   | (C~5~H~           | \-                      |
| opentadienylbitungsten | 5~)~2~W~2~(CO)~6~ |                         |
|                        |                   |                         |
| Hexacarbonyl           |                   |                         |
+------------------------+-------------------+-------------------------+
| Iron (II) tungstate    | FeWO~4~           | \-                      |
+------------------------+-------------------+-------------------------+
| Lead tungstate         | PbWO~4~           | 0.00159 @ 25ºC          |
+------------------------+-------------------+-------------------------+
| Lithium tungstate      | Li~2~WO~4~        | Very soluble            |
+------------------------+-------------------+-------------------------+
| Magnesium tungstate    | MgWO~4~           | Insoluble               |
+------------------------+-------------------+-------------------------+
| Mercury (I) tungstate  | Hg~2~WO~4~        | Insoluble               |
+------------------------+-------------------+-------------------------+
| Mercury (II) tungstate | HgWO~4~           | Insoluble               |
+------------------------+-------------------+-------------------------+
| Mesitylene-tungsten    | (CH~3~)~3         | \-                      |
| tricarbonyl            | ~C~6~H~3~W(CO)~3~ |                         |
+------------------------+-------------------+-------------------------+
| Metatungstic acid      | H~2               | 88.57 @ 22ºC            |
|                        | ~W~4~O~13~·9H~2~O |                         |
+------------------------+-------------------+-------------------------+
| Phosphotungstic acid   | H~3~\[            | Soluble                 |
|                        | P(W~3~O~10~)~4~\] |                         |
|                        | ·14H~2~O          |                         |
+------------------------+-------------------+-------------------------+
| Phosphotungstic acid   | H~3~\[            | Soluble                 |
|                        | P(W~3~O~10~)~4~\] |                         |
|                        | ·24H~2~O          |                         |
+------------------------+-------------------+-------------------------+
| Potassium tungstate    | K~2~WO~4~·2H~2~O  | 51.5                    |
+------------------------+-------------------+-------------------------+
| Potassium              | K~6~(H~2~W~       | Soluble                 |
| metatungstate          | 12~O~40~)·18H~2~O |                         |
+------------------------+-------------------+-------------------------+
| Silicotungstic acid    | H~8~SiW~12~O~42~  | 961.5 @ 18ºC            |
+------------------------+-------------------+-------------------------+
| Silver tungstate       | Ag~2~WO~4~        | 0.05 @ 15ºC             |
+------------------------+-------------------+-------------------------+
| Sodium tungstate       | Na~2~WO~4~        | 57.5 @ 0ºC              |
|                        |                   |                         |
|                        |                   | 73.2 @ 21ºC             |
+------------------------+-------------------+-------------------------+
| Sodium tungstate,      | Na~2~WO~4~·2H~2~O | 41.0 @ 0ºC              |
| dihydrate              |                   |                         |
+------------------------+-------------------+-------------------------+
| Sodium metatungstate   | Na~               | Soluble                 |
|                        | 2~O·WO~2~·10H~2~O |                         |
+------------------------+-------------------+-------------------------+
| Sodium paratungstate   | Na~6~             | 8                       |
|                        | W~7~O~24~·16H~2~O |                         |
+------------------------+-------------------+-------------------------+
| Strontium tungstate    | SrWO~4~           | 0.14 @ 15ºC             |
+------------------------+-------------------+-------------------------+
| **Tungsten (Wolfram)** | **W**             | **Insoluble**           |
+------------------------+-------------------+-------------------------+

\* insoluble compounds have a water solubility of less than 0.01g/100cc

**SOLUBILITY OF SELECTED TUNGSTEN COMPOUNDS**

Adapted from NIOSH Publication No. 77-127, *Criteria for a Recommended
Standard. Occupational Exposure to Tungsten and Cemented Tungsten
Carbide*, September 1977.

+------------------------+-------------------+-------------------------+
| **Compound Name**      | **Chemical        | **Solubility**          |
|                        | Formula**         |                         |
|                        |                   | **(g/100cc H2O)\***     |
+------------------------+-------------------+-------------------------+
| Tungsten arsenide      | WAs~2~            | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten diboride      | WB~2~             | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten dibromide     | WBr~2~            | Decomposes              |
+------------------------+-------------------+-------------------------+
| Tungsten pentabromide  | WBr~5~            | Decomposes              |
+------------------------+-------------------+-------------------------+
| Tungsten hexabromide   | WBr~6~            | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten carbide       | WC                | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten dicarbide     | WC~2~             | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten carbonyl      | W(CO)~6~          | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten dichloride    | WCl~2~            | \-                      |
+------------------------+-------------------+-------------------------+
| Tungsten tetrachloride | WCl~4~            | \-                      |
+------------------------+-------------------+-------------------------+
| Tungsten pentachloride | WCl~5~            | \-                      |
+------------------------+-------------------+-------------------------+
| Tungsten hexachloride  | WCl~6~            | Decomposes              |
+------------------------+-------------------+-------------------------+
| Tungsten hexafluoride  | WF~6~             | Decomposes              |
+------------------------+-------------------+-------------------------+
| Tungsten diiodide      | WI~2~             | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten tetraiodide   | WI~4~             | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten dinitride     | WN~2~             | Decomposes              |
+------------------------+-------------------+-------------------------+
| Tungsten dioxide       | WO~2~             | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten trioxide      | WO~3~             | Insoluble               |
| (Wolframite)           |                   |                         |
+------------------------+-------------------+-------------------------+
| Tungsten pentoxide     | W~2~O~5~ or       | Insoluble               |
|                        | W~4~O~11~         |                         |
+------------------------+-------------------+-------------------------+
| Tungsten               | WO~2~Br~2~        | \-                      |
| dioxydibromide         |                   |                         |
+------------------------+-------------------+-------------------------+
| Tungsten               | WOBr~4~           | Decomposes              |
| oxytetrabromide        |                   |                         |
+------------------------+-------------------+-------------------------+
| Tungsten               | WOCl~4~           | Decomposes              |
| oxytetrachloride       |                   |                         |
+------------------------+-------------------+-------------------------+
| Tungsten               | WO~2~Cl~2~        | Soluble                 |
| dioxydichloride        |                   |                         |
+------------------------+-------------------+-------------------------+
| Tungsten               | WOF~4~            | Decomposes              |
| oxytetrafluoride       |                   |                         |
+------------------------+-------------------+-------------------------+
| Tungsten phosphide     | WP                | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten phosphide     | WP~2~             | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten phosphide     | W~2~P             | \-                      |
+------------------------+-------------------+-------------------------+
| Tungsten silicide      | Wsi~2~            | Insoluble               |
+------------------------+-------------------+-------------------------+
| Tungsten disulfide     | WS~2~             | Insoluble               |
| (Tungstenite)          |                   |                         |
+------------------------+-------------------+-------------------------+
| 12-Tungstophosphoric   | P~2~O~5           | 86.75 @ 92ºC            |
| acid                   | ~·24WO~3~·45H~2~O |                         |
+------------------------+-------------------+-------------------------+

\* insoluble compounds have a water solubility of less than 0.01g/100cc