| With the development of industry and agriculture,water eutrophication has become increasingly serious.This has led to the emergence of cyanobacteria blooms,which release algal toxin and other secondary metabolites,causing harm to human bodies and other organisms.The phenomenon has aroused people’s great attention.Therefore,the research and establishment of a method for the rapid detection of multiple trace microcystins(MCs)in environmental water bodies is of great significance to analyze the characteristics of spatial-temporal changes of MCs in key watersheds and lakes in the country,identify the environmental factors affecting the distribution of MCs in water bodies,explore the pollution characteristics and environmental risks of MCs,and take effective control measures.In this research,the ultra-performance liquid chromatography tandem mass spectrometry is adopted to establish an online solid phase extraction research method for simultaneous analysis of eight MCs(MC-RR,-LR,-YR,-WR,-LA,-LF,-LY,-LW)in environmental water samples.The recovery rate of this method is 70%- 120%,and the minimum detection limit of the right MCs is 0.02 ng/L～0.37 ng/L.Compared with the current widely adopted high-performance liquid chromatography tandem mass spectrometry method,only 2 mL environmental water samples with leucine enkephalin as the internal standard is needed for online solid-phase extraction,and the test time is reduced from 25 minutes to 11 minutes,proving more efficient and convenient,with high sensitivity and accuracy.Chaohu Lake(August～December 2020)and Dongting Lake(3rd and 4th quarters of 2020,and 1st quarter of 2021)in the eastern plain lake area,and Dianchi Lake(August～December 2020)and Erhai Lake(August 2020～March 2021)in the Yunnan-Guizhou Plateau are selected as the research objects.Through analysis of the concentration level and spatial-temporal distribution characteristics of MCs,it has been found that in the third quarter,70.00%,23.08%,33.33%and 0.00%of point locations of Dianchi Lake,Erhai Lake,Chaohu Lake and Dongting Lake have over 1.0 μg/L in the total MCs concentration.The mean value of the total concentration of the 8 MCs in each of the points is,from high to low,Dianchi Lake(1.722 μg/L)>Chaohu Lake(1.298μg/L)>Erhai Lake(0.673 μg/L)>Dongting Lake(0.131 μg/L),where MC-LR accounts for the highest proportion,totaling 67.31%,64.46%,60.55%and 32.64%.In the fourth quarter,the mean value of the total concentration of the eight MCs in each of the points is,from high to low,Dianchi Lake(0.323 μg/L)>Erhai Lake(0.233 μg/L)>Chaohu Lake(0.095 μg/L)>Dongting Lake(0.051 μg/L).The detection rate of the eight MCs in the Yunnan-Guizhou Plateau lake area is 60.05%～99.18%.The highest detection rate is MC-LR,and the highest detection concentration occurs in Dianchi Lake in August,hitting 6.156 μg/L.The detection rate range in the eastern plain lake area is 48.92%～95.23%,the highest detection rate is MC-LR,and the highest concentration is found in Chaohu Lake in September,at 2.400 μg/L.The peaks of the total concentrations of the 8 MCs in Dianchi Lake and Erhai Lake appear in August,at 4.104μg/L and 0.852μg/L,respectively,which are earlier than those in Chaohu Lake(2.400μg/L in September)and Dongting Lake(0.201 μg/L in December).Through correlation analysis and redundancy analysis of environmental factors of each lake,it is concluded that within the confidence interval of p<0.05,the MCs of Dianchi Lake keep a significant positive correlation with ammonia nitrogen(0.51),total phosphorus(0.35),chlorophyll a(0.39),algae density(0.33)and nitrogen-phosphorus ratio(0.42),while maintaining a significant negative correlation with pH(-0.37).The MC-LA of Erhai Lake has a significant positive correlation with total nitrogen(0.72),and a significant negative correlation with dissolved oxygen(-0.63).The MC-LY,total nitrogen(0.63)and Chlorophyll a(0.64)have a significant positive correlation.The MC-YR and total nitrogen(0.64)have significant positive correlation.The other four MCs are not significantly correlated with the 10 surveyed environmental factors.The calculated results of the comprehensive human health risk value of the six MCs in each lake show that the MCs comprehensive human health risk index stand at an extremely high risk level in Dianchi Lake in August,and in Chaoju Lake in September,at 5.55 and 6.83 respectively.It is at a high risk level in Erhai Lake in August and in Dianchi Lake in September,at 1.31 and 1.05,respectively.The risk value of MC-RR in Dianchi Lake ranges from 0.13 to 2.24,that of MC-LR ranges from 0.13 to 2.03,and the maximum risk value appears in August.The risk value of MC-RR in Chaohu Lake ranges from 0.13 to 5.25,that of MC-LR ranges from 0.01 to 1.10,and the maximum risk value appears in September.On the whole,Dianchi Lake in the Yunnan-Guizhou Plateau lake area and Chaohu Lake in the eastern plain lake area have high MCs risk values in August and September,with priority given to MC-RR and MC-LR. |
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