The characteristic bad smell of sewage can be attributed to Hydrogen sulfide. It is known by other names such as, sewer gas and stink damp. The gas is found abundantly in natural gas, crude petroleum and even hot springs. The bacterial breakdown of organic matters like human and animal wastes found commonly in sewages also produces Hydrogen sulfide. Ovens, natural gas, petroleum drilling and refining produce this gas. It is easily identifiable by chemistry students when working in the laboratory. The strong pungent odor of the gas is referred to as the smell of rotten eggs.
The Swedish scientist, Carl Wilhelm Scheele was the first to encounter and identify Hydrogen sulfide gas. When he treated ferrous sulfide or pyrite (fool’s gold) with a mineral acid, he detected the release of Hydrogen sulfide gas. The gas gave rise to “Schwefelluft” or Sulfur air. He referred to the gas as “stinkede” (fetid or stinking). The smell exactly corresponded to the smell of rotten eggs. The Swedish chemist and mineralogist Torbern Olof Bergman, who was Scheele’s patron, also detected the presence of this gas in mineral acids. The publication articles for these experimental observations were in the year 1777. Scheele was the man who detected the gas Hydrogen Cyanide. And after a few years he discovered the gas Hydrogen sulfide. Later the gases were found to be very similar through many observations.
The rotten smelling Hydrogen sulfide gas is usually detected in 2 parts per billion in air. That means in an open space if Hydrogen sulfide gas of 1 ml is released, it would get uniformly diffused in the atmosphere in that ratio. The gas has a very similar electronic structure like water. Sulfur and oxygen belong to the same group in the periodic table. But Sulfur is not as electronegative as Oxygen. And as a result, the gas is not as polar as a water molecule. The intermolecular forces in the gas Hydrogen sulfide is far weaker compared to the intermolecular forces of water. As a result the melting and boiling point of the gas is lower than that of water.
The compound Hydrogen sulfide is used as an intermediate and as a reagent in the chemical laboratory. It finds use as a reducing agent for other Sulfur compounds. In the oil and gas industries the gas Hydrogen sulfide is produced as a byproduct of desulfurization process. It is also involved in the production of rayon, leather tanning and in sewage treatments the gas is found to be released. In a research based survey it was found that 5,688,172 pounds of Hydrogen sulfide is released in California from point sources annually. This was reported under the Air Toxics Hot Spots Act in California.
It is a chemical asphyxiant like carbon monoxide. Depending on the concentration of the gas, people might exhibit varying symptoms. As Hydrogen sulfide affects the absorption of oxygen, it restricts cellular respiration which can lead to bronchitis and edema in long term exposures.
At 0-10ppm : Irritation of throat, eyes and nose leading to watery eyes and nose.
At 10-50ppm: causes headaches, dizziness and nausea.
At 50-220ppm: Respiratory tract can get irritated, convulsions, can be fatal in severe cases.
The rate of dispersion is dependent on the air currents carrying the gas. The gas usually decomposes in air completely by 3 or 4 days. When inhaled, the gas can form stable compounds with the blood. Eventually it can reduce the oxygen carrying capacity of the blood and hence cause respiratory problems. People working in refineries and tanneries are overtly exposed to this gas. And they always run the danger of suffering from respiratory diseases caused due to Hydrogen sulfide. Hydrogen sulfide was found toxic to birds, animals and aquatic life.