AN EVALUATION OF THE HEAVY METAL CONTENT IN THE PLOUGH LAYER AND CROPS IN SOUTHERN JIANGSU PROVINCE

In the water system of the Taihu Lake in southern Jiangsu Province,the authors collected 3121 samples from the 0~ 20 cm plough layer soil as well as 103 samples from the seeds and root soil of rice and wheat within an area of 676 km2. The authors measured the concentrations of such heavy metals as As,Cd,Cr,Cu,Hg,Pb and Zn as well as physical and chemical indicators such as the pH value. According to the statistic analysis of these samples,the authors have found that the average content of heavy metals in these areas is richer than the average level of Jiangsu Province except for As and Hg. Compared with the Mid-II Criteria of State Soil Quality Standard( GB156018-1995),the level of pollution is HgCdCuZnAsPb. In terms of the distribution of pollutants,Hg mainly shows sheet pollution,while Cd mainly assumes point pollution. According to an analysis with Nemerowint pollution index method,the plough layer soil close to the urban area is on alert mainly for the sake of Hg,Cd and Cu,while the degree of pollution of plough layer soil in other areas is in the safe range. According to Standard GB2762-2005 and Standard NY861-2004,the content of As,Cd,Cr,Hg and Pb in rice seeds and the content of Cd,Zn and Pb in wheat seeds in the study area exceed the upper limits of the standards. Studies show that Cd,Cu and Hg in rice seeds and Cd and Cu in wheat seeds are positively related to the content of these heavy metals in the soil,suggesting that the heavy metals in crops mainly come from the soil. In contrast,other heavy metal pollutants may be mainly derived from other sources such as dustfall,irrigation,fertilizer and pesticides. The pH value of soil is negatively correlated to the content of As,Cd,Cu,Hg and Zn in rice seeds,negatively correlated to the content of Zn and Cd in wheat seeds,and positively related to the content of other heavy metals. According to the correlation analysis,As and Hg mainly come from the parent material,whereas the excessive Hg also reflects the effects of human activities. The content of other heavy metals is also significantly affected by human activities.