monomethylhydrazine (MMH), and unsymmetrical (or 1,1-) dimethlyhydrazine. Although Iraq had apparently experimented with UDMH as a rocket fuel, it is more likely that kerosene was the rocket fuel used during the Gulf War (DOD 2001).
Nitric acid, probably in the form of IRFNA, was used as an oxidizer for the propellant in the Scuds (DOD 2000). Metal corrosion is inhibited if a halogen compound, such as hydrogen fluoride or iodine, is added to red fuming nitric acid (RFNA) (DOD 2000). The oxidizer’s color and fuming properties result from the high concentration of nitric acid, relative to nitrogen dioxide, in the liquid (EFMA 1997).
The remainder of this chapter contains the committee’s evaluation of the scientific literature on adverse, persistent health effects of hydrazines and nitric acid. It begins by reviewing toxicologic information on those chemicals, then reviews human studies related to whether persistent health effects might be associated with exposure to hydrazines and nitric acid, and finally presents the committee’s conclusions.
This section provides an overview of toxicologic information on two chemicals—UDMH and RFNA—that may have been dispersed over Gulf War veterans by disintegrating Scuds. Because toxicologic data on those chemicals are sparse, the findings on similar chemicals are also reviewed. Data on hydrazine and MMH are considered in addition to those on UDMH, and information on nitric acid in general is reviewed with the extremely limited data specifically on RFNA. For each of those sets of chemicals (hydrazines and nitric acids), the following information is presented: uses, physical and chemical properties, exposure limits recommended by national and international government bodies and organizations, toxicokinetic properties, summaries of experimental studies, and any evidence of genetic susceptibility and of interactions between the chemicals in question and other substances.
The committee’s approach was to use toxicity data, primarily from experimental animal studies, for background information and as supporting evidence. Therefore, an extensive review of toxicologic studies was not appropriate here. Several organizations—for example, the Agency for Toxic Substances and Disease Registry (ATSDR 1997), the International Agency for Research on Cancer (IARC 1974, 1999a, 1999b, 1999c) the National Institute for Occupational Safety and Health (NIOSH 1976), and the National Research Council (NRC 1996, 1998, 2000)—have conducted reviews of hydrazine- and nitric acid-related compounds. The reader is referred to those sources for more detailed reviews of the toxicologic data on the compounds.
Hydrazines contain two nitrogen atoms joined by a single covalent bond. Hydrazine, UDMH, and MMH are used as rocket propellants. Hydrazine is also used for such applications as agricultural pesticides and water treatment (IARC 1999b). UDMH is also used for chemical syntheses, as an absorbent for acid gas, and as a plant-growth control agent (NRC 2000). MMH is also used as a chemical intermediate (NRC 2000). Some physical and chemical characteristics of hydrazines are listed in Table 9.1.