When considering which among a vast number of non-state actors, including terrorist groups and insurgencies in countries as diverse as Syria, Colombia, Myanmar/Burma, Great Britain, and many others may acquire and use chemical, biological, or radiological weapons against the United States or other countries, one first should make an assessment of the capacity of individual groups to produce such weaponry or, alternatively, to steal or capture them. History provides somewhat of a mixed record in this regard, especially given the relatively broad category of chemical weapons, which can include easily attainable crowd-control agents like orthochlorobenzalmalononitrile (CS), the key ingredient in the tear-gas generically known by the corporate brand Mace. Pepper spray, an inflammatory agent, is widely-available on the open market, and its use under certain circumstances would be categorized as a chemical weapon even though it’s not thought of in that regard. As chemical compounds can be manipulated for lesser or greater effect, though, any discussion of terrorist use of chemical weaponry has to at least reference the availability of these particular agents.
As has been pointed out several times in recently answered questions, the March 1995 terrorist attack by the Japanese cult Aum Shinrikyo, which planted the extremely deadly nerve gas sarin on the Tokyo subway system, killing 12 and injuring thousands more, the possibility of a terrorist group or other non-state actor developing chemical weapons on their own by discretely purchasing or stealing the necessary precursor agents that, when combined, form highly-toxic substances. To get an illustration of what is meant by this, think in terms of the “binary” chemical weapons developed by the U.S. Army during the 1980s. Chemical weapons manufactured in earlier decades that sat in storage unused began over time to degrade, posing more of a hazard to their American handlers than to any potential adversary (i.e., the Armed Forces of the Soviet Union). That response was the development of chemical weapons that were comprised of two non-lethal agents in separate canister within the body of the rocket or bomb. These weapons were essentially harmless until fired, at which point a barrier separating the two canisters, each containing a non-lethal agent, was broken, causing the two non-lethal agents to mix, creating the lethal chemical weapon. The U.S. Army’s M687 chemical weapon artillery shell contained the two chemicals methylphosphonyl difluoride and isopropyl alcohol and amine that, when combined, created sarin. So, the point here is that procuring lethal chemical weapons can be as relatively simple as understanding the way different chemical interact, basic stuff for a semi-competent chemist. As chemical engineers have been known to join terrorist organizations, the threat is very real. Note, for instance, the following passage from a May 2013 article in the Canadian news service
“A man arrested in a U.S. terror plot in New York April 22 was a graduate student studying chemical engineering at Laval University in Quebec City, CBC News has learned.
“Ahmed Abassi's major is ‘particularly chilling’ in conjunction with other evidence presented against him by the FBI, said CBC's Greg Weston.
“The FBI alleges Abassi was plotting to kill upwards of 100,000 people by contaminating the air or water supply in a major U.S. city. However, the plan did not materialize any further than discussions.” [See “U.S. Terror Suspect Studied Chemical Engineering at Quebec University,” CBC News, May 10, 2013, http://www.cbc.ca/news/canada/u-s-terror-suspect-studied-chemical-engineering-at-quebec-university-1.1333162]
So, let’s now examine a current threat emanating from the Middle East (one among many) involving the largest and most ruthless terrorist organization in modern history, the Islamic State (also known as the Islamic State of Iraq and the Levant, or the Islamic State of Iraq and Syria). As most people who follow current events are aware, the civil war raging in Syria has involved the use of chemical weapons by that country’s government and, possibly, by insurgents against whom it is fighting. One of the U.S. and other nations’ greatest concerns is the capture by terrorists of Syrian Army chemical or biological weapons [See on the problem of Syrian biological weapons the following article: “Syria’s Real Threat: Biological Weapons,” National Interest, September 19, 2013, http://nationalinterest.org/commentary/syrias-real-threat-biological-weapons-9093]. In this respect, the recent news report regarding the possible capture by the Islamic State of Syrian chemical weapons is a cause for great concern. A passage from the article in question follows:
“Allegations surfaced last week, when Kurdish fighters engaged in a long-running battle to save the Syrian town of Kobani, along the Turkish border, reportedly came under chemical attack, activists and witnesses said. About 20 people suffered "breathing problems, bleeding from the eyes, skin burns and vomiting," following an explosion in the town on the evening of Tuesday Oct. 21, local Kurdish official Idris Nassan told NBC News. ‘It appears that there was possibly a poisonous attack of some sort, maybe phosphorus or something.’” [“Does ISIS Have Access to Chemical Weapons in Iraq and Syria,” NBC News, October 28,2014, http://www.nbcnews.com/storyline/isis-terror/does-isis-have-access-chemical-weapons-iraq-syria-n234871]
Al Qaeda, of course, is also an important player in this game. Its interest in so-called weapons of mass destruction is well-documented, although its success in attaining such weaponry has fortunately been seriously limited. The level of interest, however, remains, and, as noted, that organization’s recruitment of chemical engineers represents a very serious threat to U.S. and allied interests. [See on this point “Court Document References al Qaeda-Linked Chemical Weapons Program in Somalia,” CBS News, September 19, 2013, http://www.cbsnews.com/news/court-document-references-al-qaeda-linked-chemical-weapons-program-in-somalia/].
If one had to select one or two non-state actors most likely to acquire and use chemical, biological or radiological weaponry (and the latter is more complicated given controls on radioactive materials), then, the best suspects would be the Islamic State and al Qaeda. There are many smaller but very dangerous terrorist organizations and other non-state actors that exist in the Middle East and elsewhere, and their potential cannot be ignored, but those two high-profile organizations remain the greatest threats for now.