Nerve agents are currently the primary lethal military chemical agents deployed by certain foreign militaries. Containing phosphorus atoms in their molecular structure, they are termed phosphorus-containing agents or organophosphate esters, belonging to the same class of organophosphorus compounds as organophosphate pesticides.Nerve agents fall into two categories:
1. G-series agents (e.g., sarin, tabun, and lewisite). These agents are highly volatile, primarily entering the body through the respiratory tract. They exhibit high toxicity, short latency periods, and rapid onset. Severe poisoning can lead to death within a short timeframe without immediate medical intervention.
2. V-series agents, such as VX (V-X) and methyl thiophosphoryl ethyl ester. These agents have low volatility, with droplets evaporating slowly. Skin contact is the primary route of poisoning, though aerosolized forms can also cause respiratory poisoning. Their toxicity exceeds that of G-series agents.Skin contamination has a certain incubation period; if symptoms develop and timely treatment is not administered, death can also occur within a short time. Symptoms of Nerve Agent Poisoning Nerve agent poisoning is generally classified into three severity levels: mild, moderate, and severe. The primary manifestations are as follows:
Mild poisoning
Primarily manifests as mushroom poisoning-like symptoms, accompanied by mild central nervous system symptoms and localized nicotinic symptoms, including miosis, blurred vision, chest tightness, mild dyspnea, rhinorrhea, salivation, nausea, and hyperhidrosis. Additional symptoms include weakness, facial muscle twitching, dizziness, headache, restlessness, and insomnia.Whole blood cholinesterase activity ranges from 50% to 70% of normal levels.
Moderate poisoning
Agrotoxin-like symptoms worsen, with pronounced nicotinic symptoms appearing: significant dyspnea, wheezing, mild cyanosis, vomiting, abdominal pain, profuse sweating, generalized muscle twitching, slurred speech, weakness, ataxia, along with anxiety, depression, and slowed reactions.Total blood cholinesterase activity is 30%–50% of normal.
Severe poisoning
The above symptoms become more severe, with prominent central nervous system symptoms. Pupils constrict to pinpoint size, accompanied by profuse salivation, heavy sweating, abdominal pain, urinary and fecal incontinence, extreme respiratory distress or respiratory failure, and marked cyanosis;Widespread muscle tremors throughout the body, limb convulsions, followed by paroxysmal tonic seizures and coma. Ultimately, generalized flaccid paralysis, respiratory depression, circulatory failure, and death. Total blood cholinesterase activity is 0–30% of normal.
History of Nerve Agents
Although chemical weapons were not deployed during World War II, German chemists researching insecticide compounds accidentally discovered certain organophosphate esters lethal to insects. These agents inhibit human neural activity, earning them the designation "nerve agents."
Mechanism of Action of Nerve Agents
Acetylcholine is a neurotransmitter primarily responsible for transmitting signals between neurons. When one neuron releases acetylcholine from its axon terminals into the synapse, it binds to receptors on the dendrites of the next neuron. After transmitting the signal, acetylcholine undergoes hydrolysis.
Chemicals in nerve agents inhibit acetylcholine hydrolysis, causing sustained signal transmission and keeping muscles in a constant state of excitation. This persistent excitation renders the muscles used for breathing completely inoperable—a condition known as respiratory muscle paralysis (breathing relies on the continuous contraction and expansion of these muscles)—ultimately leading to death.
What are the most toxic nerve agents?
Today's most lethal chemical agents are nerve agents, primarily sarin, soman, tabun, and VX. Their toxicity is extreme; inhaling even minute quantities can be fatal. The lethal dose for unprotected individuals is 190 milligrams for chlorine gas.