Medical Aspects of Chemical Warfare (2008) - The Black Vault

Medical Aspects of Chemical WarfareOne of the US soldiers exposed to sarin in Iraq in2004 reported to the authors that the agent smelledlike garbage, but that may have been due to impurities.Cyclosarin (GF) and VR are not as well studiedas the other agents. In animal tests GF has a toxicityintermediate between sarin and tabun, while VR hasthe same level of toxicity as VX.The G agents are volatile; VX and VR have very lowvolatility. Sarin, the most volatile, is somewhat lessvolatile than water; tabun, cyclosarin, and soman areless volatile than sarin. The G agents present a definitevapor hazard; VX and VR are much less likely vaporizeunless the ambient temperature is high.EXPOSURE ROUTESInhalational Exposure to VaporThe effects produced by nerve agent vapor beginin seconds to minutes after the onset of exposure, dependingon the concentration of vapor. These effectsusually reach maximal severity within minutes afterthe individual is removed or protected from the vapor,but they may continue to worsen if the exposurecontinues. There is no delay in onset as there is afterliquid exposure.At low Ct values (the concentration to which anorganism is exposed to a substance times the amountof time the organism is exposed; Exhibit 5-2), the eyes,nose, airways, or a combination are usually affected.The eyes and nose are the most sensitive organs; theeyes may be affected equally or unequally. There maybe some degree of miosis (with or without associatedconjunctival injection and pain) with or withoutrhinorrhea, or there may be rhinorrhea without eyeinvolvement (Table 5-4).As exposure increases slightly, a combination ofeye, nose, and lung involvement is usually seen. Thecasualty may or may not notice dim vision and maycomplain of tightness in the chest, possibly in theabsence of physical findings. At higher exposures,the effects in these organs intensify. Marked miosis,copious secretions from the nose and mouth, and signsof moderate-to-severe impairment of ventilation areseen. The casualty will complain of mild-to-severedyspnea, may be gasping for air, and will have obvioussecretions.In severe exposures, the casualty may not have timeto report the initial effects before losing consciousness,and may not remember them on awakening.One severely exposed individual later recalled to theauthors that he noticed an increase in secretions anddifficulty breathing, and another said he felt giddy andfaint before losing consciousness. In both instances,the casualties were unconscious within less than aminute after exposure to agent vapor. When reached(within minutes) by rescuers, both were unconsciousand exhibited convulsive jerking motions of thelimbs; copious secretions from the mouth and nose;labored, irregular, and gasping breathing; generalizedEXHIBIT 5-2DEFINITIONS OF Ct, LCt 50AND LD 50The terms Ct and LCt 50are often used to expressa dose of a vapor or aerosol. However, the termsdo not describe inhaled doses; they refer to theamount of compound to which an organism isexposed.• Ct is used to describe an estimate of dose. Crepresents the concentration of the substance(as vapor or aerosol) in air (usually expressedas mg/m 3 ), and t represents time (usuallyexpressed in minutes).• The Ct value is the product of the concentration(C) to which an organism is exposedmultiplied by the time (t) during which itremains exposed to that concentration. Ctdoes not express the amount retained withinan organism; thus, it is not an inhalationaldose.• Because Ct is a product of C times t, a particularvalue can be produced by inverselyvarying the values of C and t. The Ct to producea given biological effect is usually constantover an interval of minutes to severalhours (Haber’s law). Thus, an effect that isproduced by an exposure to 0.05 mg/m 3 for100 minutes is also produced by an exposureto 5 mg/m 3 for 1 minute (Ct = 5 mg/min/m 3in both cases). This generalization is usuallyinvalid for very short or very long times,however, because an organism may hold itsbreath for several seconds and not actuallyinhale the vapor, or some detoxification mayoccur over many hours.• The term LCt 50is often used to denote thevapor or aerosol exposure (Ct) necessary tocause death in 50% of the population exposed(L denotes lethal, and 50 denotes 50%of the population). In the same manner, theterm LD 50is used to denote the dose that islethal for 50% of the population exposed byother routes of administration.168