Nontargeted identification of peptides and disinfection byproducts in water.

A broad range of organic compounds are known to exist in drinking water sources and serve as precursors of disinfection byproducts (DBPs). Epidemiological findings of an association of increased risk of bladder cancer with the consumption of chlorinated water has resulted in health concerns about DBPs. Peptides are thought to be an important category of DBP precursors in water. However, little is known about the actual presence of peptides and their DBPs in drinking water because of their high sample complexity and low concentrations. To address this challenge and identify peptides and non-chlorinated/chlorinated peptide DBPs from large sets of organic compounds in water, we developed a novel high throughput analysis strategy, which integrated multiple solid phase extraction (SPE), high performance liquid chromatography (HPLC) separation, and non-target identification using precursor ion exclusion (PIE) high resolution mass spectrometry (MS). After MS analysis, structures of candidate compounds, particularly peptides, were obtained by searching against the Human Metabolome Database (HMDB). Using this strategy, we successfully detected 625 peptides (out of 17,205 putative compounds) and 617 peptides (out of 13,297) respectively in source and finished water samples. The source and finished water samples had 501 peptides and amino acids in common. The remaining 116 peptides and amino acids were unique to the finished water. From a subset of 30 putative compounds for which standards were available, 25 were confirmed using HPLC-MS analysis. By analyzing the peptides identified in source and finished water, we successfully confirmed three disinfection reaction pathways that convert peptides into toxic DBPs.

Precursors of Halobenzoquinones and Their Removal During Drinking Water Treatment Processes.

Halobenzoquinones (HBQs) widely occur in drinking water treatment plant (DWTP) effluents; however, HBQ precursors and their removal by treatments remain unclear. Thus, we have investigated HBQ precursors in plant influents and their removal by each treatment before chlorination in nine DWTPs. The levels of HBQ precursors were determined using formation potential (FP) tests for 2,6-dichloro-1,4-benzoquinone (DCBQ), 2,3,6-trichloro-1,4-benzoquinone (TCBQ), 2,6-dichloro-3-methyl-1,4-benzoquinone (DCMBQ), and 2,6-dibromo-1,4-benzoquinone (DBBQ). HBQ precursors were present in all plant influents. DCBQ precursors were the most abundant (DCBQ FP up to 205 ng/L). Coagulation removed dissolved organic carbon (DOC) (up to 56%) and HBQ precursors (up to 39% for DCBQ). The level of removal of DOC was significantly greater than the level of removal of HBQ FP, suggesting that organic matter removed by coagulation had a high proportion of non-HBQ-precursor material. Granular activated carbon (GAC) decreased the level of HBQ FPs by 10-20%, where DOC removal was only 0.2-4.7%, suggesting that the GAC was not in the adsorption mode and biodegradation of HBQ precursors may have been occurring. Ozonation destroyed/transformed HBQ FPs by 10-30%, whereas anthracite/sand filtration and UV irradiation appeared to have no impact. The results demonstrated that the combined treatments did not substantially reduce HBQ precursor levels in water.