The Guardian reports: The latest tests from Porton Down will strengthen the consensus that the nerve agent sarin was used in the deadly attack in eastern Damascus in August.
Scientists at the lab found signs of sarin in soil taken from the site of the attack, and also on clothing from a person caught up in the atrocity that the US says killed more than 1,400 people.
The UK government will not say what signatures of sarin the scientists have found, but the details are important. The specific chemicals that tests reveal are often the only solid proof that a nerve agent has been used, and what kind of chemical was unleashed.
Tests on soil and clothing will rarely pick up sarin itself, because the agent breaks down swiftly when it meets water, which could be moisture in the air or sweat from the victim. More likely they will detect traces of sarin’s breakdown products, but these must be interpreted with care.
Beyond finding intact sarin, the most convincing smoking gun for the nerve agent is a compound called isopropyl methylphosphonic acid (IMPA). This is the chemical that sarin degrades into first of all and it can come from nothing else. Among chemical weapons experts, a positive test for IMPA is generally regarded as proof of sarin.
But tests can struggle to pick up IMPA in samples much older than a week or so, because it too breaks down into other substances. One is a related compound, called methylphosphonic acid (MPA), but this is not solid proof for sarin: other agents also degrade into MPA, such as VX, soman and cylcosarin. [Continue reading…]