Boron is a widely occurring element in minerals found in the earth’s crust. Boron is of low toxicity. It is found in the environment primarily combined with oxygen in compounds called borates. Common borate compounds include boric acid, salts of boric acid (e.g., sodium tetraborates, which are also referred to as borax), and boron oxide. Industrial uses include glass and ceramics (70%), soaps, bleaches, and detergents (4%), fire retardants (2%), and agriculture (2%). Other uses, include addition to enamels and glazes, cosmetics or medical preparations.
Human exposure to boron, typically as borates or boric acid, may occur through ingestion of food and water, or through use of pesticides containing boron compounds, inhalation of boron-containing powders or dusts, or the use of boron from cosmetics or medical preparations. The most appreciable boron exposure to the general population is likely to be through ingestion of food (as boron is an essential element in plants) and, to a lesser extent, water. Boron levels reported in drinking water generally range from <1 to 3 mg boron/L.
Workers in industries such as the manufacture of fiberglass and other glass products, cleaning and laundry products, fertilizers, pesticides, and cosmetics, may also be exposed to boron compounds.
Acute-duration exposures of mining and processing workers to sodium borate dusts has been associated with mild irritation of the eyes, throat, and nose, as well as cough and breathlessness. No exposure-related changes in lung function were observed in nonsmoking workers. No studies were located regarding death in humans after inhalation exposure to boron.
Human case reports have shown that boron can be lethal following short-term oral exposure at high doses, although the dose estimation can be quite imprecise and variability in human responses to acute exposure is quite large. The minimal lethal dose of ingested boron (as boric acid) was reported to be 2–3 g in infants, 5–6 g in children, and 15–20 g in adults. However, a review of 784 human poisonings with boric acid (10–88 g) reported no fatalities, with 88% of cases being asymptomatic. Liver, kidney, central nervous system, and gastrointestinal effects and skin lesions have been found in cases following ingestion of boron.
The available information on the toxicity of inhaled boron comes from an occupational exposure study (Wegman et al. 1994) and two human experimental studies (Cain et al. 2004, 2008). These studies identified increases in nasal secretions as the most sensitive effect.
The essentiality of boron has been established for most plants and some animals, but not in humans. The use of boron as a dietary supplement has not been endorsed by the Food and Nutrition Board/Institute of Medicine and did not result in increased plasma testosterone or strength levels in bodybuilders.