Formation of Iodinated Disinfection Byproducts (I-DBPs) in Drinking Water: Emerging Concerns and Current Issues

Abstract

CONSPECTUS: Formation of iodinated disinfection byproducts (I-DBPs) in drinking water has become an emerging concern. Compared to chlorine-and bromine-containing DBPs, I-DBPs are more toxic, have different precursors and formation mechanisms, and are unregulated. In this Account, we focus on recent research in the formation of known and unknown I-DBPs in drinking water. We present the state-ofthe-art understanding of known I-DBPs for the six groups reported to date, including iodinated methanes, acids, acetamides, acetonitriles, acetaldehyde, and phenols. I-DBP concentrations in drinking water generally range from ng L −1 to low-μg L −1 . The toxicological effects of I-DBPs are summarized and compared with those of chlorinated and brominated DBPs. I-DBPs are almost always more cytotoxic and genotoxic than their chlorinated and brominated analogues. Iodoacetic acid is the most genotoxic of all DBPs studied to date, and diiodoacetamide and iodoacetamide are the most cytotoxic. We discuss I-DBP formation mechanisms during oxidation, disinfection, and distribution of drinking water, focusing on inorganic and organic iodine sources, oxidation kinetics of iodide, and formation pathways. Naturally occurring iodide, iodate, and iodinated organic compounds are regarded as important sources of I-DBPs. The apparent second-order rate constant and half-lives for oxidation of iodide or hypoiodous acid by various oxidants are highly variable, which is a key factor governing the iodine fate during drinking water treatment. In distribution systems, residual iodide and disinfectants can participate in reactions involving heterogeneous chemical oxidation, reduction, adsorption, and catalysis, which may eventually affect I-DBP levels in finished drinking water. The identification of unknown I-DBPs and total organic iodine analysis is also summarized in this Account, which provides a more complete picture of I-DBP formation in drinking water. As organic DBP precursors are difficult to completely remove during the drinking water treatment process, the removal of iodide provides a cost-effective solution for the control of I-DBP formation. This Account not only serves as a reference for future epidemiological studies to better assess human health risks due to exposure to I-DBPs in drinking water but also helps drinking water utilities, researchers, regulators, and the general public understand the formed species, levels, and formation mechanisms of I-DBPs in drinking water.

Removal of disinfection by-product precursors by ion exchange resins

“…However, the formation of I-THMs in the raw water sample is not correlated to the treated waters with much higher I-THMs formed than the correlation with the 4 treated water would have predicted. The content of ammonia in the water (as chloramines favours I-DBP formation compared to chlorine 39 ) does not explain this behaviour either as the raw water shows the same concentration as the waters treated by the IRA-410 and IRA-958 resins (around 0.17 mg L -1 ) and a lower concentration than the waters treated by PPA860S and TAN-1 resins (around 0.27 mg L -1 ). Then, the removal of NOM DBP precursors is a key factor in the control of I-DBP formation.…”

Enzymatic assays for the assessment of toxic effects of halogenated organic contaminants in water and food. A review

“…Iodide is present naturally in ground water, but concentrations are incremented by anthropogenic activities, including improper disposal of iodinated wastes, and release of iodide-containing pharmaceuticals. These increased environmental concentrations are usually linked to undesirable effects in wastewater treatment plants generating iodinated disinfection by-products (I-DBPs) (Dong et al, 2019;Duirk et al, 2011;Hapeshi et al, 2013;Kormos et al, 2010). For example, the use of oxidizing agents like chlorine, chloramine, ozone (Tian et al, 2013;Weinberg et al, 2002) or potassium permanganate (Ye et al, 2012), promotes oxidation of iodide anion to hypoiodous acid, which acts as a precursor, reacting with organic matter to generate I-DBPs.…”

“…For example, the use of oxidizing agents like chlorine, chloramine, ozone (Tian et al, 2013;Weinberg et al, 2002) or potassium permanganate (Ye et al, 2012), promotes oxidation of iodide anion to hypoiodous acid, which acts as a precursor, reacting with organic matter to generate I-DBPs. Such compounds are incorporated in drinking water at concentrations from ng/L to μg/L and ingested by humans directly (drinking water) or indirectly (cooking water) (Dong et al, 2019), alongside iodinated table salt, making calculation of exposure problematic (Becalski et al, 2006;Pan et al, 2016). Recently reviewed by Dong et al (2019), iodinecontaining compounds can be present as iodinated methanes, iodo-acids, iodo-haloacetamides, iodo-haloacetonitriles, iodo-haloaldehydes and iodo-phenols.…”

Inability of GSTT1 to activate iodinated halomethanes to mutagens in Salmonella

“…As assessed by Richardson et al (2008) in chlorinated and chloraminated drinking waters from 23 cities in the U.S. and Canada, as well as reviewed by Postigo and Zonja (2019) and Dong et al (2019), various I‐DBPs have been found in drinking water during the disinfection of waters containing iodide and/or organic iodine. The types and concentrations of I‐DBPs are influenced by the concentration of iodide (Richardson et al, 2008; Jones et al, 2012; Postigo et al, 2017), the molecular size of the natural organic matter (NOM) (Zhang et al, 2016), and the presence of iodinated X‐ray contrast media in the source water (Duirk et al, 2011; Wendel et al, 2014; Xu et al, 2017; Postigo et al, 2018; Ackerson et al, 2020).…”