Hydrogen sulfide, Sulfide

(endorsed 1996)

Guideline

Based on aesthetic considerations, the concentration of hydrogen sulfide in drinking water should not exceed 0.05 mg/L.

No health-based guideline value has been set for hydrogen sulfide, or sulfide, as the aesthetic guideline is considerably below the concentration that would cause health problems.

General description

Hydrogen sulfide is formed in drinking water by the hydrolysis of soluble sulfides, or through the reduction of sulfate by the action of microorganisms. Both processes require anoxic conditions. In well-oxygenated water, sulfide will be chemically or biologically oxidised to sulfate or elemental sulfur, and concentrations are extremely low. Higher concentrations can occur in anoxic water drawn from deep storages.

In water, hydrogen sulfide will be in equilibrium with the sulfide and hydrosulfide ions. The ratio will depend on pH, temperature and salinity. At pH 7.4, about a third will be present in undissociated form, with the remainder present as hydrosulfide. Above pH 10, the sulfide ion will be the dominant form; below pH 5, undissociated hydrogen sulfide will predominate.

Hydrogen sulfide has an obnoxious ‘rotten egg’ gas odour, with a taste and odour threshold of 0.05 mg/L. High concentrations in air can have a deceptively sweet smell and cause ‘olfactory fatigue’ (a deadening of the sense of smell).

Hydrogen sulfide is used industrially in the production of sulfur, sulfuric acid, inorganic sulfides, thiophenes and other organic compounds. It occurs as a by-product in a number of processes including petrol refining, coke ovens, paper mills, iron smelters, food processing and tanneries. It is present in sewers and is a major component of sewage odour.

Data on the concentration of hydrogen sulfide in food are scarce, although a number of foods and drinks are known to contain sulfides.

Typical values in Australian drinking water

Australian drinking water supplies have not been routinely monitored for hydrogen sulfide, or sulfide.

Treatment of drinking water

Hydrogen sulfide can be removed from drinking water by keeping the water well oxygenated.

Measurement

The sulfide concentration of drinking water can be determined using the methylene blue colorimetric method (APHA Method 4500-S2- Part D 1992). The limit of determination is 0.02 mg/L.

Health considerations

Soluble sulfides are absorbed rapidly from the gastrointestinal tract, although hydrogen sulfide is absorbed principally by the lung. Animal studies have indicated that after absorption, hydrogen sulfide is distributed to the brain, liver, kidneys, pancreas and small intestine.

An extensive review and summary of the human and animal toxicity data for hydrogen sulfide is available (IPCS 1981).

There are no data on the human health effects of ingesting water that contains hydrogen sulfide. Ingestion of sulfides has been known to cause nausea, vomiting and irritation of the mucous membranes. Inhalation of hydrogen sulfide is known to be extremely toxic to humans, with exposure to amounts as low as 5 ppm for 30 minutes or more producing headaches, dizziness, nausea, gastrointestinal disorders and breathing problems. Inhalation of concentrations above 500 ppm can cause cardiac failure and death.

Animal data are mainly from short-term inhalation studies. Effects include neurotoxic activity and distortions in cardiac rhythm.

No long-term carcinogenicity bioassays have been undertaken on hydrogen sulfide. Sodium sulfide did not induce cancers in experimental animals. Hydrogen sulfide was not found to be mutagenic in tests with different strains of bacteria.

Derivation of guideline

The guideline value of 0.05 mg/L is based on the aesthetic considerations of taste and odour. Insufficient data are available to determine a guideline value based on health considerations. The guideline value is, however, considerably lower than the concentration likely to have a harmful effect and it is therefore unlikely that a person would consume a harmful dose.

References

APHA Method 4500-S2- Part D (1992). Sulfide: Methylene blue method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

IPCS (International Programme on Chemical Safety) (1981). Hydrogen Sulfide. Environmental Health Criteria, 19. World Health Organization, IPCS.