Heavy-metal accumulation trends in Yixing, China: an area of rapid economic development

Geochemistry of soils encapsulated by urban development and dendrochemistry were evaluated to reconstruct heavy-metal accumulation trends in an area of rapid economic development in China. The urban-covered soil spans a time period of 56 years from 1950 to 2006, and the tree cores cover the period from 1977 to 2006. Results from the six heavy-metal elements (Cd, Cr, Cu, Ni, Pb, and Zn) analyzed in this study indicate that heavy-metal concentrations increase significantly in urban-covered soils dating from 1980, which is corroborated by data from corresponding tree cores. The accumulation rates of Cd, Cr, Cu, Ni, Pb and Zn (1980–2006) were estimated at 0.91, 0.84, 1.42, 1.39, 1.34 and 1.86% per year, respectively. These high rates of accumulation suggest that anthropogenic sources resulting from rapid economic development led to the magnitude and rates of heavy-metal accumulation. Although reconstruction of heavy-metal accumulation trends using the urban-covered soils (substitutes space for time) introduces some uncertainty when compared with long-term experiments, this study demonstrates that urban-covered soils can provide a vehicle by which historical rates of heavy-metal accumulation can be approximated.