[Effect of Nano Zeolites on pH, CEC in Soil and Cd Fractions in Plant and Soil at Different Cadmium Levels]

Soil incubation experiment and pot experiment were carried out to investigate the influence of nano zeolite (NZ) and ordinary zeolite (OZ) on the soil pH, cation exchange capacity, concentration of soil Cd, soil Cd fraction and Cd uptake by Chinese cabbage when exposed to different Cd pollution levels(1, 5, 10 and 15 mg·kg^-1). The results of soil incubation experiment showed that the nano zeolite and ordinary zeolite dose(5, 10 and 20 g·kg^-1) increased the soil pH and cation exchange capacity, and decreased the concentration of soil exchangeable Cd, while increased the concentration of Cd in carbonate, Fe-Mn oxide, organic matter and residual fraction. The lowest EX-Cd was observed in the high nano zeolite (20 g·kg^-1) treatment. The soil pH and cation exchange capacity was extremely negatively correlated with the concentration of soil exchangeable Cd(P<0.01),and extremely positively correlated with the concentration of soil Fe-Mn oxide Cd(P<0.01). The results of pot experiment showed that the FDC of exchangeable Cd in soil decreased by 6.4%-63.2%, and the FDC of water-extractable and ethnol-extractable Cd in Chinese cabbage decreased by 2.1%-56% and 11.8%-100% with zeolite application, respectively. Moreover, the reduction effect of nano zeolite on Cd concentration in soil and plant was better than that of ordinary zeolite. The FDC of Cd fraction in shoot of Chinese cabbage showed correlation with the FDC of carbonate Cd and organic matter Cd in soil(P<0.05) when exposed to 1 mg·kg^-1 Cd pollution. Moreover, correlation was also found in the FDC of organic matter Cd and residual Cd in soil(P<0.05) under 5 mg·kg^-1 Cd pollution.

[Effect of Nano Zeolite on Growth, Activity of Antioxidant Enzyme, and Chemical Fractions and Concentration of Cd in Chinese Cabbage]

Pot experiment was carried out to investigate the influence of nano zeolite (NZ) and ordinary zeolite (OZ) on the growth, activities of antioxidant enzyme, Cd fraction and Cd concentration in two varieties of Chinese cabbage. The results showed that the activities of SOD, CAT and POD in the shoot and root of two varieties increased, and the dry weight of shoot and the total dry weight of Chinese cabbage increased by 4.5%-96.5% and 3.4%-88.4%, respectively. The application of zeolite effectively reduced the Cd concentration of shoot and root in the two varieties of Chinese cabbage, and the reduction range increased with the increase of the application amount of zeolite. Under the low Cd condition (1mg·kg^-1 Cd), the Cd concentration of edible parts (shoots) in SD4 variety and XJC3 variety decreased by 1.0%-75.0% and 19.5%-68.9% (except the Cd₁+OZ₅/OZ₁₀ processing), respectively. Under the high Cd condition (5 mg·kg^-1 Cd), the Cd concentration of the edible parts (shoots) in SD4 variety and XJC3 variety decreased by 7.2%-53.2%(except Cd₅+OZ₁₀ processing) and 0.7%-63.0%, respectively. The Cd concentrations of the edible parts (shoots) in tow varieties of Chinese cabbage in the nano zeolite treatments decreased by 10.5%-65.7% compared with the ordinary zeolite treatments. In Cd contaminated soils (1 mg·kg^-1 and 5 mg·kg^-1 Cd),) the total extraction amount of Cd in the edible parts (shoots) of SD4 variety reduced by 12.4%-68.8% and 13.2%-55.6% (except of Cd₅+OZ₅ processing), and the total extraction amount of Cd in the edible parts (shoots) of XJC3 variety reduced by 9.4%-71.5% and 3.1%-38.7% (except of Cd₁+OZ₅ processing), respectively. The application amount of nano zeolite (NZ) and ordinary zeolite (OZ) was more, the reduction range of the total extraction amount of Cd in the edible parts (shoots) of two varieties of Chinese cabbage was greater.

[Effect of Nano Zeolite on Chemical Fractions of Cd in Soil and Uptake by Chinese Cabbage at Different Soil pH and Cadmium Levels]

Incubation experiments were carried out to investigate the influence of different nano zeolite(NZ) and ordinary zeolite(OZ) levels(0, 5, 10 and 20 g·kg^-1) on the fraction distribution coefficient (FDC) of Cd and soil CEC at different soil pH (4, 5, 6, 7 and 8) when exposed to different cadmium(Cd) levels(1, 5, 10 and 15 mg·kg^-1), and pot experiment were carried out to investigate the effects of nano zeolite(NZ) and ordinary zeolite(OZ) on the growth, Cd concentration and Cd accumulation of Chinese cabbage. The results showed that nano zeolite and ordinary zeolite decreased the concentration and FDC of exchangeable Cd (EX-F), and increased the concentration and FDC of carbonate(CAB-F), Fe-Mn oxide(FMO-F), organic matter (OM-F) and residual fraction(RES-F) in incubation experiments. At the end of incubation, the FDC of soil exchangeable Cd decreased from 72.0%-88.0% to 2.4%-10.7%. The decreasing effect of zeolite on the concentration and FDC of exchangeable Cd (EX-F) increased with the increase of zeolite, and the decreasing effect of nano zeolite (NZ) was better than that of ordinary zeolite (OZ). During the culture of 28 d, the concentration of different Cd fractions in soil was in order of EX-F>RES-F>FMO-F>CAB-F>OM-F under different pH conditions. Exchangeable fraction Cd was the dominant fraction of Cd in soil during the whole incubation. Soil CEC had significant negative correlation with soil exchangeable Cd (EX-F) (P<0.01), and significant positive correlation with the concentrations of Fe-Mn oxide(FMO-F) and organic matter (OM-F) in soil(P<0.01). Nano zeolite and ordinary zeolite effectively increased soil CEC, and soil CEC increased with the increase of the pH value of soil in the zeolite treatments. Significant negative correlation was found in soil pH with soil exchangeable Cd (EX-F)(P<0.01). The dry weight of plant tissues in Chinese cabbage increased by 14.3%-131.4% in the presence of nano zeolite(NZ) and ordinary zeolite(OZ), and Cd concentration of shoot and root decreased by 1.0%-75.0% and 3.8%-53.2%, respectively. Higher concentration and accumulation of Cd were observed in XJC3 variety than those in SD 4 variety. Compared with ordinary zeolite (OZ), nano zeolite (NZ) was better in increasing the biomass of Chinese cabbage as well as decreasing accumulation of Cd in Chinese cabbage.