The chemical attack on Syria's rebel-held Idlib province on Tuesday was one of the deadliest since the Syrian war started six years ago, and the strike appears to involve use of a chemical that is relatively easy to produce.
Chemical Bombs Dropped From Planes
Survivors of the deadly attack, which received global condemnation, claimed to have seen chemical bombs dropped from planes. The attack killed at least 70 people including women and children and injured hundreds.
It is not yet certain what deadly gas was used but doctors' reports and images of the victims suggest that the biochemical weapon used in the airstrike was the nerve agent sarin.
Doctors who were at the area reported that the victims exhibited foaming at the mouth, slow heart rate, loss of consciousness, constricted pupils, slow breathing, muscle spasms, vomiting, and other neurological symptoms that are associated with exposure nerve agents.
"The symptoms described are consistent with exposure to sarin or some other organophosphorus chemical," said Ralf Trapp, who was formerly with the Organisation for the Prohibition of Chemical Weapons (OPCW).
What Are Nerve Agents?
Nerve agents are highly toxic chemicals that can interfere with the mechanisms by which the nerves of the body transmit messages to the organs.
Exposure even to small quantities of nerve agents can cause symptoms that include pinprick pupils and spams just as those seen in videos of victims of Tuesday's chemical attack. Nerve agents tend to work fast and often cause symptoms within minutes.
The substance has been widely used in chemical warfare. They are stable, highly toxic, can be easily dispersed, and cause quick effects when absorbed via respiration or through the skin. They are also relatively easy and cheap to make.
"Nerve agents can be manufactured by means of fairly simple chemical techniques. The raw materials are inexpensive and generally readily available," the OPCW said. "The nerve agent, either as a gas, aerosol or liquid, enters the body through inhalation or through the skin. Poisoning may also occur through consumption of liquids or foods contaminated with nerve agents."
There are several types of nerve agents but sarin gained widespread notoriety after the Tokyo subway attacks in 1995 that killed a dozen people. Iraqi dictator Saddam Hussein also used sarin to kill nearly 500 Kurds in 1988.
According to the OPCW, which currently gathers evidence about the recent attack, sarin had a dominant role among lethal chemical warfare agents since the Second World War.
Sarin was developed in Germany as a pesticide. It is an odorless, colorless, and tasteless liquid that can vaporize. Other nerve agents include tabun and soman. Just like sarin, these chemicals become vapors once they are heated. Sarin, however, is more soluble in water compared with other nerve agents.
Sarin, tabun, and soman belong to a class of chemicals known as organophosphates. Pesticides are also organophosphates.
How Organophosphates Work
Organophosphates bind an enzyme that shuts down the molecule acetylcholine, which plays a role in nerve signalling. Once the enzyme is turned off, acetylcholine will build up in the muscles and can result in excessive twitching. Excess of active acetylcholine in the brain may also lead to seizures.