NSRRC Activity Report 2023

072 NSRRC ACTIVITY REPORT 2023 absorption fine structure spectroscopy (EXAFS) analysis showed more iron in 0.5LDH-CTS, which enhanced phosphate intercalation. LDHs mixed with CTS increased phosphate sorption sites. After significant degradation, iron (oxyhydrox) oxides prevailed, thereby facilitating sustained phosphate release. Mg–Fe LDHs showed the highest phosphate absorption capacity, but 0.5LDH-CTS demonstrated the potential for prolonged fertilization and soil carbon stabilization, showing the longest phosphate release time of over 2688 hours. Fe-EXAFS and P-XANES analyses revealed diverse P retention mechanisms, including isomorphic substitution and organic P binding. Over time, LDHs transformed into iron (oxyhydrox)oxides, and the Fe(II) regions in 0.5LDH-CTS also contributed to P retention, indicating their potential effectiveness as slow-release P fertilizers. Regarding food safety, an international collaborative team led by Shan-Li Wang from National Taiwan University utilized TPS 44A QSXAS and SPring-8 BL37XU μ-XRF beamlines to conduct a detailed analysis of how rice absorbs the toxic element indium from the soil. 2 Indium, a toxic element, can enter our diet through soil contamination and the consumption of rice. Areas near industrial zones often have higher indium pollution levels, posing significant health risks such as cancer. Indium can interfere with plant growth and nutrient uptake. The bioavailability of indium in plants is influenced by its form in the soil and by soil pH. In paddy fields, the form and solubility of indium can change with fluctuations in redox conditions and pH values throughout the rice growth cycle. This study used X-ray absorption spectroscopy, micro-X-ray fluorescence (micro-XRF) mapping, micro-X-ray absorption spectroscopy technologies, and sequential soil extraction methods to investigate how the chemical form and solubility of indium in flooded rice fields change at different stages of rice growth. As shown in Fig. 2 , X-ray absorption spectroscopy indicates that indium is primarily found as In(III) in association with iron hydroxides, which affects its solubility. As rice grows, the association with iron hydroxides lessens, and indium hydroxide and phosphate forms become more common because of reduced conditions that dissolve iron oxides. Sequential extractions confirm that indium is mostly found in the reducible fraction of soil, in line with the presence of In(III) bound to iron hydroxides. Soil indium distribution changes with rice growth, suggesting the dissolution of iron hydroxide bound indium and its subsequent absorption by soil particles. In Fig. 3 , micro-XRF mapping reveals indium’s presence in soil, which is correlated with minerals, thus providing insight into its uptake by rice roots, which is initially high. However, as flooding duration increases, the soil pH rises and the dissolved indium forms new compounds, reducing its bioavailability to plants and limiting its migration to the roots (as shown in Fig. 3(e) ). The authors suggest that agricultural practices such as water management could affect the bioavailability of indium and its potential environmental impact. They also recommend using alkaline or phosphate soil amendments in the early stages of rice growth to reduce the bioavailability of indium in the paddy soil, thereby reducing the health risk posed by indium. Future strategies may include using economically viable methods to immobilize indium on a larger scale. In summary, by utilizing synchrotron radiation techniques at the NSRRC, researchers are improving food production with innovative solutions to tackle the inefficiency and scarcity of phosphorus. Moreover, investigation into the absorption of hazardous indium by rice is intended to enhance food safety. These breakthroughs have the potential to establish safer agricultural practices and contribute to solving the global food crisis in a manner that aligns with the Sustainable Development Goals of the United Nations. (Reported by Chun-Chieh Wang) Fig. 2 : (a) First-derivative spectra of indium K-edge X-ray XANES and (b) indium k 3 -weighted EXAFS spectra (open circle) and linear combination fits (solid lines) of the soil samples spiked with 1.0 mmol kg −1 indium before (0 d) and after (100 d) rice growth. [Reproduced from Ref. 2]