Temporal-spatial distribution and variability of cadmium contamination in soils in Shenyang Zhangshi irrigation area,China

Heavy metal contamination in soils has been of wide concern in China in the last several decades. The heavy metal contamination was caused by sewage irrigation, mining and inappropriate utilization of various agrochemicals and pesticides and so on. The Shenyang Zhangshi irrigation area （SZIA） in China is a representative area of heavy metal contamination of soils resulting from sewage irrigation for about 30 years duration. This study investigated the spatial distribution and temporal variation of soil cadmium contamination in the SZIA. The soil samples were collected from the SZIA in 1990 and 2004; Cd of soils was analyzed and then the spatial distribution and temporal variation of Cd in soils was modelled using kriging methods. The kriging map showed that long-term sewage irrigation had caused serious Cd contamination in topsoil and subsoil. In 2004, the Cd mean concentrations were 1.698 and 0.741 mg/kg, and the maxima 10.150 and 7.567 mg/kg in topsoils （0-20 cm） and subsoils （20-40 cm） respectively. These values are markedly more than the Cd levels in the second grade soil standard in China. In 1990, the Cd means were 1.023 and 0.331 mg/kg, and the maxima 9.400 and 3.156 mg/kg, in topsoils and subsoils respectively. The soil area in 1990 with Cd more than 1.5 mg/kg was 2701 and 206.4 hnl2 in topsoils and subsoils respectively; and in 2004, it was 7592 and 1583 hm^2, respectively. Compared with that in 1990, the mean and maximum concentration of Cd, as well as the soil area with Cd more than 1.5 mg/kg had all increased in 2004, both in topsoils and subsoils.

Spatial distribution of Cd and Cu in soils in Shenyang Zhangshi Irrigation Area(SZIA),China

Heavy metal contamination of soils,derived from sewage irrigation,mining and inappropriate utilization of various agrochemicals and pesticides,and so on,has been of wide concern in the last several decades.The Shenyang Zhangshi Irrigation Area(SZIA) in China is a representative area of heavy metal contamination of soils resulting from sewage irrigation for about 30 years.This study investigated the spatial distribution and temporal variation of soil cadmium(Cd) and copper(Cu) contamination in the SZIA.The soil samples were collected from the SZIA in 1990 and 2004;Cd and Cu in soils was analyzed and then the spatial distribution and temporal variation of Cd and Cu in soils were modeled using Kriging methods.The results show that long-term sewage irrigation had caused serious Cd and Cu contamination in soils.The mean and the maximum of soil Cd are markedly higher than the levels in second grade standard soil(LSGSS) in China,and the maximum of soil Cu is close to the LSGSS in China in 2004 and is more than the LSGSS in China in 1990.The contamination magnitude of soil Cd and the soil extent of Cd contamination had evidently increased since sewage irrigation ceased in 1992.The contamination magnitude of soil Cu and the soil extent of Cu contamination had evidently increased in topsoil,but obviously decresed in subsoil.The soil contamination of Cd and Cu was mainly related to Cd and Cu reactivation of contaminated sediments in Shenyang Xi River and the import of Cd and Cu during irrigation.The eluviation of Cd and Cu in contaminated topsoil with rainfall and irrigation water was another factor of temporal-spatial variability of Cd and Cu contamination in soils.