Accumulation, Sources And Ecological Effect Of Heavy Metals In Multi-medium Along Yangtze River Of Nanjing

There were lots of surveys and researches about soil environmental geochemical in our country, which had been revealed that the concentrations of heavy metals in the soil, such as Cd along Nanjing Yangtze River region was anomal. However the causes of heavy metals anomalies, ecological effects and health risks to humans had not be concluded. Therefore the significance obviously is there for carrying on studying about accumulation characteristic,sources and ecological effect of heavy metals in multi-medium along Yangtze River of Nanjing,which has important reference value of risk assessment of heavy metals in soils and environmental management as well. A area along Yangtza River of Nanjing was selected as a case study area in this research. Concentrations of heavy metals and isotopic ratios in topsoil, surface sediment, soil and sediment profiles, plants, fertilizers and atmospheric deposition were measured for analysis of spatial variation of soil heavy metal anomaly. Positive matrix factorization (PMF) model and multivariate statistical analysis were applied as tools to identify the main sources of heavy metals in the topsoil of a typical vegetable production base. The results have also been compared with those obtained through Pb stable isotopic technique. Geo-accumulation index, and human body heavy metal risk of plant consumption were used to assess the heavy metal accumulation risk of soil, sediment and plant, human intake of risk assessment. Results are as follows:(1) Mean value of cadmium (Cd), arsenic (As), mercury (Hg), lead (Pb), copper (Cu), zinc (Zn) and chromium (Cr) in topsoil were greater than their respective soil background values in Nanjing. Concentrations of Cd, Hg and Cu in some soil samples were greater than the Grade ‖ of the Standard according to the Soil Environmental Quality of China, implying higher heavy metals accumulations in the soils. The average content of Cd, As, Hg, Pb, Cu, Zn, and Cr in surface sediment was 0.65,15.8,0.13,42.1,45.8,124 and 85.3mg/kg. Mean Concentrations of As、 Pb、Cu、Zn and Cr were found to be above the criteria of environmental protection agency(EPA) of US. Anthropogenic factors(AF) is slightly lower than the enrichment factor (EF) of soil heavy metals in the area along Nanjing Yangtze River,AF was significantly lower than EF of sediment heavy metals.(2) The contents of Cd and Pb in tuber vegetable, Pb and Cr in rice,Cr in leafy vegetable and wheat were 0.15,0.13,1.07,6.95,0.78 and 1.39mg/kg, respectively, which were over standard of maximum level of contaminants in food (GB2762-2005). Concentrations of Cd, Pb and Zn in tuber vegetable were higher than leaf vegetable and fruit vegetable, but concentrations of As, Hg, Cu and Cd in leaf vegetable were higher than others.(3) Heavy metal contents in agricultural area of Baguazhou and industrial area along Yangtze River of Nanjing were generally high. Spatial distribution of the heavy metals in topsoil of agricultural district in Baguazhou, except Cr, was characterized by a trend of tending to be higher in the southeast and lower in the northwest, which was consistent with the spatial distribution of soil organic matter. The contents of heavy metal in sediment showed an overall upward trend from upstream to downstream in Yangtze River, moreover, Baguazhou agricultural area and industrial area heavy metals in sediment contents were significantly higher than other regions. Heavy metal content in sediment profiles of Baguazhou agricultural area was generally high, including in the underlying sediment.(4) Four sources were obtain by PMF model, agricultural, dust, industrial and natural source, which contribution rates were 30.8%,33.0%,25.4% and 10.8%, respectively, the contribution of atmospheric deposition to the heavy metal accumulation in the soils through PMF model and Pb stable isotopic technique were similar. Accumulation and distribution of the heavy metals in the soils was also related to the terrain, the layout of agriculture and industry, the perennial dominant wind direction, traffic pollution, and soil parent material in the study area.(5) Geo-accumulation index of Cd in sediments of industrial land was 0.04, which reached slight-medium pollution, the sample of contamination was 23.0%. The degree of monomial potential ecological risk factor of Cd and Hg was moderate potential ecological risk. Health risk of heavy metals via rice consumption was significantly higher than others.