Peptide bonds affect the formation of haloacetamides, an emerging class of N-DBPs in drinking water: free amino acids versus oligopeptides.

Wenhai Chu,Naiyun Gao,Dongmei Li,Xin Li,Yang Deng,Daqiang Yin,Tengfei Chu

doi:10.1038/srep14412

Abstract

Haloacetamides (HAcAms), an emerging class of nitrogenous disinfection by-products (N-DBPs) of health concern, have been frequently identified in drinking waters. It has long been appreciated that free amino acids (AAs), accounting for a small fraction of the dissolved organic nitrogen (DON) pool, can form dichloroacetamide (DCAcAm) during chlorination. However, the information regarding the impacts of combined AAs, which contribute to the greatest identifiable DON portion in natural waters, is limited. In this study, we compared the formation of HAcAms from free AAs (tyrosine [Tyr] and alanine [Ala]) and combined AAs (Tyr-Ala, Ala-Tyr, Tyr-Tyr-Tyr, Ala-Ala-Ala), and found that HAcAm formation from the chlorination of AAs in combined forms (oligopeptides) significantly exhibited a different pattern with HAcAm formation from free AAs. Due to the presence of peptide bonds in tripeptides, Tyr-Tyr-Tyr and Ala-Ala-Ala produced trichloroacetamide (TCAcAm) in which free AAs was unable to form TCAcAm during chlorination. Moreover, peptide bond in tripeptides formed more tri-HAcAms than di-HAcAms in the presence of bromide. Therefore, the peptide bond may be an important indicator to predict the formation of specific N-DBPs in chlorination. The increased use of algal- and wastewater-impacted water as drinking water sources will increase health concerns over exposure to HAcAms in drinking water.

Highlights

As a result of rapid population growth and rising water demand, drinking water source waters are facing threats of insufficiently treated wastewater effluents or algal blooms
The use of wastewater-impacted water as drinking water sources increases concerns of the exposure of nitrogenous disinfection by-products (N-DBPs) (e.g., HAcAms), because wastewater-induced dissolved organic nitrogen (DON) plays a key role as N-DBP precursors
Free amino acids (AAs) only accounts for a small fraction of dissolved organic nitrogen (DON) pool in source waters

Summary

Introduction

As a result of rapid population growth and rising water demand, drinking water source waters are facing threats of insufficiently treated wastewater effluents or algal blooms These pollution sources are characterized by higher levels of dissolved organic nitrogen (DON) that can potentially react with certain disinfectants (e.g., chlorine) to form unwanted nitrogenous disinfection by-products (N-DBPs) in drinking water treatment plants (DWTPs)[1,2,3]. Alanine (Ala) cannot form any HAcAm but might serve as a chloroform precursor[15,18] It was still unclear whether the formation of HAcAms from the chlorination of oligopeptides and free AAs behaves significantly differently due to the presence of peptide bonds in the oligopeptides. Two free AAs, Tyr (HAcAm precursor) and Ala (Non-HAcAm precursor), and four oligopeptides, Tyr-Ala, Ala-Tyr, Tyr-Tyr-Tyr, and Ala-Ala-Ala (Fig. 1) were selected as precursor compounds in this study, because they share similar molecular structures except the presence or absence of peptide bonds on HAcAm formation

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