Travel Reference
In-Depth Information
Iodine Disinfection
During World War II, a search for a simple, reliable water disinfectant was initiated at
Harvard University because chlorine-based systems were too undependable. The investig-
ating team found that diatomic iodine (I
2
) and the various ions resulting from the dissoci-
ation of molecular iodine in water consistently and reliably disinfects water containing as
many as ten million bacteria per milliliter, a concentration approximately ten times greater
than grossly polluted water. (The effectiveness of iodine was demonstrated on raw sewage
fromtheCambridge,Massachusetts,sewagesystem.)Unlikechlorine,iodineisfast,resists
inactivation by organic compounds, is active over a wide pH range, and is available in
stable preparations.
At73°F(23°C),eveninmoderately turbidwaterwithmoderate amountsoforganiccol-
or,aniodine concentration of8mg/l (8partspermillion) eradicates bacteria, viruses,para-
sites, and parasitic cysts other than
Cryptosporidia
. A contact time of only ten minutes
already includes a considerable margin of safety. (About ninety seconds is adequate for
eliminating bacteria and viruses.)
However, an iodine concentration of 8 mg/l (8 parts per million) is only needed to des-
troy parasitic cysts. A concentration of 0.5 to 1.0 mg/l eliminates other microorganisms.
If filters are used to eliminate
Cryptosporidia
and other parasites, only such small concen-
trations are needed. The only currently available preparation that readily supplies such a
limited quantity of iodine is a saturated iodine solution. Tablets could be broken up or dis-
solved in much larger quantities of water (two gallons.)
Iodine Disinfection Precautions
In cold water (32° to 41°F or 0° to 5°C) the chemical activity of iodine is slower, just
as all chemical reactions are slower at lower temperatures. An increase in contact time to
twenty minutes has been recommended to ensure complete disinfection.
Cloudy, heavily contaminated water requires more iodine to compensate for binding
of the disinfectant by organic compounds; however, doubling the iodine concentration or
doubling the contact time is sufficient.
If the water has been filtered, such precautions are probably unnecessary, but appropri-
ate studies have not been published.
Masking Iodine's Taste
Inwaterthathasbeenfilteredanddisinfectedwith0.5to1.0mg/lofiodine,thelowcon-
centration of iodine cannot be tasted by most people. If larger quantities of iodine are used
andindividualsfindthetasteobjectionable,severalmethodsformaskingitstasteareavail-
able. Because such procedures inactivate the iodine, they must not be used before enough
time has elapsed for microorganisms to be destroyed.
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