The Transformation of Microcystin-LR during Tap Water Treatment Process

摘要

Objective To establish a liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for the determination of microcystin-LR (MC-LR) in drinking water, investigate its removal efficiency during tap water advanced treatment process and analyze its degradation products in the tap water. Methods Water samples were collected from each point of tap water advanced treatment process and treated by mixing, filtration, concentration, elution, nitrogen blow and re-dissolvement. The samples were analyzed by LC/MS/MS to determine the MC-LR concentration and its removal efficiency during treatment process. The combination of actual water enrichment and laboratory simulated water were used to qualitative analyze the MC-LR degradation products by Orbitrap mass spectrometry. Results The linearity of MC-LR ranged from 2 pg/L to 200 pg/L with the detection limit of 0.0079 pg/L and the limit of quantification of 0.0263 pg/L. The recovery rate of MC-LR from different contration in drinking water were from 94.88% to 101.47%. The intra-day precision was 2.51%-7.93% and the intra-day precision was 3.24%-8.41%. The average concentration of MC-LR in source water was 0.631 pg/L, 94.0% of which can be removed by ozone exposure, biological pre-treatment and chlorination. The remaining can hardly be removed by sand filtration, ozone exposure, activated carbon, ultrafiltration and other processes. The MC-LR average concentration in the finished water maintained at about 0.036 pg/L. Four degradation products were identified in the laboratory simulated water of the mixture of MC-LR and liquid chlorine in the mass ratio of 1:10. Conclusion the established MC-LR detection method can be well applied to the monitoring of MC-LR in drinking water due to its simple pre-treatment process and good methodological validation parameters. The removal efficiency of treatment processes was different.