Tungsten (W), atomic number 74, is a refractory metal known for its extremely high melting point and remarkable hardness. This durability makes it highly valued for use in heating elements, high-speed cutting tools, and light bulb filaments. As a heavy metal, people often question the safety of everyday interaction, specifically whether touching the metal poses a health risk. Understanding its safety profile requires differentiating between the pure metal and its various chemical compounds and alloys.
Dermal Safety of Elemental Tungsten
Elemental tungsten in its solid, bulk form is considered biologically inert and presents virtually no risk of toxicity through casual skin contact. The metal is highly stable and does not readily react with oxygen or acids, making it resistant to corrosion. This inertness is maintained even when exposed to the biological fluids found on the skin’s surface.
The protective outer layer of the skin, the epidermis, effectively prevents the absorption of solid tungsten metal particles. Because pure tungsten is insoluble in water and biological systems, no significant amount of the element can pass through the skin barrier into the bloodstream. Therefore, handling items like tungsten jewelry or tools made from the pure metal is generally regarded as safe.
The Role of Compounds and Alloys in Toxicity
Toxicity concerns related to tungsten arise not from the pure, solid metal but from forms that are far more bioavailable to the body. These hazardous forms are typically found in industrial settings, where tungsten is chemically altered or combined with other elements. The two most concerning categories are cemented carbides and soluble tungsten compounds.
The most significant industrial risk is associated with cemented carbide, often called “hard metal,” a composite of tungsten carbide (WC) powder mixed with a binder. This binder is most frequently cobalt (Co). The toxicity observed in hard metal manufacturing is primarily attributed to the cobalt component, which can leach from the particles and cause a toxic response.
Tungsten carbide particles act in combination with cobalt, often enhancing the overall toxic effect beyond what cobalt alone would cause. This mixture increases the body’s uptake of cobalt and promotes a synergistic toxic reaction when inhaled as fine dust. This combination, rather than the tungsten carbide itself, drives severe health outcomes in workers.
Another concern is soluble tungsten compounds, such as tungsten oxides and tungstate salts (e.g., sodium tungstate). Unlike the metal, these forms are easily dissolved in water and are much more readily absorbed by the body if inhaled or ingested. This solubility is the key factor that allows tungsten to enter the systemic circulation and cause adverse effects.
Health Consequences of Internal Exposure
When bioavailable tungsten, such as soluble salts or fine alloy dust, enters the body, it leads to specific health consequences, primarily through inhalation in occupational settings. The main route of internal exposure is the inhalation of fine particulates generated during the grinding or processing of hard metal alloys. These particles are small enough to bypass the body’s natural defenses and deposit deep within the lungs.
One severe outcome of industrial exposure is Hard Metal Disease, a form of occupational lung disease. This disease is characterized by a progressive scarring of the lung tissue, known as interstitial fibrosis, or a unique pattern called giant cell interstitial pneumonia. These conditions impair the lung’s ability to transfer oxygen, leading to persistent symptoms like shortness of breath and chronic cough.
Soluble tungstates that enter the bloodstream interfere with the body’s metabolic processes by interacting with the trace element molybdenum. Molybdenum is required for several important enzymes, and because tungsten and molybdenum are chemically similar, tungsten can competitively replace molybdenum in these enzymes. This replacement effectively inactivates the enzymes, creating a functional molybdenum deficiency that may affect purine metabolism.
Because of these risks from dust and soluble forms, regulatory bodies like the Occupational Safety and Health Administration (OSHA) have established strict exposure limits for airborne tungsten. These regulations differentiate between insoluble tungsten compounds, which have a permissible exposure limit of 5 milligrams per cubic meter of air over an eight-hour workday, and soluble compounds, which are limited to 1 milligram per cubic meter. These precautions protect workers from the hazards posed by the dust and chemical forms.