# Removal of Heavy Metal Cd Element from Paddy Soil by Geo-Electrochemical Technology
## 4 Results and Discussion
### Variation in Cd Accumulation and Transport Capacity in Various Parts of Rice  
The capacity of heavy metals to accumulate and be transported to different parts of rice can be reflected by the bioconcentration factor (BCF) and the translocation factor (TF) [40]. The BCF is the ratio of the heavy metal element content in various rice organs to the heavy metal element content in the soil. It can be used to characterize the difficulty of heavy metal element migration in the soil-rice system. The larger the coefficient, the stronger the ability of heavy metals to migrate from the soil to the plant. The BCF of Cd in various tissues and organs of rice in the T2 and T3 experimental groups is shown in Figure 5. According to Figure 5, there was a certain difference in the Cd BCF in various tissues and organs of rice in the T3 control group, which did not use the GT, and the T2 experimental group, which used the GT. In both experimental groups, the Cd BCF in rice plants from high to low was in the order of rice roots > rice stems > rice leaves > rice grains (brown rice), which is consistent with the change characteristics of Cd content in various parts of rice discussed in Section 4.2. At the same time, according to Figure 5, relative to the T3 control group, the Cd BCF in various parts of rice in the T2 experimental group decreased, among which the decrease in the root BCF was the most significant (\(p<0.05\)). That shows that the GT had an influence on the accumulation capacity of Cd in the paddy soil in various tissues and organs of rice.  
The TF refers to the ratio of the heavy metal content in the subsequent parts of rice (stem, leaf, and brown rice) to that in the antecedent parts (root, stem, and leaf) [41]. The TF is used to evaluate the transport capacity of heavy metals between different parts of the plant. The larger the TF, the stronger the transport capacity of that part for heavy metals [42]. Figure 6 shows the translocation factors of Cd from root to stem, stem to leaf, and leaf to brown rice in the T3 control group with no GT and the T2 experimental group with the GT. According to Figure 6, the translocation factors of Cd in rice plants in the T3 control group from high to low were in the order of \(\mathrm{TF_{stem/root}}\) > \(\mathrm{TF_{leaf/stem}}\) > \(\mathrm{TF_{brown~{}rice/leaf}}\). That indicates that the roots and stems of rice had a strong transport capacity for Cd, whereas the leaves had a relatively weak capacity. Relative to the T3 control group, the \(\mathrm{TF_{stem/root}}\) of the T2 group that used the GT significantly decreased (\(p\) < 0.05), but the \(\mathrm{TF_{leaf/stem}}\) and \(\mathrm{TF_{brown~{}rice/leaf}}\) increased. This result indicates that the GT affects the process of rice stems and leaves to transport Cd, but the most crucial aspect is that it affects the process of rice roots to transport Cd. That reduced the accumulation of Cd in the aboveground parts of rice plants from the source, ultimately reducing the Cd content in brown rice. The combined effect of the BCF and the TF made the Cd content in the rice grains of the T2 experimental group that used the GT the lowest, meeting the national food safety standard.