## 5 Conclusions  
In summary, the accumulation of BDE-153 in the amaranth roots was significantly affected by the Cd dose. A low concentration of Cd promoted the uptake of BDE-153 by the amaranth roots and a high concentration inhibited the uptake of BDE-153 by the amaranth roots. Interestingly, the interaction of BDE-153 with Cd also inhibited the migration of Cd from the roots to the shoots of the amaranth. According to the kinetic results on the pollutants accumulated by amaranth, the concentrations of Cd and BDE-153 in the roots, stems, and leaves of the amaranth increased with prolongation of the culture time, but the rate of increase decreased with prolongation of the culture time. In addition, the interaction of BDE-153 with a high concentration of Cd (5 mg/L) significantly reduced the biomass and chlorophyll content, enhanced the toxicity to the root tip plasma membrane, and increased the antioxidant enzyme activity compared to with Cd or BDE-153 alone. Overall, this study provides data support showing that reasonable environmental risk assessment and pollution control technology should also consider the concentration range of combined pollution.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app14062631/s1](https://www.mdpi.com/article/10.3390/app14062631/s1)]([https://www.mdpi.com/article/10.3390/app14062631/s1](https://www.mdpi.com/article/10.3390/app14062631/s1)). Figure S1: Effects of different treatment conditions on biomass (a) and chlorophyll (b) of amaranth. The same letters in the figure indicate that the difference is not significant (\(p<0.05\)) (the same below). (Cd0-Cd3 represented the concentrations of Cd were 0, 0.1, 1 and 5 mg/L, respectively. B0-B2 represented the concentrations of BDE-153 were 0, 5 and 20 ug/L, respectively.) Different letters represent significant differences in data at the \(p<0.05\) level (LSD's test); Table S1: Initial concentrations of BDE-153 and Cd in different nutrient solutions; Table S2: Plant microwave digestion setting program; Table S3: Accumulation of Cd in roots, stems and leaves of Amaranth in different treatment groups (mg\(\cdot\)kg\({}^{-1}\) dry weight); Table S4: Accumulation of BDE-153 in the roots, stems and leaves of Amaranth in different treatment groups (ng\(\cdot\)g\({}^{-1}\) dry weight); S1: Hoagland solution components; S2: Sample cleaning and GC-MS analysis; S3: Apical plasma membrane integrity and apical -O\({}_{2}\)- fluorescence intensity; S4: Method for determination of antioxidant enzyme activity. Reference [43] are cited in the supplementary materials.  
**Author Contributions:** Writing, W.P.; experimental design and data measurement and analysis, J.W.; providing graphical representations, S.C.; organisation and modification, S.W.; supervision, conceptualisation, responsibility for the research activity, reviewing, and editing, C.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by Ministry of Science and Technology of China (2023 YFC3706803) and the Fundamental Research Funds for the Central Universities and the 111 program, the Ministry of Education, China (T2017002).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflicts of interest.