Spatial-Temporal Variation And Source Apportionment Of Soil Heavy Metals In Peri-Urban Area

Peri-urban areas are not only a buffer protecting the zoology, environment, and climate of a city, but also a supplier of large amounts of food to city residents and a dump site for disposal of city waste and garbage as well. Our country is in a rapid promotion of urbanization and industrialization, and the economic development is also in a fast speed. The peri-urban area is facing a increasingly serious problem of soil heavy metal pollution. Therefore, it is urgent to carry out the investigation of soil heavy metal in peri-urban area.In this paper, based on early research data of top soil and related data of the peri-urban area of Nanjing, field investigation and 109 samples collecting was carried out. Contents of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn was analysis in laboratory. Combined with GIS and related standard of soil heavy metal content, this paper carried out the following research:The characteristics of soil heavy metals content and spatial-temporal variation was explored by the Inverse Weighted Distance interpolation and Raster Calculator. By the method of single factor pollution index, Nemerow pollution index and potential ecological risk index, pollution characteristics of soil heavy metals was obtained. The status of environmental capacity of soil heavy metal was estimated and evaluated by single factor and comprehensive environmental capacity index. Through the correlation analysis, principal component analysis and the spatial quantitative analysis method, the probable source of soil heavy metals was confirmed. The content and capacity characteristics of three time points as 2022,2032 and 2042 were predicted by the dynamic environment capacity theory.The results show that:average content of 8 heavy metals of the peri-urban area of Nanjing was 14.0,0.20,77.6,44.7,0.17,33.9,36.2,103.7mg·kg-1. Both of the 8 heavy metals are showing a general accumulation phenomenon. The concentrations of 8 heavy metals are below the green standard in most of the area, but less to maintain regional background level. Meanwhile, the edible agricultural products without pollution can be basically ensured. The Nemerow pollution index was at Alert level while the potential ecological risk index was at a slight ecological risk level. Compared with 2002, heavy metal accumulation of varying degrees appeared in most of the area while parts with intense human activity at a fast speed. Concentration rates of 8 heavy metals were 56.91%, 61.06%,6.07%,60.15%,38.69%,19.94%,23.92% and 56.17%. Cd, Cr, Cu, Ni and Zn are concentrated mostly around the towns and factories in general, while Hg and Pb are concentrated mostly around traffic artery, and As was mainly concentrated in the rural areas.The existing environment capacity of 8 heavy metals of the peri-urban area of Nanjing are 36.13,0.223,387.81,12.03,0.301,13.66,481.05,216.59 kg·hm-2, while their environmental capacity index are 0.83,0.90,0.90,0.30,0.74,0.48,0.95,0.78. As, Cd, Cr, Hg, Pb and Zn are on middle capacity level, while Cu is on the alert level, and Ni is at the low capacity level. The comprehensive capacity index is 0.74, showing that the soil of the whole study area is on middle capacity level and slightly polluted. In 2022,2032 and 2042, the content of each element is rising, and the environment capacity is decreasing. Compared to 2012, the content growth rate and the environment capacity reduce rate are also increasing. Along with the heavy metal content increasing, the environment capacity will reduce, and there will be more large area confront severe pollution and become the overload region.Cr, Cu, Ni and Zn may be derived from waste discharging of industrial production. Hg, Pb and a part of Zn may be derived from the transportation and the operation of Lukou Airport. Cd and the other part of Zn may be derived from city expansion and the fishery development in the Qinhuai River. As may be derived from livestock and poultry breeding, Sewage discharging and sludge application.Heavy metals in peri-urban area of Nanjing are concentrating in the procession of urbanization and industrialization. We must find where they come from and take actions as soon as possible.