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Toxins

Castor plant: Ricinus communis

Toxins are poisonous biochemicals that are produced by living organisms. Toxins are distinct from other chemical agents in that they are more structurally complex and are naturally occurring (although a few toxins can be synthetically produced in laboratories). Unlike other types of biological agents—bacteria, viruses, fungi, and plants—toxins are not living organisms. This is significant in that toxins do not self-reproduce, and do not respond to antibiotic drugs. Because of their unique characteristics, toxins are prohibited by both the Chemical Weapons Convention (CWC) and the Biological Weapons Convention (BWC).

The BWC specifically prohibits the development, production, or stockpiling of "microbial or other biological agents, or toxins whatever their origin or method of production . . . ." Likewise, the CWC contains a sweeping ban on the development, production, acquisition, stockpile, retention, transfer, or use of "toxic chemicals and their precursors." The Convention's definition of "toxic chemical" clearly includes toxins: "any chemical which, through its chemical action on life processes, can cause death, temporary incapacitation or permanent harm to humans or animals. This includes all such chemicals, regardless of their origin or their method of production, and regardless of whether they are produced in facilities, in munitions, or elsewhere."

Schedule 1 of the CWC includes two toxins—saxitoxin and ricin—perhaps for several reasons. For one, these two toxins have been produced as weapons by one or more nations in the past. Also, both of these toxins can be obtained relatively easily from natural sources, and can be produced synthetically in laboratories. Hundreds of different toxins have been identified in nature to date, and scientists discover new toxins every year. Toxins vary widely in their toxicity, or ability to cause adverse effects on living systems. By weight, botulinum toxin, the causative agent of botulism, is the most toxic substance known. Toxins may be produced by simple organisms, such as bacteria or algae, aquatic invertebrates, or higher animals or plants. Most known toxins are protein toxins produced by bacteria. Botulinum toxin is produced by a species of bacteria, Clostridium botulinum. The toxin ricin is derived from the beans of the castor plant, Ricinus communis. Snake venoms are also toxins.

Unlike most chemical weapon agents, many toxins and toxin-producing organisms can be used for legitimate pharmaceutical purposes. The castor bean, from which ricin is derived, is used for numerous industrial purposes, including the production of medicines, textiles, lubricants, waxes, polishes, candles, crayons, fertilizer and livestock feed. Ricin itself is being studied for potential applications in chemotherapy and bone marrow transplants. Botulinum toxin is used medically to treat certain neuromuscular disorders, and has gained popularity as a cosmetic treatment for wrinkles in recent years. Researchers believe conotoxin, a toxin derived from cone snails, has potential for treating conditions such as epilepsy and multiple sclerosis.

Toxins can induce adverse physiological responses similar to those induced by toxic chemicals, but the intensity of the toxic response is more severe when induced by toxins. Different toxins poison in different ways. Because toxins vary widely in both mechanism of action and potency, the symptoms they cause and the time of onset vary as well. A particular toxin can also cause varying symptoms, depending on the route of exposure and the amount of toxin encountered.

Generally speaking, there is no highly effective treatment for toxin exposure. Treatment usually consists of supportive measures to manage adverse clinical symptoms. For some toxins, antibody preparations called antitoxins do exist, which are capable of neutralizing individual toxins. Antitoxins are not widely used in clinical treatment, however, because they carry certain risks. The most effective countermeasure to toxin exposure is vaccination. Vaccine development is underway for many toxins; however, since the risk of toxin exposure to the general population is considered to be relatively low, there is little commercial incentive to develop toxin vaccines. For military purposes, physical protective measures, such as the protective mask and decontamination systems, developed for chemical threats, are, for the most part, effective against toxins.

In terms of offensive use, the physical characteristics of toxins, in general, make them more likely to be used in small-scale terrorist attacks or assassinations than for large-scale warfare. The main reason for this is that most toxins are difficult to generate on a large scale. To date, the large majority of toxins cannot be produced synthetically, and tremendous amounts of their natural sources would be required to obtain sufficient amounts of toxin to inflict mass casualties, either via aerosol or through contamination of food or water supplies. Toxins that are proteins are only effective when inhaled or introduced directly into the vascular system. Because they are degraded by the human digestive system, they would be poor candidates for the contamination of food or water supplies. In addition, most toxins are not very stable as aerosols.

There have been numerous attempts in modern history, both successful and unsuccessful, to use toxins as weapons on a small scale. Perhaps the best known such incident occurred in 1978, when a Bulgarian dissident named Georgi Markov was assassinated in London. While waiting at a bus stop, Markov was jabbed in the leg with an umbrella. He died four days later. The attacker was never apprehended, but a tiny pellet was found in Markov’s leg wound that was determined to have contained a small amount of ricin.

The Japanese cult Aum Shinrikyo made at least three unsuccessful attempts to disperse aerosolized botulinum toxin between 1990 and 1993. Cult members produced the toxin from C. botulinum bacteria obtained from soil samples. No illnesses or deaths resulted from any of these attempts. It is not known why the attempts failed, although poor toxin production or mechanical failures are likely reasons.

The difficulties involved with producing toxins in large quantities do not completely rule out the possibility of toxins being used as large-scale weapons, however. The former Soviet Union is known to have produced large quantities of both ricin and botulinum toxin weapons through its offensive biological weapons program during the Cold War. The Iraqi government under Saddam Hussein also produced a large number of botulinum toxin weapons.

The most potent toxins present a real threat to public health from natural and, potentially, from terrorist sources. Additionally, the unique characteristics of toxins present challenges for both medical and defensive countermeasures. Continued research into the nature of toxins will certainly result in new insights, not only as to how to protect against them, but also in how they might be used for beneficial purposes.