## 3 Results
### Accumulation and Transfer of the Combined Pollutants in Amaranth
#### 3.1.1 Cd Content in the Roots, Stems, and Leaves of Amaranth Affected by BDE-153  
As shown in Table S3 and Figure 1, after 8 days of hydroponics, amaranth root systems under different pollution treatments accumulated Cd from the nutrient solution. Regardless of Cd alone, the Cd content in the amaranth roots, stems, and leaves increased significantly with an increasing Cd concentration in the nutrient solution. For example, when treated with Cd alone, the Cd content in the roots, stems, and leaves of the 5 mg/L Cd treatment group was 6.4 times, 20.9 times, and 5.3 times that of the 0.1 mg/L Cd treatment group, respectively. The translocation factor decreased with an increase in the Cd concentration in the nutrient solution, indicating that the toxicity of Cd in amaranth increased with the increase in Cd concentration, which inhibited the accumulation of Cd in amaranth (Figure 1).  
Under the composite treatment of Cd and BDE-153, with an increase in the BDE-153 concentration in the nutrient solution, the Cd content in the roots, stems, and leaves of the amaranth was higher than that of the single Cd contamination treatment group, indicating that BDE-153 promoted the uptake of Cd by the amaranth to a certain extent, which may be the result of the cotransporter of Cd and BDE-153 pollutants at a certain concentration. However, the translocation factor of Cd decreased with an increase in the BDE-153 concentration, which indicated that the interaction or competition between BDE-153 and Cd had a certain inhibitory effect on the transfer of Cd from the amaranth roots to the aboveground parts, and the higher the concentration of BDE-153 was, the more obvious the inhibitory effect was. In addition, the translocation factors of all treatment groups were between 0.17 and 0.44, which were less than 1, indicating that the absorption and enrichment ability of Cd in the underground parts of the amaranth was much greater than that in the aboveground parts.  
Combined with Table S3 and Figure 1, it can be concluded that the addition of BDE-153 will promote the uptake of Cd from nutrient solution by amaranth but will inhibit the transfer of Cd from the roots to the shoots in amaranth to a certain extent. This may be due to the addition of low-concentration pollutants, which promotes the secretion of carbohydrates and organic acids in the roots and changes the composition of the root exudates, thus improving the uptake of Cd from the solution by the plants [3]. At the same  
Figure 1: Distribution and translocation factors of Cd in different tissues and organs of amaranth under different treatments. (Cd\({}_{1}\)–Cd\({}_{3}\) represents Cd concentrations of 0.1, 1, and 5 mg/L, respectively. B\({}_{0}\)–B\({}_{2}\) represents BDE-153 concentrations of 0, 5, and 20 mg/L, respectively).  
time, studies have shown that BDE-153 can cause damage to plants' cell walls, resulting in an increased uptake of pollutants by the plant roots [30]. Under the interaction of pollutants, the toxic effect of the pollutants on the roots of amaranth is greater, which leads to the failure of the roots to transport the heavy metal Cd to the shoots.