Posted: October 14, 2019

Proposals due November 5, 2019

Halogenated acetonitriles (HANs), also referred to as haloacetonitriles, are a group of nitrogenous disinfection byproducts (N-DBPs). They are formed during chlorine, chloramine, or chlorine dioxide oxidation of anthropogenic and naturally occurring substances, including algae, fulvic acid, and proteinaceous material. N-DBPs, including HANs, are more toxic than regulated carbonaceous DBPs, trihalomethanes (THMs), and haloacetic acids (HAAs), with HANs contributing significantly to the overall toxicity of treated water. In addition, comparative toxicity studies (Plewa et al. 2008) show that iodinated and brominated HANs are more cytotoxic and genotoxic than their chlorinated analogues.

Several studies (Mitch et al. 2009, Simpson and Hayes 1989) have reported the occurrence of HANs in treated waters. The most frequently detected HAN species (HAN4) are trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), and dibromoacetonitrile (DBAN).

While the World Health Organization is considering guidelines for DBAN and DCAN, there are no regulations for HANs in the United States. However, considering the reports of increased frequency of detection and new evidence of HAN toxicity, future regulations may be considered for the protection of public health.

Previous studies (Chuang et al. 2013, Lee et al. 2007) have shown that bulk organic matter parameters, such as dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and bromide levels, play important roles in HAN formation. For example, high levels of bromide lead to the formation of the more toxic brominated HAN species. Another important factor is the type of disinfectant used; the reactivity of various precursors is different with chlorine versus chloramine.

Though HANs have been detected in drinking water for over a decade, surprisingly little is known about their precursors in water supplies. Much of the available literature on HAN precursors focuses on a relatively small number of low molecular weight model compounds (e.g., amino acids, aspartic acid), and it is thought that aromatics that produce THMs/HAAs also produce HANs. Nitrogen source tracking with application of 15N-labeled monochloramine demonstrated that approximately 60-90% of DCAN from different dissolved organic matter isolates was from inorganic nitrogen incorporation from chloramine. Higher DCAN formation was exhibited from hydrophobic fractions than from transphilic and hydrophilic fractions in chloramination. Colloidal and transphilic fractions enriched with proteins and amino sugars tend to have higher DCAN yields in chlorination. There tends to be a weak correlation between DON and HANs.

HANs have been shown to exhibit greater stability in chloraminated systems than in chlorinated systems. Decay of HANs in chlorinated distribution systems can result in higher potential health risks due to degradation byproducts, such as haloacetamides.

HANs are polar compounds, are usually water-soluble with low octanol/water partition coefficients, and are not expected to be removed by adsorption. Recent studies (Stanford et al. 2019) demonstrated that HAN formation is unaffected or even increased by granular activated carbon treatment, and DBAN emerges as a dominate risk in finished drinking water. While HANs can decay and eventually form THMs and HAAs upon free chlorination or at alkaline conditions, they continue to form during chloramination.

The scientific community has realized through the study of other N-DBPs that watershed, wastewater, and in-plant chemicals can be precursors for N-DBPs and HANs. The frequent occurrence, stability, and significant toxicity of HANs and their degradation products can result in critical risks to human health.

There is a need to identify the most common precursors for HANs, assess control measures to remove them, and understand their formation and stability in potable water systems.

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