Effects of FeO nanoparticles and nano hydroxyapatite on Pb and Cd stressed rice (Oryza sativa L.) seedling.

Nowadays, Lead (Pb) and Cadmium (Cd) contamination in rice is an important worldwide environmental concern. FeO nanoparticles (FeO NPs) and Nano hydroxyapatite (n-HAP) are promising materials to manage Pb and Cd contamination. This study systematically investigated the effect of FeO NPs and n-HAP on Pb and Cd stressed rice seedlings' growth, oxidative stress, Pb and Cd uptake and subcellular distribution in roots. Furthermore, we clarified the immobilization mechanism of Pb and Cd in the hydroponic system. FeO NPs and n-HAP could reduce Pb and Cd uptake of rice mainly through decreasing Pb and Cd concentrations in culture solution and combining with Pb and Cd in root tissues. Pb and Cd were immobilized by FeO NPs through complex sorption processes and by n-HAP through dissolution-precipitation and cation exchange, respectively. On the 7th day, 1000 mg/L FeO NPs reduced the contents of Pb and Cd in shoots by 90.4% and 95.8%, in roots by 23.6% and 12.6%, 2000 mg/L n-HAP reduced the contents of Pb and Cd in shoots by 94.7% and 97.3%, in roots by 93.7% and 77.6%, respectively. Both NPs enhanced the growth of rice seedlings by alleviating oxidative stress and upregulating glutathione secretion and antioxidant enzymes activity. However, Cd uptake of rice was promoted at certain concentrations of NPs. The subcellular distribution of Pb and Cd in roots indicated that both NPs decreased the percentage of Pb and Cd in the cell wall, which was unfavorable for Pb and Cd immobilization in roots. Cautious choice was needed when using these NPs to manage rice Pb and Cd contamination.