Amino Acids as Potential Precursors to Odorous Compounds in Tap Water during Spring Runoff Events

Abstract

The onset of spring runoff in northern climates and tap water odor events are difficult to predict because common water quality parameters cannot fully explain the intermittent odor events that occurred over past decades. Studies have shown that small polar water-soluble compounds, such as amino acids (AAs), leach first from ice/snowmelt. AAs are known to produce odorous compounds, such as aldehydes and chloroaldimines, upon chlorination. Therefore, we proposed that AAs may serve as markers for small and soluble organics that contribute to the odor of chlorinated tap water. Here, we studied the occurrence of AAs in source water collected at two water treatment plants and the odor profiles of tap water at >300 homes during the 2021 and 2022 spring runoff events. AA concentrations were at baseline levels (<100 ng/L) during the 2021 runoff but much higher (up to 5500 ng/ L) in 2022 and associated with an escalation in odor complaints. AA concentrations peaked at the onset of the 2022 spring runoff and corresponded with the strongest reported odor intensities in tap water. We obtained high resolution MS and MS/MS spectra of chloroaldimines and confirmed the formation of chloroaldimines under chlorination of the six AAs detected in source water. The results indicate that AAs signal the onset of spring runoff and represent small polar water-soluble compounds that may contribute to tap water odor problems.

Water Analysis: Emerging Contaminants and Current Issues

“…In another study, Craven et al solved a years-long mystery as to what chemicals were causing taste and odor events in Edmonton's drinking water following spring runoff (from melting snow). 104 These taste-and-odor events could not be explained by the commonly occurring geosmin or methylisoborneol, algal metabolites that plague most drinking water plants around the world. Instead, the authors found high amino acid levels following these spring runoff events (increasing from <100 ng/L to 5500 ng/L), accompanied by taste-and-odor complaints.…”