Assessment of heavy metal contamination of surface soils from typical paddy terrace wetlands on the Yunnan Plateau of China

Little research has been done to investigate heavy metal contamination in paddy soils along different altitudes under domestic sewage irrigation. Total concentrations of As, Cr, Cd and Pb were determined in surface paddy soils from Mengpin (MP) and Quanfuzhang (QFZ) paddy terraces on the Yunnan Plateau of China in December, 2004, in order to assess their contamination status. Results showed that the average concentrations of As and Cd in both terrace soils were significantly (p < 0.01) greater than the reference concentrations, while lower for Pb in both soils. However, as for Cr, the average concentrations are higher in MP soils while lower in QFZ soil than the reference concentration, while. Compared with MP soils, QFZ soils had lower heavy metal concentrations. However, only Cd greatly exceeded the guide value of soil quality. The contamination factor (Cfi) values were generally moderate for As and Cd, and low for Pb in both sites. As for Cr, they were moderate in MP soils but low in QFZ soils. The contamination degree (Cd) values were generally moderate, showing a decreasing tendency along the increasing altitudes in MP terrace, while slowly increasing tendency in QFZ terrace.