Crystals or yellow to brown solid; [Sax] Sold as filaments, powders, whiskers, and crystals; [Hawley]
A micronutrient for plants; Used to make alloys, neutron absorbers, oxygen scavengers, composite materials, semiconductors, and rocket fuels; [Hawley] No known function in animal cells, but present at about 1 ppm; Human diet contains about 10-20 mg/day; [Ullmann] Boron (B2O3, BN, BBr3, B(COC2H5)3, SiBr4, BCl3, BF3, and B2H6) is used as a doping agent in semiconductor manufacturing. [CSH, p. 50]
Powder is a dust explosion hazard. Toxic by ingestion; [Sax] May cause irritation, but not generally considered hazardous to handle boric acid and borates; [Ullmann] Boron deficiency may cause reproductive injury in fish; Excess boric acid causes testicular damage in high-dose feeding studies of animals; [ACGIH] Boron is a "hepatotoxic agent." [Zimmerman, p. 4] Minimal Risk Level (acute or intermediate oral dose) = 0.2 mg/kg/day (Develop.); Acute inhalation dose = 0.3 mg/m3 (Resp.); [ATSDR] See "Boric acid."