The recent report by Khan et al. of an unexpectedly high concentration of free
iodine in water filters, which may have led to the high proportion of abnormal thyroid function tests in Peace Corps workers, is of concern for travel advisors when asked to recommend suitable means of water sterilization. Many travelers use
iodine based filters and/or chemicals for purification of water when traveling in areas with contaminated water supplies and may therefore be at risk of excess
iodine intake. Aside from
iodine impregnated resin filtration systems,
tetraglycine hydroperiodide tablets, tincture of
iodine 2% and more commonly,
chlorine-based proprietary products are widely used to sterilize water for drinking, and usually purchased by travelers without advice on how they should be used. A single
tetraglycine hydroperiodide tablet in a liter of water releases 8 mg of
iodine in comparison to the 10 mg/liter released from the iodinated resin pumps described by Khan et al. Although the instructions for using
iodine tincture are imprecise, the normal recommendation is 5 drops per liter of water, increasing this to 12 drops where Giardia
cysts may be present. The lower of the two doses would yield about 2 mg/liter of free
iodine per liter depending on the pipette used, although, because of the
potassium iodide present in the formulation, a total of 4 mg
iodine would be available for absorption.