Investigation and Evaluation of the Heavy Metal Pollution in Farmland of A Typical County in Yangtze River Delta

The contents of Cr, Cu, Zn, Pb, As, Hg and Cd in the farmland of a typical county in Changshu city in Yangtze River delta were investigated through widespread sampling soils close to the factories. The results showed that the contents of heavy metals in topsoil (0~20 cm) were significantly higher than that in the subsoil (20~40 cm). The ratio of Cd, As, Cu, Zn, Pb, Hg and Cr content in the topsoil to the subsoil averaged 1.81, 1.46, 1.30, 1.30, 1.15, 1.14 and 1.03, respectively, which suggested an accumulation trend of the heavy metals in the topsoil. The content of heavy metals in the soils varied among different districts, and was higher in the south-west part than that in the north-east part in Changshu city. Among the heavy metals, Hg pollution was the most serious one, followed by Cu, Cd, Zn, and Pb. No pollution of As and Cr was found in the soils investigated according to the monomial pollution index. As estimated by Nenerow aggregate pollution index, the P value was 0.93, which indicated the comprehensive pollution status of heavy metals in soils, suggested that the soils investigated in Changshu city were generally clean according to the standard of the second grade of GB 15618-1995.