Health effects of tungsten
Contents
Introduction
Tungsten is a naturally occurring element that, in most environments, is a solid. In nature, it occurs in rocks and soil as minerals, but never as the pure metal. Two kinds of tungsten-bearing mineral rocks, called wolframite and scheelite, are mined commercially. The mineral ore is processed to recover the tungsten and turn it into either chemical compounds or metal. Elemental tungsten, like elemental copper or gold, is a metal. Its color can range from tin white (for the pure metal) to steel gray (for metal that has impurities in it). Tungsten can be used as a pure metal or mixed with other metals to make alloys. Tungsten alloys tend to be strong and flexible, resist wear, and conduct electricity well. Tungsten and its alloys are used as light bulb filaments, as the part of x-ray tubes where x-rays are formed, as a catalyst to speed up chemical reactions, as a component of steel in high-speed tools, in turbine blades, in phonographic needles, as welding electrodes, as gyroscope wheels, as counterbalance and fishing weights, in darts, and in golf club components. They can be used in bullets (as a replacement for lead) and in armor penetrators (as a substitute for depleted uranium). Chemical compounds of tungsten are used for many purposes. Cemented tungsten carbide, a hard substance used to make grinding wheels and cutting or forming tools, is the most common tungsten compound. Other tungsten compounds are used in ceramic pigments, as fire retardant coatings for fabrics, and as fade-resistant dyes for fabrics.
Pathways for tungsten in the environment
Tungsten occurs naturally in the environment, in minerals, but not as the pure metal. As an element, tungsten can be neither created nor destroyed chemically, although tungsten can change forms in the environment.
Tungsten is released into air as fine dust-like particles by weathering. Emissions from hard metal industries also increase tungsten levels in air. The amount of tungsten that has been measured in the ambient air is, in general, less than 10 billionths of a gram per cubic meter (or parts per billion [ppb]). Very small dust particles of tungsten in the air fall out onto surface water, plant surfaces, and soil either by themselves or when rain or snow falls. These tungsten particles eventually recycle back in the soil or in the bottoms of lakes, rivers, and ponds, where they stay and mix with tungsten that is already there.
Tungsten in water originates mainly from dissolution of tungsten from rocks and soil that water runs over and through. Tungsten has not been detected in the vast majority of surface water and groundwaters of the United States. Some exceptions include areas near mines and natural deposits, and also in Churchill County (City of Fallon), in Nevada, where tungsten has been detected in municipal water and groundwater. Only a very small fraction of tungsten in water originates from the settling of dust out of the air. Most tungsten products of human-origin that enter waterways originate from industry discharges of waste water. Tungsten in water may be in either soluble or insoluble forms. Insoluble tungsten in water can settle to the bottom where it enters sediment. Some insoluble tungsten compounds, however, can remain suspended in ocean water for many years, requiring as long as 1,000 years to settle to the bottom.
Tungsten occurs naturally in soil as a mineral, or component of soil. It occurs in amounts that vary over a wide range from less than 1 to as high as 83 thousandths of a gram per kilogram of soil. Another way to say this is that the tungsten concentration ranges from 1 to 83 parts per million (ppm) in soil by weight. Disposal of coal ash, incinerator ash, and industrial wastes may increase the amount of tungsten in soil. A portion of tungsten in soil does not dissolve in water, but remains bound and is not likely to move deeper into the ground and enter groundwater. The remaining soluble portion may move deeper into the ground and enter groundwater if the pH is greater than 7. In the environment, chemical reactions can change the water-soluble tungsten compounds into insoluble forms. In some cases, water-insoluble tungsten compounds can change to soluble forms. In general, exposure to water-soluble tungsten compounds in the environment will pose a greater threat to human health than water-insoluble forms.
Exposure to tungsten
You can be exposed to low levels of tungsten by breathing air, drinking water, or eating food that contains tungsten. The average ambient concentration of tungsten in air has been reported to be less than 10 nanograms in a cubic meter of air (1 nanogram is 1 billionth of a gram). Cities have higher levels of tungsten in the air because tungsten is released from industry. Tungsten has been detected in municipal water from Fallon, Nevada. However, the amounts of tungsten in drinking water are generally not known. This is probably because the tungsten levels are lower than the laboratory methods are able to detect without concentrating samples, or the laboratory does not measure for tungsten. The amounts in foods are generally not known, possibly for the same reasons. Tungsten in plants was either taken up by the plant or was attached to the plant as a component of the soil. The concentration of tungsten in onions collected from Denmark is 17 micrograms in a kilogram of fresh vegetables. Although very limited data are available, exposure to tungsten from air, drinking water, and food is expected to be insignificant.
In certain workplaces, you can be exposed to levels of tungsten in air that are higher than background levels, which are very small or none. Exposures are mostly in the form of tungsten metal or tungsten carbide. Occupational exposure to tungsten occurs primarily at places where individuals use hard metals containing tungsten or are engaged in the machining of these metals. This includes the grinding (pointing) of tungsten metal welding electrodes prior to use. Occupational exposure to tungsten carbide occurs during the machining of tungsten carbide tools in the manufacturing process. The total number of individuals occupationally exposed to tungsten or its compounds has been estimated to be about 47,000.
Tungsten metal and metal alloys occur in consumer products such as electronics, light bulb filaments, cemented tungsten carbide grinding wheels, carbide tipped tools, and "green" bullets. No other consumer products or products used in crafts, hobbies, or cottage industries were identified that contain significant amounts of tungsten. It is unlikely that tungsten present in consumer products poses a hazard. However, appropriate dust masks are recommended for amateur craftsmen engaging in activities that may potentially produce tungsten carbide dust (e.g., metal grinding).
Pathways for tungsten in the body
Tungsten can enter your body from the food you eat or the water you drink, from the air you breathe, or from contact with the skin. When you eat, drink, breathe, or touch things containing tungsten compounds that can easily be dissolved in water, tungsten enters your blood and is carried to all parts of your body. Most of the tungsten that enters your blood is rapidly released from your body in the urine. When you eat or drink things containing tungsten, much of the tungsten passes through your digestive system and is released from your body in the feces. When you breathe air that contains tungsten, some of the tungsten moves quickly to your bloodstream from the lungs, and some of the tungsten is cleared from your lungs in mucus that is either swallowed or spit out. When you swallow tungsten that was first in your lungs, it passes through your digestive system as if you had eaten it. Some enters your blood from your digestive system and some passes out with the feces. A small portion of the tungsten that enters your blood may spend some time in bone, fingernails, or hair. Some of this tungsten is slowly eliminated from your body through the urine and feces.
Health effects of tungsten
Scientists use many tests to protect the public from harmful effects of toxic chemicals and to find ways for treating persons who have been harmed.
One way to learn whether a chemical will harm people is to determine how the body absorbs, uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal testing may also help identify health effects such as cancer or birth defects. Without laboratory animals, scientists would lose a basic method for getting information needed to make wise decisions that protect public health. Scientists have the responsibility to treat research animals with care and compassion. Scientists must comply with strict animal care guidelines because laws today protect the welfare of research animals.
You are not likely to experience any health effects that would be related to exposure to tungsten or tungsten compounds. Tungsten compounds have caused breathing problems and changed behavior in some animals given very large amounts of tungsten compounds, but you are not likely to be exposed to amounts of tungsten in the air you breathe or the food or water you take into your body that would be large enough to cause similar effects. If you are a worker who has inhaled tungsten heavy metal dust, your exposure would help determine if health effects similar to those seen in animals might occur.
Health effects of tungsten on children
This section discusses potential health effects in humans from exposures during the period from conception to maturity at 18 years of age.
Children could be affected in the same ways as adults. In adult animals, very large amounts of tungsten compounds have been shown to cause breathing problems and changes in behavior. However, it is not likely that children would be exposed to amounts of tungsten in the air they breathe or the food or water they consume that would be large enough to cause effects similar to those that were seen in the animals. Animal studies have shown that tungsten in the blood of a pregnant mother can enter the blood of a fetus in the womb. Studies in dairy cows have shown that tungsten may also enter the milk. There is no information to suggest that the effects seen in animals could not occur in humans. We do not know whether unborn babies, babies, and children might differ from adults in their susceptibility to health effects from exposure to tungsten or tungsten compounds.
Reducing risk of exposure to tungsten
If your doctor finds that you have been exposed to substantial amounts of tungsten, ask whether your children might also have been exposed. Your doctor might need to ask your state health department to investigate.
Children living near waste sites containing tungsten are likely to be exposed to higher environmental levels of tungsten through breathing contaminated air, drinking contaminated water, touching soil, and eating contaminated soil. Children sometimes eat dirt, which should be discouraged. Parents should supervise to see that children wash their hands frequently and before eating. Parents should consult their family physicians about whether (and how) hand-to-mouth behaviors in their children might be discouraged. If your community's drinking water has been reported to contain elevated levels of tungsten, you should take advantage of alternative water sources such as bottled water for drinking. Some children may be exposed to tungsten by contact with a family member who works in a facility using tungsten or who works with tungsten carbide grinding wheels. If you work at a facility that uses tungsten or have tungsten dust on your clothes, change your clothes and clean your hair and skin before leaving your job or work site and returning home. Do not bring objects home such as work tools that may be contaminated with tungsten.
Further Reading
| Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content. |
1 Comment
Robert Johannesburg wrote: 11-15-2011 02:43:15
This was really interesting and informative. I was a little confused, though, when you said that it does not occur naturally as a pure metal. Aren't all metals that way? They are usually mixed in with rock and soil as an ore, and must be mined out? Also, you said that tungsten is most commonly found as two substances, one of which is carbide. When this is made into tungsten carbide tools, how durable are they? Are they long-lasting? I've been thinking about getting some, but I am not sure how good they are. ( http://duragrit.com )