[Soil record of black carbon during urbanization and its environmental implications].

This investigation selected the city of Nanjing, Jiangsu province of China, as the study area, and analyzed the concentrations of organic carbon (OC) and black carbon (BC) of ten soils profiles in three different groups, by wet chemical oxidation methods. The results showed that the concentration of BC ranged from 0.22 g x kg(-1) to 32.19 g x kg(-1) in all urban soil profiles, and the average concentration of BC reached 4.35 g x kg(-1). The average concentration of BC of the first group from ancient residential areas was 0.91 g x kg(-1), and that of the second group affected by ancient industrial activities was 8.62 g x kg(-1), the third group influenced by the modern industrial and traffic emission was 3.72 g x kg(-1). The ratio of BC/OC ranged from 0.03 to 1.59 in all profiles, and the average was 0.29. The average ratio of BC/OC of three groups appeared in this order: the highest exists in the second group, followed by the third group, and the last is the first group. These data mean that some BC particles produced by local biomass and/or fossil fuel burning due to the industrial and transport activities during urbanization are recorded in soils. In addition, the contents of BC and the ratio of BC/OC may reflect different processes of human activities and pollution intensities of urban soils. It is concluded that the soil BC in urban area is mainly coming from fossil fuel burning, more specifically, BC in surface layer (present layer) is mainly from the exhaust particles of motor vehicles (especially diesel engine), while in ancient layer (cultural layer) it is possibly related to the historical coal use.

Historical change of heavy metals in urban soils of Nanjing, China during the past 20 centuries.

Two typical areas, including once commercial and residential quarters of Nanjing, China, were studied by investigating soil properties especially heavy metals of soils in various cultural layers formed in different Chinese Dynasties. The age of the soil profiles was dated by both archaeological and 14C chronological methods. The results showed that urban soils in the old commercial/workshop quarter of Nanjing were generally contaminated by heavy metals Cu, Zn, Pb, but their concentration levels varied significantly among the cultural layers formed in different dynasties. The substantial increase of heavy metals appeared in three historical periods, i.e., South Dynasty (222-589 AD), the earlier Ming (1368-1644 AD) and the late Qing (1644-1912 AD) in one area. The tremendous input and storage of heavy metals in soils was explained by the primitive smelting and the strengthened metal processing activities, which might be due to the requirement of weapon making or other industries, in the changing social conditions of the corresponding periods. Soils in the once noble political, cultural centers did not show significant increase of heavy metals. The difference in the distribution pattern of heavy metals revealed the contrasting history of the site uses. The change of contaminant level in soils is believed to be a reflection of various human activities in the city during the past 20 centuries.