Hydrogen sulfide toxicity

The mechanism of hydrogen sulfide toxicity is in part similar to that of cyanide. Like cyanide, hydrogen sulfide can inhibit the enzyme cytochrome oxidase resulting in tissue hypoxia. Specific health effects are discussed in greater detail below. 

The usefulness of urinary thiosulfate as an indicator of nonfatal hydrogen sulfide toxicity has been studied (Kangas and Savolainen 1987). Urinary samples for thiosulfate were obtained from volunteers exposed by inhalation to 8, 18, or 30 ppm of hydrogen sulfide for 30-45 minutes (the occupational exposure limit of 10 ppm for 8 hours was never exceeded). Excretion of urinary thiosulfate increased linearly up to 15 hours postexposure. Beyond 15 hours, the urinary thiosulfate concentration remained low, possibly indicating that most of the absorbed hydrogen sulfide was metabolized or excreted within 15 hours. 

Alterations in blood heme metabolism have been proposed as a possible indicator of the biological effects of hydrogen sulfide (Jappinen and Tenhunen 1990), but this does not relate to the mechanism of toxicity in humans. The activities of the enzymes of heme synthesis, i.e., delta-aminolevulinic acid synthase (ALA-S) and heme synthase (Haem-S), were examined in 21 cases of acute hydrogen sulfide toxicity in Finnish pulp mill and oil refinery workers. Subjects were exposed to hydrogen sulfide for periods ranging from approximately 1 minute to up to 3.5 hours. Hydrogen sulfide concentrations were considered to be in the range of 20-200 ppm. Several subjects lost consciousness for up to 3 minutes. 

Beauchamp RO, Bus JS, Popp JA, et al. 1984. A critical review of the literature on hydrogen sulfide toxicity. Crit Rev Toxicol 13 25-97. 

Samer E, Hultman BG, Berglund AE. 1988. Anaerobic treatment using new technology for controlling hydrogen sulfide toxicity. Tappi Journal 71 41-45. 

Numerous experimental animal studies have examined hydrogen sulfide toxicity. Many of them are summarized below and in Table 7—4. Most animal studies have examined effects at doses well above the proposed SEALs of 10 and 20 ppm. Less information available about the range of lower concentrations that cause eye irritation. The results of the animal studies reviewed are generally consistent with the human data. 

Poda, G.A. 1966. Hydrogen sulfide can be handled safely. Arch. Environ. Health 12(6) 795—800. Prior, M.G., A.K.Sharma, S.Young, and A.Lopez. 1988. Concentration-time interactions in hydrogen sulfide toxicity in rats. Can. J. Vet. Res. 52(3) 375—379. 

Hazard Dangerous fire risk ignites by friction contact with water or acids liberates poisonous and flammable hydrogen sulfide. Toxic by inhalation, strong irritant. TLV 1 mg/m3 STEL 3 mg/m3. 

Barium poisonings are uncommon and usually result from accidental contamination of food sources, suicidal ingestion, or occupational inhalation exposure. The water-soluble barium salts (acetate, carbonate, chloride, fluoride, hydroxide, nitrate, and sulfide) are highly toxic, whereas the insoluble salt, barium sulfate, is nontoxic because it is not absorbed. Soluble barium salts are found in depilatories, fireworks, ceramic glazes, and rodenticides and are used in the manufacture of glass and in dyeing textiles. Barium sulfide and polysulfide may also produce hydrogen sulfide toxicity (see p 224). 

Based on a log acid dissociation constant (pKa) of 7.0 for hydrogen sulfide, as the sample pH decreases, H2S concentrations increase and toxicity increases [63,64]. Because of these imique speciation trends, the graduated pH manipulation can be used to characterize ammonia and hydrogen sulfide toxicity as well as other toxicants showing this type of behavior (e.g., some metals). 

The second hazard is toxicity. The toxic materials may have direct effects. An example is pulmonary paralysis from hydrogen sulfide. Toxic materials can be asphyxiants that intermpt oxygen transport. An example is carbon monoxide. Toxic materials may be irritants at very low concentrations and lethal at higher levels, such as eye irritants that reduce vision. 

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