Silica nanoparticles alleviate mercury toxicity via immobilization and inactivation of Hg(ii) in soybean (Glycine max)

Mercury (Hg) pollution is a worldwide concern. Silica nanoparticles (nano-SiO2) can be released into ecosystems through natural and anthropogenic (engineered nano-SiO2) processes. Here, the influence of two sizes (30 nm and 50 nm) of artificial nano-SiO(2)on Hg accumulation in soybean plants, the chemical form and distribution of Hg in plant tissues and the levels of chlorophyll and antioxidant enzymes in plants were investigated. The results showed that both sizes of nano-SiO(2)amendments alleviated the growth inhibition induced by Hg and reduced the accumulation (62.2-83.6% in roots; 67.9-75.7% in stems; 45.0-70.7% in leaves lower with nano-SiO(2)amendmentsvs.Hg-only exposure) and translocation (transport rates: 0.18-0.19 with nano-SiO(2)amendmentsvs.0.22-0.26 Hg-only exposure) of Hg in soybean seedlings. Compared with the Hg-only exposed groups, nano-SiO(2)amendments significantly reduced the Hg concentrations in the epidermis and pericycle of the roots and stems, especially the pericycle measured by synchrotron radiation X-ray fluorescence (SRXRF). The application of nano-SiO(2)also ameliorated the chlorophyll decrease (15.3-50.1% higher with nano-SiO(2)amendmentsvs.Hg-only exposure) and antioxidant enzyme increase (20.7-33.2% lower with nano-SiO(2)amendmentsvs.Hg-only exposure) induced by Hg stress. Additionally, the RS-Hg-SR bonding form in the roots of nano-SiO(2)treated groups significantly decreased when compared with that of Hg-only exposed groups, and over 85% of the total Hg content was present in the form of R-Hg-Cl, which was largely consistent with the original Hg exposure species and indicated a low incorporation rate of Hg into plant tissues. This study explored the mechanism of nano-SiO(2)against Hg toxicity in plants, and offered a new passivating agent option for Hg remediation.