Arsenic in water: origin, dangers, regulations and filtration
Arsenic is an element naturally present in the Earth's crust. It can be found in some groundwater when the rocks and minerals that contain it gradually release arsenic compounds. Past mining, metallurgical, industrial or agricultural activities can also contribute to its presence in the environment. Prolonged exposure to inorganic arsenic through drinking water is associated with serious health effects, including skin lesions and an increased risk of certain cancers.
- Chemical symbol
- As
- Atomic number
- 33
- Family
- Metalloid
- EU Value
- 10 µg/L
What is arsenic?
Arsenic is a chemical element with the symbol As and the atomic number 33. It is classified as a metalloid, meaning it is an element with properties intermediate between those of metals and non-metals.
In the environment, arsenic is generally associated with other elements in rocks, soils and ores. It can exist in different chemical forms, organic or inorganic. In the context of drinking water, the inorganic forms are the primary health concern.
Good to know: the presence of arsenic in water does not necessarily imply industrial pollution. In many regions, it can have a natural geological origin.
What is arsenic used for?
Arsenic and some of its compounds have been used in various sectors. Many uses have been strictly restricted or abandoned due to their toxicity, but arsenic retains certain specialized industrial and medical applications.
- manufacturing of certain semiconductors and electronic components, notably in the form of gallium arsenide;
- use in certain alloys and metallurgical processes;
- former wood preservatives containing arsenic compounds;
- former arsenic-based pesticides, herbicides and pest control products;
- controlled medical use of certain compounds, notably arsenic trioxide in the treatment of specific forms of leukemia.
The utility of an arsenic compound does not mean it is safe. The risks depend on its chemical form, the dose, the route of exposure and the duration of exposure.
How does arsenic get into water?
Natural geological origin
One of the main sources of arsenic in groundwater is the release of compounds naturally present in rocks and minerals. Subsurface chemical conditions can promote their dissolution or mobilization in water.
Mining and metallurgical activities
The extraction and processing of ores can displace or concentrate materials containing arsenic. Mine tailings, drainage water and former industrial sites can therefore constitute local sources of contamination.
Legacy agricultural and industrial uses
Some arsenic-based pesticides and wood preservatives have contributed to lasting soil contamination. Arsenic can then reach surface water or groundwater through runoff and infiltration.
Combustion and atmospheric deposition
The combustion of certain coals or materials containing arsenic can lead to atmospheric emissions. After deposition on soils or aquatic surfaces, these emissions can contribute to local environmental contamination.
Arsenic III and arsenic V: why is this distinction important?
In water, inorganic arsenic is notably encountered in two oxidation states: trivalent arsenic, generally referred to as As(III), and pentavalent arsenic, generally referred to as As(V).
Their ratio depends in particular on the pH, the redox potential and the characteristics of the water. This distinction is important, because the two forms do not exhibit exactly the same chemical behavior and may not be removed with the same efficiency by a single treatment process.
| Form | Common notation | Frequent context | Consequence for treatment |
|---|---|---|---|
| Trivalent arsenic | As(III) | Can be favored in certain groundwater exhibiting reducing conditions. | May require a prior oxidation step to improve the efficiency of certain processes. |
| Pentavalent arsenic | As(V) | Can be more present in certain waters exhibiting oxidizing conditions. | Is generally captured better by several adsorption, coagulation or filtration processes. |
Attention: an analysis result expressed only as "total arsenic" does not always reveal the exact ratio of As(III) and As(V). Similarly, a filtration test on arsenic should not be extended to both forms if the protocol does not specify the speciation tested.
What are the health risks of arsenic?
The effects depend on the chemical form, the concentration and the duration of exposure. The main concerns related to drinking water involve repeated or prolonged exposure to inorganic arsenic.
Chronic exposure
Prolonged exposure to inorganic arsenic through drinking water and food can cause skin lesions and increase the risk of certain cancers. Associations have also been observed with cardiovascular disease, diabetes and certain developmental effects.
Documented effects may notably include:
- skin pigmentation changes;
- thickening of certain areas of the skin;
- precancerous skin lesions;
- increased risk of skin, bladder and lung cancer;
- cardiovascular damage;
- peripheral neurological damage;
- possible effects on development in case of early exposure.
Acute exposure
High ingestion over a short period can cause acute poisoning accompanied by digestive, cardiovascular, neurological or multisystemic symptoms. A suspected case of acute poisoning requires immediate medical attention.
The regulatory value is not an absolute boundary between a total absence of risk and an immediate danger. It is used to govern drinking water quality and limit the population's long-term exposure.
What are the effects of arsenic on the environment?
Arsenic is naturally present in the environment, but some human activities can locally increase its concentration or mobility. It does not degrade like an organic molecule: it can change its chemical form, attach to particles or minerals, or move between soil, sediment and water.
At high concentrations, it can be toxic to aquatic organisms, plants and microorganisms. Its behavior strongly depends on the characteristics of the environment, notably pH, the presence of iron, manganese, organic matter and redox conditions.
What is the regulatory limit for arsenic in drinking water?
The European Union sets a parametric value of 10 micrograms per liter for arsenic in water intended for human consumption. This value corresponds to 0.010 milligrams per liter.
| Reference | Value | Type of value |
|---|---|---|
| European Union | 10 µg/L | Parametric value set by the European Directive on the quality of water intended for human consumption. |
| World Health Organization | 10 µg/L | Provisional guideline value used for arsenic in drinking water. |
| United States – EPA | 10 ppb | Maximum regulatory concentration applicable to public water systems subject to federal regulation. |
In water with a density close to that of pure water, 1 ppb is approximately equivalent to 1 µg/L. This approximation allows for comparing results expressed in ppb in American reports with values expressed in µg/L in Europe.
How to tell if water contains arsenic?
Dissolved arsenic generally cannot be identified by the taste, smell or appearance of the water. Therefore, clear, odorless water can contain arsenic.
The reliable method is to have a sample analyzed by a competent laboratory. Depending on the objective, the analysis may measure:
- total arsenic;
- inorganic arsenic;
- the ratio between As(III) and As(V);
- other parameters useful for selecting treatment, such as iron, manganese, pH or phosphates.
For a home supplied by a private well, the analysis must be adapted to the geological context and the recommendations of the relevant health authorities. A single test result does not guarantee that the concentration will remain the same over time.
What technologies can reduce arsenic in water?
The appropriate treatment depends on the form of the arsenic, its concentration and the complete composition of the water. Technologies described in technical and scientific documents include:
- adsorption on specialized media based on iron oxides or hydroxides;
- activated alumina under certain conditions of use;
- coagulation, flocculation and filtration in collective treatment facilities;
- certain adapted ion exchange processes;
- reverse osmosis when the system is correctly sized;
- prior oxidation of As(III) to As(V), when this operation is necessary for the chosen process.
Standard activated carbon alone should not be considered a universal solution for arsenic. Performance depends on the exact formulation of the media, the chemical form of the arsenic, water quality, flow rate, contact time and the remaining filter capacity.
After installing a treatment system intended to reduce arsenic, a check analysis of the treated water is recommended. Periodic testing then makes it possible to verify that the media is not saturated and that the system remains effective under real conditions of use.
Imperial testing results for arsenic
Arsenic is included in the performance analysis table published for the Monderma Imperial GF and Imperial AMB filters. Tests were conducted by Envirotek Laboratories in the United States.
Arsenic: result indicated in the Envirotek table
Interpretation limit: the row in the table dedicated to arsenic does not specify whether the substance tested was exclusively in As(III) form, As(V) form, or another determined form. The result should therefore not be indiscriminately extended to all water sources or all chemical forms of arsenic.
Laboratory performance corresponds to test protocol conditions. Actual results may vary depending on water composition, initial concentration, flow rate, maintenance, and the duration of cartridge use.
Testing performed according to an NSF/ANSI protocol does not necessarily mean that the complete product is NSF certified for the reduction in question. Official certifications and analysis reports should be consulted separately.
Consult Monderma certifications and analysesFrequently asked questions about arsenic in water
Can you see or smell arsenic in water?
No. Dissolved arsenic generally cannot be detected by the color, taste, or smell of water. Only appropriate analysis can determine its concentration.
Is arsenic in water always of industrial origin?
No. In many regions, it occurs naturally in underground rocks and minerals. However, mining, metallurgical, agricultural, or industrial activities can contribute to some local contamination.
What is the limit for arsenic in drinking water?
The parametric value set by the European Union is 10 µg/L. The World Health Organization also maintains a provisional guideline value of 10 µg/L. U.S. federal regulations set a limit of 10 ppb.
Does boiling water remove arsenic?
No. Boiling does not remove dissolved arsenic. Losing some water to evaporation may even increase its concentration in the remaining volume.
Does an activated carbon filter always remove arsenic?
No. Standard activated carbon is not a universal guarantee against arsenic. One must verify the existence of testing specific to the filter model and take into account the chemical form of the arsenic as well as the water composition.
What is the difference between As(III) and As(V)?
These are two oxidation states of inorganic arsenic. They do not behave exactly the same in water and are not treated with the same ease. Some processes require oxidizing As(III) to As(V) prior to filtration.
How can you check if a filter remains effective?
The most reliable method is to have the water analyzed before and after treatment. Periodic analyses are recommended when the presence of arsenic is known or suspected.
Related contaminants
Arsenic belongs to the category of trace elements and metalloids. You can also consult other fact sheets dedicated to metals and elements that may be present in water.
Scientific and administrative sources
This fact sheet prioritizes public organizations, international institutions, and governmental scientific databases. No commercial blogs, comparators, or affiliate sites are used as health sources.
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World Health Organization – Arsenic
Overview of the main sources of exposure and health effects related to
arsenic.
View the official WHO fact sheet -
World Health Organization – Chemical fact sheet on arsenic
Information regarding the presence of arsenic in water, health effects,
and guideline value.
View the WHO chemical fact sheet -
European Union – Directive (EU) 2020/2184
Official text regarding the quality of water intended for human
consumption.
View the directive on EUR-Lex -
EUR-Lex – Essential drinking water standards
Official summary presenting, among other things, the parametric value of
10 µg/L for arsenic.
View the official summary -
Environmental Protection Agency – Arsenic Rule
History of U.S. regulation and the maximum value of 10 ppb in drinking
water.
View the official EPA page -
PubChem – National Institutes of Health
Data on the element arsenic, its symbol, atomic number, and main chemical
properties.
View the PubChem sheet -
Monderma – Certifications and laboratory analyses
Certifications, reports, and analysis table for the filters in question.
Consult Monderma certifications and analyses
