2. Relevance to Public Health 2.1 Background and Environmental Exposures to Boron in the United States

Boron is a widely occurring element in minerals found in the earth’s crust. It is the 51 most common element found in the earth’s crust and is found at an average concentration of 8 mg/kg (approximately 0.0008%). 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. U.S. borate mining and production mainly occurs in Kern, San Bernardino, and Inyo Counties, California. Borate-containing minerals are mined and processed to produce borates for several industrial uses in the United States. Industrial uses include glass and ceramics (70%), soaps, bleaches, and detergents (4%), fire retardants (2%), and agriculture (2%). Other uses, including metallurgy, nuclear applications, sale to distributors, addition to enamels and glazes, and ingredients in cosmetics or medical preparations, make up the remaining 19%. There are 189 pesticide products registered in the United States that contain boric acid or one of its sodium salts as an active ingredient.