Application of Pb isotopic geochemical mapping to establishment of environmental background and pollution sources

Based on great quantity of lead isotopic data of rocks and ores derived from various mantle and crust in Continental China, and global comparison of isotopic and elemental system, the indexes and mapping methods of isotopic geochemistry for the division of geochemical provinces are proposed. The major geochemical provinces in Continental China and their geochemical steep zones, i.e. boundaries, have been established through large scale mapping of lead isotopic vectors. The division of geochemical provinces can not only provide important basis for the paleo-continent reconstruction, geochemical exploration and evaluation of resources, but also can be applied to establishment of environment background and pollution sources. Quantitative criterion of lead pollution sources and levels from Lead isotopic tracing must be dependent on well establishment of natural Lead isotopic background. The results of lead isotopic mapping in the South China Sea showed two depositing areas: sediments from the Red River were related to the Indo-china geochemical province and sediments from the Pearl River system were related to the Cathaysia geochemical province. Lead isotopic data indicated that the major lead pollution sources of aerosols in the Eastern China should derive from local Pb-Zn-Cu consumption in various industries.
According to the lead isotopic and element data of aeolian dust, aerosol and soil from urban areas in the Pearl River Delta, China, the atmosphere lead pollution should not only come from automobile exhausts but also from industry. There were clearly different lead isotopic compositions for lead from natural background, pollution of automobile exhausts and industrial pollution. The air pollution of lead in Guangzhou and Foshan showed mixing of two sources between industrial lead from the Fankou Pb-Zn giant deposit and automobile exhaust lead, and the pollution lead in Foshan is mainly from industry. Lead isotopic tracing is a reliable method for differentiating the three different kinds of lead sources and evaluates extent of lead pollution. It was found that the serious lead pollution from automobile exhausts has been incorporated into the soils at least within 10 meters and above the depth of 40 centimeters along the Guang-Fo express way. The Pb concentration of this pollution is about 10-30 ppm. The study of chemical compositions showed that the pollution lead of automobile exhausts was predominately adsorbed in soils and aerosols. The aeolian dusts were mainly composed of aluminosilicates and metal sulfides or sulfates with different molar fractions, which may imply that the industrial pollution lead in eolian dusts was mainly occurred as sulfides. The source regions of aerosols were probably related to homogenous mixing of multi-sources.
The Project was supported by the National Natural Science Foundation of China (40772201).