Status Of Pollution By Heavy Metals In A Uranium Mining Area And Screening Of Plants For Heavy Metal Concentration

Soil is the fundamental material base on which humans live. If the soil is contaminated, it causes problems with respect to food safety, forest productivity and general environmental health. Our country is extremely short of usable land, and much of the land is polluted by waste products from mining activities. Since the 1960 s, more than ten uranium tailing ponds have been built as part of the construction and development of uranium mines and the metallurgy industry in China. These uranium tailings bring huge potential hazards. Therefore the phytoremediation of lands polluted by heavy metals and radioactivity in uranium tailings is an urgent topic for research. Phytoremediation of the soil occurs when plants remove heavy metals from the soil. We separated the plants into two groups: plants that concentrate heavy metals at levels higher than in the soil(the enrichment coefficient>1) are called plants for heavy metal concentration; and plants that take up heavy metals at levels lower than in the soil and the enrichment coefficient is less than and equal to 1 are called plants for heavy metal high uptake.The objective of this study was the analysis of soil, water and plants collected from the area around the uranium processing plant, the tailings dam and the waste residue contained within the tailings pond. Using field investigation and laboratory analysis as research methods, the dominant plants in the uranium mining area were gathered and identified. The content of heavy metals(U, As, Cd, Cr, Cu, Ni, Pb and Zn) in soil, water and plants was analyzed by ICP-AES. Statistical analysis was carried out using SPSS17.0statistical software, and the level of significance was set as ? = 0.05. The differences of the heavy metal content in soil, water and plants in different regions were compared by analysis of variance and the post-hoc Tukey test with all the data tested for a Gaussian distribution. The correlations of heavy metals in soil, water and plants were determined by the Pearson correlation coefficient. The pollution status of the heavy metals in soil and water was evaluated according to the single factor pollution index, the Nemerow composite index, the heavy metals accumulation index and the potential ecological pollution index. Plants that accumulated heavy metals in concentrations greater than those in the soil, and those that absorbed heavy metals in concentrations below those in the soil were screened by the enrichment coefficient, the transfer coefficient, the root retention rate and national background values of heavy metal elements.The main conclusions are as follows:(1) The soil from the area around the uranium processing plant, waste residue and the tailings dam is all highly polluted by heavy metal elements, and the degree of pollution is tailing dam > the area around the uranium processing plant > the waste residue. The soil from all 3 areas was found to be polluted by U, Cd, Pb and Zn. The pollution indices used indicate that the amounts of U and Cd are in the very highly toxic range, and the amounts of Pb and Zn are in the highly toxic range. The area around the uranium processing plant and the waste residue are also polluted by Cu, and the tailing dam is also polluted by As;(2) The water from the area around the uranium processing plant, waste residue and tailing dam is highly polluted by heavy metal elements, and the degree of pollution is the waste residue> the area around the uranium processing plant > the tailing dam. The water from all 3 areas was found to be polluted by U; The waste residue is also polluted by Cd,Ni and Zn; The tailing dam is also polluted by Cr;(3) Pennisetum alopecuroides can concentrate As, Cu, Ni, Pb and Zn, and can take up U;Commelina communis can concentrate As, Cu, and Ni, and can take up Pb and Zn;Erigeron annuus can concentrate As and Cu, and can take up Zn;Pteris multifida can concentrate As, Cu and Pb, and can take up U and Zn;Aristolochia debilis can concentrate As and Cu, and can take up Zn;Eleusine indica(L.) Gaertn can concentrate As, Cu and Zn,and can take up U;Pokeberry Root can concentrate As, Cu, Ni, Pb and Zn, and can take up U and Cd; Bidens frondosa can concentrate Cu, and can take up Cd; Polygonum hydropiper and Miscanthus floridulu can concentrate Cu;(4)The positive correlations were significant or extremely significant between Zn and U,Cd, Pb, Ni, As and Cu, and between Cu and U, Cd, Pb, Ni, and Zn in the soils of the area around the uranium processing plant, the waste residue and the tailings dam. This suggests that plants can increase the absorption of U, Cd, Pb, Ni and As by increasing the absorption of Cu and Zn.In conclusion, restoration effects can be greatly enhanced if plants can be used to take up and concentrate heavy metals from the soil, thereby helping with the decontamination of the soil.