| The problem of metals pollution arises along with the rapid development of industry, which have been a major constraint to the sustainable development. Biochar, due to its high surface area, well-developed microspore, CEC, has a very strong capacity to absorb and fix the trace metals. The effects of biochar input on the environmental behavior and the environmental effects of heavy metals in contaminated soil have been confirmed, it makes sence to protect the soil environment, improve soil quality, reduce toxic metals to the transfer of the food chain, and has positive and long-term prospect. In this study, rice straw and water hyacinth were used as raw material, which were prepared for producing biochars (here and after known as BCR and BCW, respectively). These two biochars were added to contaminated soils and incubated over 30 days, the chemical fractions were extracted and column leaching test were performed. Based on the analyzed results, BCR and Fe-modified BCR (BCFe) was incorporated into Cd and As contaminated soils and carried out pot experiment with rice, to study the effects of BCR and BCFe on metals accumulation in crops. The main results are as follow:l.Biochar displayed positive influence on improving acid soil characters, increased soil pH and CEC upon the incorporated proportion of biochars.2. Biochars amended soil after 30d incubation, CaCl2-extractbale Cd/Pb and KH2PO4 extractable As declined to various degrees. Most prominently, CaCl2-extractbale Cd and Pb was both decreased by 73.3% upon the incorporation of 2% BCW. Simultaneously, after 2%BCW incorporation into soil, SPLP-extractable Cd, Pb and As decreased by 60%,31.9% and 9.6%, respectively.3. Based on the early results,2%BCW and CK was chosen for the following leaching column tests. Cd level in the leachate was decreased successively by the presence of 2% BCW throughout the test, which have relatively little influence on As solubilization. While it enhanced soil Pb leachability at the early stage of acid leaching, which indicated biochar amendment would increase the risk of Pb solubility.4. Sequential extraction of Cd, Pb and As was performed with soil± 2% BCW before and after acid leaching. With 2% BCW incorporation, readily exchangeable Cd concentrations were reduced and the non-labile fraction of Cd was enhanced, so 2% BCW enhanced Cd immobilization and reduced Cd ecotoxicity. But 2% BCW showed the potential risk of soil Pb and As mobilization with labile-As and carbonate-associated-Pb increasment.5. The differences of Cd/As accumulation in various organs have been studied from pot experiment. BCR increased pH in Rice rhizosphere at the early stage of rice growing. Besides, BCR decreased Cd concentration by 8.4-66.2%, and BCFe decreased As concentration by 11.3-50.9% in the pore water throught growth period.6. BCR decreased Cd concentration in the roots, chaff, unpolished rice by 48.9-68.4%,36.0-69.7%,26.1-48.7%, respectively. While BCFe decreased As accelerating in the roots, stem, chaff and unpolished rice by 25.8-28.7%,13.1-28.8%,21.1-22.9%,3.5-8.8%.Biochars have shown a potential to reduce heavy metal bioavailability in soil. Effect of biochars on metals activity depends on the type and proportion. BCR and BCW enhanced Cd immobilization, and BCFe enhanced As immobilization. |
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