Chromium
Two oxidation states with entirely different toxicity. Trivalent chromium is an essential trace nutrient; hexavalent chromium is a carcinogen. Most regulation measures total chromium, which does not distinguish them.
Key facts
- Contaminant group
- Metal
- World Health Organization — guideline
- 50 µg/l total chromiumDesignated provisional; WHO notes the guideline may be too high for hexavalent chromium specifically.
- European Union — legal limit
- 25 µg/l total chromiumReduced from 50 µg/l by the recast Drinking Water Directive.
- United Kingdom — legal limit
- 50 µg/l total chromium
- United States — legal limit
- 100 µg/l total chromiumCalifornia has a separate hexavalent-specific standard, reflecting the speciation problem.
Where it comes from
- Electroplating, leather tanning and pigment manufacture
- Stainless steel production and corrosion
- Cooling tower corrosion inhibitors, historically
- Natural weathering of chromium-bearing rock, which can produce hexavalent chromium in oxidising alkaline groundwater
How it behaves in water
Trivalent chromium is poorly soluble and binds to soil. Hexavalent chromium is highly soluble, mobile in groundwater, and not retarded by sorption — so a hexavalent plume travels far further and faster than a trivalent one.
How it is measured
Regulatory limits are almost always for total chromium. Speciating into trivalent and hexavalent requires a separate method, and without it a compliant total result can conceal a hexavalent problem.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| World Health Organization | 50 µg/l total chromium | guideline | Designated provisional; WHO notes the guideline may be too high for hexavalent chromium specifically. |
| European Union | 25 µg/l total chromium | legal limit | Reduced from 50 µg/l by the recast Drinking Water Directive. |
| United Kingdom | 50 µg/l total chromium | legal limit | — |
| United States | 100 µg/l total chromium | legal limit | California has a separate hexavalent-specific standard, reflecting the speciation problem. |
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
Inhaled hexavalent chromium is an established human carcinogen and IARC classifies it in Group 1. The evidence for carcinogenicity by ingestion is weaker but sufficient to have driven hexavalent-specific standards. Trivalent chromium is an essential nutrient at trace intake.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Reduction of hexavalent to trivalent followed by coagulation and filtration | Boiling |
| 2 | Strong-base anion exchange for hexavalent chromium | Activated carbon alone |
| 3 | Reverse osmosis | Water softening |
| 4 | Coagulation with ferrous iron | Standard sediment filters |
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