| Heavy metal pollutions were dormant, perennial and irreversible which severely effect human health and ecosystem security. It had been the unfailing research field in environmental science. With human's exploiters to nature, all kinds of pollutants were released to aquatic environment. Sediments were not only the carriers and accumulators of heavy metal, but also the latent pollution resources to environment. It was of great importance in the research on heavy metal pollution extents and distribution rule and tracing potential heavy metal source.Determination of the sedimentary records of metal accumulation can indicate the historical evolution of the anthropogenic impact in the environment and the effectiveness of existing efforts at controlling contaminant input. Meanwhile, the transformation of speciation in sediments was significant in bioavailability evaluation. The change of heavy metal concentration and speciation were closely related to the environmental effect. Research on the variation of metal concentration and speciation transformation was of great practical significance and theoretical value.This paper was focus on Dianshan River which is one of the most important water sources of Shanghai. We study the distribution, speciation and transformation rule of Cu, Cd, Cr, Hg, Pb and As in sedimentary record. In addition, the history of development of industries and agriculture were also taken into account to study the heavy metal pollution history in the study area. The main results were as follows:1. The concentrations of heavy metals in sediments were raged from 16.012 to 60.731 mg/kg for Cu, 0.119 to 4.532 mg/kg for Cd, 10.474 to 57.831 mg/kg for Cr, 33.972 to 83.710 mg/kg for Pb, 43.088 to 145.658μg/kg for Hg and 4.473 to 15.281 mg/kg for As respectively. Concentrations of Cd and Pb were higher than the circumjacent rivers and were not attained the state's standard for the environmental soil respectively.2. The vertical distribution of metals showed that concentration of Cu, Cr, Pb and Hg were decreased with depth and most of their maximal concentration were distributed in the top and upside of the sediment while the minimal concentration were distributed in the bottom and downside of the sediments. Nearly all the metals presented obvious decreasing trend in 0-5cm depth and the decreasing rate were fast. We concluded that because of the aggravating pollutions from human activity, the concentrations of heavy metals increasing vastly. The correlative analyses between the metals showed Cd had no correlation with other metals which indicated its sourse may different from other metals.3. In foundation of evaluations for potential ecosystem risks of heavy metals in sediments of Dianshan River, Cu, Cr, Hg and As were under pollution while Pb and Cd were in different extents of pollution. The geo-accumulation index of Cd and Pb were decrease with depth which indicated the pollution of Cd and Pb become more severely in recent years. This trend was more obviously in the sediment above 9cm depth.4. Metal speciation results showed fraction B1(the acid -soluble fraction) of As, Pb and Cu decreased with depth, fraction B2(reducible fraction) and fraction B3 (oxidizable fraction) together constituted a fairly constant percentage for metals which could indicate a transfer from one fraction to the other. The fraction B4 (residual fraction) of As and Pb decreased with depth while the fraction B4 of Cu showed opposite trend. The changes of oxidation-reduction potential in sediment were the main cause of transformation between fraction bound to Fe and Mn oxides, fraction bound to carbonates and fraction bound to organic matter and sulfides.5. In the sediments of Dianshan River, As was mainly remain in unavailable fractions, both Pb and Cu were mainly remain in mid- available fractions. Base on the RSP (ratios secondary phase and primary phase) of metals, As was under pollution but its pollution extent was decreasing with depth, Cu was in light pollution and its pollution also decreasing with depth, Pb was in severe pollution and its pollution extent was increasing with depth. Because of the serious pollution of Pb, it would be a potential threatens to the whole ecosystem in a long time. The Ratios secondary phase and primary phase of the metals were compared with the Geo-accumulation indexs of the metals which showed the evaluation for potential ecosystem risk based on metal speciation was more effective than the one based on metal concentration in evaluating the transfer characteristic and ecosystem risk.6. Comparison between the concentration of heavy metal and development of Shanghai indicated the increasing trend in heavy metal was in consistent with the development of industries, agriculture and economy and the population rise. The development of industries, agriculture, economy and the population rise were comparatively slow from early post-Liberation days to reform and opening-up days, meanwhile the increasing rate in metal concentration was also slow. From reform and opening-up days to now, the concentration of metals increasing quickly with the fast development of industries, agriculture and economy.
|
PDF Full Text Request