Sarin in Syria – the UN evidence

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After much speculation as to whether chemical weapons had been used in Syria, last week the UN issued a report from their inspectors.  They reported solid scientific evidence of detection of chemical agents. What were the conclusions?

On the basis of the evidence obtained during our investigation of the Ghouta
incident…chemical weapons have been used…on a relatively large scale.

On the 16th September the United Nations (UN) issued a report from their weapons investigation mission in Syria, headed by Professor Sellstrӧm.  In particular the report dealt with samples analysed from people and the environment in the Ghouta area of Damascus following an incident on 21st August 2013.  This report followed speculation and much media interest as to whether chemical weapons had been used in this area.  In particular it had been alleged that Sarin (also known as GB) had been used. As a toxicologist I was particularly interested in the biological samples collected and what they showed.

For background on Sarin please see this post

The team in Syria collected 30 samples from the environment around the reported incidents and also obtained hair, urine and blood samples from 36 patients who were displaying some classic symptoms of organophosphate poisoning (such as loss of consciousness, shortness of breath and eye irritation/blurred vision).  There were 34 blood samples, 15 urine samples and 3 hair samples obtained.  These samples were divided and sent to two labs for analysis.

In one lab 29 out of 34 blood samples tested positive, in the other 31 out of 34.  Only one of the labs had reported urine results – of which 14 out of 15 were positive.  The report did not go into detail as to what analyte was detected in these samples – so it may have been sarin itself or a breakdown product IMPA (also called IPMPA in the report) – the structure of which is shown below (taken from Chemistry World).  None of the three hair samples were positive.

Sarin (left) and IMPA (right)

The results show a small discrepancy between the numbers reported by each lab for the blood samples. Does this mean one lab was more reliable than the other?  The report doesn’t go into detail of the limits of detection or the methodologies used by the two labs, which is a real shame for an analytical geek like me! Different instruments may well explain the slightly differing results as one may be able to detect much lower levels in the blood than the other.  They also reported that none of the three hair samples were positive – why was that?  Hair samples are used to show historical exposure to a drug or poison.  Drugs/poisons that are incorporated into the growing hair through the blood supply will not test positive for a week or ten days after the event, as the hair grows out of the follicle.  If the hair samples were collected within a day or two of the incident I would not expect them to be positive.  When analysing the hair samples the first step should be to wash the outsides of the hair.  This is to ensure any contamination on the outside of the hair is removed and only any drug or poison actually ingested by the person is measured. If they went back to the same people and collected a hair sample one month or so after the incident that would give us a much better indication of their exposure.  As it happens in this case they have shown exposure to sarin via blood and urine samples – with a very high positive rate.

The environmental samples were collected from a range of items – from soil to bedsheets in an apartment to suspected parts of armaments found near to the scene of the attacks.  These were found to be positive for sarin and breakdown products

The UN team concludes:

The positive blood and urine specimens provide definitive evidence of exposure to Sarin by a large proportion of the survivors assessed by the investigation mission

It appears that the chemical weapon sarin has been used, resulting in the death of many and the injury of many more.  As to who fired the shells, there has been much conjecture but I will leave Russia and the US to argue that amongst themselves.

The final rather understated word goes to the inspection team:

This result leaves us with the deepest concern


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About Dr Tom Bassindale

Dr Tom Bassindale is a forensic scientist, and the founder of We Are Forensic. He is currently the subject lead for chemistry and forensic science at Sheffield Hallam University. He's managed hundreds of forensic toxicology cases, and is an experienced court witness. He has specialist expertise in forensic toxicology and drug testing in sport. And yes... he watches CSI.