Antimony (Sb), a metalloid element, is a common component in ammunition manufacturing. It is used primarily to enhance the performance of the main projectile material, typically lead, creating a lead-antimony alloy that is structurally superior for ballistic purposes. However, the inclusion of this element introduces significant environmental and health concerns due to its inherent toxicity and mobility once released.
Why Antimony is Used in Bullet Alloys
Pure lead is a soft, dense metal that lacks the necessary structural integrity for modern high-velocity ammunition. If a bullet is too soft, it can deform severely upon firing or impact, which compromises accuracy and penetration. To counteract this softness, manufacturers alloy the lead with other metals to increase its hardness and tensile strength.
Antimony is the preferred additive, typically making up between 1% and 5% of the lead alloy mass in commercial and military ammunition. This addition creates a much stiffer projectile that resists deformation from the intense pressure within a gun barrel. The resulting alloy improves the bullet’s ability to maintain its shape, which is crucial for consistent ballistic performance and deeper penetration. Furthermore, the hardened alloy reduces lead residue left behind in the barrel’s rifling (fouling), which degrades a firearm’s accuracy over time.
Exposure Risks and Environmental Pathways
Antimony is released into the environment through two primary pathways: shooting ranges and field contamination. At indoor and outdoor firing ranges, the act of firing aerosolizes antimony-containing particles from the primer and the bullet’s base. These activities generate fine dust and particulate matter that can be inhaled or ingested by shooters and range employees.
The accumulation of spent rounds in the soil of outdoor ranges creates a chronic environmental reservoir for antimony contamination. Over time, the metallic antimony in the fragmented bullets weathers and corrodes, releasing soluble antimony compounds into the environment. Research has shown that antimony concentrations in range soils can be orders of magnitude higher than natural background levels, sometimes reaching tens of thousands of milligrams per kilogram. Antimony compounds are often highly mobile, leaching into groundwater or surface runoff.
In natural settings, such as hunting areas, the fragmentation of lead-antimony bullets upon impact with game or natural barriers also disperses the metalloid. This leaves small fragments in the environment, which can introduce antimony into the food chain if scavengers or other animals consume contaminated tissue or soil. The high mobility of antimony in certain soil conditions means that it can pose a greater risk of water contamination than lead, which tends to bind more tightly to soil particles.
Health Effects of Antimony
Exposure to antimony, whether acute or chronic, can lead to adverse health outcomes. Inhaling high concentrations of antimony dust, such as that found in poorly ventilated shooting ranges, can cause acute symptoms like irritation of the respiratory tract, eyes, and skin. Other immediate effects following significant exposure may include headache, nausea, vomiting, and abdominal pain.
With long-term exposure, more serious health issues can develop, affecting multiple organ systems. Chronic inhalation has been associated with pneumoconiosis, a form of lung disease. Antimony exposure is also linked to cardiovascular stress, sometimes manifesting as altered electrocardiograms, and it can contribute to liver damage. The U.S. Department of Health and Human Services has identified antimony trioxide, a common compound of the metalloid, as a substance reasonably anticipated to be a human carcinogen.