| Tailings resulted from mining and smelting activities of non-ferrous metal mineral resources. Tailings storging form great tailings waste lands, which not only occupy land but may also cause secondary pollution of the surrounding environment.Revegetation of tailing waste lands is a general practice to stabilize tailings, prevent secondary pollution and beautify the environment; planting the crops that can be used for multiple application ways, bring high economic value will become a rising current about tailings reclamation. Recently, many researches have been focused on the effects of chelating agents on the phytoremediation of heavy metal contaminated soil. Some researches showed that chelating agents not only were able to increase heavy metal bioavailability in contaminated soils, but also enhanced heavy metals accumulation of plants.These studies were mainly focused on:(1) Extraction of heavy metals and mineral elements in tailing of different times and agricultural contaminated soil around mine area using biodegradable (EDDS) and Non-biodegradable (EDTA) Chelators;(2) Pot experiments were conducted to investigate the growth and lead-zinc accumulation of maize seedlings in amendment substrates mixed with lead-zinc tailings and soil with the addition of EDTA. The ratios of lead-zinc tailings to soil in pot substrates were0:100,25:75,50:50,75:25, and100:0, marked as TA00, TA25, TA50, TA75, and TA100, respectively;(3) Pot experiments were conducted to study the effects of single and combined addition of EDTA and NTA on growth and heavy metal accumulation in castor seedlings, in which the ratio of Pb-Zn tailings to soil in the substrates was1:1;(4) Pot experiments were conducted to study the effects of single and combined addition of EDTA and NTA on the subcellular distribution of Pb and Zn in the roots, stems and leaves of castor seedlings.(5) A Survey on heavy-metal content in plants in lead-zinc tailings dam covering soil. The aim of the present studies is to elucidate the mechanisms of increasing heavy metal bioavailability in soils and increasing heavy metal absorption and translocation from soils to plant shoots by chelating agents, which provides a theoretical basis for the phytoremediation on the lead-zinc tailing waste lands. The main results were shown as following:(1) The results of chelating agents extraction showed that the extraction efficiency for Pb by EDDS was higher than EDTA from two mine tailings simples; the extraction efficiency of Cu and Zn by EDDS and EDTA were similar, and all lower. The extraction efficiency of Cu and Zn by EDDS and EDTA was higher than Pb. The extraction rates of Mn increased evidently at the presence of the two chelators, and the solution of Fe were also slightly enhanced.(2) The results of pot experiments by maize seedlings showed that the main factors restricting the maize growth were the poor nutrition and rich Pb and Zn with high concentrations in substrates. Maize grew normally in test substrates without EDTA, and no apparent phyotoxity was observed. However, biomass of maize clearly decreased with the addition of EDTA, and the higher decrease degree of the maize biomass was found in the amendment substrates with larger proportion of lead-zinc tailings. The addition of EDTA significantly enhanced the accumulation of Pb and Zn by maize, and the accumulation amount of Pb by maize was higher than that of Zn. The accumulation amount of Pb and Zn in maize was smaller in substrates with50%tailing and50%soil than that in100%tailings, however, the weaker decrease degree of biomass, average of plant height, and root indexes of maize was observed for the former than the latter. We prospose that the amendment of50%soil in tailings seems reasonable for reclamation of lead-zinc tailing waste lands.(3) The results of pot experiments by castor seedlings showed that the biomass and root morphological parameters of castor clearly decreased with the addition of chelating agents, and greater decreases in them were observed in castor grown in chelating agents containing higher proportions of EDTA. The decrease of root tips was more evident than the rest of root morphological parameters, and which reached extremely significant level compared with the control at the same time (P<0.01). Compared with the CK treatment, chlorophyll a, b, and a+b decreased significantly(P<0.0.5), the decrease extent of chlorophyll b is more than chlorophyll a. The activity of SOD, CAT and POD increased first and then decreased with the increase of EDTA in chelating agents. The contents of Pb and Zn by castor generally increased with addition of chelating agents, the increment of Pb contents was higher than Zn. The addition of chelating agents significantly enhanced the accumulation of Pb and Zn in castor, and more Pb accumulated than Zn. The addition of chelating agents advanced obviously the translocation of Pb and Zn from roots to shoots in castor, the maximum value of translocation factor of Pb and Zn were got at the addition of3mmol/kg EDTA and3mmol/kg NTA. Castor have strong endurance and the ability of heavy metal accumulation, and it is reasonable for reclamation of Pb-Zn tailing waste lands.(4) The results showed that the subcellular distributions of Pb and Zn had significant relationship with the ability of heavy metal uptake and accumulation in castor. The addition of EDTA and NTA could evidently advance the absorption and accumulation of Pb and Zn in castor and affect on their distribution in cell wall and organelle fractions. Most of Pb and Zn was bound to the cell wall fraction and secondly cytoplasm fraction (except the addition of NTA singly) in root of castor. Most of Pb and Zn was bound to cytoplasm fraction and secondly the cell wall fraction in stems and leaves of castor. Under the inducement of EDTA and NTA, there were increasing Pb and Zn bound to cell wall, which mostly came from organelle fraction in roots of castor, there were increasing Pb and Zn bound to cytoplasm fraction in stems and leaves of castor, the addition of EDTA and NTA enhanced the compartmentalizing of Pb and Zn in stems and leaves of castor.(5) The study about native plants which followed by topsoil and colonized successfully on lead-zinc tailings dam covering soil showed the accumulation factors of Zn, Pb and Cu about ten species dominant plants were all less than1; Zn, Pb and Cu contents of their shoots and leaves did not reach the standard of hyperaccumulator. Abelmoschus moschatus Medic, Aralia decaisneana Hance, Phytolacca acinosa roxb and Rubus corchorifolius L.f. exhibited higher transportation abilities for Zn and Cu from roots to shoots. But accumulation abilities were low, the accumulation of Zn, Pb and Cu were all listed in the order of leaves> roots> shoots, and three kinds of plants were well metal-tolerant plant. Miscanthus Jloridulus exhibited higher accumulation potentiality for Zn, Pb and Cu, it has strong adaptability and great biomass, can be used for metal immobilization of Pb/Zn tailings waste lands.In conclusion, these results indicated:(1)The extraction efficiency for Pb by EDDS was higher than EDTA from two mine tailings, the extraction efficiency of Cu and Zn by EDDS and EDTA were similar, and all lower;(2) When the ratio of lead-zinc tailings to soil was1:1, the extraction effect of Pb and Zn by maize was the most significant in all of amendment substrates;(3) The inhibition that castor growth beared was smaller than rest chelating treatments, and accumulation amount of Pb and Zn by castor was higher than that of rest, the extraction effect of Pb and Zn by castor was the most significant in all of that under the addition of3mmol/kg EDTA and3mmol/kg NTA;(4) Under the inducement of EDTA and NTA, most of Pb and Zn was bound to the cell wall fraction in root of castor, most of Pb and Zn was bound to cytoplasm fraction in stems and leaves of castor;(5) There was some native plants those can be used for revegetation in plants colonization on lead-zinc tailings dam covering soil. |
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