| Soil heavy metals (Cd, Cu, Pb, Zn, etc.) in Iron and steel enterprises plant area are usually several times of regional soil background value, resulting in a serious of heavy metals contamination. Selection of good heavy metal cumulation plants for ecological restoration is a commonly used biological measure, and screening plant species with a variety of cumulation capacity and adaptable is currently the focus of attention. In this study, siting in the steel mills and coking plant of WISCO, physical and chemical properties as well as the four heavy metals Cd, Cu, Pb, Zn, and other elements in the roots, branches, leaves of20major green plant as well as the soil were measured, the Cumulation factor, cumulation factor, transfer coefficient index of heavy metals in the roots, branches and leaves are calculated, the ability of different plant organs enrichment, comprehensive enrichment and transit capacity are compared, the relationship of plant enrichment characteristics and soil factors are analyzed. The results of the study provide a scientific basis for the ecological restoration in heavy metal contaminated areas in iron and steel enterprises. This study achieved following conclusions:(1) The content of Cd, Cu, Pb, Zn in steel plant soil exceeded the background value of soil in Hubei Province34times,20times,15.7times and11.2times respectively; while in coking plant are39.6times,16times,22times and8.5times respectively. Content of Cd, Cu, Pb, Zn in the soil of these two regions are more than three times of the value in Soil Environmental Quality Standards of The National Standard of The People’s Republic of China (GB15618-1995). This indicates the soil in the plant areas is seriously contaminated.(2) The contents of four heavy metals in plants in Steel Mill are in the order of Zn> Pb> Cu> Cd; while in coking plant are in the order of Zn> Cu> Pb> Cd. This is consistent with the trend of heavy metal content in the soil. The different tolerance mechanisms of plants lead to the different characteristics of the heavy metal enrichment. Different plants can absorb up to51times the same kinds of heavy metals. The cause of the significant difference may be related to soil heavy metal content and interspecific differences.(3) Plants have the strongest cumulation of Zn, Cedrus deodara has strong cumulation of Cd; Viburnum awabuki has strong cumulation of Cd, Zn; Oxalis corymbosa has strong cumulation of Cu, Zn; Eribotrya japonica has strong cumulation of Cu and Pb; Nerium oleander has strong cumulation of Pb and Zn; Reineckea carnea has strong cumulation of Pb; Prunus cerasifera, Syringa pubescens, Ligustrum lucidum, Photinia serrulata has strong cumulation of Zn. All these plants’ metal cumulation factors are greater than0.5, in which Viburnum awabuki on Cd has the greatest cumulation factor, reached0.741. Cedrus deodara, Viburnum awabuki, Eribotrya japonica, Nerium oleander, and Ligustrum lucidum grow well in plant areas in WISCO, and have strong resistance, fewer pests and diseases, which are ideal species to repair the heavy metal pollution in the region. The cumulation factor of Privet and auspicious grass on Cd, oleander on Pb, Mahonia Fortunei and Camellia japonica on Zn is close to0.5, which have a certain potential for repairing contaminated soil. Cinnamomum Camphor, Magnolia grandiflora, Pittosporum tobira, which has weak cumulation of heavy metals, could be Avoidance Plant and can be used as green species of the contaminated area.(4) Plants, which enrich more heavy metals in shoot, can be used for phytoremediation of contaminated soil, such as Eribotrya japonica, Ligustrum lucidum, Platanus hispanica, Oxalis corymbosa, Reineckea carnea; plants, which enrich more heavy metals in roots, can be used for plant curing technology, such as Ligustrum lucidum, Lagerstroemia indica, Viburnum awabuki, Nerium oleander. The cumulation factor of the root of Law Green reaches0.919, close to the screening standard of hyperaccumulators; plants, which grow normally, but can enrich few heavy metals in the plant, can be used as a pioneer of revegetation in heavy metal contaminated areas, such as Maqnolia grandiflora, Cinnamomum camphora, Piitosporum tobira.(5) Pb has a significant positive correlation with Cd and Cu in the plants of the study area, the absorption and accumulation of plants of Pb and Cd and Cu could have a synergistic effect. And no obvious relationship is observed among other heavy metals.(6) Most of Cd, Cu, Pb stays in the roots of the plants, which could have some relationship to plant’s metal tolerance mechanism. By a certain structure or physiological characteristics of the roots, plants limit the heavy metal ions move from the roots to the shoots, maintaining a low heavy metal content in shoots. Or, excrete the heavy metals from leaves to reduce heavy metal toxicity of shoot. And generally, the aerial parts of plants contain more Zn than roots. It is possibly because Zn is one of the elements necessary for plant growth, and it is livelier, and has stronger transfer ability.(7) Zn has the strongest transfer ability in plants among four heavy metals, followed by Cd, Cu, and Pb has the worst. Within the selected20species of plants, none of the cumulation factors is greater than1, and therefore none of the plants meet the standard of hyperaccumulators, but many plants have transport coefficient which is greater than1, the transfer coefficient of Pb in Piitosporum tobira reached6.760, which is the highest of all plants. The aboveground portion of the wood has a high biomass, so that the heavy metals absorbed from the underground part is transfered to the aerial parts constantly, which is not only conducive to absorbing heavy metals, but also beneficial to the aboveground transfer and recycling, which has a certain meaning to the heavy metal extraction and ecological restoration in contaminated areas.(8) P, Pb and Zn in soil factors has a significant positive correlation with the characteristics of plant cumulation, PH value, organic matters has a significant negative correlation with the characteristics of plant cumulation, and K and Cd has a weak negative correlation with characteristics of plant cumulation, meanwhile, N and Cu has no correlation with plant cumulation characteristics. General Transporter Factor of plant only has a weak positive correlation with soil organic matter, no correlation with other factors. Studies have reported that the lower soil PH value, the better the plants to absorb heavy metals. Organic matter can hinder plant uptake of heavy metals in the soil, the right amount of phosphorus was able to promote plant uptake of heavy metals in the soil. Weakly correlated or uncorrelated may be due to the difference of the form of heavy metals in soil and plant species. |
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