Co-utilization of sepiolite and ferromanganese ore reduces rice Cd and As concentrations via soil immobilization and root Fe-Mn plaque resistance

Study on the adsorption performance of carbon-magnetic modified sepiolite nanocomposite for Sb(V), Cd(II), Pb(II), and Zn(II): Optimal conditions, mechanisms, and practical applications in mining areas

A carbon-magnetic modified sepiolite nanocomposite (γ-Fe2O3/SiO2-Mg(OH)2@BC) was synthesized using a hydrothermal method, consisting of γ-Fe2O3, activated sludge biochar (BC), and alkali-modified sepiolite. Its ability to remove heavy metals such as Sb(V), Pb(II), Cd(II), and Zn(II) was investigated through adsorption experiments. Using response surface optimization, the optimal adsorption conditions were determined: adsorption time = 3.78 h, pH = 2.63, initial concentration = 15.78 mg/L, temperature = 35.14°C, and adsorbent dosage = 100.71 mg. Characterization results revealed that the main adsorption mechanisms included complexation, π-π interactions, and electrostatic attraction. Kinetic and isotherm model analyses indicated that the adsorption process of γ-Fe2O3/SiO2-Mg(OH)2@BC adhered to the pseudo-second-order kinetic model and the Freundlich isotherm model, primarily involving multilayer chemical adsorption. The application of this composite material in complex aquatic environments in antimony mining areas demonstrated promising practical results, as well as excellent regeneration performance. This study provides technical and theoretical support for the treatment of complex heavy metal wastewater in antimony mining areas and lays a foundation for the development of novel carbon-magnetic modified nanocomposite adsorbents.

Sepiolite immobilizes soil Cd to optimize microbial community structure thereby promoting wheat growth and reducing Cd accumulation

Immobilization remediation is a widely employed technology that effectively reduces the migration rate and bioavailability of cadmium (Cd). Sepiolite, a commonly used remediation agent, has proven effective in decreasing soil Cd availability and reducing Cd accumulation in agricultural products. However, further investigation is needed to understand the impact of sepiolite on soil environmental quality and microbial communities. If we add sepiolite to the soil, the soil microbial community structure will be improved, and the abundance of bacteria associated with Cd-fixing and plant growth-promoting will be enhanced, which will significantly immobilize soil Cd thereby enhancing Cd tolerance and reducing Cd uptake in wheat. In this study, field experiments were conducted to assess the effects of sepiolite on wheat yield traits, Cd concentration in various organs, Cd transport and enrichment coefficients in wheat, soil pH and Cd availability, and soil microbial communities. The findings confirm that applying sepiolite in the field enhanced the main yield traits of wheat, significantly elevated soil pH by 0.30-1.04 units, reduced Cd bioavailability by 55.46 % -93.27 % (P < 0.05), and decreased Cd accumulation in wheat by regulating Cd transport and enrichment in different plant organs. The most substantial changes were observed when the sepiolite application rate reached 4500 kg ha-1. Moreover, the study noted an increase in the relative abundance of dominant species such as Bacteroidota, Acidobacteria, Myxococcota, and Patescibacteria at the phylum level, as well as Sphingomonas at the genus level (3.35 % -39.27 %). This shift indicated an optimized microbial community structure. Furthermore, the relative abundance of soil Cd fixing and promoting bacterial communities, including Massilia, Pseudomonas, and Pantoea, respectively increased by 80.20 %, 64.91 %, and 85.19 % when the usage of sepiolite reaches 4500 kg ha-1. The research underscores that sepiolite can effectively immobilize Cd in soil, enhance the microbial community structure of Cd-contaminated soil, reduce Cd accumulation in wheat, and promote the safe production of agricultural products.

Foliar application of zinc and selenium regulates cell wall fixation, physiological and gene expression to reduce cadmium accumulation in rice grains

Zinc (Zn) and selenium (Se) are beneficial elements for crops, enhancing crop quality and alleviating heavy metal toxicity. However, there is limited research on the role of foliar Zn and Se in the mechanism of reducing cadmium (Cd) uptake in crops. A field experiment was conducted to investigate the effect on subcellular distribution, leaf antioxidant enzyme activities, and the transcriptional regulation in the process of Cd accumulation of rice grains after foliar applications of Zn, Se, and their mixed solutions (ZnSe). The results show that Zn and ZnSe reduced Cd content in the grains of three different rice (13.9 %-21.8 %/11.9 %-29.5 %) by enhancing the fixation capacity of Cd in the flag leaf by improving the binding efficiency between pectin and Cd in the cell wall. Increased flag leaf antioxidant enzyme activities further mitigated the toxic effects of Cd on rice, while Zn and ZnSe treatments upregulated genes related to metal-binding proteins and antioxidant enzymes and downregulated metal transport genes. This study systematically elucidates the mechanisms by which foliar application of ZnSe alleviates Cd toxicity through the regulation of gene expression and physiological functions, providing a theoretical basis for reducing Cd accumulation in rice and ensuring the safe production of food.

Long-term effects of compound passivator coupled with silicon fertilizer on the reduction of cadmium and arsenic accumulation in rice and health risk evaluation

Cadmium (Cd) and arsenic (As) are precedence-controlled contaminants in paddy soils, that can easily accumulate in rice grains. Limestone and sepiolite (LS) compound passivator can obviously reduce Cd uptake in rice, whereas Si fertilizer can effectively decrease rice As uptake. Here, the synergistic effects of the LS compound passivator coupled with Si fertilizer (LSCS) on the soil pH and availability of Si, Cd, and As, as well as rice grain Cd and As accumulation and its health risk were studied based on a 3-year consecutive field experiment. The results showed that the LSCS performed the best in terms of synchronously decreasing soil Cd and As availability and rice Cd and As uptake. In the LSCS treatments, soil pH gradually decreased with the rice-planting season, while soil available Cd and As contents gradually increased, suggesting that the influence of LSCS on Cd and As availability gradually weakened with rice cultivation. Nonetheless, the contents of Cd and inorganic As (i-As) in rice grains treated with LSCS were slightly affected by cultivation but were significantly lower than the single treatments of LS compound passivator or Si fertilizer. According to the Cd and As limit standards in food (GB2762-2022), the Cd and i-As content in rice grains can be lowered below the standard by using the 4500 kg/hm2 LS compound passivator coupled with 90 kg/hm2 Si fertilizer in soil and spraying 0.4 g/L Si fertilizer on rice leaves for at least three years. Furthermore, health risk evaluation revealed that LSCS treatments significantly reduced the estimated daily intake, annual excess lifetime cancer risk, and hazard quotient of Cd and i-As in rice grains. These findings suggest that LSCS could be a viable approach for reducing Cd and As accumulation in rice grains and lowering the potential health risks associated with rice.