Identification Of Sn Hyperaccumulators And Adsorption-desorption Mechanisms Of Contaminated Soil Remediation

With the continuous mining of tin ores as well as wide applications of tin and its compounds, tin has entered into the soil and groundwater environments in various ways, and tin contamination and organic-inorganic tin compound pollution of soil have become increasingly serious. At present, studies on governance and restoration of tin and its compounds contaminated soils have been little done, especially, the work of Sn hyperaccumulators screening systematically has hardly been reported internationally. The critical content of Sn hyperaccumulator has not been established; at the same time, Sn hyperaccumulator has not yet been reported in the world. In view of this, by selecting ornamental plants as screening objects and setting different concentrations of Sn contaminated soil and water, soil potted simulation tests and hydroponic experiments were carried out in order to study tolerance characteristics and accumulation traits of ornamental plants. This work aims at identifying Sn hyperaccumulators with high tolerance and accumulation ability to tin and its compounds in soils and exploring the mechanisms of phytoremediation of Sn contaminated soils.The main findings are as follows.(1) In73kinds of tested ornamental plants,25species showed strong tolerance to Sn. Compared with blank control, height, aboveground biomass and root biomass of plants did not reduced significantly in Sn pollution conditions and the plants did not show obvious poisoned symptoms.(2)3kinds of ornamentals with Sn ultra-accumulation characteristics were screened out by pot-culture experiments and hydroponic experiments. Ligusticum sinense, Platycodon grandiflorus, and Arundinella anomala Steud.had strong tolerance and Sn-accumulation ability to Sn, reached the critical content standard of Sn hyperaccumulators, and the transfer coefficients of shoots of plants were greater than1. It roughly met the main characteristics of hyperaccumulator, and it could be basically viewed that the three species were potential Sn hyperaccumulators. However, in the following Sn hyperaccumulators confirmation test, Ligusticum sinense and Platycodon grandiflorus did not present strong Sn-enrichment and transferring abilities in Sn contaminated soils, which were different from laws found in contaminated water.(3) Whether Sn contaminated soil or water, Arundinella anomala Steud.had high Sn-enrichment and transferring abilities. In all treatments, the Sn concentration of shoots was larger than that of roots, which meant the aboveground transfer coefficient was greater than1.0, and the Sn content of the aboveground reached the critical concentration levels of Sn hyperaccumulator (100mg kg-1) and was100times of a common plant under the same growing conditions. Moreover, Arundinella anomala Steud. had strong tolerance to Sn contaminated soil or water. In conclusion, Arundinella anomala Steud. could be viewed as Sn Hyperaccumulator based on the above characteristics.(4) Other plants with high tolerance to Sn contaminated soil or water such as Achillea millefolium, fineleaf schizonepeta herb, Lolium perenne L., Sedum hybridum, Agrimoniapilosa Ledeb., Astilbechinensis(Maxim.) Franch.etSav., Eragrostis pilosa (L.) Beauv. and so on had strong Sn-accumulation capacity, and they had enormous biomasses. Although they had not reached the standards of Sn Hyperaccumulator, they had extensive application prospects in bioremedination of Sn contaminated water or soils.(5) The study on the adsorption and desorption of Sn(II) on the tested soil showed that the adsorptive and desorptive behavior of Sn by the tested soil can be basically described using the Langmuir equation. Compared with the enormous adsorptive capacity of Sn by the soil, the corresponding desorptive capacity of Sn was rather weak. Sn in soil presented feeble mobility and was difficult to release into the groundwater and soil, nevertheless, it might be considered as the pollutant with high ecological risk because of the large amount of Sn accumulated in soil. The adsorption of Sn by the soil could be divided into three stages including the high-speed adsorption stage, the slowdown adsorption stage, and zero-approaching adsorption at the established adsorption equilibrium. The total amount of Sn desorbed from the soil increased with time, but the velocity of Sn desorbing from the soil decreased. The influence of pH value on the adsorption behavior of Sn was remarkable, and the adsorptive capacity of Sn in acidic or alkaline soil environment was lower than that in slightly neutral environment.