New chemical forensics test could help track down terrorists responsible for nerve gas attacks.

Suppose, just after the Fourth of July fireworks begin on the Charles River, a team of terrorists located 100 meters apart along Boston’s Esplanade simultaneously empty several canisters of the odorless nerve agent sarin on the ground amongst the holiday crowd. The liquid agent quickly evaporates into a deadly, invisible vapor, spreading through the crowd. Within seconds symptoms appear in the hundreds of people exposed—blurred vision, drooling, sweating, coughing, chest tightness, breathing difficulty, nausea, and diarrhea. Those exposed to more concentrated amounts experience loss of consciousness, convulsions, paralysis, and respiratory failure.

In the growing confusion and panic, the terrorists slip away into the night, undetected. Apprehension, prosecution, and imprisonment are not likely. No one noticed them. Everyone was watching the fireworks. Police have no leads.

Or do they? The developing field of chemical forensics may offer clues.

Government scientists, led by chemist Carlos Fraga at the Pacific Northwest National Laboratory, are reporting the development of a unique chemical forensic tracking technology that could help law enforcement trace the residues from terror attacks involving nerve gas and other chemical agents back to the companies or other sources where the perpetrators obtained ingredients for the agent.

Nerve substances, such as sarin, are among the most toxic and fast-acting chemical warfare agents in existence. Sarin is lethal in amounts as small as 36 ppm. A single drop of sarin the size of a pinhead can kill an adult, as the Japanese learned in 1995 when the Aum Shinrikyo religious sect released sarin in the Tokyo subway, killing 13 and injuring over 5,500.

Although traces of nerve agents remain after such attacks, prior to Fraga’s work there has been no practical way of tracing the agent back to its source ingredients. Fraga’s team found a way to do that using a technique called “impurity profiling”—a way of identifying impurities in chemicals or illegal drugs that allows the chemical to be matched to the impurities in the precursor chemicals, pinpointing the likely source.

Impurity profiling has been used for several years to track seized drugs, helping law enforcement determine dealer-user relationships, drug sources, distribution networks, and smuggling routes by connecting seized drugs to precursors. Impurity profiling also has the potential to trace counterfeit pharmaceuticals and herbal medicines, banned pesticides, and homemade explosives.

Fraga adopted the technique to track nerve agents like sarin because of the high threat of a terrorist chemical attack. The researchers found that up to 88% of the impurities in source chemicals used to make sarin appear also in the finished product, and that these impurities are unique, much like fingerprints.

“This means potentially tracing a chemical threat agent like sarin to the specific lot number and commercial manufacturer that produced the precursor used to make the sarin collected from a crime scene,” Fraga said. Once the manufacturer of the precursor is known, then purchasing and shipping records may point to the buyer.

Fraga said that to his knowledge, this is the first time impurities have been demonstrated for matching a synthetic chemical product to its specific precursor source.

This new piece of evidence obtained through impurity profiling could provide useful leads that complement those obtained by traditional pieces of crime-scene evidence, like latent fingerprints, trace DNA, and camera footage.

Kevin Lothridge, CEO, National Forensic Science Technology Center, said Fraga’s technique is the same concept as the Drug Enforcement Administration’s cocaine, heroin, and methamphetamine signature programs. “This type of forensic intelligence can be useful in a range of investigations, from drug cases to terrorism,” Lothridge said. “It adds another technique to the analytical toolbox to help investigators advance the intelligence they are able to gather.”

Nothing Special
The PNNL method requires no special equipment, other than standard laboratory gas chromatography/ mass spectrometry instruments.

“What is most remarkable is that the chemical impurity profiles can be recovered mostly intact from sarin samples even after multiple processing procedures, such as distillation and two solvent extraction steps,” Fraga said.

Fraga said this development is important for a couple of reasons. First, he said he hopes that this and similar work will deter future chemical attacks by letting terrorists know there are now ways to track them.

“Second, by developing a forensic capability, we have a greater chance of finding perpetrators of chemical attacks or their sources of materials before they can strike again,” he said. “And third, our work can potentially be applied to other threats, such as illicit drugs and homemade explosives.”

Lawrence Kobilinsky, chair of the Department of Sciences at John Jay College of Criminal Justice, believes Fraga may be on to something valuable in the fight against terrorism.

“This work promises to provide a new approach to fighting chemical terrorists and chemistry-oriented criminals,” Kobilinsky said.

While sarin attacks have not yet occurred in the U.S., they could at any time. Kobilinsky said terrorists would not think twice about using biological, chemical, or radiological weapons to cause mass destruction of populations in Western nations. “The anthrax attacks were a wake-up call for law enforcement and homeland security,” he said.

In the event of a nerve agent attack, Kobilinsky said authorities must neutralize the effects of such attacks and ultimately trace the source of the weapon. Sometimes, different groups claim credit for a terrorist attack when it is clear that only one group was responsible. “This technique can help assign blame on those who are truly responsible for a chemical attack,” Kobilinsky said.

Origin of Impurities
Rashid Chotani, MD, director, Chemical and Biological Defense Programs at TASC (Chantilly, VA), said in order to validate impurity profiling in the context of chemical warfare, the researchers may need to explore the origins of the impurities to increase the confidence of their results.

“Given the number of sources for agents and precursors— in the U.S. alone about 100 facilities deal with chemicals that are ‘scheduled’ under the Chemical Weapons Convention—this new technique would work best when traditional forms of investigation have narrowed the sample size to a few possible locations,” he said.

Chotani said this technique could potentially enable investigators to link the agent back to a specific laboratory, assuming that sufficient precursor materials remain in the laboratory to identify any impurities.

Fraga concedes his work is in the preliminary, proof-of -concept stage of development, that there is a great deal of work required to determine what can and cannot be done with impurity profiling. He said one of the first tasks is to try to understand the sources and causes of variability for the impurity profiles obtained from chemical agents and their precursors, a step necessary to quantitatively determine if the impurity profiles from different samples match and what the error rates are if the profiles match.

In the near term, Fraga proposes to combine the impurity profiles obtained for sarin and precursors with other impurity profiles and chemical characteristics that are not being captured by current analytical approaches.

“We anticipate that these new measurements will independently make the same connection we made between sarin and its specific precursor stocks, thereby increasing the level of confidence in a match,” he said.

Fraga does not wish to over-sell his technique nor see its value reduced, like that of compositional analysis of bullet lead (CABL). CABL is similar to impurity profiling in that the chemical components present in bullet lead can provide forensic information.

However, according to a 2004 report (Weighing Bullet Lead Evidence, The National Academies Press) CABL has been over-sold in court and therefore its usefulness and credibility has diminished, Fraga said. “We are therefore trying hard to understand the limitations of impurity profiling to avoid over-selling it.”

Douglas Page writes about forensic science and medicine from Pine Mountain, California. He can be reached at