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Iodine As a Drinking Water Disinfectant

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Iodine As a Drinking Water Disinfectant Iodine as a drinking water disinfectant Draft Document 5.4 24 October 2016 Version for Public Review Contents Contents ............................................................................................................................................... i List of abbreviations ............................................................................................................................ 1 1 Introduction ......................................................................................................................................... 2 2 Disinfectant mode of action and efficacy ............................................................................................ 3 2.1 Chemistry basics ........................................................................................................................... 3 2.1.1 Water solubility, taste, odour and colour .............................................................................. 3 2.1.2 Chemical speciation of iodine in water and corresponding disinfection powers .................. 4 2.1.2.1 Effect of pH ..................................................................................................................... 5 2.1.2.2 Effect of temperature ..................................................................................................... 7 2.2 Efficacy of iodine ........................................................................................................................... 7 2.2.1 Bactericidal efficacy of iodine ................................................................................................ 7 2.2.2 Disinfection in the presence of turbidity ............................................................................... 8 2.2.3 Iodine based disinfection products ........................................................................................ 8 2.2.3.1 Iodine solutions ............................................................................................................... 8 2.2.3.2 Resins ............................................................................................................................ 11 2.2.4 Comparison of efficacy with chlorine .................................................................................. 13 3 Safety and toxicity of iodine .............................................................................................................. 14 3.1 Human exposure ......................................................................................................................... 14 3.2 Guideline values .......................................................................................................................... 15 3.2.1. WHO drinking-water quality guidelines .............................................................................. 15 3.2.2 Other values ......................................................................................................................... 15 3.3 Human toxicity data .................................................................................................................... 17 3.3.1 Toxicokinetics ....................................................................................................................... 17 3.3.1.1 Absorption .................................................................................................................... 17 3.3.1.2 Distribution ................................................................................................................... 17 3.3.1.3 Metabolism ................................................................................................................... 17 3.3.1.4 Elimination .................................................................................................................... 18 3.3.2 Acute toxicity ....................................................................................................................... 18 3.3.3 Repeat dose toxicity ............................................................................................................. 18 3.3.3.1 Systemic effects ............................................................................................................ 18 3.3.3.2 Neurotoxicity................................................................................................................. 20 3.3.3.3 Reproductive and developmental toxicity .................................................................... 20 i 3.3.2.4 Carcinogenicity .............................................................................................................. 21 3.4 Animal toxicity studies ................................................................................................................ 21 3.4.1 Toxicokinetics ....................................................................................................................... 21 3.4.2 Acute toxicity ....................................................................................................................... 22 3.4.3 Repeat dose toxicity ............................................................................................................. 22 3.4.3.1 Systemic toxicity ........................................................................................................... 22 3.4.3.2 Reproductive and developmental toxicity .................................................................... 22 3.4.3.3 Carcinogenicity .............................................................................................................. 23 3.4.5 In vitro toxicity studies ......................................................................................................... 23 3.5 Vulnerable populations ............................................................................................................... 23 3.6 Toxicity of organoiodides produced as DBPs .............................................................................. 25 3.6.1 Formation and occurrence of iodinated by-products (I-DBPs) ............................................ 25 3.6.2 Toxicological evaluations of iodinated by-products ............................................................ 25 3.7 Summary ..................................................................................................................................... 27 4 Environmental considerations ........................................................................................................... 29 5. Discussion .......................................................................................................................................... 30 6 References ......................................................................................................................................... 33 Appendix 1: Methodology .................................................................................................................... 40 ii List of abbreviations CT (mg-min/L) product of disinfectant concentration (mg/L) and contact time (min.) DBP disinfection by-product DIAA diiodoacetic acid EC50 half maximal effective dose HOCL hypochlorous acid HIO hypoiodous acid I2 iodine IAA iodoacetic acid - IO3 iodate IWPD Individual water purification device LC50 median lethal dose – dose required to kill half the members of a test population after a specified test duration NTU nephelometric turbidity unit OCl- hypochlorite OI- hypoiodite PBI protein bound iodine PMTDI provisional maximum tolerable daily intake POU point of use PPM parts per million SHBG sex hormone-binding globulin THM trihalomethane TOC total organic content TOI total organic iodine TRH thyrotropin releasing hormone TSH thyroid stimulating hormone 1 1 Introduction Disinfection of water has been perhaps the single greatest beneficial technology with respect to reducing risks to public health from contaminated drinking water. Numerous disinfectant techniques have been developed over the centuries that are used in a wide range of applications ranging from large and small public drinking water plants to point-of-use and point-of-entry treatment devices. Chlorine has been used for more than 100 years, and several other disinfectants have been studied extensively, but there are still questions that exist in many cases with respect to optimisation of biocidal effectiveness under a range of conditions (i.e., efficacy), the chemistry of formation and the toxicological significance of disinfectant by-products (DBPs), interactions with other water constituents, and the effectiveness and toxicology of disinfectant residuals. Most chemical disinfectants can react with natural organic matter or breakdown to produce unwanted by-products. Many newer products and applications are being developed and marketed for use, particularly in developing countries and even more unanswered questions exist about some of those products, including efficacy and DBP formation. Iodine is an essential nutrient, and has been generally used as an antiseptic for skin wounds, as a disinfecting agent in hospitals and laboratories, and in pharmaceuticals. In terms of disinfection, iodine is commonly used in the form of tablets and solutions for water treatment during emergencies and by travellers (Ongerth et al., 1989; Backer and Hollowell, 2000). At regular intervals there is renewed interest in the use of iodine as an alternative disinfectant to chlorine (and other disinfectants) for drinking water. Iodine-based disinfection
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