particles primarily in an occupational setting. The risk posed by that exposure would depend on the particle size distribution, which determines whether a particle is inhalable and, if it is inhalable, where in the respiratory tract it is deposited, which might affect solubility and absorption. Thus, the major route of concern is ingestion.

The outstanding oxidizing ability of perchlorate led to its early use as a propellant and an explosive (Mendiratta et al. 1996). France, Germany, Switzerland, and the United States began production in the 1890s. Before the 1940s, annual global production of perchlorate was estimated to be 1,800 tons. In the middle 1940s, annual perchlorate production increased dramatically to 18,000 tons because of demand by the military and aerospace industry. Current production values are difficult to estimate because ammonium perchlorate is classified as a strategic compound.

Perchlorate is used primarily as an oxidizer in solid rocket fuels and propellants (Mendiratta et al. 1996). Ammonium perchlorate is the perchlorate salt most commonly used for that purpose. Perchlorate is also used in explosives, pyrotechnics, and blasting formulations. Magnesium perchlorate and lithium perchlorate are used in dry batteries. Other uses have been reported (EPA 2002a; Mendiratta et al. 1996).

Over the past 50 years, perchlorate has been used to diagnose and treat