Temporal microcystin dynamics of the source water and finished water in a waterworks of Lake Taihu

Abstract

Harmful cyanobacteria blooms, which are caused by water eutrophication, is still one of the serious water environment problems encountered by the whole world. In order to estimate the current status of microcystins (MCs) in the source water and finished water of Lake Taihu, we examined the concentrations of intracellular MC (intraMCs) and extracellular MC (extraMCs) and related physiochemical parameters of the source water and finished water in a waterworks in August 2014. Our results showed that the mean concentration of intraMCs in the source water was 7165.5 ng/L, dominated by MC-LR and MC-RR, with the mean concentration of 3408.7 and 3398.8 ng/L, respectively, and MC-RR accounted for 56.1% of the total MCs. The extraMCs in the source water were still on a low level with the mean and maximum value of 142.6 and 512.8 ng/L, respectively. However, the concentrations of intraMCs in finished water were relatively on a low level (mean value of 0.77 ng/L) with the removal efficiency above 99.98%. Although extraMCs in finished water were also detected on a low level (mean value of 21.71 ng/L), the concentration and detection frequencies of extraMCs were significantly higher than those of intraMCs with removal efficiency of 62.9%-81.8%. Data analysis showed that the significant and positive correlation was observed between concentrations of intraMCs and extraMCs in source water. Meanwhile, intraMCs were significantly correlated with total nitrogen (TN), ammonium (NH4+-N), total phosphorus (TP), chemical oxygen demand (CODMn) and turbidity, while extraMCs were significantly and positively correlated with TN, TP, CODMn, turbidity and chlorophyll-a. In addition, according to stepwise multiple linear regression analysis, TP could explain most of the variance of intraMCs in source water, while the variations of extraMCs could be primarily explained by intraMCs. Finally, according to non-carcinogenic risk index, MCs in finished water presented a relative low threat to the people there, while the risks will be higher when considering carcinogenic risk.