| Soil cadmium（Cd） pollution is becoming more and more serious in China and remediation technology of Cd contaminated soil is growing concern. In Situ Chemical Reduction（ISCR） of cadmium in soils is considered to be an economical, efficient and easy method to remediate cadmium contaminated soil through reducing the mobility and bioavailability of Cd in the soil. The key aspects of this technique lie in choosing appropriate amendment. Zeolite, as a soil amendments, was extensively used in soil Cd contamination remediation for its good adsorption and ion-exchange capacities. However,due to the defects such as the blockage of channel etc., there are certain limitations in heavy metal adsorption and fixed using ordinary zeolite. Nano zeolites,the unique structure endows it with enhanced huge specific surface area and superior adsorption capacity, showing good application prospects in soil Cd contamination remediation. However, the investigation about the application of nano zeolites in soil Cd contamination remediation is less in the domestic and abroad at present, and the study on the remediation mechanism of nano zeolite to Cd-contaminated soil and the relations of application rate to soil Cd contamination remediation and plant growth are not clearly. Nano zeolite（NZ） and ordinary zeolite（OZ） as soil amendments, soil incubation experiments were carried out to investigate the influence of different nano zeolite and ordinary zeolite levels(0, 5, 10 and 20 g·kg-1) on the changing trends in fraction distribution coefficient（FDC） of Cd with incubation time（0, 1,4, 7, 14, 21 and 28 d） as well as soil physical and soil p H and cation exchange capacity when exposed to different concentrations of Cd(1, 5, 10 and 15 mg·kg-1) and at different soil p H（4.0, 5.0, 6.0, 7.0 and 8.0）. The soil culture experiment was carried out to investigate the influence of different nano zeolite and ordinary zeolite levels(0, 5, 10 and 20 g·kg-1) on growth and Cd accumulation in cabbage, soil Cd fraction,p H and cation exchange capacity when exposed to low(1 mg·kg-1 Cd) and high(5 mg·kg-1 Cd) concentrations of Cd. Meanwhile, the remediation of different nano zeolite and ordinary zeolite levels(0, 750, 1500 and 3000 kg·mu-1) were studied in Cd-contaminated vegetable garden soil. The main results are summarized as follows:（1） The results of soil incubation experiments showed that the redistribution of soil Cd fraction was observed at day 0 to 4, day 7 to 21 and day 28 in soil incubation experiments of different Cd pollution levels. The most obvious change in all fractions of Cd in soils was found in the exchangeable（EX-F）, carbonate（CAB-F） and Fe-Mn oxide（FMO-F） during the 28-day incubation. Addition of NZ and OZ decreased the fraction distribution coefficient（FDC） of EX-F Cd, while the FDC of CAB-F, FMO-F, organic matter fraction（OM-F） and residual fraction（RES-F） Cd increased. The FDC of EX-F Cd were increased by 12.8%-24.1% and 12.1%-40.9%, 20.0%-29.7% and 8.0%-14.1%, 18.4%-30.9% and 4.2%-8.0%, 13.3%-29.7% and 4.4%-10.3% with application of NZ and OZ when exposed to Cd levels of 1,5,10 and 15 mg·kg-1 at the end of culture（28d）, respectively. The reduction of EX-F Cd increased with the increase of zeolite application, and the reduction of EX-F Cd in the NZ treatments was markedly greater than those in the OZ treatments.（2） Different fraction distributions of Cd in soil were observed in different soil p H treatments. When p H value was 4.0 to 6.0, the redistribution of soil Cd fraction was found at day 0 to 1 and day 4 to 28. The most obvious changes in all fractions of Cd in soils were observed in EX-F, FMO-F and RES-F. The redistribution of soil Cd fraction was found at day 0 to 4, day 7 to 14 and day 21 to 28 when p H value was 7.0 and 8.0. The most obvious changes in all fractions of Cd in soils were observed in EX-F, CAB-F, FMO-F and RES-F. Addition of NZ and OZ decreased the FDC of EX-F Cd, while the FDC of CAB-F, FMO-F, OM-F and RES-F Cd increased. The FDC of EX-F Cd increased by 27.7%-42.0% and 6.3%-37.1%, 8.7%-30.1% and 6.1%-11.2%, 28.2%-32.5% and 2.4%-10.7%(exception for the 10 g·kg-1 OZ treatment), 26.3%-35.0% and 17.2%-28.9%, 17.0%-30.6% and 1.6%-18.8% with application of NZ and OZ in soil with p H value 4.0,5.0,6.0,7.0 and 8.0 at the end of culture（28d）, respectively. The FDC of EX-F Cd was higher at low p H of 4.0, and the reductions in FDC of EX-F Cd were also greater.（3） Soil p H and CEC greatly increased by NZ and OZ at different Cd levels in soils, and increased with increasing application amount of NZ and OZ. Furthermore, soil CEC effectively increased by NZ and OZ at different levels of p H in soils, and increased with the application amount of NZ and OZ. Soil p H and CEC showed significant negative relationships with EX-F Cd（P<0.01）. Compared with two kinds of zeolites, the increases of p H and CEC in the NZ treatments were greater than those in the OZ treatments.（4） The results of soil culture experiment showed that the concentration and accumulation of Cd in shoots and roots of cabbage significantly increased with increasing exogenous Cd concentrations compared to the Cd-absent control（Cd0+Z0）. The concentrations of Cd in shoots and roots of cabbage obviously decreased with the increasing application amount of NZ and OZ. At low Cd(1 mg·kg-1) and high Cd(5 mg·kg-1) in soils, the concentrations of Cd in two cultivars of cabbage, ?shan dong si hao‘（SD 4） and ?xin jin cai san hao‘（XJC 3）, reduced by 19.5%-82.4% and 17.0%-68.7% compared with the control, respectively. The effect of decreasing Cd concentrations in NZ treatments was markedly greater than that in OZ treatments. Compared to OZ, the concentrations of Cd in cabbage reduced by 10.5%-65.7% in the NZ treatments. Accumulation of Cd also significant decreased in the high dose of OZ(20 g·kg-1) and medium(10 g·kg-1) and high(20 g·kg-1) dose of NZ. Compared to ?SD 4‘ cultivar, ?XJC 3‘ cultivar showed greater Cd-accumulation ability, in which the concentration and accumulation of Cd were higher than that in ?SD 4‘ cultivar.（5） When exposed to Cd, the biomass of cabbage were increased by the all dose of NZ and low and medium dose(≤10 g·kg-1) OZ, while the biomass of ?SD 4‘decreased by the high zeolite(20 g·kg-1). The ?XJC 3‘ cultivar obtained higher biomass in the medium(10 g·kg-1) and high dose(20 g·kg-1) of two kinds of zeolites when exposed to Cd level of 5 mg·kg-1. The content of amino acid, ugar and vitamin C in shoots of cabbage increased by in addition of the low and medium(≤10 g·kg-1) dose of NZ and OZ. However, the content of nitrate increased when NZ and OZ were added. The increase of the growth and quality was markedly greater in the NZ and OZ treatments with low and medium dose(≤10 g·kg-1).（6） In field experiments yield of cabbage significantly increased with the increase NZ and OZ application amount. The highest yield was found in the medium dose(1500 kg·mu-1) of NZ by 8133.2 kg·mu-1, followed by the high dose(3000 kg·mu-1) of OZ by 7924.3 kg·mu-1. However, there was no remarkable difference of yield between NZ and OZ treatments（P<0.05）. Addition of NZ and OZ with the low and medium dose(≤1500 kg·mu-1) increased the content of amino acid, ugar and vitamin C in shoots of cabbage, while significant effect on nitrate was not found. Compared to the OZ treatments, the content of amino acid, ugar and vitamin C increased by 3.6%-20.8%,30.9%-50.7%(exception for the 3000 kg·mu-1 NZ treatment) and 28.5%-55.3% in addition of NZ. The content of nitrate was also higher in the NZ treatments than that in the OZ treatments. The concentration of available Cd significantly decreased by 19.1%-24.1% and 11.1%-19.9%, concentration of Cd in cabbage tissues decreased by 8.1%-37.4% and 9.9%-25.4% after with application of NZ and OZ, respectively. And the reduction of the available Cd increased with increasing zeolites doses. Compared with two kinds of zeolites, the yield and quality of cabbage in the OZ treatments were markedly greater than that in the NZ treatments, when addition of zeolites with the low and medium dose(≤1500 kg·mu-1). |
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