Arsenic Pollution: Sources, Impacts, and Management

Arsenic is one of the most dangerous naturally occurring contaminants on the planet. It sits at the top of the World Health Organization’s list of ten chemicals of major public health concern, and for good reason. An estimated 230 million people worldwide are exposed to arsenic-contaminated groundwater, with nearly 94% of them living in Asian regions. Understanding where arsenic comes from, how it affects human health, and what we can do to remove it from our water is essential for both environmental science students and communities living in affected areas.

What is arsenic and why does it matter? 🔗

Arsenic is a toxic metalloid that occurs naturally in the Earth’s crust at an average concentration of about 1.5-5 mg/kg. It exists in both organic and inorganic forms, with inorganic arsenic – particularly arsenite (As(III)) and arsenate (As(V)) – being far more toxic. The International Agency for Research on Cancer (IARC) classifies arsenic as a Group 1 human carcinogen. To protect public health, both the WHO and the U.S. Environmental Protection Agency (EPA) have set a maximum contaminant level (MCL) of 10 micrograms per litre (μg/L) for inorganic arsenic in drinking water. Despite this standard, elevated arsenic levels in drinking water have been reported in over 100 countries.

Sources of arsenic pollution 🔗

Arsenic enters the environment through three broad categories of sources: geogenic (natural geological), anthropogenic (human-caused), and biogenic (biological). Each plays a different but interconnected role in the global arsenic pollution cycle.

Geogenic sources 🔗

The most significant source of arsenic contamination in groundwater is natural geological formations. Arsenic is found in more than 200 minerals, most commonly in sulfide minerals such as arsenopyrite and arsenic-substituted pyrite. When these minerals interact with groundwater under specific chemical conditions – particularly in reducing (low-oxygen) environments – arsenic is released into the water through a process called reductive dissolution. This happens when iron-bearing minerals dissolve under anoxic conditions, releasing the arsenic they had previously trapped.

Large-scale natural contamination is found in two main types of geological settings: strongly reducing alluvial aquifers (such as those in Bangladesh, India, China, and Hungary) and inland arid or semi-arid basins (such as in Argentina and Mexico). In Southeast Asia, where millions depend on shallow tube wells for drinking water, geogenic arsenic mobilization from recently deposited alluvial sediments has created one of the world’s most severe environmental health crises. Other geological processes that release arsenic include weathering of rocks, volcanic activity, and geothermal fluid discharge into surface waters.

Anthropogenic sources 🔗

While natural processes are the dominant source of arsenic in groundwater, human activities have significantly increased arsenic’s mobility and spread. The main anthropogenic sources include mining and smelting operations, combustion of fossil fuels, industrial effluents, and the use of arsenic-based pesticides and herbicides in agriculture.

Mining is one of the most prominent human-linked causes of arsenic pollution. Because gold and arsenic-bearing minerals frequently coexist, gold mining activities carry a particular risk of mobilising arsenic into surrounding water systems. The Ashanti region of Ghana and the Ron Phibun district in southern Thailand are well-documented examples where mining has directly caused arsenic contamination in local groundwater. Other industrial inputs include the manufacture of glass, ceramics, electronic components (such as gallium arsenide microchips), wood preservatives like chromated copper arsenate (CCA), and various pigments and paints. Coal burning has also been identified as a significant source in countries like China, Slovakia, and Turkey.

Biogenic sources 🔗

Biogenic arsenic contamination is linked to living organisms and natural biological processes. Certain bacteria can transform arsenic from less toxic pentavalent forms to more toxic trivalent forms, which increases groundwater contamination. The decay of organic matter in soil and sediments also releases bound arsenic into the surrounding environment. While biogenic sources are generally less prominent than geogenic and anthropogenic ones, they play an important role in the overall biogeochemical cycling of arsenic – especially in environments where microbial activity is high, such as waterlogged soils and wetlands.

Health impacts of arsenic exposure 🔗

Arsenic affects virtually every organ system in the human body. The health effects depend on the level and duration of exposure, the form of arsenic involved, and individual susceptibility factors such as nutrition and genetics.

Cancer risks 🔗

The link between chronic arsenic exposure and cancer is one of the most well-established in environmental health. Long-term ingestion of inorganic arsenic through drinking water is associated with cancers of the skin, lungs, bladder, kidney, and liver. The U.S. EPA classifies inorganic arsenic as a human carcinogen based on evidence connecting it to cancers in multiple organ systems. Skin cancer is often the earliest and most visible sign of chronic arsenic exposure, frequently accompanied by characteristic skin lesions such as hyperpigmentation and keratosis (hardened patches on the palms and soles). Some of these keratinised lesions can progress to invasive carcinoma over time.

Cardiovascular and metabolic diseases 🔗

Beyond cancer, arsenic exposure is strongly associated with cardiovascular disease and metabolic disorders. Studies have linked chronic exposure to increased risks of ischemic heart disease, peripheral vascular disease, and hypertension. The WHO notes that arsenic-induced myocardial infarction can be a significant contributor to excess mortality in affected populations. Diabetes is another major concern; research consistently shows that people exposed to elevated arsenic levels face a higher risk of developing type 2 diabetes. Neurological effects, including peripheral neuropathy (damage to nerves in the hands and feet), have also been documented in populations with chronic exposure.

Developmental and reproductive effects 🔗

Arsenic exposure during pregnancy is particularly dangerous. It can cross the placenta, putting unborn children at risk. Pregnant women who chronically consume arsenic-contaminated water face increased risks of spontaneous abortion, stillbirth, and preterm birth. Exposure in utero and during early childhood has been linked to impaired cognitive development and increased mortality from multiple cancers, lung disease, and heart attacks in young adults – with latency periods that can extend over decades. This means the damage done by arsenic early in life may not become apparent until adulthood.

Environmental impacts 🔗

Arsenic doesn’t just harm humans. It accumulates in soils and aquatic ecosystems, disrupting plant growth, reducing agricultural productivity, and causing biodiversity loss. Arsenic-contaminated irrigation water can lead to residue build-up in crops, entering the food chain and creating a cycle of exposure that extends far beyond direct water consumption. Rice, in particular, is known to absorb arsenic from paddy soils, making it a significant dietary source of exposure in regions where rice is a staple food.

Management strategies for arsenic contamination 🔗

Removing arsenic from water is technically challenging because arsenic changes its chemical behaviour depending on pH, redox conditions, and the presence of other dissolved substances. However, several treatment technologies – ranging from conventional to emerging – have been developed and deployed with varying degrees of success.

Oxidation 🔗

Arsenite (As(III)) is more toxic and more difficult to remove from water than arsenate (As(V)). Most treatment technologies work best on arsenate. Therefore, the first step in many arsenic removal systems is oxidation – converting As(III) to As(V). This can be achieved through chemical oxidation using agents like chlorine, potassium permanganate, or ozone, or through biological oxidation using arsenic-oxidising bacteria. An innovative low-cost approach called SORAS (Solar Oxidation and Removal of Arsenic) uses sunlight and citric acid (from lemon juice) to photochemically oxidise arsenic in the presence of iron, achieving removal efficiencies of up to 99.5% under optimised conditions.

Coagulation and filtration 🔗

Coagulation-flocculation followed by filtration is one of the most widely used conventional methods. It involves adding a coagulant – typically an iron or aluminium salt – to water, which causes arsenic to bind with the resulting flocs. These flocs settle out or are filtered from the water. While this method is relatively economical, it can sometimes show removal efficiencies below 90% and generates sludge that requires safe disposal.

Adsorption 🔗

Adsorption is another popular approach where arsenic binds to the surface of a solid medium. Activated alumina, iron-based adsorbents (such as granular ferric hydroxide), and newer nanomaterial-based adsorbents are commonly used. Iron-based materials are particularly effective because arsenic has a strong natural affinity for iron compounds. The U.S. EPA conducted 50 full-scale demonstration projects between 2003 and 2011, and adsorptive media systems were the most commonly tested technology, accounting for 28 of those projects.

Ion exchange 🔗

Ion exchange uses specialised resins to swap arsenic ions for less harmful ones (such as chloride). It is effective for arsenate removal but less so for arsenite, again making pre-oxidation important. Ion exchange systems can treat large volumes of water but produce a concentrated brine waste stream that needs proper handling. They are better suited for community-level water systems than for household use.

Membrane filtration 🔗

Membrane technologies such as reverse osmosis (RO) and nanofiltration can remove arsenic very effectively – often achieving removal rates above 95%. However, they are energy-intensive and expensive, making them less practical for rural communities in developing countries where arsenic contamination is most severe. RO systems also produce a reject water stream with concentrated arsenic that requires disposal.

Subterranean arsenic removal (SAR) 🔗

One of the most promising emerging technologies is Subterranean Arsenic Removal (SAR). Unlike conventional methods that treat water above ground, SAR works in situ – within the aquifer itself. The process involves injecting oxygenated water into the anaerobic aquifer, which creates aerobic conditions that promote the growth of naturally occurring arsenic- and iron-oxidising bacteria. These bacteria convert dissolved arsenic and iron into insoluble forms that become immobilised in the aquifer sand. The result is that arsenic and iron are trapped underground rather than extracted and disposed of as waste.

A SAR plant operating in Ghetugachi village in West Bengal, India, successfully reduced arsenic concentrations from 154 parts per billion (ppb) to 13 ppb while serving about 600 people and two schools. The operating cost was approximately $30 per month for producing 10,000 litres of safe water daily. SAR’s key advantages are that it requires no chemicals, generates zero waste, and uses no electricity – making it uniquely suited for resource-limited communities in developing countries.

Biological methods 🔗

Biological remediation (or bioremediation) uses microorganisms to detoxify or immobilise arsenic. Certain bacteria can oxidise arsenite to the less toxic arsenate form, while others can reduce, adsorb, or precipitate arsenic from solution. Phytoremediation – using arsenic-accumulating plants like the brake fern (Pteris vittata) – has also shown promise for cleaning up contaminated soils. While biological methods are generally cost-effective and environmentally friendly, they are currently best suited for smaller-scale applications and require further research for wide-scale deployment.

The road ahead 🔗

Addressing arsenic pollution requires a multi-pronged approach. Prevention – through the provision of safe, alternative water sources – remains the most critical action. Where alternative sources are not available, treatment technologies must be selected based on local conditions, including arsenic concentration, water chemistry, available resources, and community size. Hybrid approaches that combine physical, chemical, and biological methods are increasingly seen as the most effective strategy.

Equally important is ongoing monitoring and awareness. Many arsenic-affected communities, particularly in Africa and parts of Latin America, still lack sufficient data on the extent of contamination. Without awareness, there can be no action. Governments, international organisations, and researchers must continue to invest in mapping arsenic hotspots, developing affordable technologies, and educating vulnerable populations about the risks of arsenic exposure and the solutions available to them.

What do you think? With promising low-cost technologies like SAR already making a difference in places like West Bengal, what do you believe is the biggest barrier to scaling arsenic remediation in developing countries – is it technology, funding, political will, or awareness? And how might communities take a more active role in protecting their own water sources from arsenic contamination?

References

1. https://www.who.int/news-room/fact-sheets/detail/arsenic
2. https://www.cancer.org/cancer/risk-prevention/chemicals/arsenic.html
3. https://link.springer.com/article/10.1007/s40726-016-0028-2
4. https://www.nature.com/articles/s43017-024-00519-z
5. https://pubmed.ncbi.nlm.nih.gov/18982996/
6. https://www.mdpi.com/2673-4672/4/2/13
7. https://ehp.niehs.nih.gov/1205875/
8. https://iwaponline.com/wst/article/87/12/3108/95727/A-mini-review-on-arsenic-remediation-techniques
9. https://www.clu-in.org/contaminantfocus/default2.focus/sec/Arsenic/cat/treatment_technologies/
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