 |
Introduction Application of chemical agents in the context of armed conflict is as old as organized warfare. Examples frequently cited are the use of poisoned arrows and various kinds of irritant, toxic, or hypnotic smokes. In the war between Athenians and Spartans (431 - 404 BC), a chemical compound was developed consisting of wood saturated with sulphur and pitch and burned under the walls of besieged cities in order to generate choking fumes. In the war of Constantine against the Saracens in 673 AD, a compound known as "Greek Fire" was composed of sulphur, quicklime, pitch, resin, and petroleum. This was a flaming mixture, usually delivered against the enemy by means of syringe-like objects having the form of dragons and other monsters with widely opened jaws. It was also used by the Saracens against the Christians during the Crusades. Chemical weaponry was first used in the United States in the Civil War at the siege of Charleston. Wood was saturated with sulphur and burned under the parapets around the city hoping that favorable winds would propel huge clouds of choking smoke to drive out the defenders. French law enforcement is reputed to have been the first police organization to have used a chemical lacrimator (tear-producing) in a hand-thrown device. At the start of World War I (1914-1918) the French Army had limited stocks of hand and rifle grenades, loaded with a liquid tear-producing agent called Ethylbromacetate. Scarcely a week goes by without press reports of tear gas being used in a public setting, typically the dispersal of demonstrators or the subduing of a barricaded criminal. Recent years have seen the use of large amounts of tear gas in several countries including Chile, Panama, South Korea, and Israel. Some 15 chemicals have been used worldwide as tear gas agents. Four of these Chloroacetophenone (CN), O-chloro-benzylidene-malononitrile (CS), 10-chloro-5, 10-dihydrophenarsazine, and bromo-tolunitrile have been used extensively. In the United States, Britain, and Europe, CN and CS have been employed most widely.
The highlighted agents above are described in detail
in following pages since they are the most widely known and, historically, most widely
used agents. Health Hazards and Toxicology of Chemical Agents Most of the lacrimator and the common blistering agents are alkylating agents, tending to attach themselves to atoms such as oxygen, nitrogen, and sulfur. All three of these atoms occur in proteins, and oxygen and nitrogen are found in nucleic acids - both DNA and RNA. Once proteins (enzymes) or nucleic acids become alkylated, they are generally unable to function normally; the ultimate result may vary from a mild irritation to cancer. Thus, alkylating agents have been implicated as the causative agents in carcinogenesis, mutagenesis, and teratogenesis1. CS (Orthochlorobenzylidenemalononitrile) for example is an effective alkylating agent because the two strongly electron-withdrawing nitrile (CN) groups, reinforced by the chlorobenzene ring, place a positive charge on the bridge carbon atom. The result is a hyperactive bridge carbon that can be attacked directly with nucleophilles such as water or thiol groups. While studying the chemical agents, it is important to understand the hazardous effects of these agents on humans and animals. The following are basic toxicological terminologies: LD50: Lethal Dose 50, also called "Median Lethal Dose", is the quantity of a chemical compound that, when applied directly to test organisms, is estimated to be fatal to 50% of those organisms under the stated conditions of the test by any route other than inhalation. LD50 is usually expressed as milligrams or grams of material per kilogram of animal weight (mg/kg or g/kg, where 5000 mg = 5g = 1 teaspoonful). The phrase "Rat, Oral, LD50 : 200 mg/kg" for example means that 200 milligrams of the chemical per each kilogram of body weight is the lethal dose that killed 50% of a group of test rats. These data are used to help establish the degree of hazard to man. 1 "Harvest of Death", by J.B. Neilands & Gordon H. Orians. Published by "Collier-Macmillan Limited", London, 1972. LC50: Lethal Concentration 50, also called "Median Lethal Concentration", is the concentration of a material in air (air-borne) that is expected to kill 50% of a group of test animals when administered as a single exposure in a specific time period, usually 1 hour through inhalation and respiratory route. The LC50 is expressed as parts of material per million parts of air, by volume (ppm) for gases and vapors, as micrograms of material per liter of air, or milligrams of material per cubic meter of air (mg/m3) for dusts and mists, as well as for gases and vapors. TLV: Threshold Limit Value, refers to airborne concentrations of substances and represents conditions and levels under which it is believed that nearly all those exposed repeatedly, day after day, will experience no adverse health effects. ICt50: Median incapacitating dosage. This is the concentration of chemical multiplied by the time (duration) of exposure that will affect 50% of an exposed population.
|
