Seasonal Changes Of Microcystins In Surface Water Of Northern China And Its New Monitoring Methods

In recent years,with the increasing eutrophication of water bodies,the microcystins pollution caused by cyanobacteria blooms has been followed closely.Microcystin is a hepatotoxin produced by cyanobacteria,which have a strong carcinogenic effect.The molecular structure of microcystins is complex and various.It exists stably in trace forms in various eutrophic natural water bodies.It is difficult to eliminate effectively in the traditional treatment process,which poses a great potential threat to human health.Therefore,it is of great significance to monitor and study the concentration and seasonal variation of microcystins in water bodies for preventing and controlling microcystin pollution,reducing the harm of algae toxins and protecting human health.This paper firstly optimized and validated the Enzyme-linked immunosorbent assay(ELISA)kits necessary for experiments.Then based on the optimized method,the concentration and seasonal changes of microcystins were monitored for a long time in the Yuqiao reservoir,the Er Wangzhuang reservoir and the constructed wetland of the Dongli District of Tianjin.In addition,an optical immunosensor for the detection of microcystins was prepared according to the polarization-dependent absorption characteristics of graphene.The main results were as follows:(1)The new SAES-ELISA was successfully optimized by introducing shaking(400rpm)during Antibody incubation and Conjugate incubation.Furthermore,accuracy was significantly improved beyond 85% by using the 4-parameter curve fitting method.The CV of Inter-assay and intra-assay were less than 15%,the limit of detection(LOD)and limit of quantification(LOQ)were 0.011μg/L and 0.032μg/L,respectively.Recovery was determined by spiking environmental water samples.Recovery within 70%-130% was observed.In addition,the experimental results showed that the variability of the kit was only 1%,and the optimized ELISA kit had excellent performance.(2)Essential parameters required for method validation were separated from nonessentials in the test of the ELISA kits,which were the necessary parameters: Standard curve/linearity,precision,accuracy,LOD,LOQ,recovery rate and instrumental errors;unessential parameters: authenticity,stability,robustness,specificity/selectivity,sensitivity/responsiveness,cross-reactivity/inclusiveness,matrix effects and deviation / interference.In addition,this study provided a standardized procedure for ELISA kits validation,which can be applied to most biochemical experiments.(3)Comparing the seasonal variation of microcystin concentration in three different research areas of the Yuqiao reservoir,the Wangzhuang reservoir and the Dongli district artificial wetland,the variation of microcystin concentration in the regional water body can be summarized as: Summer > Autumn > Spring > Winter,irrespective of the eutrophication state and the division of water function area in the study area,providing support for the establishment of scientific early warning mechanisms for the prevention and treatment of microcystins.(4)The study found that the constructed wetland system had a stable removal effect on the low concentration of microcystins in the raw water,with an average removal rate of 57.34%.The removal of microcystins between various plant combinations,phragmites communis / lythrum salicaria / irises,typha latifolia / lythrum salicaria /leaf reeds / irises,and phragmites communis / lythrum salicaria,and the average removal rates were 58.9%,57.5% and 62%,respectively.(5)The reduced graphene oxide with thickness of 8nm was prepared by high temperature thermal reduction after spin coating.According to the polarization dependent absorption properties of graphene under total internal reflection,an optical immunosensor was developed for the detection of microcystins.The sensor had good sensitivity and reproducibility,which is 0.08V/(μg/L)and 3.7% respectively.It also had a good linear relationship with the MC-LR concentration of microcystins as 0.15-5μg/L.The average recovery rate of water samples and water samples in reservoirs were between 80% and 106%,which showed good prospects for application.