What Is Antimony?

Antimony is a naturally occurring trace element with the chemical symbol Sb. It is commonly grouped with heavy metals in drinking water because it is persistent, inorganic, toxic at elevated concentrations, and not biodegradable. Chemically, antimony behaves as a metalloid: it has properties between metals and nonmetals and can occur in several oxidation states depending on groundwater chemistry.

In the environment, antimony is most often associated with sulfide minerals, especially stibnite, an antimony sulfide ore. It can also be present with arsenic, lead, copper, silver, zinc, and gold deposits. In drinking water, antimony is usually measured at very low concentrations, but localized exceedances can occur near mineralized bedrock, mine tailings, smelters, shooting ranges, landfills, industrial discharge areas, or plumbing systems containing antimony-bearing alloys.

Antimony is not an essential nutrient for humans. The drinking water concern is primarily chronic ingestion: repeated exposure over months or years may contribute to adverse health effects, particularly involving the gastrointestinal system, liver, cardiovascular system, blood chemistry, and general systemic toxicity. Because antimony has no taste, odor, or color at levels of health concern, laboratory analysis is required to detect it.

Scientific Identity

Elemental antimony is identified by the symbol Sb and CAS number 7440-36-0. In water, however, antimony is rarely present as shiny elemental metal. It occurs as dissolved ionic or oxyanion species, as complexes with hydroxide, chloride, sulfide, or organic matter, or as particulate-bound antimony attached to iron oxides, manganese oxides, clays, or suspended sediment. The form present strongly affects mobility and treatment performance.

The two most important oxidation states in natural waters are antimony(III), often written Sb(III), and antimony(V), written Sb(V). Sb(III) is generally more toxic and can be more difficult to remove under some treatment conditions. Sb(V) is commonly present in oxygenated waters as antimonate species, while Sb(III) may occur under reducing or low-oxygen conditions, in geothermal settings, in deeper groundwater, or near sulfide-rich mineral deposits. Changes in oxidation-reduction conditions can shift antimony between these forms.

Antimony’s chemistry overlaps with arsenic in several ways, but the two elements are not identical in treatment behavior. Both can form oxyanions and both may be mobilized from mineral deposits, yet antimony can bind differently to adsorption media and ion exchange resins. For this reason, a treatment system designed for arsenic should not be assumed to remove antimony unless antimony-specific testing confirms performance.

How Antimony Enters Drinking Water

Natural geology is a major source of antimony in some groundwater supplies. Wells drilled into mineralized zones, sulfide-bearing bedrock, volcanic formations, geothermal areas, or sedimentary units enriched with trace metals may produce water containing dissolved antimony. Weathering of stibnite and related minerals can release antimony into groundwater, especially where oxidation of sulfide minerals generates acidic or metal-rich drainage.

Mining and ore processing can create concentrated sources. Waste rock, mine tailings, smelter residues, and drainage from abandoned or active mining areas may leach antimony along with arsenic, lead, zinc, copper, cadmium, or sulfate. Even where mining has stopped, tailings and disturbed rock can remain chemically reactive for decades. Surface water and shallow wells downstream of these areas can be vulnerable, particularly during storm runoff or seasonal changes in groundwater flow.

Industrial sources include flame retardant manufacturing, metal alloy production, glass and ceramics manufacturing, plastics and polyester production, ammunition, batteries, pigments, and historical smelting operations. Antimony trioxide is widely used as a flame retardant synergist in plastics and textiles. Industrial releases may reach water through wastewater discharge, contaminated soils, landfill leachate, or atmospheric deposition near processing facilities.

Distribution systems and building plumbing can also contribute. Antimony may be present in some metal alloys, solders, fittings, brass components, pump parts, or lead-antimony alloys. Corrosive water, low pH, high chloride, high sulfate, stagnation, and elevated temperature can increase leaching from susceptible materials. This plumbing-related pathway is usually site-specific and may be more evident in first-draw samples than in flushed samples.

Occurrence and Exposure

Antimony in drinking water is usually a localized problem rather than a uniform regional contaminant. Public water supplies may monitor for antimony under national or local drinking water regulations, but private wells often have no routine testing requirement. Households using private wells near mineralized bedrock, mines, smelters, industrial corridors, landfills, or old shooting ranges should treat antimony as a plausible trace-metal risk.

Groundwater exposure is most important because antimony can dissolve from minerals and persist in aquifers. Shallow wells may be affected by surface contamination, while deeper wells may encounter naturally reducing water in which antimony is more mobile. Water with elevated iron, manganese, arsenic, sulfate, or low pH may indicate geochemical conditions where trace metals deserve broader testing, although antimony can occur without obvious visible signs.

Diet, air, occupational contact, and consumer products can also contribute to total antimony exposure, but drinking water becomes more significant when concentrations are elevated or when water is used for infant formula, cooking, beverages, and daily consumption. Boiling does not remove antimony; it can slightly concentrate dissolved metals as water evaporates. For households with confirmed antimony above a health-based guideline, untreated water should not be used for long-term drinking or food preparation.

Health Effects and Risk

Antimony is considered a high-priority drinking water contaminant when present above health-based limits because chronic ingestion can produce systemic toxicity. Health effects reported in toxicological studies and occupational literature include gastrointestinal irritation, nausea, vomiting, diarrhea, changes in blood chemistry, liver effects, and cardiovascular effects. The risk depends on concentration, duration, chemical form, age, nutritional status, and co-exposure to other metals.

Sb(III) compounds are generally regarded as more toxic than Sb(V) compounds, but routine drinking water tests often report total antimony rather than speciation. Because speciation is not usually included in standard compliance testing, health evaluations typically compare total antimony to regulatory or guideline values. This conservative approach is appropriate because water chemistry may change between the aquifer, treatment system, storage tank, and tap.

Antimony is less strongly associated with bioaccumulation in humans than some metals such as mercury or cadmium, but it can persist in the body for a period after exposure and may affect multiple organ systems. Infants, pregnant people, individuals with kidney or liver disease, and people consuming large volumes of water may have less margin of safety. Co-occurrence with arsenic, lead, thallium, beryllium, or other toxic metals increases the need for a complete risk assessment rather than focusing on antimony alone.

Short-term exposure to slightly elevated antimony is generally less concerning than long-term daily ingestion. However, very high concentrations, such as those that may occur in contaminated industrial or mining settings, warrant immediate action. If test results show antimony above the applicable drinking water standard or guideline, the safest response is to switch to a verified alternative drinking water source or install certified treatment while investigating the source.

Testing and Monitoring

Antimony cannot be detected by sight, taste, or odor. Testing requires a certified laboratory using trace metals methods such as inductively coupled plasma mass spectrometry, commonly abbreviated ICP-MS, or inductively coupled plasma optical emission spectroscopy, ICP-OES, when detection limits are appropriate. Graphite furnace atomic absorption may also be used in some laboratories. Results are typically reported as micrograms per liter, written as µg/L, or milligrams per liter, written as mg/L.

For private wells, antimony should be included in a broad metals panel when the well is near mining activity, sulfide-bearing bedrock, industrial land use, landfill influence, or unexplained corrosion. A useful panel often includes arsenic, lead, cadmium, chromium, selenium, barium, beryllium, thallium, nickel, copper, zinc, iron, manganese, pH, alkalinity, hardness, sulfate, chloride, and total dissolved solids. These companion results help identify geochemical patterns and select treatment.

Sampling technique matters. If the concern is aquifer contamination, collect a flushed sample after the plumbing has been cleared according to laboratory instructions. If the concern is plumbing leaching, collect both a first-draw sample after stagnation and a flushed sample. The difference between the two can help distinguish source-water antimony from corrosion-related antimony. Samples should be collected in laboratory-provided bottles and preserved as directed, often with acid preservation for dissolved metals.

After treatment is installed, retesting is essential. A point-of-use reverse osmosis system should be tested at the treated tap after installation and periodically thereafter. For ion exchange or adsorption systems, monitoring should include influent and effluent samples because breakthrough can occur before taste or appearance changes. If water chemistry changes seasonally, annual testing may not be enough for high-risk wells.

Treatment Methods

Antimony treatment should be selected based on measured concentration, oxidation state where known, competing ions, pH, total dissolved solids, and whether the source is groundwater or plumbing corrosion. The most reliable residential approach for drinking and cooking water is usually point-of-use reverse osmosis, provided the system is properly certified, maintained, and verified by post-treatment testing.

Reverse osmosis deserves special attention for antimony because it is often the most practical high-performance residential option. A properly functioning RO system uses a semi-permeable membrane to separate dissolved ions from treated water. Antimony, whether present as charged oxyanions or associated dissolved species, is generally reduced substantially when the membrane is intact and operating within its design range. RO is especially appropriate when antimony occurs with arsenic, selenium, thallium, beryllium, barium, uranium, nitrate, or elevated total dissolved solids.

RO can fail or underperform if the membrane is old, fouled by iron or manganese, scaled by hardness, damaged by chlorine beyond its tolerance, operated at low pressure, or bypassed by faulty seals. High levels of suspended solids, iron bacteria, or manganese can clog pretreatment cartridges and reduce flow. In hard water, scale control or softening may be needed upstream. RO also produces a reject stream, so installation must account for drainage and water use efficiency.

Point-of-use RO at the kitchen sink is usually sufficient when the goal is safe water for drinking, cooking, coffee, tea, and infant formula. Whole-house, point-of-entry RO is rarely the first choice because it is expensive, produces large wastewater volumes, requires pretreatment, and may create corrosive low-mineral water that needs stabilization. Point-of-entry treatment may be justified when antimony is also a bathing, inhalation aerosol, livestock, irrigation, or whole-building process concern, or when multiple taps must provide treated potable water. For most homes, a certified point-of-use RO system plus post-installation laboratory confirmation is the preferred strategy.

Regulations and Guidelines

Antimony is regulated or assigned guideline values in many drinking water programs, but the exact legal limit varies by country and jurisdiction. In the United States, the U.S. Environmental Protection Agency has established a federal drinking water standard for antimony under the National Primary Drinking Water Regulations. Public water systems subject to this rule must monitor and comply according to EPA and state implementation requirements. State rules may be equivalent to or more stringent than federal requirements.

The World Health Organization has published a health-based guideline value for antimony in drinking water. WHO guideline values are not automatically enforceable laws; they are used by countries as scientific reference points when developing national standards. Other jurisdictions, including the European Union, Canada, Australia, and individual countries or provinces, may use their own limits, monitoring frequencies, and compliance definitions.

Private wells are typically not regulated like public water systems. In many regions, the well owner is responsible for testing, interpretation, and treatment. A private well can exceed a health-based antimony guideline even when nearby public water is compliant. If antimony is detected near or above the applicable limit, results should be reviewed with a certified laboratory, local health department, water treatment professional, or hydrogeologist familiar with local geology.

Because regulatory values may change as toxicology is reassessed, PureWaterAtlas recommends comparing laboratory results to current local standards and internationally recognized health-based guidelines. When multiple contaminants are present, treatment decisions should be based on the most protective combined approach, not on antimony alone.

Related Contaminants

Frequently Asked Questions

Is antimony a metal or a metalloid?

Antimony is scientifically classified as a metalloid, but it is commonly managed with heavy metals in drinking water programs because it is an inorganic trace element with toxic effects at elevated concentrations. Its water chemistry includes metal-like behavior, oxyanion formation, and strong interactions with mineral surfaces.

How do I know if antimony in my water comes from the well or from plumbing?

Compare a first-draw sample with a flushed sample. Higher antimony in the first-draw sample may indicate leaching from plumbing, fittings, solders, or pump components after water has been stagnant. Similar levels in both samples suggest the source may be the aquifer or incoming supply. A laboratory and local water professional can help design the sampling plan.

Does boiling remove antimony?

No. Boiling does not destroy or remove antimony because it is an element. As water evaporates, dissolved antimony can become slightly more concentrated. If antimony is above a health-based limit, use properly treated water or an alternative water source for drinking and cooking.

Will a refrigerator filter or carbon pitcher remove antimony?

Most refrigerator filters and basic carbon pitchers are designed for chlorine taste, odor, and sometimes lead or select organics. They should not be assumed to remove antimony unless the product is specifically certified or independently verified for antimony reduction. Standard activated carbon alone is not considered a dependable antimony treatment.

Is reverse osmosis enough for antimony?

Reverse osmosis is often the best residential option for reducing antimony in drinking water, especially at a dedicated kitchen tap. However, it must be properly installed, maintained, and tested. Pretreatment may be needed for iron, manganese, hardness, sediment, or chlorine, and post-treatment laboratory testing is the only way to confirm actual antimony reduction in a specific home.