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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 outbreak
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 a bacteria
were the size of a car, a virus would be the size of a cell phone). Cyrptosporidia
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.
water treatment methods now in place (including floculation, 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.
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.
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.
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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the 5 agents 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.
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)
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
instillation 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)
epidemiology of plague following its use as a biological weapon would
differ substantially from that of naturally occurring infection. 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)
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,
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)