Revealing the impact of side-chains in amino acids on the formation of haloacetamides during chlorination

Abstract

Haloacetamides (HAMs) is a class of highly toxic emerging nitrogenous disinfection byproducts (N-DBPs) in drinking water, however the factors influencing the formation of HAMs by amino acids remain incompletely understood. Besides, a quantitative data regarding how many HAMs in chlorinated drinking water can attribute to amino acids in source water is lacking. To address this gap, HAMs formation during chlorination for 20 amino acids with different side-chains was analyzed. HAMs yield of 20 common amino acids during chlorination was 0.04-132 μg/mg-C. For different side-chains in amino acids, carboxyl group exhibited the highest HAM’s yield at 65.9 μg/mg-C, followed by aromatic rings (10.2 μg/mg-C), and containing nitrogen (10.1 μg/mg-C), respectively. In contrast, hydroxyl groups, sulfur-containing amino acids and those with only hydrogen and alkyl groups showed the lowest HAM’s yield (<1 μg/mg-C). HAM yields of basic and neutral amino acids were lower than that of acidic amino acids. HAM yields of nonpolar amino acids were lower than polar amino acids. The HAM formation potentials of amino acids in source water during chlorination were 14.8-5138 ng/L, with an average of 576 ng/L. Aspartic acid, asparagine, and histidine accounted for as much as 97% of the theoretical HAMs formation. The theoretical calculation found that amino acids in source water contribute about 3.2% of HAMs in chlorinated drinking water, which is close to that of lab-controlled experiments (4.3%), suggesting that the role of amino acids on HAMs in chlorinated drinking water is overvalued. Our study reveals the role of precursor’s side-chains on toxic DBP formation as well their potential contribution to drinking water DBPs.