Iodinated DBPs

Iodine is present in water environment mainly in the species of iodide, iodate, and organic iodine. During oxidation or disinfection processes, iodide or other iodine species in water can react with oxidants/disinfectants and organic precursors, generating a class of DBPs. Some of them have been proved to have “carcinogenic, teratogenic and mutagenic” properties, and were known as iodinated DBPs (I-DBPs). I-DBP includes many species. Several major species have been identified, such as iodinated trihalomethanes, iodinated acetic acids, iodinated haloacetamides, iodinated haloacetonitriles, and aromatic I-DBPs. Generally, I-DBPs are more toxic than the brominated and chlorinated analogs. Currently, there is still a lack of drinking water quality standards specific for I-DBPs in USEPA or WHO. But in China, iodinated trihalomethanes and iodinated acetic acids have been introduced into the national and local (Shanghai and Shenzhen City) drinking water standards. Overall, the formation mechanism of I-DBPs involves oxidizing iodine sources to reactive iodine species, which then undergo iodine substitution reactions with organic precursors in water to produce I-DBPs. However, factors affecting I-DBPs generation in water treatment processes are complex. The species of iodine source, the types of disinfection/oxidation method, and the structure of organic precursors all have important effects on I-DBP formation. From the perspective of iodine sources, iodide, organic iodine, and various iodine-based disinfectants can all produce I-DBPs. Iodate is chemically stable and does not directly produce I-DBPs during oxidation/disinfection processes. However, it can be converted to iodide through UV radiation or zero-valent iron reduction and indirectly produce I-DBPs during the oxidation/disinfection. The fundamental method to control the risk of I-DBPs is to remove iodine from the water source. However, there are technical difficulties in completely separating different species of iodine from water. The relevant study has become one of the hot issues in recent years. In addition, reducing organic precursors and optimizing or changing oxidation/disinfection processes are also effective in decreasing I-DBP formation. As for the formed I-DBPs, UV photolysis, advanced oxidation processes, and activated carbon adsorption have been reported as effective methods to remove I-DBPs directly.