Barium (Ba) is the fifth element in Group IIA in the periodic table. It has an atomic number of 56, an atomic weight of 137.33, and a valence of 2. The average abundance of Ba in the earth’s crust is 390 ppm; in soils it is 63 to 810 ppm; in streams it is 10 mg/L; in US drinking waters it is 49 μg/L; and in groundwaters it is 0.05 to 1 mg/L. It is found chiefly in barite (BaSO4) or in witherite (BaCO3). Barium’s main use is as a constituent of mud slurries used when drilling oil and exploration wells, but it is also used in pigments, rat poisons, pyrotechnics, and in medicine.
The solubility of barium in natural waters is controlled by the solubility of BaSO4, and somewhat by its adsorption on hydroxides. High concentrations of barium occur in some brines. Concentrations exceeding 1 mg/L constitute a toxicity hazard in the marine environment. The U.S. EPA primary drinking water standard MCL is 1 mg/L.
Perform analyses by the atomic absorption spectrometric methods (Section 3111 D or E), the electrothermal atomic absorption method (Section 3113 B), or the inductively coupled plasma methods (Sections 3120 or 3125).