Boron and boranes have varied functions in the electronics, metalworking, chemical, pulp and paper, ceramics, textile and construction industries. In the electronics industry, boron, boron tribromide and boron trichloride are used as semiconductors. Boron is an igniter in radio tubes and a degasifying agent in metallurgy. It is also used in pyrotechnic flares. Diborane, pentaborane and decaborane are utilized in high-energy fuel. Boron trichloride, diborane and decaborane are rocket propellants, and triethylboron and boron serve as igniters for jet and rocket engines. 10Boron is employed in the nuclear industry as a constituent of neutron-shielding material in reactors.
In the metalworking industry, many of the boranes are used in welding and brazing. Other compounds are employed as flame retardants and as bleaching agents in the textile, paper and pulp, and paint and varnish industries. Boron oxide is a fire-resistant additive in paints and varnishes, while sodium tetraborate, borax and trimethyl borate are fireproofing agents for textile goods. Both borax and sodium tetraborate are used for the fireproofing and artificial aging of wood. In the construction industries, they are components of fibreglass insulation. Sodium tetraborate also serves as an algicide in industrial water and as an agent in the tanning industry for curing and preserving skins. Borax is a germicide in cleaning products, a corrosion inhibitor in antifreeze, and a powdered insecticide for crack and crevice treatment of food-handling areas. Decaborane is a rayon delustrant and a mothproofing agent in the textile industry, and sodium borohydride is a bleaching agent for wood pulp.
In the ceramics industry, boron oxide and borax are found in glazes, and sodium tetraborate is a component of porcelain enamels and glazes. Sodium perborate is employed for bleaching textile goods and for electroplating. It is used in soaps, deodorants, detergents, mouthwash and vat dyes. Boron trifluoride is used in food packaging, electronics, and in the nuclear industry’s breeder reactors.
Boron is a naturally occurring substance that is commonly found in food and drinking water. In trace amounts it is essential to the growth of plants and certain types of algae. Although it is also found in human tissue, its role is unknown. Boron is generally regarded as safe (GRAS) for use as an indirect food additive (e.g., in packaging), but compounds containing boron can be highly toxic. Boron is present in a number of industrially useful compounds, including borates, boranes and boron halides.
Boron toxicity in humans is seen most commonly following chronic use of medicines containing boric acid and in cases of accidental ingestion, especially among young children. Occupational toxicity usually results from exposure of the respiratory system or open skin wounds to dusts, gases or vapours of boron compounds.
Acute irritation of eyes, skin and the respiratory tract can follow contact with almost any of these materials in usual concentrations. Absorption can affect the blood, respiratory tract, digestive tract, kidneys, liver and central nervous system; in severe cases, it can result in death.
Boric acid is the most common of the borates, which are compounds of boron, oxygen and other elements. Acute exposure to boric acid in liquid or solid forms can cause irritation, the severity of which is determined by the concentration and duration of exposure. Inhalation of borate dusts or mists can directly irritate the skin, eyes and respiratory system.
Symptoms of this irritation include eye discomfort, dry mouth, sore throat and productive cough. Workers usually report these symptoms after acute boric acid exposures over
10 mg/m3; however, chronic exposures of less than half this can also cause irritant symptoms.
Workers exposed to borax (sodium borate) dust have reported chronic productive cough, and, in those who have experienced long exposures, obstructive abnormalities have been detected, though it is unclear whether these are related to exposure.
Borates are readily absorbed through open skin wounds and from the respiratory and digestive tracts. After absorption borates exert predominant actions upon the skin, central nervous system and digestive tract. Symptoms generally develop rapidly, but may take hours to evolve following skin exposures. Following absorption, the skin or mucous membranes may develop abnormal redness (erythema), or surface tissue may be shed. Chronic exposure may cause eczema, patchy hair loss and swelling around the eyes. These dermatologic effects may take days to develop after exposure. The individual may experience abdominal pain, nausea, vomiting and diarrhoea. Vomitus and diarrhoea may be blue-green in colour and may contain blood. Headache, excitement or depression, seizures, lethargy and coma may develop.
In instances of acute poisoning, anaemia, acidosis and dehydration develop, accompanied by rapid, weak pulse and low blood pressure. These effects may be followed by irregular heart rhythm, shock, kidney failure and, in rare cases, liver damage. Victims appear pale, sweaty and acutely ill. Most of these severe findings have been present just before death from acute borate toxicity. However, when victims are diagnosed and treated in time, the effects usually are reversible.
The reproductive effects of borates are still unclear. Boric acid exposure inhibited sperm motility in rats and, at higher levels, led to testicular atrophy. Animal and tissue studies of genotoxicity have been negative, but infertility has been demonstrated in both males and females after chronic boric acid feedings. Offspring have shown delayed and abnormal development including abnormal rib development. In humans, there is only suggestive evidence of decreased fertility among the few workers who have been evaluated in uncontrolled studies.
Boron trihalides—boron trifluoride, boron chloride and boron bromide—can react violently with water, liberating hydrogen halides such as hydrochloric and hydrofluoric acids. Boron trifluoride is a severe irritant of the lungs, eyes and skin. Animals studied after lethal exposures showed kidney failure and kidney tubule damage, pulmonary irritation and pneumonia. Examinations of a small number of exposed workers showed some decreases in pulmonary function, but it was unclear whether these were related to exposure.
Boranes (boron hydrides)—diborane, pentaborane and decaborane—are extremely reactive compounds which can explode on contact with oxygen or oxidizing agents. As a group they are severe irritants which can quickly cause chemical pneumonia, pulmonary oedema and other respiratory injuries. In addition, boranes have been reported to cause seizures and neurological damage with long-lasting neurological deficits and psychological symptoms. These compounds must be handled with extreme caution.
There is no evidence of boron or the borates causing cancer in chronic experiments with animals or in studies of exposed humans.
Table 1 - Chemical information.
Table 2 - Health hazards.
Table 3 - Physical and chemical hazards.
Table 4 - Physical and chemical properties.