[Vertical distribution pattern and ecological risk assessment of heavy metals in a sediment core from Pumoyum Co, Tibet]

The sediment core was collected in Pumoyum Co, a lake located in southern Tibetan Plateau, in July 2008. Samples were digested using microwave equipment and analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), to determine the content of heavy metals in the sediments. The average concentrations for Cr, Co, Ni, Cu, Zn, Cd, Pb, Mn and Fe were 26.4 μg x g(-1), 6.64 μg x g(-1), 16.2 μg x g(-1), 26.2 μg x g(-1), 50.2 μg x g(-1), 0.363 μg x g(-1), 16.8 μg x g.(-1), 0.302 mg x g(-1) and 9.84 mg x g(-1) , respectively. The concentrations of analysed metals in Pumoyum Co were slightly higher than those in Antarctic, but lower than those from Dianchi in Yunnan, Daihai in Inner Mongolia, the Great lakes in North America and Taihu in China, which were obviously affected by anthropogenic activities. Overall, these metals in sediments from Pumoyum Co represented a low concentration level. Vertical profiles of heavy metals in the sediment core kept stable without large fluctuation and the concentrations in surface slices were relatively higher. Results of principle component analysis and cluster analysis indicated that organic matter and Mn were affected by surface runoff markedly while other metals were mainly correlated to natural diagenetic weathering and atmospheric deposition. Sediment quality guideline and potential ecological risk index were introduced to assess sediment quality and both of their results indicated that the Pumoyum Co as a whole can be ranked as low potential ecological risk.