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

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.

Integration of solid phase extraction with HILIC-MS/MS for analysis of free amino acids in source water.

Amino acids (AAs) are prevalent in source water, particularly during spring run-off. Monitoring of amino acids in source water is desirable for water treatment plants (WTP) to indicate changes in source water quality. The objective of this study was to establish analytical procedures for reliable monitoring of amino acids in source water. Therefore, we examined two different methods, large volume inject (LVI) and solid phase extraction (SPE), for sample preparation prior to HILIC-MS/MS. The LVI-HILIC-MS/MS method can provide fast and sensitive detection for clean samples, but suffers from matrix effects, resulting in irreproducible separation and shortening column lifetime. We have demonstrated that SPE was necessary prior to HILIC-MS/MS to achieve reproducible and reliable quantification of AAs in source water. A natural heterocyclic amine 1-methyl-1,2,3,4-tetrahydro-ß-carboline-3-carboxylic acid (MTCCA) was also included in the method to indicate changes in other natural nitrogenous compounds in source water. The SPE-HILIC-MS/MS method was able to achieve limits of detection from 2.6-3400 ng/L for the amino acids and MTCCA with RSDs (n=3) of 1.1%-4.8%. As well, retention times (RT) of the analytes were reproducible with variation less than 0.01 min (n=3) through the entire project. We further applied the SPE-HILIC-MS/MS method to determine AAs in authentic source water samples collected from two drinking water treatment plants (WTPs) during the 2021 spring run-off season. The results support that the SPE-HILIC-MS/MS method does not require derivatization and can provide reliable, accurate, and robust analysis of AAs and MTCCA in source water, supporting future monitoring of source water quality.

Correlations between retinal nerve fiber layer and visual field in eyes with nonarteritic anterior ischemic optic neuropathy.

PURPOSE: To evaluate correlations between retinal nerve fiber layer (RNFL) thickness with visual field (VF) sensitivities in eyes with nonartertic anterior ischemic optic neuropathy (NAION). DESIGN: Case-control study in an academic, institutional setting. METHODS: One eye from 21 patients with NAION and 32 healthy participants were included in this prospective study. Humphrey visual field (HVF) sensitivities were obtained from standard achromatic HVF test (24-2 SITA). RNFL was measured with scanning laser polarimetry (SLP, GDx-VCC) and optical coherence tomography (OCT, StratusOCT). Correlations were evaluated between RNFL and sensitivities from global, hemifields, and regional locations of the VF pertinent to the RNFL distribution. A total of 15 NAION eyes had inferior altitudinal HVF defects, and their global and regional RNFL was compared with that of control eyes. The main outcome measure was correlation between HVF sensitivities and RNFL. RESULTS: Correlations of global, hemifield, and sectorial HVF sensitivities with RNFL were greater when RNFL was measured with OCT than with SLP, except for nasal and inferonasal sectors. RNFL thickness was far lower in the hemiretinas corresponding to the relative unaffected hemifield in eyes with altitudinal VF defect compared with controls. CONCLUSIONS: In patients with NAION, RNFL measured by OCT provided better correlation to HVF changes than SLP did. Both instruments showed decreased RNFL in NAION eyes with altitudinal VF defects compared with control eyes, demonstrating loss of RNFL even in sectors of the optic disk that corresponded to relatively unaffected hemifield, suggesting greater damage beyond the extent estimated by VF methods.