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The Soft Machine: Travel Health column

AND A PARASITE RUNS THROUGH IT
By CARRIE BEALLOR (continued from previous page)


Halogenation refers to the use of halogens such as chlorine or iodine to disinfect water. The effectiveness of this method depends on the micro-organisms in question, the concentration of the halogen and the exposure time. Higher concentrations enable rapid disinfection, but less can be used if you allow for longer exposures. Higher doses are necessary if there are particles or nitrates in the water. If the water is cold, a longer exposure time or higher concentration is required.
(Photo by Robert J. Brodey)


Chlorine, found in most tap water, is available as a liquid or in tablet form. It loses effectiveness with exposure to heat, air or moisture and bottles should be replaced every three to six months. The upside of chlorine is that it has been used for hundreds of years and is cheap and relatively safe. The downside is that it is less stable and persistent than iodine, and concentrated liquids are corrosive and can stain clothing and other items if spilled. If ingested in a concentrated form, it can cause corrosion of mucosal membranes in the mouth and upper gastrointestinal tract.

Iodine is available in solutions of water, ethyl alcohol or glycerol, in tablets as tetraglycine hydroperiiodide, as crystals or as resins or resin filters. Iodine is also cheap, but is more stable and less pH-sensitive than chlorine. It is, however, toxic in high doses, and there is some danger of chronic iodine poisoning with prolonged ingestion. Taking iodine during pregnancy can cause fetal thyroid disease and it can unmask underlying thyroid disease. Studies have shown that taken in recommended doses, iodine is safe for periods of three to six months. Pregnant women, individuals with a known iodine allergy and people with active thyroid disease should not take it and should consult a physician for specific advice.
(Photo by Robert J. Brodey)


Most commercial preparations add 4mg of iodine per litre and 5mg of chlorine per litre to non-turbid water and require roughly 45 minutes at 30*C, one hour at 15*C, and two hours at 5*C for disinfection. The required dose can be reduced by initial sedimentation, coagulation-flocculation, filtration, increasing the temperature of the water, a longer exposure time and/or final filtration. Drink crystals can be used to improve the taste after disinfection.

One last point is about carbonated beverages. These are generally safe to drink because the low pH from the carbonation process kills most pathogens. Flavoured beverages usually have an even lower pH due to added food acids and may be considered even safer.

Despite all efforts, illness may still occur. If treatment is required, a good recollection of recently ingested foods and beverages can be a great help in pinpointing the source of infection.

Note:The information in this article is intended as a general guideline to safe water and should in no way replace proper consultation with a physician or at a travel clinic. It is the responsibility of the traveller to obtain individual medical counselling, especially with regards to personal risks and medications. All instructions included with water purification or disinfection products should be followed as outlined by the manufacturer unless otherwise specified by a physician.

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