As investigations continue into the attempted assassination of a former Russian double agent and his daughter in Britain, findings released this week have renewed focus on the class of nerve agents allegedly used. And experts say that the UK event and a suspected chemical-weapons attack last week in Syria provide fresh impetus for international efforts to beef up forensic capabilities.
On 12 April, the Organisation for the Prohibition of Chemical Weapons (OPCW) confirmed that its independent tests of environmental and biological samples identified the same poison used in the assassination attempt as forensic scientists at Britain’s national Defence Science and Technology Laboratory at Porton Down in Wiltshire did in their investigation. The attack happened in the nearby city of Salisbury on 4 March. The OPCW, based in The Hague in the Netherlands, is responsible for enforcing the 1997 Chemical Weapons Convention, which bans the production and use of such arms.
The organization did not name the chemical agent publicly, but will share its identity and structure with states party to the convention, in a classified report. More details may emerge at a special meeting of the OPCW’s Executive Council to discuss the report, scheduled for 18 April. The UK government has said that the compound belongs to a class of nerve agents known as Novichoks.
The watchdog also agreed that the toxic chemical was very pure. That points to it having being made by “a highly proficient team and in a well-refined process”, says Alastair Hay, an environmental toxicologist at the University of Leeds, UK. The OPCW did not say where the agent might have been made; the UK government has alleged that the Russian state was directly behind the attack, but critics say that this is a politically motivated claim and that there is no forensic evidence to back it up.
Chemical detective work
Experts say further investigations could provide more clues. Forensic inquiries into chemical attacks typically involve standard tools such as gas and liquid chromatography, which are used to separate a substance into its components. Researchers then study those compounds with analytical techniques such as high-resolution mass spectrometry, nuclear magnetic resonance spectroscopy, isotope-ratio mass spectrometry and inductively coupled plasma mass spectrometry.
Forensic methods can build up chemical signatures of the components of a sample to give investigators leads about how it was made, says Brad Hart, director of the Lawrence Livermore National Laboratory’s Forensic Science Center in Livermore, California. The varying ratios of stable isotopes of component elements, for example, can provide information about where the starting materials came from, he says.
Other sample components can offer clues about the methods of synthesis, potential starting materials and the sophistication of manufacture, he adds. “Anything detected in the sample that is not the primary product is of interest as a potential signature,” says Hart. “These typically include unreacted starting materials, products of side reactions, breakdown or decomposition products of the primary product or other signatures.”
But it’s not yet possible to definitively identify the geographical or institutional source of a chemical weapon using chemical forensics alone, he says.
The OPCW report came just days after an alleged chemical-weapons attack on the city of Douma in Syria, on 7 April. An OPCW fact-finding mission is on its way to the country and will begin work on 14 April. The team will interview witnesses and collect samples and evidence such as autopsy reports and photographs. Experts say that such attacks underscore the need to increase international chemical-forensic capacity for investigation, and intensify research in the field.
The OPCW is already taking steps in this direction. From 12–14 February, it held the first meeting of its science board’s newly created temporary working group — made up of leading scientists and experts from national defence and other labs — charged with carrying out an in-depth review of the state-of-the-art of chemical forensics.
And in April last year, international researchers, treaty experts, law-enforcement agencies and industrialists formed the Chemical Forensics International Technical Working Group, an ad hoc group aiming to identify research gaps and other factors that hinder investigators using forensics to track down the source of chemical weapons.
A first glimpse of the group’s plans came at the OPCW’s February science meeting from Carlos Fraga, a chemical-weapons specialist at the Pacific Northwest National Laboratory in Richland, Washington, and a driving force behind the international technical working group. The working group is proposing to develop a database of signatures of chemical weapons and their precursors. During the destruction of the world’s chemical-weapons stockpiles, researchers gathered vast amounts of analytical data that could be added to the database, along with unpublished data collected during the OPCW’s routine inspections of chemical plants, and by OPCW-designated labs.
Nature 556, 285-286 (2018)