They are oxidizing agents, and all form anions by accepting an electron. The elements below fluorine in the periodic table also form numerous oxyanions. The atomic weight of bromine is 79.909. Naturally occurring bromine consists of 50.57% 79Br and 49.43% 81Br. Bromine is a dense mobile dark liquid at room temperature that freezes at −7 °C and boils at 58 °C (Cotton & Wilkinson, 1962). Bromide commonly exists as salts with sodium, potassium and other cations, which are usually very soluble in water. It also forms the strong acid, hydrobromic acid (HBr), and the weaker hypobromous (HOBr), bromous (HBrO2) and bromic (HBrO3) oxyacids. Basic solutions of OBr− are stable at 0 °C but rapidly disproportionate to Br− and BrO3 − at temperatures of about 50 °C and above

Bromide is commonly found in nature along with sodium chloride, owing to their similar physical and chemical properties, but in smaller quantities. Bromide concentrations in seawater are generally in the range of 65 mg/l to well over 80 mg/l in some confined sea areas; chloride, on the other hand, is present at concentrations ranging from 18 980 mg/l to over 23 000 mg/l (Al-Mutaz, 2000). Concentrations of bromide in fresh water typically range from trace amounts to about 0.5 mg/l. Concentrations of bromide in desalinated waters may approach 1 mg/l. The typical daily dietary intake of bromide in the United States of America is 2–8 mg (Nielsen & Dunn, 2009) from grains, nuts and fish. The average bromide intake from dietary sources in the Netherlands is reported as 8.4–9.4 mg/day (EMEA, 1997). The intake of bromide from food would be lower in bottle-fed infants.