| The rapid development of industry not only brings abundant material wealth to human society, but also causes environmental pollution. As an unbiodegradable contaminantsand, heavy metals exists persistently in all the environment and biological systems, therefore causes global contaminations, and presents a great threat to human health and ecosystem. Lake sediment is an important storage of heavy metals, so the study on the variation of heavy metals in sediment is very beneficial to explore their migration and transformation in enviroment, as well as to ensure the safety of ecology and human, and to provide reference industrial layout planning.Yangzong lake, one of the nine lakes in Yunnan Province which is in a mining and industrial region has experienced both steady and abrupt heavy metal pollutions during last decades, especially the catastrophic Arsenic pollution occurred in 2008 exerts a strong impact on both local water-ecology and the administration measurement adoption. In 2013, a 60 cm long sediment core was taken from the center of lake(24°54’24.21’’ N,103°00’19.99’’ E), all samples in core was sliced into sub-samples and kept into the polyethylene bags and vacuum freeze-drying for analysis. Using 120 Pb and 137 Cs method and CRS model, the chronology of sediment core was established. Heavy metal pollution history in the Yangzong Lake during last 200 years was discussed and we reach the following conclusion.(1) In the laboratory, accurately weighed samples were digested with HCl-HNO3-HClO4, this incomplete digestion method without hydrofluoric acid(HF) have been verified by our experimental. The concentration of heavy metals and the stable isotopes of lead were analyzed by Inductively Coupled Plasma Mass Spectrometry, and the analytical average recovery was 95%- 105% with RSD of less than 5% for all the heavy metals. This experiments show that our method is feasible.(2) The results showed that concentrations of metals Cr in sediment varied from 33 mg/kg to 116 mg/kg; Co varied from 10.89 to 69.30 mg/kg; Ni varied from 20.19 to 69.30 mg/kg; Cu varied from 86.46 to 223.19 mg/kg; As varied from 35.44 to 479.12 mg/kg; Cd varied from 3.04 to 10.47 mg/kg; Pb varied from 32.61 to 147.72 mg/kg; Zn varied from112 to 523 mg/kg respectively.(3) Using Geoaccumulation index(Igeo) to evaluate the contamination of heavy metals. The Igeo threshold of trace metals As, Cu, Cd, Zn and Pb is exceeded the risky threshold. The results indicated that pollution intensity of As was very serious, and pollution intensity of Pb, Zn and Cd was serious, but no evidence of contamination of Cu, Cr, Ni and Co.(4) Factor analysis(PCA) has been used to explore the different element associations and possible geochemical controls or lacustrine input affected by terrestrial anthropogenic impact in the catchment. The Yangzong Lake was experienced both steady and abrupt heavy metal pollutions during last decades and the sedimentary environmental process can be divided into three periods.(5) Combining the stable isotopic composition of Pb with concentrations results in surface sedment, the result show that the metal Cr mainly originated from the erosion of soils in the catchment, and similarly, Co, Ni and Cu are also derived from natural sources mainly, but they had different input pathways. Atmospheric trace metal of Pb might be considered as a result of non-point sources from some industrial activities, among them Pb, Cu, Zn and Cd related to the coal and ores consumption from nearby aluminum manufacturer and thermal power plant. As mainly derived from point sources including untreated wastewater and impact of rain from junkyard.(6) Despite the water quality has been improved and the concentration of heavy metals reduced after harnessing and protection management, it is necessary to establish a complete environmental monitoring and protecting system, especially when the natural lake system has been strongly altered or even destroyed. |
PDF Full Text Request