RESUMO
The effects of nano-magnesium hydroxide and common magnesium hydroxide (100, 200, and 300 mg·kg-1) on the forms of cadmium in different types of cadmium contaminated soils (1, 5, 10, and 15 mg·kg-1) were studied under 28 days of continuous culture experiment. In the neutral soil, during the 28 days of culture, soil exchange Cd (EX-Cd) form distribution ratio (FDC) decreased at first and then increased with the culture time increasing under treatment of 1, 5, 10, and 15 mg·kg-1 Cd. The minima of soil EX-Cd FDC were found on the 14th day under 1 mg·kg-1 Cd and 5 mg·kg-1 Cd treatments, whereas the minima of soil EX-Cd FDC were observed on the 4th day under 10 mg·kg-1 Cd and 15 mg·kg-1 Cd treatments. The FDC of soil carbonate bound Cd (CAB-Cd), iron manganese oxidized Cd (FeMn-Cd), and organic bound Cd (OM-Cd) increased at first, then decreased, and finally, became stable, and the maxima of soil CAB-Cd, FeMn-Cd, and OM-Cd FDC were found on the 4th day, whereas the minima of soil CAB-Cd, FeMn-Cd, and OM-Cd FDC were observed on the 14th day. Soil residual Cd (RES-Cd) FDC increased gradually and then tended to becomes stable during the 28 days of culture. The soil EX-Cd FDC was 66.7%-81.8% at 1, 5, 10, and 15 mg·kg-1 Cd treatments, which was the main form of the soil. The FDC of soil Cd forms was in the order of EX-Cd > CAB-Cd > RES-Cd > FeMn-Cd > OM-Cd. Soil EX-Cd FDC reached the lowest value on the 14th Day. Soil EX-Cd FDC was reduced by nano-magnesium hydroxide and common magnesium hydroxide, and it decreased with the increase of the amount of magnesium hydroxide. During 0-28 days of culture, the soil EX-Cd FDC decreased by 11.4%-67.7%, 7.8%-37.2%, 7.7%-36.4%, 5.0%-28.8% (nano-magnesium hydroxide) and 0.5%-49.5%, 0.6%-15.0%, 1.0%-18.1%, 0.7%-14.6% (ordinary magnesium hydroxide) at 1, 5, 10, and 15 mg·kg-1 Cd treatments, respectively. The EX-Cd content of alkaline soil reached the lowest value on the 7th day of culture, and the EX-Cd content of acidic soil reached the lowest value on the 21st day under 1, 5, and 10 mg·kg-1 Cd treatments. The content of EX-Cd in neutral, acidic, and alkaline soils decreased with the increase of magnesium hydroxide content, and the content of EX-Cd in soil decreased with the increase of magnesium hydroxide amount. At the same amount, the effect of passivating soil EX-Cd under nanometer magnesium hydroxide treatment was superior to ordinary magnesium hydroxide treatment.
RESUMO
In a preliminary experiment, 91 pepper varieties were screened, and one variety each with high Cd accumulation (X55), medium Cd accumulation (Daguo 99), and low Cd accumulation (Luojiao 318) were selected to study the effect of different cadmium levels (0, 5, and 10 mg·kg-1 Cd) on cadmium migration and enrichment ability, and its subcellular distribution and chemical form. The results showed that under the stress of Cd, shoot dry weight of pepper plants was in the order X55>17>27. At the same level of Cd, the Cd transfer coefficient of fruit was 17>27 and X55. Cadmium concentrations in each subcellular component of the pepper fruits were 27 > 17 > X55. Cadmium concentration in subcellular component of the roots, stems, leaves, and fruits of the pepper plants was in order of cell wall (F1) > organelle (F2) > cell soluble component (F3). Cadmium was limited in cell wall and plays an important role in detoxification mechanism and resistance of Cd in pepper plants. The morphological content of various Cd forms in the pepper fruits of the three varieties increased with the increase of Cd treatment level, in the order CdNaCl > CdHAC > CdR > CdHCl > CdW > CdE. CdNaCl and CdHAC account for a large proportion of Cd in pepper fruits, which may be an important defense mechanism for reducing the biological toxicity of Cd.
