Temporal-Spatial Distributions and Variabilities of Soil Cd, Pb and Zn in Szia, China.
Lina Sun, Shenyang Key Laboratory of Environmental Engineering, Shenyang Univ, PO Box1041, South Wanghua Street 21, Dadong District, Shenyang, 110044, China and Yaohua Zhang, Liaoning Research Institute of Geology and Mineral Resources, Shenyang, 110032, China.
Sewage irrigation,application of composed pesticides and chemical fertilizers have caused serious soil contamination due to heavy metal accumulation during last decades. The soil contamination caused by Heavy Metals (HMs) induced not only the security problems of ecological systems, but also the menace of food chain. The Shenyang Zhangshi Irrigation Area (Szia, with an area of 28000 ha, located in the west suburbs of Shenyang city, China), is one of the most representative areas of heavy metal contamination due to more than 30-year sewage irrigation with 2.4 - 24 mg kg-1 Cd concentration, 9.4 - 502.2 mg kg-1 Pb concentration and 38 - 532 mg kg-1 Zn concentration, respectively. Even more, the rice Cd concentration was detected from 1.0 to 2.0 mg kg-1. Although Szia had been partly rezoned from crop planting to industry use since 1992, there are still many districts used for planting vegetables and crops currently. In this paper, the spatial distributions and temporal variations of soil Cd, Pb and Zn in Szia were studied using Geostatistical techniques (Kriging package). The results indicated that the long time sewage irrigation had caused serious Cd, Pb, Zn contamination in soils. The frequency distributions and the logarithmic frequency distributions of Cd, Pb and Zn were evidently abnormal. The kurtosis coefficients of Cd, Pb and Zn were 0.608, 0.184 and 1.206 (2004), 14.13, 2.262 and 3.245 (1990) in topsoil, respectively. The skewness coefficients were 0.389, 0.536 and 1.166 (2004), 0.704, 2.231 and 1.211 (1990) in topsoils, respectively. In 1990, the mean and the maximum concentrations of soil Cd were 1.023 mg kg-1 and 9.400 mg kg-1 in topsoils and 0.331 mg kg-1 and 3.156 mg kg-1 in subsoils, respectively, which markedly exceeded the Second Grade Standard of Soil (SGSS) in China (GB15618-1995) but the mean of Cd in subsoils less than the LSGSS ( 0.6 mg kg-1). As for Pb and Zn, the mean concentrations were 109 mg kg-1and 166 mg kg-1 ,which were much more than the upper threshods of background ,and the maximum concentrations were 502 mg kg-1and 532 mg kg-1, respectively, which were also over the the SGSS. In 2004, both of the mean and the maximum concentrations of Cd increased in top/subsoils (from 1.023 mg kg-1 and 9.40 mg kg-1 to 1.698 mg kg-1 and 10.15 mg kg-1 for topsoils, and from 0.331 mg kg-1 and 3.156 mg kg-1 to 0.741 mg kg-1 and 7.567 mg kg-1for subsoils ). For the cases of Pb and Zn, the tendencys were just opposite in the topsoils and same in the subsoils with different extents. The soil dimension with more than 1.5 mg kg-1 Cd concentration increased from 2701 ha (in 1990) to 7592 ha (in 2004) in the topsoils, and from 206.4 ha (in 1990) to 1583 ha (in 2004) in the subsoils. The soil dimensions of Pb and Zn concentrations (more than the SGSS) decreased in the topsoils from 304 ha to 0.00 ha and from 1031 ha to 114.3 ha, respectively. But the soil dimensions of Pb and Zn concentrations (more than the upper threshold of background) increased from 763 ha to 4593 ha and from 619.2 ha to 1273 ha, respectively. Those features may be related to the transportation of contaminated soil by people due to industry development in SZIA and the mobilisation of Cd in contaminated soils and sediments with eluviation of rainfall and irrigation water. Keywords: Temporal-spatial distribution, Soil contamination, Heavy metals, SZIA, China Lina Sun*1,2, Yaohua Zhang3, Ying jiang3, Haibo Li1, Xin Lin1, Yushuang Li1, Hong Wang1 1. Shenyang University,Shenyang 110044, China; 2. Shenyang Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110066, China; 3. Liaoning Research Institute of Geology and Mineral Resources, Shenyang 110032, China