| Rice (Oryza sativa L.) is one of the most important food crops in China, and is staple food for more than60%of Chinese population. However, mining activity has contaminated the soils in which the rice grows around some mining and smelting areas of Hunan Province in recent decade years. Contamination rice of heavy metal has become the focus of attention. Consequently, how to remediate rice paddy soils contaminated with heavy metals and how to control transfer of heavy metals from paddy soils to rice are serious problems need to be solved. In this study, a series of field experiments were carried out in a heavy metal contaminated paddy field (Pb, Cd, Cu and Zn) near Matian country (MTC) of Shizhuyuan Mine Zone in Chenzhou City and Zhupo country (ZPC) of Shuikoushan Mine Zone in Hengyang City, southern Hunan Province, China, respectively. The researches included three sets of experiments, which were the field experiment of heavy metal accumulation in different rice cultivars, the pot experiment of screening amendment for remedying heavy metal soils, and the field experiment of applying combined amendments to remediate heavy metal soils and planting rice on. The main objectives of this study were to investigate the differences of heavy metal accumulation in different rice cultivars, to screen safe rice cultivars which were appropriate for planting on the contaminated soils remedied with combined amendments, to investigate the effects of two combined amendments (LS and HZ) on the bioavailability of heavy metals in rhizosphere soil and non-rhizosphere soil, to study the effects of LS and HZ on heavy metal uptake and accumulation in rice plants, and to investigate the transfer laws of heavy metals in "non-rhizosphere soil-rhizosphere soil-ron plaque-rice plant". The main results were as follows:(1) Significant differences of Pb, Cd, Cu, and Zn concentrations were observed in33rice varieties (consisting of1conventional rice "Huanghuazhan",6varieties of two-line indica hybrid rice, and26varieties of three-line indica hybrid rice), and significant differences of Pb, Cd, Cu, and Zn accumulation and distribution were also found in rice tissues (root, straw, husk and brown rice) of33rice varieties. Roots were the main tissues of Pb and Cd accumulation, and aerial parts were the main parts of Cu and Zn accumulation. Xiangfeiyou8118and Youyou128were the safe rice cultivars due to low Pb concentration, and Jinshanyou2115and Fengyou9were the safe rice cultivars for Cd low concentration. There were no significant differences of heavy metal concentrations in brown rice of different hybrid cultivars (p>0.05). The mean Pb concentrations in brown rice decreased in the order Huanghuazhan> three-line indica hybrid rice> two-line indica hybrid rice, and the mean Cd, Cu and Zn concentrations of brown rice decreased in the order indica hybrid rice (two-line indica hybrid rice and three-line indica hybrid rice)> Huanghuazhan.(2)6amendments (limestone, hydroxyhistidinet, bentonite, diatomite, sepiolite and zeolite) were applied as single and combination to paddy soil with multi-metal (Pb, Cd, Cu, and Zn) contamination. The LS (2:1) and HZ (2:1) were the most effective combined amendments to decrease Pb and Cd concentrations in MgCl2and TCLP extracts, compared with other single and combined amendments. The Pb and Cd concentrations in MgCl2extracts were reduced by65.9%and95.8%; and in TCLP extracts by43.0%and98.6%, respectively, when0.6%of LS (2:1) was applied. The Pb and Cd concentrations in MgCl2extracts were reduced by69.9%and92.5%; and in TCLP extracts by45.2%and98.0%, respectively, when0.6%of HZ (2:1) was applied.(3) Application of LS and HZ (0.2%～0.8%) significantly increased soil pH values and cation exchange capacity (CEC), and resulted in an obvious decrease in heavy metal (Pb, Cd, Cu, and Zn) concentrations of MgCl2and TCLP extracts of rhizosphere soils and non-rhizosphere soils. Due to affects of rice roots, the effects of two combined amendments on soil basic properties (pH and CEC) and heavy metal concentrations of MgCl2and TCLP extracts in non-rhizosphere soils were significantly greater than those in rhizosphere soils. The mechanism of heavy metal bioavailability reduction was an outcome of rising soil pH, CEC and soil colloid adsorption capacity, and soil pH increased was the major factor.(4) LS and HZ obviously inhibited uptake and accumulation of Pb, Cd, Cu, and Zn in different tissues of rice plants. Compared with the control, the concentrations of Pb, Cd, Cu, and Zn in brown rice at MTC were decreased by27.8%～55.8%,23.2%～43.8%,25.9%～37.4%, and7.9%～14.7%, respectively, and in brown rice at ZPC decreased by10.6%～31.8%,16.7%～25.5%,11.5%～22.1%, and11.7%-16.3%respectively, as a result of0.2%o0.8%ddition of LS. Compared with the control, the concentrations of Pb, Cd, and Cu in brown rice at MTC were decreased by35.4%～47.8%,2.8%～16.3%, and11.2%～55.9%, respectively, and in brown rice at ZPC decreased by5.1%～40.8%,16.7%～20.0%,8.1%～16.2%, and13.3%～21.7%, respectively, as a result of0.2%o0.8%ddition of HZ. Pb concentration of brown rice at MTC was0.185mg/kg, and less than the tolerance limit of contaminants in foods of China National Standards (GB2762-2012, Pb<0.2mg/kg), when the addition of HZ was0.4%.(5) Application of LS and HZ (0.2%～0.8%) gradually decreased bioaccumulation factor (BCF) and translocation factor (TF) of heavy metals in rice. Rice root, straw, and husk had different abilities of accumulation and translocation heavy metals. Straw had a stronger ability of transferring Pb and Cd to husk, and husk had a stronger ability of transferring Cu and Zn to brown rice, while, the ability of transferring heavy metals of rice root was weaker than straw and husk. Therefore, in the heavy metal contaminated paddy soils, rice root uptake and accumulation of Pb and Cd from soils, and transportation of Pb and Cd into straw were not the major factors that effected Pb and Cd accumulation in brown rice. While Pb and Cd were transported into husk via xylem of rice stem, and Pb and Cd were transported into brown rice via phloem of husk were the key factors that effected Pb and Cd concentrations of brown rice. |
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