# Combined Effect of Ferrous Ion and Biochar on Cadmium and Arsenic Accumulation in Rice
## 3 Results
### Cd and As Contents in Rice Tissues  
The Cd contents and distribution in the root, straw, husk, and grain were affected by applied amendments (Figure 4). The distribution of Cd in rice tissues completely followed as order root \(>\) straw \(>\) husk \(>\) grain in this study. In all amendments, 1 BC-1 Fe(II) treatment could promote the uptake of Cd in rice tissues. We noted that all treatments promoted the root absorption of Cd, but only 1 BC-Fe(II) showed significantly difference, which was increased by 262% compared to control. In addition, the highest content of Cd in straw, husk, and grain under 1 BC-1 Fe(II) treatment, while the lower Cd content was presented in BC, 3 BC-1 Fe(II) and 5 BC-1 Fe(II) treatments. Figure 4 shows that the grain Cd content was highest in 1 BC-1 Fe(II) treatment, which is 1.3 \(\pm\) 0.3 mg\(\cdot\)kg\({}^{-1}\), while the other three treatments are lower. What needs to be illustrated is that the yield of rice in control treatment was significantly affected due to special growing conditions of excessive heavy metal in soil without BC and Fe(II) amendment. Therefore, the plants growth was inhibited, resulting in low yields and inability to digest analysis of grain. Based on the distribution of Cd in plant tissue after treatments, we suppose that the trend of Cd uptake in grain is consistent with root, husk, and straw under the four treatments, Cd content in grain will be lower than 1 BC-1 Fe(II) treatment while higher than control, 3 BC-1 Fe(II), and 5 BC-1 Fe(II) treatments.  
The sequence of As accumulation in plant is root \(>\) straw \(>\) husk \(>\) grain; this is consistent with the distribution of Cd. The contents of As in root, straw, husk and grain are 22.00-78.08 mg\(\cdot\)kg\({}^{-1}\), 1.01-3.02 mg\(\cdot\)kg\({}^{-1}\), 0.10-0.19 mg\(\cdot\)kg\({}^{-1}\) and 0.01-0.23 mg\(\cdot\)kg\({}^{-1}\), respectively, which indicates that there is a significant difference in the uptake of As in different tissues. Compared to control, there was no marked difference of As contents in plant tissues under BC treatment, indicating that BC had no  
Figure 3: The effect of different treatments on available Cd and As in soil. Different letters indicate that the differences are statistically significant (\(p<0.05\)). The data are mean \(\pm\) standard error (\(n=3\)), bars represent standard errors (\(n=3\)). Control, untreated soil; BC, applied 1% biochar; 1 BC-1 Fe(II), applied 0.5% biochar and 0.5% ferrous sulfate; 3 BC-1 Fe(II), applied 0.75% biochar and 0.25% ferrous sulfate; 5 BC-1 Fe(II), applied 0.83% biochar, and 0.17% ferrous sulfate.  
significant effect on inhibiting tissues uptaking As. Conversely, the As uptake in tissues increasing with the mass decreased of Fe(II) in BC+Fe(II) treatments, and 1 BC-1 Fe(II) treatment was more prominent. Similarly, the growth of rice has been inhibited in untreated soil (control), resulting in low yields and inability for digest analysis of grain, which analyzed the distribution of As under different treatments and speculated that the As content in grain was the same as that in BC treatment.