| The heavy metals pollution in paddy soils, especially the edible portions of agricultural products pollution was taken more attention by pedologists and environmentalists. Due to the complexity of the pollution sources and the seriousness of the pollution degree, it is not easy to move the polluting sources out and hard to avoid utilizing the polluted soils. Therefore, it necessary to study the control and security utilization of heavy metals pollution soil in industrial and mining area. Moreover, the characteristic of heavy metal transfers in soil-rice system should be researched by multipoint corresponding study from field in study areas, which can supply scientific evidences to control and utilize safely the polluted soils.Taking the farmlands of industrial and mining area that located in central Hunan province as the research object, Geostatistical methods were applied to collect the topsoil of paddy soils (red soil and purple soil parent material) and the rice plants of the corresponding points from field. The Pb, Cd and Zn concentration of soils and rice plants and the basic properties in the topsoils were analyzed. The Single Factor Pollution Index was applied to evaluate heavy metal pollution in soil; the ecological risks of soils were discussed by the method of Potential Ecological Risk; while the brown rice health risk assessment was explored by the method of health risk assessment that human exposure to heavy metals. The enrichment factor, transfer factor, accumulation factor were used to study the characteristics of heavy metal transfer in soil-rice system.The main results of the study were summarized as follows:(1) The paddy soils of study area were polluted seriously by heavy metals, and the pollution degree of heavy metals followed the sequence as Cd> Pb> Zn. The assessment results from Single Factor Pollution Index showed that there were100%,96.02%,99.50%of sampling sites in proportion belonging to serious pollution level for Cd, Zn, and Pb, respectively. The assessment results from Potential Ecological Risk showed that most of sampling sites were at light ecological risk level for Zn, Pb, while most of sampling sites were at extremely high ecological risk level for Cd. Integrated Potential Ecological Risk Index of three heavy metals presented that44.78%of sample sites was at higher level in the tested area.(2) The brown rice was polluted by heavy metals Cd and Pb in the study area. Based on the agricultural industry standard of the People’s Republic of China (NY419-2006) and the limited standards of pollutants in food (GB2762-2005), we found that the over standard rate of Cd, Pb in brown rice were90.36%,83.13%, but Zn was0. The assessment results from brown rice health risk showed that there were86.75%,3.61%of sampling sites in proportion having health risks for Cd, Pb respectively, and none of them has Zn health risks.(3) Geostatistical methods were applied to study the spatial distribution features of heavy metals in soils. From Ordinary Kriging interpolation map, we can see that the northwest and southeast of research area were suffered seriously Zn and Cd pollution, but the serious Pb pollution appeared in east. The content of three heavy metals increased from west to east gradually. In order to study the characteristics of heavy metals’ vertical distribution of soils, the soil profile samples were collected. The result showed that the content of heavy metals decreased as the increasing of soil deep, the content of Cd and Zn went to stable when the soil deep is50cm, while Pb was in40cm.(4) According to the heavy metals content of different organs in rice plants, we found that the order in brown rice was Zn> Cd> Pb, while the root, stem leaf and husk were Zn> Pb> Cd. The results showed that the order enrichment factor of heavy metals in the rice organs was root> stem> husk>brown rice. The order enrichment factor of heavy metals in root was Cd>Pb>Zn, while stem leaf, husk and brown rice were Cd>Zn>Pb. There is a significant correlation between content of Cd in rice plants and total content and available content of Cd in soils, and the same result found on Pb. The content of heavy metals in different orangs of rice plant may have definite correlation with soil physicochemical properties.(5) The factor of heavy metal transfer in soil-rice system (TF for short) is the rate of the elements’ cumulant in plants and the corresponding elements’ total content in soils. While the factor of heavy metal accumulation (AF for short) is the rate of the element’s cumulant in the edible part of plants and the corresponding elements’ content in result showed that the heavy metal transfer factors in soil-rice system and the accumulation factors of brown rice were different in different parent material soils. The TF of Pb, Cd and Zn in soil-rice system is0.088%,0.537%,0.141%respectively; when the rice roots were not included, the TF of Pb, Cd and Zn is0.020%,0.260%,0.086%respectively. The TF of Pb in purple soils was significantly greater than in red soils, but not did for Cd, while the Zn was not more significant in red soils than in purple soils. But when the rice root was not included, the Pb TF was significantly greater in purple soils than in red soils, and not did for Cd and Zn. The AF of Pb, Cd and Zn in brown rice was0.33%,6.53%,7.44%respectively. The AF of Cd in red soils was significantly greater than in purple soils, but did not found the same rule to Cd and Zn, the Cd in red soils was not more significant than in purple soils, while the Zn in purple soils was not more significant than in red soils.When the heavy metal polluted soils were remediated and controlled or reused safely, the soil type should be taken into consideration, at the same time, the feasibility of technology should be taken into account. The quantity of Pb, Cd and Zn which were taken away is0.30kg,0.07kg,1.60kg, respectively, by harvesting aerial part of rice (which include rough rice and straw) per hectare annually. And the removal amount of Pb, Cd and Zn only accounted for0.02%,0.26%,0.09%of total content of soils, respectively. Therefore, there is a great limitation to remediate the heavy metal polluted paddy soils only by harvest, the measures that combine physical, chemical and biological technologies should be taken. |
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