What Is Arsenic and Where Does It Come From?

Arsenic is a naturally occurring metalloid element found in the Earth's crust. It exists in two primary forms in water: arsenite (As III) and arsenate (As V). While arsenate is more common in oxygenated surface waters, arsenite predominates in anaerobic groundwater conditions and is considered more toxic and more difficult to remove.

Natural sources of arsenic in water include the dissolution of arsenic-bearing minerals such as arsenopyrite, realgar, and orpiment. Geological formations in regions of South Asia, parts of the western United States, and Latin America are particularly prone to elevated arsenic levels in groundwater.

Anthropogenic sources include mining and ore processing, coal combustion, wood preservation using chromated copper arsenate (CCA), and historical use of arsenic-based pesticides in agriculture. Industrial wastewater discharge can also introduce arsenic into surface water supplies.

Health Effects of Arsenic in Water

Chronic exposure to arsenic in drinking water is associated with a wide range of serious health effects. The International Agency for Research on Cancer (IARC) classifies arsenic as a Group 1 carcinogen, meaning there is sufficient evidence that it causes cancer in humans.

Long-term ingestion of arsenic-contaminated water has been linked to cancers of the skin, bladder, lung, kidney, and liver. Non-cancer health effects include cardiovascular disease, peripheral neuropathy, diabetes, and skin lesions such as keratosis and hyperpigmentation.

Exposure during pregnancy may result in adverse developmental outcomes, including low birth weight and impaired cognitive development. Children are particularly vulnerable due to their lower body weight relative to water intake.

The World Health Organization estimates that over 140 million people in at least 50 countries consume water containing arsenic above the guideline value of 0.010 mg/L, making it one of the most widespread water quality concerns globally.

Regulatory Limits for Arsenic in Drinking Water

The EPA MCL of 0.010 mg/L (10 parts per billion) was established in 2001, lowering the previous standard of 0.050 mg/L. This revision reflected updated scientific understanding of arsenic's carcinogenicity at low concentrations.

How to Test for Arsenic in Water

Arsenic cannot be detected by taste, odor, or appearance, making laboratory analysis essential. Standard analytical methods include inductively coupled plasma mass spectrometry (ICP-MS) per EPA Method 200.8, and graphite furnace atomic absorption spectrometry (GFAAS).

Field test kits based on the Gutzeit method are available for screening purposes, though they provide less precision than laboratory methods. For compliance testing and system design, certified laboratory analysis specifying both As(III) and As(V) concentrations is recommended, as the arsenic species present will influence treatment system selection.

Treatment Methods for Arsenic Removal

Reverse Osmosis

Reverse osmosis systems are highly effective for arsenic removal, particularly for arsenate (As V), achieving rejection rates above 95%. For water containing arsenite (As III), pre-oxidation to convert arsenite to arsenate is recommended to maximize removal efficiency. RO is suitable for both point-of-use and commercial-scale applications.

Adsorptive Media

Iron-based adsorptive media, including granular ferric hydroxide (GFH) and iron oxide-coated sand, offer effective arsenic removal through surface adsorption. Filtration systems utilizing these media are particularly well-suited for community and municipal treatment where RO may not be practical.

Activated Alumina

Activated alumina operates through a ligand exchange mechanism and is effective at removing arsenate at pH levels below 6.5. It requires periodic regeneration or replacement and is commonly used in point-of-entry systems.

Coagulation and Filtration

Iron-based coagulants such as ferric chloride and ferric sulfate effectively coprecipitate arsenic, particularly arsenate, during conventional water treatment. This method is widely used in municipal treatment plants and can reduce arsenic concentrations to below 0.005 mg/L when properly optimized.

Ion Exchange

Strong base anion exchange resins can remove arsenate from water, though they are less effective for arsenite. This method is best suited for waters with low sulfate and TDS concentrations, as competing anions can reduce arsenic removal efficiency.

Frequently Asked Questions

What level of arsenic in water is considered safe?

The U.S. EPA Maximum Contaminant Level (MCL) for arsenic in drinking water is 0.010 mg/L (10 ppb). The WHO guideline value is also 0.010 mg/L. Any concentration above this level requires treatment before the water is considered safe for consumption.

What is the best treatment method for arsenic removal?

Reverse osmosis (RO) is one of the most effective methods for arsenic removal, achieving over 95% rejection for arsenic(V). Adsorptive media such as iron-based adsorbents and activated alumina are also highly effective, particularly for point-of-use and point-of-entry applications.

How does arsenic get into drinking water?

Arsenic enters water supplies primarily through natural geological processes, including dissolution from arsenic-bearing minerals in rock and soil. Industrial activities such as mining, smelting, and the historical use of arsenic-based pesticides also contribute to contamination of groundwater and surface water.

Need to Remove Arsenic from Your Water?

ForeverPure provides commercial and industrial water treatment systems engineered for arsenic removal, including reverse osmosis units, adsorptive media filters, and complete treatment trains. Our engineering team can design a solution based on your specific water analysis and flow requirements.

Contact ForeverPure for a customized arsenic removal solution.