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The subject of terrorist attacks on water supplies is cause for concern given the numerous possible agents and methods that could be used by a terrorist organization. The key to preventing such events is understanding the toxins likely to be used as well as possible treatment methods to prevent outbreaks and protect the integrity of a water source.

Most of the potential threats to drinking water might consist of the following but are not limited to A) a deliberate introduction of biological contaminants like viruses, cysts, E. coli, anthrax spores, etc. The size of the contaminant is important because the pore size of a filter must be smaller than the size of the contaminant in order to effectively reduce levels. Bacteria are about 1 micron in size (some smaller, some larger). Many viruses are about 100 - 200 times smaller than bacteria (I just read that if bacteria were the size of a car, a virus would be the size of a cell phone). Cryptosporidia and Giardia cysts are several times larger than most bacteria. Biological contaminants dumped into the water source of a city would be highly diluted by the time they reached a treatment plant.

Also, water treatment methods now in place (including flocculation, filtration, and disinfection), would effectively remove or kill most types of infectious agents before they entered the distribution system. B) Deliberate introduction of some type of hazardous chemical compound. I have not read much about specific chemicals that are thought to be possible threats to drinking water, but the consensus seems to be that they would be synthetic organic compounds or possible radioactive compounds rather than non-radioactive inorganic chemicals. The concentration of many organic chemicals is effectively reduced by activated carbon filters, however. Reverse Osmosis and Distillation are better at reducing inorganic contaminants, but with proper design are effective at significantly reducing all contaminants.

Again, not knowing what specific chemicals might be used, it is impossible to know how effective an activated carbon filter would be against these potential threats. C) Physical attacks against water companies, waste treatment facilities (in an effort to contaminate water), or reservoir dams (in an effort to disrupt water supplies and cause damage from flooding). Which treatment method works best against danger? According to Water Quality Association (WQA) Technical Director Joe Harrison, reverse osmosis (RO) and distillation have been proven to take out the largest variety of contaminants or terrorist agents most completely.

Activated Carbon Blocks are also effective at preventing most contaminants from entering a drinking water system. Additionally, there are systems that combine two or more of those technologies into one system. Many RO systems will have a carbon block, for example. These POU technologies are sound for a multitude of terrorism agents, both biological and chemical in nature - the primary reason POU equipment is playing such a significant role in securing the safety of water supplies for American troops worldwide.

"RO and activated carbon are the highest tech treatment methods we have, so the Army is using them," Harrison explained. What toxins might be used? A recent medical review stated the following regarding possible biological agents: "The Journal of the American Medical Association (JAMA) has issued consensus reviews on five agents it considers the most likely candidates for a biological attack: anthrax, botulinum toxin, plague, smallpox, and tularemia. The reviews include the history of each agent, its epidemiology, diagnosis, vaccination, and therapy options, and links to additional research."

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Of the 5 agents discussed by the JAMA articles, only two - Anthrax spores and Francisella tularensis - are capable of surviving in water. Anthrax spores can be filtered effectively by a good sub-micron filtration system. Francisella tularensis would be more difficult to filter with a standard home filter unless it can effectively remove particles in the 0.1 - 0.2 micron size, but standard water treatment chlorination will effectively kill it.

Botulism-No instances of waterborne botulism have ever been reported. Although the potency of botulinum toxin has led to speculation that it might be used to contaminate a municipal water supply, this scenario is unlikely for at least 2 reasons. First, botulinum toxin is rapidly inactivated by standard potable water treatments (eg, chlorination, aeration). Second, because of the slow turnover time of large-capacity reservoirs, a comparably large (and technically difficult to produce and deliver) inoculum of botulinum toxin would be needed. In contrast with treated water, botulinum toxin may be stable for several days in untreated water or beverages. Hence, such items should be investigated in a botulism outbreak if no other vehicle for toxin can be identified. (February 28, 2001)

Anthrax-There is little information available about the risks of direct contamination of food or water with anthrax spores. Although human infections have been reported, experimental efforts to infect primates by direct gastrointestinal installation of anthrax spores have not been successful..... Vegetative bacteria (that is, the "hatched" spores) have poor survival outside of an animal or human host; colony counts decline to undetectable within hours following inoculation into water. This contrasts with the environmentally hardy properties of the B. anthracis spore, which can survive for decades. (the size of anthrax spores have been variously reported in different sources as about 1.0 micron and from 2-6 microns) (May 12, 1999)

Plauge-The epidemiology of plague following its use as a biological weapon would differ substantially from that of naturally occurring infection. The intentional dissemination of plague would most probably occur via an aerosol of Y. pestis, a mechanism that has been shown to produce disease in nonhuman primates. (May 3, 2000)

Smallpox- It was reasoned that if the virus were able to persist in nature and infect humans, there would be cases occurring for which no source could be identified. Cases of this type were not observed. Rather, when cases were found, there were antecedent human cases with whom they had direct contact. (June 9, 1999)

Tularemia-Tularemia's epidemic potential became apparent in the 1930s and 1940s when large waterborne outbreaks occurred in Europe and the Soviet Union and epizootic-associated cases occurred in the United States... Humans become infected with F. tularensis by various modes, including bites by infective arthropods, handling infectious animal tissues or fluids, direct contact with or ingestion of contaminated water, food, or soil, and inhalation of infective aerosols... Standard levels of chlorine in municipal water sources should protect against waterborne infection. (The size of the F. tularensis bacterium is 0.2 X 0.3-0.7 micron) (June 6, 2001)

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