Zinc

(endorsed 1996)

Guideline

Based on aesthetic considerations (taste), the concentration of zinc in drinking water should be less than 3 mg/L.

No health-based guideline value is proposed for zinc.

General description

Zinc is widely distributed and occurs in small amounts in almost all rocks, commonly as the sulfide.

It is used as a coating to prevent corrosion of iron and steel products, and in the manufacture of brass. Zinc oxide is an important component in the manufacture of paint and rubber products, including tyres.

In surface and ground waters, the concentration of zinc from natural leaching is usually less than 0.01 mg/L. Tap water can contain much higher concentrations as a result of corrosion of zinc-coated pipes and fittings. Zinc concentrations in galvanised iron rainwater tanks are typically 2 mg/L to 4 mg/L but have been reported as high as 11 mg/L.

Taste problems can occur if the zinc concentration in drinking water exceeds 3 mg/L. Water with a zinc concentration above 5 mg/L tends to be opalescent, develops a greasy film when boiled, and has an undesirable dry ‘metallic’ taste.

Zinc is present in plant and animal tissues, and food is the major source of zinc intake. Drinking water usually makes a negligible contribution to total intake.

Typical values in Australian drinking water

In major Australian reticulated supplies, the concentration of zinc ranges up to 0.26 mg/L, with a typical concentration of 0.05 mg/L.

Treatment of drinking water

Zinc concentrations in drinking water can be reduced by alum coagulation at pH 6.5–7 (30% removal) or by lime softening at pH 9.5 to pH 10 (60% removal).

Measurement

The concentration of zinc in drinking water can be determined by flame atomic absorption spectroscopy or inductively coupled plasma emission spectroscopy (APHA Method 3500-Zn Parts B or C 1992). The limits of determination are approximately 0.02 mg/L.

Health considerations

Zinc is an essential element for humans. The recommended intake for adults is 12 mg per day. Nutritional zinc deficiency results in retarded growth, anorexia, mental lethargy, skin changes and night blindness.

Approximately 20–30% of dietary zinc is absorbed by the gastrointestinal tract. Highest concentrations are found in the liver, kidney, bone, retina, prostate and muscle.

In humans, consumption of very high amounts of zinc can result in nausea, vomiting, diarrhoea and abdominal cramps. The major effects of long-term exposure to zinc are copper deficiency, anaemia and gastric erosion.

In animal studies, zinc has been reported to reduce the toxic effects of nickel and cadmium. High doses over long periods may, however, be toxic to nerve cells of mammals.

There is no evidence that occupational exposure to zinc increases the risk of cancer.

Zinc has been shown to induce chromosomal aberrations in mammalian cells, but is inactive in bacterial mutation tests.

Derivation of guideline

The guideline value for zinc in drinking water has been based on the taste threshold of 3 mg/L. Higher zinc concentrations can impart an undesirable taste and a cloudy appearance. Zinc concentrations over 0.5 mg/L may indicate corrosion problems.

References

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

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