Organic chloramines in drinking water: An assessment of formation, stability, reactivity and risk

Abstract

Although organic chloramines are known to form during the disinfection of drinking water with chlorine, little information is currently available on their occurrence or toxicity. In a recent in vitro study, some organic chloramines (e.g. N-chloroglycine) were found to be cytotoxic and genotoxic even at micromolar concentrations. In this paper, the formation and stability of 21 different organic chloramines, from chlorination of simple amines and amino acids, were studied, and the competition between 20 amino acids during chlorination was also investigated. For comparison, chlorination of two amides was also conducted. The formation and degradation of selected organic chloramines were measured using either direct UV spectroscopic or colorimetric detection. Although cysteine, methionine and tryptophan were the most reactive amino acids towards chlorination, they did not form organic chloramines at the chlorine to precursor molar ratios that were tested. Only 6 out of the 21 organic chloramines formed had a half-life of more than 3 h, although this group included all organic chloramines formed from amines. A health risk assessment relating stability and reactivity data from this study to toxicity and precursor abundance data from the literature indicated that only N-chloroglycine is likely to be of concern due to its stability, toxicity and abundance in water. However, given the stability of organic chloramines formed from amines, more information about the toxicity and precursor abundance for these chloramines is desirable.

Chlorination of Amino Acids: Reaction Pathways and Reaction Rates

“…19 However, organic chloramines formed from amino acids have been found to be unstable. 20,21 In our study of 18 organic chloramines formed from amino acids, we found that 12 had a half-life of less than 90 minutes. 20 Consequently, as the time between chlorination of drinking water and final distribution to the end consumer increases, it becomes more likely for consumers to be exposed to the degradation products of organic chloramines, rather than the organic chloramines themselves.…”

“…20,21 In our study of 18 organic chloramines formed from amino acids, we found that 12 had a half-life of less than 90 minutes. 20 Consequently, as the time between chlorination of drinking water and final distribution to the end consumer increases, it becomes more likely for consumers to be exposed to the degradation products of organic chloramines, rather than the organic chloramines themselves. T herefore, a full assessment of the health impact of organic chloramine formation in drinking water must include the identification of stable by-products from the reaction of amino acids and chlorine.…”

“…Effect of a reactive secondary functional group on the formation of organic monochloramines and dichloramine s. T he formation of organic monochloramines and/or organic dichloramines (to be referred to as monochloramines and dichloramines) from the chlorination of amino acids is controlled by the Cl:AA ratio and by the presence of secondary functional groups that may also react with chlorine. 20,32 Formation experiments using a Cl:AA = 0.8 were used in this study to produce monochloramines, while avoiding dichloramine formation. In our previous work, we used LC-UV-HRMS to confirm formation of both Nchloroisoleucine and N-chlorovaline after the chlorination of isoleucine and valine, respectively.…”

“…T he Cl:AA ratios were chosen because previous studies have shown that only organic monochloramines form at Cl:AA = 0.8 and only organic dichloramines form at Cl:AA = 2.8. 20,22 T he conditions used for the reaction were: pH 7.5 at room temperature (20-25 ºC). Reaction mixtures were reacted in the dark in air tight vials.…”

Identification and characterization of phenylacetonitrile as a nitrogenous disinfection byproduct derived from chlorination of phenylalanine in drinking water

“…Amino acids are major constituents of dissolved nitrogenous organic matter, contributing about 75% of the dissolved nitrogen in surface waters (Hagedorn et al, 2000). As N-DPB precursors, amino acids and their transformation products formed during the water treatment process are attracting more attention due to possible health effects (Dotson and Westerhoff, 2009;How et al, 2016). Amino acids are commonly detected in source or drinking waters affected by extensive algal growth or wastewater discharge (How et al, 2014;Ishizawa et al, 2010).…”