Unveiling the Role of Dissolved Organic Matter on the Hg Phytoavailability in Biochar-Amended Soils

Abstract

Biochar can effectively reduce the phytoavailability of mercury (Hg) in soil, but the mechanisms are not fully understood. In this study, the dynamic changes in Hg content adsorbed by the biochar (BC-Hg), Hg phytoavailability in the soil (P-Hg), and soil dissolved organic matter (DOM) characteristics were determined over a 60-day treatment period. Biochar obtained at 300 °C, 500 °C and 700 °C reduced the P-Hg concentration assessed by MgCl2 extraction by 9.4%, 23.5% and 32.7%, respectively. However, biochar showed a very limited adsorption on Hg, with the maximum BC-Hg content only accounting for 1.1% of the total amount. High-resolution scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) results showed that the proportion of Hg atoms in biochar after 60 d was barely detectable. Biochar treatment can shift soil DOM toward higher aromatic content and molecular weight. Additionally, the addition of high-temperature biochar increased more humus-like components, but low-temperature biochar increased more protein-like components. Correlation analysis and partial least squares path modeling (PLS-PM) showed that biochar promoted humus-like fractions formation to reduce the Hg phytoavailability. This research has deepened the understanding of the mechanisms by which biochar stabilizes Hg in agricultural soils.

Remediation of Cadmium and Lead in Mine Soil by Ameliorants and Its Impact on Maize (Zea mays L.) Cultivation

“…An elevation in soil pH is instrumental in remediating contaminated soils, primarily because most metals become less mobile under alkaline conditions, thereby decreasing their bioavailability [30]. Furthermore, this rise in soil pH enhances the negative charge, which in turn promotes the precipitation and adsorption of metals onto the soil surface [31]. Additionally, the introduction of ameliorants not only alters the soil's physicochemical properties but also effectively reduces the availability of cadmium (Cd) and lead (Pb) by inducing modifications in the soil's structure [32].…”