Travel Reference
In-Depth Information
Artificial flavorings added to hide the taste usually contain ascorbic acid, which reacts
with iodine and impairs its antimicrobial activity. Potable Aqua® is now supplied with
ascorbic acid tablets—to be added after disinfection is complete—to eliminate the iodine
taste. A less convenient technique is to convert the iodine to tasteless sodium iodide with
anequalweightofsodiumthiosulfate.Thewatercanbefilteredthroughactivatedcharcoal,
which, by adsorption, physically removes the iodine (and some odors, inorganic materials,
and microorganisms but not enough to make the water suitable for consumption).
Inclear water,therate atwhichmicroorganisms aredestroyed byhalogens isdependent
on contact time and iodine concentration. If time is available for more prolonged disinfec-
tion, lower concentrations of iodine can be used. One-half the standard concentration of
iodine is equally effective as a disinfectant if allowed to act for twice the usual time; one-
fourththestandardconcentrationisaneffectivedisinfectant ifallowedtoactforfourtimes
the usual time. Even lower iodine concentrations could be used, but less than 2.0 mg/l usu-
ally cannot be tasted. (Some individuals prefer a barely detectable trace of iodine as assur-
ance that the water has been disinfected.) A common practice is to add a small quantity of
iodine to water that is to be disinfected and leave it overnight.
Persons with known thyroid dysfunction should determine how they react to water dis-
infected with iodine at home before relying on iodine water disinfection in the wilderness
orwhiletraveling.Theuncommonindividualswhoareallergictoiodine,includingiodine-
containing compounds in radiographic contrast media, and those with thyroid dysfunction
whoreactadverselymustnotuseiodineforwaterdisinfection.Forsuchindividualsafiltra-
tionsystemtophysically removebacteria, parasites, andparasitic cysts,followedbychlor-
ine or ultraviolet light offers a reliable alternative to kill viruses.
Iodine Toxicity
Several publications have claimed that the iodine used for water disinfection is danger-
ously toxic. The skull and crossbones on bottles of tincture of iodine is familiar. However,
iodine is only weakly poisonous. The third edition of Goodman and Gilman's
Textbook of
Pharmacology
states,“thatiodineishighlytoxic…isapopularfallacy.”Thelethaldoseis
2 to 3 g, but survival after ingestion of 10 g has been reported. Iodine in such large quant-
ities is a strong gastrointestinal irritant and causes immediate vomiting, which eliminates
most of the iodine. That remaining in the gastrointestinal tract is largely neutralized by
the intestinal contents. The immediate treatment for iodine poisoning is administration of
starchy food.
Accidental iodine poisoning is rare; almost all fatalities are suicidal, but successful sui-
cide is uncommon if the person receives medical care. Between 1915 and 1936 no deaths
occurred among 327 individuals who arrived alive at Boston City Hospital following at-
tempted suicide with iodine.
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