Basic results of multi-target geochemical survey in the Nanjing area and its relevant problems

Abstract：The Nanjing area is a typical representative of the very thick Quaternary cover areas in the Yangtze River delta. This paper reports some basic results obtained since multi-target geochemical survey has been carried out in the area. Through experiments, some key technical criteria and requirements have been worked out and generalized. The authors think that it is feasible to take samples from topsoil at a depth of 0 to 20 cm and deep soil at a depth of ≤150 cm respectively, use the –20 mesh fraction of soil and adopt sampling densities of one sample per square kilometer for topsoil and one sample per 4 square kilometers for deep soil. Two belts polluted by some heavy metallic elements exist in topsoil in the Nanjing areas, and marked enrichment of heavy metallic elements in topsoil has direct influence on the safety of crops and vegetables in the study area. At last, the authors discuss a number of questions as to how to determine the geochemical background values in studied soils, how to examine and appraise environmental geochemical anomalies and how to treat the relationship between the total content of some elements and their effective concentrations in topsoil and so on, and propose relevant suggestions.