Chromium is a brittle metal that occurs naturally in the environment in rocks, soils, plants and living creatures.  Pure chromium is found primarily in China and Eastern Russia, while most chromium is mined as a mixed ore in Kazakhstan and South Africa.  It is used extensively in industrial processes, particularly in stainless steel production, dyes, as a anti-corrosive ingredient in paints and coatings and wood preservatives, in metal plating, and leather tanning.  

Chromium occurs primarily as Chromium-3 (trivalent) and Chromium-6 (hexavalent).  Tests for Total Chromium include both types.

Hexavalent chromium is the type of chromium that is mined as various chromium salts, is used industrially, and is the type typically seen in environmental pollution.  It is both toxic and carcinogenic.  People who work with chromium or are exposed to amounts over the standard for a long time are at risk of damage to the skin and respiratory system, or to acute poisoning.  Steel and pulp mills are typical sources of pollution, historically.

As a nutrient, chromium-3 is considered non-toxic and in tiny amounts is essential to mammalian health. The US National Institute of Health suggests an "Adequate Intake" of chromium to be 20-30 ug/day for adults.*

Sources of environmental chromium pollution: chromium contamination of water is caused by disposal of industrial wastes, leakage from settling ponds, and airborne deposition of chromium from smoke stacks.

 

Exposure Limits (Chromium, total)

Maine Maximum Exposure Guideline limit: 20 ppb or .02 mg/L

EPA Maximum Contaminant Level (MCL):  100 ppb or 1.0 mg/L

EPA Maximum Contaminant Level GOAL (MCLG): 100 ppb or 1.0 mg/L

USA Primary Drinking Water Standard limit: 100 ppb or 1.0 mg/L

Exposure Limits (Chromium, hexavalent)

To date, only California has established a Public Health Goal for Cr-6: .02 ppb or 0.00002 mg/L

 

 

Additional Resources

EPA, "Chromium in Drinking Water": https://www.epa.gov/dwstandardsregulations/chromium-drinking-water

"Chromium" in Mindat mineral database: https://www.mindat.org/min-1037.html

"Hexavalent Chromium" in Wikipedia: https://en.wikipedia.org/wiki/Hexavalent_chromium

CDC Toxic Substances Portal: "Chromium"

*National Institute of Health Recommended Daily Allowances - Elements: https://www.ncbi.nlm.nih.gov/books/NBK56068/table/summarytables.t3/?report=objectonly

MEL Test Methods for Chromium

Drinking Water - EPA 200.7 R4.4 (SDWA compliant)
Wastewater - EPA 200.7 R4.4 (NPDES compliant)
Solids - EPA 6010B, 6010C (SW846/RCRA and Clean Water Program compliant)

Sample Requirements

Drinking water and Wastewater:

Container: plastic, glass
Volume: 250 mL
Hold Time: 6 months if preserved with HNO3 to pH<2, otherwise 2 weeks
Preservation: HNO3 to pH<2

Solids:
Container: plastic, glass, baggie
Volume: a least 150g
Hold Time: 6 months
Preservation: n/a