Safety of iodine based water sterilization for travelers

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.