Australasian Science Magazine

By Prof Alastair Hay, Professor of Environmental Toxicology, University of Leeds

An expert on the effects of exposure to chemical warfare agents and the field investigation of alleged chemical warfare incidents answers questions on the Syrian chemical weapons attack.

Q: What are the alleged chemical arsenals that Assad possesses? And the rebels?
A: “We do not know for certain. All the information is based on leaked intelligence assessments. The US, UK and France all claim that some samples they have tested from victims exposed in earlier alleged attacks indicate use of the nerve agent sarin.”

Q: What does the evidence from Syria suggest?
A: “The video evidence with its graphic imagery as well as testimony from doctors suggests that people were exposed to some very potent organophosphate agent. Nerve agents like sarin are organophosphate compounds and extremely potent. There are a range of other nerve agents which all have similar effects on the body. These other agents are more and less toxic than sarin and have varying degrees of persistence in the environment. But even those less toxic are still extremely potent and lethal in small doses.”

Q: What treatment will victims require?
A: “They will need treatment with an antidote like atropine, which may be augmented by another drug, an oxime like praladoxime, which pulls nerve agent off affected sites. Convulsions may be controlled with a sedative like diazepam. Supplementary oxygen will also be needed as many will have had restricted breathing and be unable to inhale sufficient oxygen. Nerve agents inhibit an enzyme called acetylcholinesterase which is present in the nervous system. This enzyme regulates messages between nerves and muscles. With inhibition by nerve agents, muscle activity becomes much reduced and breathing very laboured because muscles which regulate breathing are affected like all others. Treatment with antidotes may have to continue until the body synthesizes new acetycholinesterase in sufficient quantity to restore normal muscle activity. In some cases, but by no means all, nerve agents may come off a proportion of the enzyme and some function is regained. But this cannot be assumed. Those severely poisoned in Syria will need treatment for many days and possibly longer.”

Q: Will it be too late to get evidence of chemical weapons use at this stage?
A: “No. For those severely poisoned, but still alive, it is possible to find sarin and its breakdown products for up to 4 – 6 weeks post exposure. Blood can also be collected from those who have died and from any dead or incapacitated animals. Soil samples may retain evidence for weeks and even longer. Tests done on craters in Iraq where chemical weapons had been detonated 4 years previously were positive for mustard gas and sarin. So these agents were still there 4 years after the munitions had exploded. In Syria it may be a little more complicated if there has been continued shelling of the areas where chemical weapons fell. This would make it more difficult to find the precise location where the chemical weapon exploded necessitating soil sampling over a wider area. But the chances of positive results are still high at this stage. Spent munitions will provide incontrovertible evidence as these will have traces of the chemical agent itself, the explosive used to fracture the weapon, and combustion products of the chemical weapon and the explosive. The signature thus obtained will be a sort of hallmark and unequivocal.”

Q: What test will be done in the laboratory?
A: “A range of tests will be done in laboratories. Most will involve gas chromatography and mass spectrometry. Chromatography enables mixtures to be separated into discrete chemicals, and in the mass spectrometer chemicals are split into very specific fragments; these fragments enable a precise identity of chemicals to be established. Most mass spectrometers have a library of chemical fragments and the substances being tested are compared with material in the library. In some instances substances being tested are completely new and the result from the mass spectrometer will only suggest the most likely chemical structure and identity of the substance.

“In terms of testing the blood and urine of those affected, experts will be looking for nerve agents themselves and also the specific metabolites they produce. In the case of sarin, for example, sarin itself or its characteristic metabolite isopropylmethylphosphonic acid (IMPA) may both be found in blood and urine samples if that was the agent used.”

Q: Which are the most likely targets in case the US and the UK attack Syria? Will they be airbases and artillery in order to stop the launching of future chemical attacks or will they attack chemical weapons storage sites?
A: “I do not know the answer to this one. All I feel reasonably sure about is that they will not attack chemical weapons depots as they will not want to run the risk of these agents being released through bombing. So I would hope that this would be the plan.”

Q: In case they target chemical weapons storage sites, what would be the effect on the local population?
A: “If these sites were hit it is highly likely that chemical agents would not be destroyed but dispersed. How far they would travel is an unknown, as would be the number of people who may be exposed. It would be very counterproductive to attack chemical weapons sites. It is more important that these sites remain intact, that no weapons move out of them, and that eventually the munitions be destroyed in a controlled way and the chemical agents incinerated.”

Q: What safety measures should be put in place to avoid a chemical disaster if the sites were hit?
A: “The safest approach would be for people to remain indoors with windows and doors shut and cloth placed around door frames to prevent any seepage around and under doors. If there were chimneys these should be blocked off in some way to stop anything coming down them. After a time the concentration of chemical in the house would be the same as that outside, but if the attack were over in a couple of hours and agent dispersed in this time, these measures would offer protection. For agents spreading around for a longer time such measures would be much less effective. Only full protective clothing and gas masks offer real protection and I doubt the population would be issued these. So I sincerely hope that chemical weapons sites would not be bombed and certainly not if they are close to any centre of population.”

Q: Have chemical weapons storage sites been attacked on previous occasions?
A: “Yes. In Iraq. Release of the chemical agents resulted in most of them blowing downwind and triggering chemical weapons alarms over a hundred miles away. Measured concentrations of the chemical agents were low but there is disagreement about whether these agents were responsible for what US servicemen and others call “Gulf War Syndrome", a non-specific illness which involves severe fatigue and other symptoms. However, there is no guarantee that attacks on dumps in Syria would result in the same pattern of spread as local weather conditions may be very different. Agents might spread more readily in Syria and in higher concentrations, but we have no certainty about this.”

Science Media Centre