Phosphorus, Selenium, Tellurium, and Sulfur

Abstract

Phosphorus and sulfur are elements 15 and 16 in the periodic chart and selenium and tellurium are in the same group as sulfur. Sulfur was not covered in the previous edition, but sulfur and its compounds have been added in this edition because of the importance of sulfur compounds. Elemental phosphorus is produced as a by-product or intermediate in the production of phosphate fertilizer. Environmental contamination with phosphorus results from its manufacture into phosphorus compounds and during the transport and use of these compounds. In the manufacturing process, phosphate rock containing the mineral apatite (tricalcium phosphate) is heated and elementary phosphorus is liberated as a vapor. Phosphorus is used to manufacture explosives, incendiaries, smoke bombs, chemicals, rodenticides, phosphor bronze, and fertilizer. The use of phosphate fertilizers results in increased nutrients in fresh water and is a major source of environmental pollution. Phosphorus exists in several allotropic forms: white (or yellow), red, and black (or violet). The last is of no industrial importance. Elemental yellow phosphorus extracted from bone was used to make “strike anywhere” matches. In 1845, the occupational disease “phossy jaw,” a jaw bone necrosis, was recognized in workers who manufactured such matches. A prohibitive tax imposed in 1912 on matches made from yellow phosphorus led to the use of less toxic materials, red phosphorus and phosphorus sesquisulfide. The United States appears to have lagged behind European countries in that signatories of the Berne Convention of 1906 agreed not to manufacture or import matches made with yellow phosphorus. Occasional injuries continued to result from using yellow phosphorus to manufacture fireworks until 1926, when an agreement was reached to discontinue the use of yellow phosphorus for this purpose. The world production of elemental phosphorus exceeds 1,000,000 metric ton. It is manufactured either in electric or blast furnaces. Both depend on silica as a flux for the calcium present in the phosphate rock. Nearly all of the phosphorus produced is converted into phosphoric acid or other phosphorus compounds. Red phosphorus does not ignite spontaneously but may be ignited by friction, static electricity, heating, or oxidizing agents. Handling it in an aqueous solution helps prevent fires. Phosphorus (white yellow) can be absorbed through the skin, respiratory tract, and gastrointestinal (GI) tract. Experimental investigations on rats show the highest retention 5 days after oral administration in the liver, skeletal muscle, GI tract, blood, and kidney. Phosphorus is converted to phosphates in the body. Urinary excretion, the chief mode of elimination, is largely in the form of organic and inorganic phosphates. Selenium (Se), a nonmetallic element of the sulfur group, is widely distributed in nature. It is obtained along with tellurium as a by-product of metal ore refining, chiefly from copper. About 16 ton is mined a year globally. Because selenium is present in fossil fuels, up to 90% of the selenium content in ambient air is emitted during their combustion. Air pollution concentrations averaged from 0.38 ng/m3 in remote areas to 13 ng/m3 in urban areas. The mass medium diameter was 0.92 mm. The worldwide emissions of 10,000 ton/year from natural sources exceed the atmospheric emissions from anthropogenic sources (5100 ton). However, 41,000 ton is emitted into the aquatic ecosystems. The largest contributors are electric power generating plants that produce 18,000 ton; manufacturing processes account for 12,000 ton. Most of the world's selenium today is provided by recovery from anode muds of electrolytic copper refineries. Selenium is recovered by roasting these muds with soda or sulfuric acid or by melting them with a soda and niter. One of the important uses of selenium is in photoelectric cells. Toxic gases and vapors may be released in a fire involving selenium. Selenium can react violently with chromic oxide (CrO3), lithium silicon (Li6Si2), nitric acid, nitrogen trichloride, oxygen, potassium bromate, silver bromate, and fluorine. Selenium is an essential trace metal. Because of data suggesting that it may inhibit chemical carcinogenesis, it has been widely promoted as a dietary supplement. Selenium may replace sulfur and forms selenoproteins in plants and animal systems. It interacts with a wide variety of vitamins, xenobiotics, and sulfur-containing amino acids. Selenium reduces the toxicity of many metals such as mercury, cadmium, lead, silver, copper, and arsenic. Selenium and most of its compounds are readily absorbed by oral intake or by breathing. Dermal exposure generally does not result in elevated selenium blood concentration. After absorption, high concentrations are found in the liver and kidney. In humans, dimethylselenide is formed and may account for the garlic odor of the breath. In farm animals (cattle, sheep, hogs, and horses), toxicity from intake of feed containing excessive selenium has resulted. Elemental tellurium (Te) has some metallic properties, although it is classed as a nonmetal or metalloid. The name is derived from the Latin word for earth. Tellurium is occasionally found naturally, more often as telluride of gold, calaverite. The elemental form has a bright luster, is brittle, readily powders, and burns slowly in air. Tellurium exists in two allotropic forms, as a powder and in the hexagonal crystalline form (isomorphous) with gray selenium. The concentration in the earth's crust is about 0.002 ppm. It is recovered from anode muds during the refining of blister copper. It is also found in various sulfide ores along with selenium and is produced as a by-product of metal refineries. The United States, Canada, Peru, and Japan are the largest producers. Tellurium's industrial applications include its use as a metallurgical additive to improve the characteristics of alloys of copper, steel, lead, and bronze. Elemental tellurium is poorly absorbed, but its more soluble compounds may undergo some oral absorption. Soluble tellurium can be absorbed through the skin, although ingestion or inhalation of fumes presents the greatest industrial hazard. A metallic taste in the mouth may result from excessive absorption. The characteristic sign of tellurium absorption is the garlic-like odor attributed to dimethyltelluride in the breath and sweat. This may persist for many days after exposure. Urinary and fecal (biliary) excretion also occurs. Urinary excretion is probably more important than respiratory excretion in eliminating absorbed tellurium. Tellurium is complexed to plasma proteins, and little is found in the red blood cells. In the nervous system, tellurium accumulates in the gray matter, not the white matter, when injected intracerebrally. The metal is found in phagocytic and ependymal cells and in lysosomes as fine needles. The whole-body retention model assumes a long half-life, based on tellurium dioxide. Sulfur (S) occurs naturally as a yellow, water-insoluble solid. The name is from the Latin “sulphur.” Early Greek physicians mention sulfur and the fumes from burning sulfur in religious ceremonies. Sulfur constitutes about 0.053% of the earth's crust and occurs in two allotropic crystalline forms, rhombic and monoclinic. Below 96°C, only the rhombic form is stable. Large sedimentary deposits of almost pure sulfur are mined in Texas and Louisiana. Sulfur can be extracted from crude oil in the refining process, as well as from stack gases resulting from coal combustion. Sulfur occurs in fossil fuels and in metal (Fe, Pb) ores. Exposure may occur in numerous operations related to the mining and recovery of sulfur. The recovery of sulfur as a by-product accounts for a larger portion of the world's production than the mined mineral. Sulfur is one of the most important raw materials, particularly in the fertilizer industry. Organic sulfur compounds occur in garlic, mustard, onions, and cabbage and are responsible for the odor of skunks. Sulfur occurs in living tissue and is part of some amino acids. Unlike many other inorganic elements, sulfur itself is relatively nontoxic. Sulfur and some of its salts have been used medicinally. The consumption of sulfur is a measure of national industrial development and economic activity. Sulfur is most often used as a chemical reagent, rather than as part of a finished product. Exposure to sulfur particulates produces tracheobronchitis, characterized by cough, sore throat, chest pain, and lightheadedness. Keywords: phosphorus; selenium; tellurium; sulfur; selenium compounds; selenium compounds; tellurium compounds; sulfur compounds; phossy jaw; phosphorus poisoning; phosphoric acid; sulfides; chlorides; fluorides; sulfuric acid; sulfides; selenides