War Gases

toxic chemical warfare agents designed to incapacitate enemy manpower during combat. They penetrate the organism through the respiratory tract, skin, mucous membranes, or digestive tract. Depending on certain physical and chemical properties, they spread over the combat zone in the form of a vapor, liquid, or aerosol. They are easily synthesized from available, inexpensive starting materials.

War gases were first used by Germany during World War I in the attack on Ypres, Belgium, on Apr. 22, 1915, when 180 tons of chlorine were released from cylinders. There were 15,000 casualties, including 5,000 deaths. Chlorine is only moderately toxic, and it was the unavailability of protective equipment, which appeared only one year later, that was responsible for the large number of casualties. The subsequent search for new war gases was mainly directed toward producing toxic agents that could overcome the new protective measures and improving methods of disseminating these substances. Germany and the Entente countries used more than 50 different toxic compounds in the course of the war. The most effective were phosgene, diphosgene, chloropicrin, mustard gas, diphenylchloroarsine, and diphenylcyanoarsine. Altogether, the combatant countries produced a total of about 150,000 tons of various war gases between 1914 and 1918, of which 125,000 tons were used. These toxic agents proved to be quite effective; their use resulted in about 1 million casualties, and the proportion of injured personnel was as high as 90 percent in certain operations.

After World War I, attempts were repeatedly made to prohibit the use of chemical and bacteriological agents in warfare. The first international legal act to prohibit the use of such agents was the Geneva Protocol (1925). In spite of the protocol, the use of chemical warfare by certain capitalist countries continued, as did the development of new chemical warfare agents. Lewisite, adamsite, and cloroacetophenone were developed toward the end of World War I. A report appeared in 1929 on a new vesicant, phosgene oxime, and the discovery of β, β′, β″-tri chlorotriethylamine, or nitrogen mustard, was announced in 1935. Intensive efforts were made in Germany during the 1930’s to synthesize phosphorus-containing agents that would paralyze the nervous system; in general, such chemicals are called nerve gases. The first nerve gases were dialkylfluorophosphates, with the general formula (RO)₂P(O)F; dialkylamidoalkylcyanophosphates, with the formula (R₂N)(RO)P(O)CN; and alkylmethylfluorophosphonates, with the formula (RO)CH₃P(O)F. Early researches on nerve gases resulted in the synthesis of such agents as tabun, sarin, and soman. It is clear that the Germans intended to rely heavily on chemical warfare during World War II, since the production capacity for the synthesis of toxic agents in Germany reached 180,000 tons by 1943, including about 20,000 tons of phosphorus-containing agents.

The successful syntheses of a new class of extremely toxic phosphorus-containing agents, phosphorylthiocholines, were reported in the capitalist countries during the 1950’s. Starting in the middle of that decade, the psychotomimetic agents were discovered. These chemicals disturb psychic activity in healthy individuals in concentrations as low as about 0.1 mg/l; typical examples are lysergic acid diethylamide and the quinuclidine ester of diphenyloxyacetic acid.

The toxicity of war gases is the principal criterion that determines their mode of use. Most chemical warfare agents act by inhibiting various enzymes as a result of interaction with the enzyme’s functional groups. For example, lewisite acylates sulfhydryl groups, thus deactivating the enzyme. Hydrogen cyanide forms iron complexes in intracellular oxidative enzymes, thus interrupting the oxygen supply to the cells. Phosphorus-containing agents phosphorylate the enzyme choline esterase, which plays a major role in the transmission of nerve impulses. The degree of toxicity of a war gas depends on the selectivity with which it blocks enzymatic activity. In a number of cases, the toxic agent is so chemically stable that its effects are therapeutically irreversible. For example, it is practically impossible to regenerate enzyme systems that have been deactivated by phosgene or mustard gas. On the other hand, antidotes do exist that are powerful enough to counteract several lethal doses of phosphorus-containing agents, lewisite, and hydrogen cyanide.

A strict classification of toxic chemical agents is difficult to devise. The most important criteria for classification are physiological effect and behavior of the substance under combat conditions (see Table 1). According to the latter criterion, toxic chemical agents are either stable, unstable, or fuming. Unstable agents have high vapor pressures and contaminate the atmosphere by forming a cloud that is rapidly dissipated with the wind. Stable agents are liquids with low vapor pressures that form an aerosol cloud; some of the liquid settles in droplets in the immediate vicinity of application. Fuming toxic agents are solids with very low vapor pressures; they form a poisonous, dense fog.

The entire system of defense that protects personnel against war gases must include measures for detection and decontamination, as well as for the actual shielding from contact with the gas. In order to employ protective measures in time, the toxic agent must be detected, and its type and concentration determined. Detection through instrumentation, which is the most reliable means, is based on the chemical behavior of the agent. For example, the poisons can react to form colored compounds, or they can effect a change in a biochemical process, such as an enzyme-mediated catalysis.

The simplest methods of detection make use of either papers that are impregnated with indicators or tubes that contain indicators packed into ampuls or adsorbed onto a filler; the indicators change color upon contact with vapors or droplets of the chemical agent. The indicators must be sensitive to concentrations that are about an order of magnitude lower than the minimum effective dose of the toxic agent. Thus, the most highly toxic phosphorus-containing agent, which paralyzes the nervous system, is detected by a biochemical method that is sensitive to concentrations of war gas as low as 10^–6–10^–7 mg/l. Automatic, continuously operating gas detectors provide a constant check on the level of contamination in the air.