Chromium

(endorsed 1996)

Guideline

Based on health considerations, the concentration of hexavalent chromium (Cr(VI)) in drinking water should not exceed 0.05 mg/L. If the concentration of total chromium exceeds this value then a separate analysis for hexavalent chromium should be undertaken.

General description

Chromium is present in the environment in the trivalent (Cr(III)) and hexavalent (Cr(VI)) states.

Trivalent chromium is the most common naturally occurring state. Most soils and rocks contain small amounts of chromium oxide, and weathering, oxidation and bacterial action convert this insoluble compound into soluble Cr(III) salts.

Trivalent chromium salts are used in leather tanning, manufacture of catalysts, paint pigments, fungicides, and ceramic and glass manufacture.

Trivalent chromium is an essential trace element for humans, with food being the major source of intake.

Hexavalent chromium occurs infrequently in nature. Its presence in water is generally the result of industrial and domestic chromium waste discharges. Hexavalent chromium compounds are used in the metallurgical industry for chrome alloy and chrome metal production, and in the chemical industry as oxidising agents.

Hexavalent chromium is not considered to be an essential nutrient and harmful effects due to chromium have been attributed to this form.

Total chromium concentrations in drinking water are usually less than 0.005 mg/L although concentrations between 0.06 mg/L to 0.12 mg/L have been reported overseas.

Typical values in Australian drinking water

In major Australian reticulated supplies concentrations of total chromium range up to 0.03 mg/L, with typical concentrations usually less than 0.005 mg/L.

Treatment of drinking water

Chromium can be removed from drinking water sources by coagulation/filtration, ion exchange, reverse osmosis and lime softening. Trivalent chromium can be oxidised to hexavalent chromium with disinfectants, particularly chlorine, chlorine dioxide and ozone.

Measurement

The total chromium concentration in drinking water can be determined by inductively coupled plasma emission spectroscopy or graphite furnace atomic absorption spectroscopy (APHA Method 3500-Cr Parts B or C 1992). The limit of determination is approximately 0.01 mg/L.

Hexavalent chromium (Cr(VI)) can be determined with a colorimetric method using diphenylcarbizide (APHA Method 3500-Cr part D 1992). The limit of determination is 0.005 mg/L.

Health considerations

The absorption of chromium after ingestion is low and depends on the valence state. Hexavalent chromium is more readily absorbed from the gastrointestinal tract than trivalent compounds. It is able to penetrate cell membranes, and within cells it is reduced to Cr(III) and forms complexes with proteins and genetic material.

An extensive review and summary of the human and animal toxicity data for chromium is available (IPCS 1988).

Epidemiological studies have found an association between inhalation of hexavalent chromium compounds and lung cancer, especially in humans occupationally exposed during chromate production. There is no evidence that organs other than the lung are affected or that ingestion of hexavalent chromium compounds can cause cancer.

There are sufficient animal data to indicate that many hexavalent chromium compounds are carcinogenic. Hexavalent chromium compounds also cause mutations and chromosome aberrations in a variety of test systems. The mutagenic activity can be decreased or abolished by reducing agents, such as gastric juice.

In animal studies, orally administered trivalent chromium compounds have not been shown to induce cancer or to induce mutations in genetic material.

The International Agency for Research on Cancer has concluded that hexavalent chromium is carcinogenic to humans (Group 1, sufficient evidence of carcinogenicity in humans); and that trivalent chromium is not classifiable as to its carcinogenicity to humans (Group 3, inadequate evidence in humans and inadequate evidence in animals) (IARC 1990).

Derivation of guideline

The guideline value for chromium in drinking water is based on a World Health Organization assessment and should be reviewed when more toxicological data become available. It was adopted after consideration of the following points:

• The guideline value of 0.05 mg/L has been used in many countries for a number of years with no known cases of chromium toxicity.

• The value was originally set following a conservative assessment of studies on the toxicity of hexavalent chromium to rats (Mackenzie et al. 1958).

• Trivalent chromium is essential for human health and has no known toxic effects.

• Data are insufficient to determine whether a higher value would be equally safe.

Analysis for the separate valence states of chromium is time consuming and hence the guideline value applies to total chromium. If concentrations of total chromium exceed the guideline value, it is recommended that separate analyses for Cr(VI) and Cr(III) be undertaken.

References

APHA Method 3500-Cr Part B (1992). Chromium: Atomic Absorption method for total chromium. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

APHA Method 3500-Cr Part C (1992). Chromium: Inductively Coupled Plasma method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

APHA Method 3500-Cr Part D (1992). Chromium: Colorimetric method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

IARC (International Agency for Research on Cancer) (1990). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: chromium, nickel and welding. World Health Organization, IARC, 49.

IPCS (International Programme on Chemical Safety) (1988). Chromium. Environmental Health Criteria, 61. World Health Organization, IPCS.

MacKenzie RD, Byerrum RU, Decker CF, Hoppert CA, Langham RF (1958). Chronic toxicity studies: II. Hexavalent and trivalent chromium administered in drinking water to rats. American Medical Association Archives of Industrial Health, 18:232–234.