Sulfur is the 14th most abundant element in the earth’s crust. Sulfate is produced in the environment from the oxidation of elemental sulfur, sulfide minerals, or organic sulfur. Soils are thought to average 850 mg of sulfate/kg and sea water 885 mg of sulfate/L (Field, 1972). Industrial sulfate results from the burning of sulfur-containing fossil fuels, household wastes (e.g., detergents), and effluents from tanneries, steel mills, sulfate-pulp mills, and textile plants. Sulfuric acid accounts for an estimated 80 percent of commercial sulfur production (NRC, 1980). Additionally, thousands of tons of sulfate compounds are produced each year; annual production of sodium sulfate was estimated at 792 tons in 1987 (EPA, 1990).
Most public water supplies contain sulfate concentrations of less than 500 mg/L (EPA, 2001). Sulfate levels in water around 250 mg/L and above are detectable due to an off odor and taste, and this generally causes those exposed to water with higher concentrations of sulfate to switch to bottled water sources for drinking. Still, adaptation to water with a high sulfate content is known to occur. Extremely high sulfate concentrations in water have been recorded; for example, 1,500 mg/L in a coal mine in Pennsylvania and 63,000 mg/L in a zinc mine in Idaho (Moore, 1991).
Sulfur dioxide (SO2) emissions represent a growing concern for industrialized countries. Sulfur dioxide in the air can react with atmospheric water to produce sulfuric acid, resulting in acid rain (Drever, 1988). This can lead to increased soil acidity and elevated levels of sulfate in ground water (Drever, 1988). Moore (1991) estimated that global SO2 emissions have more than doubled over the last 50 years.
Sulfate improves growth in farm animals consuming diets deficient in sulfur amino acids and very low in sulfate. Thus sulfate salts are sometimes used as growth-promoting feed additives for chickens, turkeys, and pigs.
Sulfate is produced in the body from the transsulfuration of methionine to cysteine, followed by the oxidation of cysteine to pyruvate and inorganic sulfate. These processes occur as a result of protein turnover, as well as from degradation of excess protein-derived methionine or cysteine. Inorganic sulfate also results from the metabolism of several organic and inorganic sulfur compounds present