Arsenic
A naturally occurring metalloid that is the largest chemical mass-poisoning exposure in drinking water worldwide, principally through groundwater in the Bengal basin and parts of South and South East Asia.
Key facts
- Contaminant group
- Metal
- World Health Organization — guideline
- 10 µg/lProvisional, set by measurement and treatment feasibility rather than by an acceptable risk level.
- European Union — legal limit
- 10 µg/l
- United Kingdom — legal limit
- 10 µg/l
- United States — legal limit
- 10 µg/lLowered from 50 µg/l in 2001.
- Bangladesh — legal limit
- 50 µg/lA higher national standard than the WHO guideline, reflecting the scale of the contamination and the practical limits of remediation.
Where it comes from
- Natural dissolution from arsenic-bearing sediments and volcanic rock — by far the dominant source globally
- Mining and smelting waste
- Historic arsenical pesticides and wood preservatives
- Geothermal water
How it behaves in water
Mobility depends on redox conditions and pH. Arsenite (As III) dominates in reducing groundwater and is both more toxic and harder to remove than arsenate (As V), which dominates in oxidising conditions. Effective treatment usually begins by oxidising As III to As V.
How it is measured
Measured in micrograms per litre, usually by ICP-MS. Field test kits exist and were widely used in the Bangladesh well-screening programmes, but have poor precision near the limit.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| World Health Organization | 10 µg/l | guideline | Provisional, set by measurement and treatment feasibility rather than by an acceptable risk level. |
| European Union | 10 µg/l | legal limit | — |
| United Kingdom | 10 µg/l | legal limit | — |
| United States | 10 µg/l | legal limit | Lowered from 50 µg/l in 2001. |
| Bangladesh | 50 µg/l | legal limit | A higher national standard than the WHO guideline, reflecting the scale of the contamination and the practical limits of remediation. |
Table sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- European Commission — Drinking Water Directive (EU) 2020/2184 and reporting. Open — attribution required · European Commission reuse policy (Decision 2011/833/EU)
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- United States Environmental Protection Agency — Safe Drinking Water Information System. Open · US Government work — public domain
Health context
Long-term ingestion causes skin lesions, and is causally associated with cancers of the skin, bladder and lung. IARC classifies arsenic and inorganic arsenic compounds in Group 1. Effects arise from chronic exposure over years, not from single exposures.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Coagulation with iron salts followed by filtration | Boiling, which concentrates it |
| 2 | Adsorption onto iron oxide or activated alumina media | Activated carbon alone |
| 3 | Reverse osmosis | Sediment filtration |
| 4 | Ion exchange, for arsenate | Conventional chlorination without a removal step |
| 5 | Oxidation to As V before any of the above | — |
Occurrence
The affected populations are concentrated where deep tube wells were installed to escape microbially contaminated surface water — a case where solving one water problem created another.
Relationships
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- Peer-reviewed scientific literature — Open-access hydrology, water chemistry and water use research. Public but restricted · Publisher terms — public access, reuse not clearly granted