Photosynthetic bacteria belonging to the families Chromatiaceae and Chlorobiaceae oxidize hydrogen sulfide to elemental sulfur and sulfate in the presence of light and the absence of oxygen.

Complaints were mostly related to the odour of hydrogen sulfide gas.

Then the gases are passed over zinc oxide at ca 700 K and hydrogen sulfide is removed:

Hydrogen sulfide gas is rapidly absorbed through the lung.

EFFECTS ON MAN Adequate systematic studies of the relationship between hydrogen sulfide exposure and health status in the general population have not been carried out.

Acute hydrogen sulfide intoxication is a dramatic, often fatal event.

Controlled exposure of human subjects to concentrations of hydrogen sulfide gas exceeding about 75 mg/m3 (50 ppm) has been deemed to involve excessive risk because of the possibility of injury to the lungs (Sayers et al., 1925; National Research Council, USA, 1979).

Efforts should be made to estimate the dose of hydrogen sulfide associated with acute poisoning.

(1962) Hydrogen sulfide intoxication.

In a document prepared by the National Research Council of the National Academy of Sciences of the USA (National Research Council, USA, 1979), the observation was made that application of the terms "acute", "subacute" and "chronic" to hydrogen sulfide exposure was both imprecise and misleading.

(1969) Preliminary air pollution survey of hydrogen sulfide.

" Acute intoxication: Effects of a single exposure [seconds- minutes]a to massive concentrations of hydrogen sulfide that rapidly produce signs of respiratory distress.

(1954) Hydrogen sulfide eye inflammation -- treatment with cortisone.

"Chronic hydrogen sulfide intoxication" has been applied by some authors to describe a prolonged state of symptoms resulting from a single or repeated exposure to concentrations of hydrogen sulfide that do not produce clear-cut manifestations of either acute or subacute illness.

Much higher concentrations of hydrogen sulfide have been measured near point sources.

(1977) Hydrogen sulfide poisoning: review of 5 years' experience.

At concentrations of 1500-3000 mg/m3 (1000-2000 ppm), hydrogen sulfide gas is rapidly absorbed through the lung into the blood, which initially induces hyperpnoea (rapid breathing).

Many other instances of sequelae following acute hydrogen sulfide intoxication have been reported.

(1972) The evaluation of gas detector tube systems: hydrogen sulfide.

EFFECTS ON EXPERIMENTAL ANIMALS Very little information is available on the effects of low level concentrations of hydrogen sulfide gas on experimental animals; most published data have emphasized the effects of exposure to lethal or near-lethal concentrations of the gas.

The diagnosis of "sequelae after acute hydrogen sulfide poisoning" was made in 15 cases.

(1966) A near-fatal case of hydrogen sulfide poisoning.

Sub-acute intoxication: Effects of continuous exposure [up to several hours]a to mid-level 140 to 1400 mg/m3 (100 to 1000 ppm) concentrations of hydrogen sulfide.