Question

7. Does the dose rate of a nerve agent affect the body's response? Explain. What is the effect of daily exposure to small doses of a nerve agent over several days?

Answer 1

7. Nerve agents (NA) are toxic chemical warfare agents developed during World war II. They include GA (tabun), GB (sarin), GD (soman), GF (cyclosarin) and VX (methylphosphonothioic acid). They are orthophosphorous esters. When sarin is inhales in less than 2 mg.min/m dose, it cause very less acetylcholinesterase depression. There is only slight headache observed. However, high dose rate of 15 mg/min/m, it cause bronchosplasms, eye pain, conjunctiva, respiratory failure and death. NA can be absorbed by skin, eye, and respiratory system. NA inhibit the acetylcholinesterase enzyme, which breaks down neurotransmitter acetylcholinesterase. This results in accumulation of acetylcholine at different sites, such as nerve ending to parasympathetic nerves to the smooth muscle of the iris, ciliary body, bronchial muscles, gastrointestinal tract etc. Hence, there is increased voluntary muscle contractions. Both nicotinic and muscarinhic effects are seen. Mild doses only cause tension, anxiety, jitteriness, restlessness, emotional lability, and giddiness. Occasionally nausea and vomiting may be seen. When the dose increases, confusion and ataxia may result, producing casualties. Thus, effect of NA depends on its dose rate as there is incaresed depression of acetylcholinesterase and increased levels of acetylcholine.

When there is daily exposure to small doses of NA, the symptoms may be seen only after several days. Continuous exposure will escalate the symptoms every days after onset of symptoms. Even after symptoms subside, there is increased susceptibility seen that persists upto 3 months. This increased susceptibility is not limited to only the NA that was initially exposed to.