Sequestration of strontium, nickel, and cadmium on glomalin-related soil protein: Interfacial behaviors and ecological functions

Immobilization mechanisms of Sr(II), Ni(II), and Cd(II) on glomalin-related soil protein in mangrove sediments at the microscopic scale

Glomalin-related soil protein (GRSP) is a significant component in the sequestration of heavy metal in soils, but its mechanisms for metal adsorption are poorly known. This study combined spectroscopic data with molecular docking simulations to reveal metal adsorption onto GRSP's surface functional groups at the molecular level. The EXAFS combined with FTIR and XPS analyses indicated that the adsorption of Cd(II), Sr(II), and Ni(II) by GRSP occurred mainly through the coordination of -OH and -COOH groups with the metal. The -COOH and -OH groups bound to the metal as electron donors and the electron density of the oxygen atom decreased, suggesting that electrostatic attraction might be involved in the adsorption process. Two-dimensional correlation spectroscopy revealed that preferential adsorption occurred on GRSP for the metal in sequential order of -COOH groups followed by -OH groups. The presence of the Ni-C shell in the Ni EXAFS spectrum suggested that Ni formed organometallic complexes with the GRSP surface. However, Sr-C and Cd-C were absent in the second shell of the Sr and Cd spectra, which was attributed to the adsorption of Sr and Cd ions with large hydration ion radius by GRSP to form outer-sphere complexes. Through molecular docking simulations, negatively charged residues such as ASP151 and ASP472 in GRSP were found to provide electrostatic attraction and ligand combination for the metal adsorption, which was consistent with the spectroscopic analyses. Overall, these findings provided new insights into the interaction mechanisms between GRSP and metals, which will help deepen our understanding of the ecological functions of GRSP in metal sequestration.

Microplastics emerge as a hotspot for dibutyl phthalate sources in rivers and oceans: Leaching behavior and potential risks

Dibutyl phthalate (DBP) as a plasticizer has been widely used in the processing of plastic products. Nevertheless, these DBP additives have the potential to be released into the environment throughout the entire life cycle of plastic products. Herein, the leaching behavior of DBP from PVC microplastics (MPs) in freshwater and seawater and its potential risks were investigated. The results show that the plasticizer content, UV irradiation, and hydrochemical conditions have a great influence on the leaching of DBP from the MPs. The release of DBP into the environment increases proportionally with higher concentrations of additive DBP in MPs, particularly when it exceeds 15 %. The surface of MPs undergoes accelerated oxidation and increased hydrophilicity under UV radiation, thereby facilitating the leaching of DBP. Through 30 continuous leaching experiments, the leaching of DBP from MPs in freshwater and seawater can reach up to 12.28 and 5.42 mg g-1, respectively, indicating that MPs are a continuous source of DBP pollution in the aquatic environment. Moreover, phthalate pollution index (PPI) indicates that MPs can significantly increase DBP pollution in marine environment through land and sea transport processes. Therefore, we advocate that the management of MPs waste containing DBP be prioritized in coastal sustainable development.

Enhanced Cr(VI) stabilization by terrestrial-derived soil protein: Photoelectrochemical properties and reduction mechanisms

Glomalin-related soil protein (GRSP) is a stable iron-organic carbon mixture that can enhance heavy metal sequestration in soils. However, the roles of GRSP in the transformation and fate of Cr(VI) have been rarely reported. Herein, we investigated the electrochemical and photocatalytic properties of GRSP and its mechanisms in Cr(VI) adsorption and reduction. Results showed that GRSP had a stronger ability for Cr(VI) adsorption and reduction than other biomaterials, with the highest adsorption amount of up to 0.126 mmol/g. The removal efficiency of Cr(VI) by GRSP was enhanced (4-7%) by ultraviolet irradiation due to the hydrated electrons produced by GRSP. Fe(II) ions, persistent free radicals, and oxygen-containing functional groups on the GRSP surface as electron donors participated in the reduction of Cr(VI) under dark condition. Moreover, Cr(III) was mainly adsorbed on the -COOH groups of GRSP via electrostatic interactions. Based on 2D correlation spectroscopy, the preferential adsorption occurred on the GRSP surface for Cr(VI) in the sequential order of CO → COO- → O-H → C-O. This work provides new insights into the Cr(VI) adsorption and reduction mechanism by GRSP. Overall, GRSP can serve as a natural iron-organic carbon for the photo-reduction of Cr(VI) pollution in environments.

Research progress and prospect of glomalin-related soil protein in the remediation of slightly contaminated soil

Soil pollution caused by organic pollutants and potentially toxic elements poses a serious threat to sustainable agricultural development, global food security and human health. Therefore, strategies for reducing soil pollution are urgently required. Arbuscular mycorrhizal fungi (AMF)-assisted phytoremediation is widely recognized for its ability to remediate slightly-contaminated soil. Glomalin-related soil protein (GRSP) production by AMF is considered a vital mechanism of AMF-assisted phytoremediation. GRSP is widespread in soils and may contribute to the remediation of slightly contaminated soils. GRSP facilitates stabilization of pollutants in soils by interacting with pollutants owing to its abundant functional groups, recalcitrance, and long turnover time. It also enhances soil bioremediation and phytoremediation by stimulating soil microbial activity, improving soil structure, and providing nutrients for plants. However, research on GRSP is still in its early stages, and studies on contaminated soil remediation are limited. The effectiveness of GRSP in situ remediation remains to be proved. This review summarizes current knowledge regarding the GRSP distribution and its contribution to the remediation of slightly contaminated soils. Additionally, we present strategies to increase the GRSP content in contaminated soils, as well as prospects for future studies on the use of GRSP in contaminated soil remediation. This study focuses on recent developments that aim to improve awareness of the role of GRSP in soil remediation and relevant future directions.

Change in glomalin-related soil protein along latitudinal gradient encompassing subtropical and temperate blue carbon zones

Glomalin-related soil protein (GRSP), an abundant and eco-friendly bioproduct associated with arbuscular mycorrhizal fungi (AMF), contributes significantly to the soil particle aggregation and carbon sequestration. Although much research has been conducted on the storage of GRSP at different spatio-temporal scales in terrestrial ecosystems. However, the deposition of GRSP in large-scale coastal environments has not been revealed, which hinders an in-depth understanding of GRSP storage patterns and environmental controls, and this knowledge gap has become one of the key uncertainties in understanding the ecological functions of GRSP as blue carbon components in coastal environments. Therefore, we conducted large-scale experiments (spanning subtropical and warm temperate climate zones, coastlines over 2500 km) to test the relative contributions of environmental drivers that shape unique GRSP storage. In salt marshes of China, we found that the abundance of GRSP ranges from 0.29 mg g-1 to 1.10 mg g-1, and its concentration decreases with increasing latitude (R2 = 0.30, p < 0.01). The GRSP-C/SOC of salt marshes ranged from 4 % to 43 % and increased with the increase in latitude (R2 = 0.13, p < 0.05). The carbon contribution of GRSP does not follow the trend of increasing abundance, but is limited by the total amount of background organic carbon. In salt marsh wetlands, precipitation, clay content and pH are the main factors influencing GRSP storage. GRSP is positively correlated with precipitation (R2 = 0.42, p < 0.01) and clay content (R2 = 0.59, p < 0.01), but negatively correlated with pH (R2 = 0.48, p < 0.01). The relative contributions of the main factors to the GRSP differed across climatic zones. Soil properties, such as clay content and pH, explained 19.8 % of the GRSP in subtropical salt marshes (20°N < 34°N), however, in warm temperate salt marshes (34°N < 40°N), precipitation explained 18.9 % of the GRSP variation. Our study provides insight into the distribution and function of GRSP in coastal environments.