Evaluation of β-D-glucuronidase and particle-size distribution for microbiological water quality monitoring in Northern Vietnam

In many karst regions in developing countries, the populations often suffer from poor microbial water quality and are frequently exposed to bacterial pathogens. The high variability of water quality requires rapid assays, but the conventional cultivation-based analysis of fecal indicator bacteria, such as Escherichict coil (E. coli), is very timeconsuming. In this respect, the measurement of the enzymatic activity of E. coil could prove to be a valuable tool for water quality monitoring. A mobile automated prototype device was used for the investigation ofp-Dglucuronidase (GLUC) activity at a remote karst spring, connected to a sinking surface stream, in Northern Vietnam. To assess the relationship between GLUC activity, discharge dynamics and contamination patterns, multiple hydrological, hydrochemical, physicochemical and microbiological parameters, including discharge, turbidity, particle-size distributions, and E. coli, were measured with high temporal resolution during ten days of on-site monitoring. A complex contamination pattern due to anthropogenic and agricultural activities led to high E. coil concentrations (270 to >24,200 MPN/100 ml) and a GLUC activity between 3.1 and 102.2 mMFU/100 ml. A strong daily fluctuation pattern of GLUC activity and particle concentrations within small size classes (<10 pm) could be observed, as demonstrated by autocorrelations. A Spearman's rank correlation analysis resulted in correlation coefficients of rs = 0.56 for E. coil and GLUC activity and rs = 0.54 for GLUC activity and the concentration of 2-3 mu m particles. On an event scale, correlations were found to be higher (rs = 0.69 and 0.87, respectively). GLUC activity and E. coli displayed a general contamination pattern, but with significant differences in detail, which may be explained by interferences of e.g. viable but non-culturable cells. Although further evaluations are recommended, GLUC activity is a promising, complementary parameter for on-site and near real-time water quality monitoring. (C) 2016 Elsevier B.V. All rights reserved.