Evaluation On Heavy Metal Contamination In Some Typical Mine Zone Soils In Hunan Province And Research On Chemical Amelioration Of Heavy Metal Contaminated Soils And Soybean Planting

In order to analysis and evaluation heavy metal pollution of soybean and soybean planting soils round some mine zones in Hunan province, sampling and surveys were conducted in Shizhuyuan and Baoshan in Chenzhou, Qingshuitang in Zhuzhou, Shuikoushan in Hengyang. At the same time, experiments of chemical amelioration of heavy metal contaminated soils with calcium carbonate and hydroxyapatite and soybean planting were conducted in Shizhuyuan (Chenzhou) and Shuikoushan (Hengyang). The purposes of these experiments were to study the effects of calcium carbonate and hydroxyapatite addition on exchangeable Pb, Cd, Zn contents in the tested soils, to analysze and compare the effects of calcium carbonate and hydroxyapatite addition on biomass of soybean plants and accumulation and distribution of heavy metals in each organs of soybean plants. The primary results of the experiments were as follows:(1) Among the 21 soil samples collected,11 samples were polluted with single Cd, and the rset 10 samples were polluted with Pb and Cd. No serious Zn pollution was found in these samples. The 5th sample in Guiyangbaoshan in Chenzhou was found the most serious polluted by heavy metals in all 21 samples. The soybean seeds from 6 soil sites were subject to a complex pollution of Pb, Cd, and Zn pollution to some extent, and the rest 15 samples were subject to a serious pollution of Pb and Cd. The contents of Pb and Cd in all samples exceeded national standards of contaminants in foods.(2) Significant or highly significant linear relations were found between exchangeable Pb, Cd, and Zn contents in soils and contents of Pb, Cd, Zn in different organs of soybean plants. Thus, we could generally calculate Pb, Cd, Zn contents in different organs of soybean plants, and simply evaluate security on soybean by measuring exchangeable contents of heavy metals in soils.(3) Application of calcium carbonate and hydroxyapatite to contaminated soils in Shizhuyuan (Chenzhou) and Shuikoushan (Hengyang) reduced contents of exchangeable Pb, Cd, and Zn in the soils, and exchangeable Pb, Cd, and Zn contents in soils decreased obviously with increase in amount of calcium carbonate and hydroxyapatite. The growth conditions of soybean plants were improved greatly, and the absorption of Pb, Cd, Zn from soils onto soybean plants were inhibited effectively due to addition of calcium carbonate and hydroxyapatite, so as to reduce toxicity of soil heavy metals to soybean plants and biomass soybean increase greatly.(4) The optimal amount of calcium carbonate was 2.0 g·kg-1, which made yields of soybean seeds increased 47.5% in Shizhuyuan (Chenzhou), Pb and Cd contents in soybean seeds decreased 73.0% and 53.8%, respectively. Meanwhile, yields of soybean seeds increased 26.4%, Pb and Cd contents in soybean seeds decreased 51.8% and 47.5%, respectively, in Shuikoushan (Hengyang). The optimal amount of hydroxyapatite was 4.0 g·kg-1, which made yields of soybean seeds increased 57.8% in Shizhuyuan (Chenzhou), Pb and Cd contents in soybean seeds decreased 72.7% and 12.3%, respectively. Meanwhile, yields of soybean seeds increased 23.9%, Pb and Cd contents in soybean seeds decreased 70.8% and 5.9%, respectively, in Shuikoushan (Hengyang). Although application of calcium carbonate and hydroxyapatite to the contaminated soils could reduce effectively heavy metal contents in soybean seeds, Pb and Cd contents in soybean seeds were still higher than the national standards in foods of 0.2 mg·kg-1.