Abstract: The Taihu Lake is the third largest fresh water lake in China.Recently,it has seen heavy cyanobacterial blooms in the lake almost every year.Samples of cyanobacteria were collected from Nanquan area of the Taihu Lake in July,September and October 2008 for analysis of contents of 19 elements(Na,Mg,K,Ca,Zn,Mn,Fe,Al,Cu,Cr,Co,Ni,As,Se,Mo,Ag,Tl,Cd and Pb) therein and variation of the composition,using an Agilent 7500ce inductively coupled plasma mass spectroscopy(ICP-MS).All the 19 elements,except for Tl,which was undetectable,evidently accumulated to varying levels in the cyanobacteria.The concentrations of Ca,K,Na,Mg,Al and Fe were commonly>1 000 μg·g-1 dry weight(esp.Ca and K were>4 000 μg·g-1 dry weight).From July to October,Ca remained relatively stable in concentration,while K,Mg and Na gradually increased.The concentrations of Al and Fe were the highest in July,but dropped sharply in September.Mn,Zn,Ni,and Cu,found to be moderate in concentration(10-100 μg·g-1 dry weight),peaked in July and bottomed in September and October.In contrast,Co,Mo,and Se were measured to be low in concentration(<1 μg·g-1 dry weight).And some toxic elements As(5-15 μg·g-1 dry weight),Cr,Cd,Pb and Ag(<5 μg·g-1 dry weight) were detected in cyanobacteria,and usually peaked in concentration in July.Based on the aforementioned results and the provincial government reports on the physical removal of cyanobacteria in the Taihu Lake in 2007-2009,it is estimated that approximately 595.89 t of K,544.03 t of Ca,181.18 t of Mg,83.06 t of Al,63.97 t of Na,55.45 t of Fe,2.99 t of Mn,2.26 t of Zn,1.67 t of Ni,1.11 t of Cu,0.76 t of As,94.5 kg of Cr,82.70 kg of Cd,45.01 kg of Se,37.64 kg of Pb,32.27 kg of Co,5.41 kg of Mo and 2.46 kg of Ag were consequently removed from the Taihu Lake during the same period.The findings of this study may serve as fundamental insights for further investigation of the elemental effect on the occurrence and development of cyanobacterial water blooms,and furthermore,provide important evidence for making use of the bioaccumulation properties of cyanobacteria to reduce toxic element loads and conserve the fishery environment of the Taihu Lake.

Key words: Taihu Lake, water-bloom cyanobacterium, bioaccumulation, element