Simultaneous enhancement of soil properties along with water-holding and restriction of Pb-Cd mobility in a soil-plant system by the addition of a phosphorus-modified biochar to the soil

The fate and ecological risk of typical diamide insecticides in soil ecosystems under repeated application

Diamide insecticides are the third most widely used class of pesticides worldwide. However, the long-term impacts of repeated diamide applications on soil ecosystems remain unclear. This study investigated chlorantraniliprole (CLP) and cyantraniliprole (CYP) effects on soil ecosystems through simulated repeated exposures. Results showed both exhibited slow degradation in the soil, with repeated applications extending their persistence, particularly for CLP. Both significantly inhibited soil alkaline nitrogen and organic matter accumulation, while reducing urease and sucrase activities, with CLP exerting stronger inhibitory effects. Metagenomic analysis indicated that CLP and CYP notably reduced soil microbial diversity. Additionally, the two insecticides altered the soil microbial community structure and inhibited carbon-nitrogen metabolic pathways. Further analysis revealed that CLP treatment significantly decreased the relative abundances of Mesorhizobium and Marmoricola, whereas CYP treatment primarily reduced Clostridium_sensu_stricto_1. All of these genera exhibited significant positive correlations with key metabolic pathways in soil carbon and nitrogen cycling. Notably, the relative abundance of Sphingomonas increased significantly following CLP and CYP treatments, demonstrating potential degradation capabilities. Overall, both CLP and CYP posed ecological risks to soil ecosystems, with CLP exhibiting more severe impacts. These findings revealed the need for strengthened scientific management in actual production.

Treated wastewater reuse and its impact on soil properties and potato and corn growth

Water scarcity is a growing challenge in semi-arid regions. Many farmers have resorted to treated wastewater (TWW) as an available and low-cost water source. This study investigated the impact of irrigating potato (Solanum Tuberosum) and corn (Zea mays) with tertiary-treated (TW) and secondary-treated (SW) wastewater compared to freshwater, over two years. We studied the impact of TWW reuse on soil properties, soil microbes, crop yield, and potato tuber health. Irrigation of both corn and potato with TW significantly increased organic matter (OM) content; on average across both years and crops OM increased by about 35 % under SW and 42 % under TW. TWW irrigation also increased cation exchange capacity (CEC) by the second year under SW and TW in potato (average 67 %), and by the second year under TW in corn (average 13 %). TWW also enhanced soil fertility with no heavy metals contamination. However, potato field irrigated with SW showed high levels of total and thermotolerant coliforms in soil, exceeding predefined thresholds, in the second season. No microbial contamination was recorded in TW-irrigated fields, however, it raised salinity concerns compared to control with 935 mg Na /kg in TW soil compared to 465 mg/kg in control soil during the first season in potato soil. Significant increases in potato tillers, number of tubers (average 6 tubers/plant in TW vs 3 tubers/plant in the control), and tuber weight were recorded in season two under TW irrigation. Both SW and TW increased corn biomass during both seasons. In conclusion, TW is a sustainable alternative water source that enhances crop yields and improves soil quality. This study highlighted the critical role of TWW management and monitoring to address challenges such as salinity and microbial contamination. Further research is required to optimize TWW long-term reuse sustainable agriculture, balancing crop benefits while safeguarding human health.

Reducing Cd and Pb Accumulation in Potatoes: The Role of Soil Passivators in Contaminated Mining Soils

This work aimed to explore safe techniques for the utilization of farmland surrounding mining areas contaminated with heavy metals-specifically cadmium (Cd) and lead (Pb)-in order to achieve food security in agricultural production. A potato variety (Qingshu 9) with high Cd and Pb accumulation was used as the test crop, and seven treatments were set up: control (CK), special potato fertilizer (T1), humic acid (T2), special potato fertilizer + humic acid (T3), biochar (T4), calcium magnesium phosphate fertilizer (T5), and biochar + calcium magnesium phosphate fertilizer (T6). The remediation effect of the combined application of different passivators on the accumulation of cadmium and lead in potatoes in the contaminated soil of a mining area was studied. The results showed that, compared with CK, all passivator treatments improved the physical and chemical properties of the soil and reduced the available Cd and Pb content in the soil and in different parts of potatoes. The T6 treatment yielded the most significant reduction in the available Cd and Pb content in the soil, the Cd and Pb content in the potato pulp, and the enrichment factor (BCF) and transfer factor (TF) of the potatoes. Compared with T4 and T5, the content of available Cd in the soil decreased by 1.22% and 4.71%, respectively; the soil available Pb content decreased by 3.13% and 3.02%, respectively; the Cd content in the potato pulp decreased by 68.08% and 31.02%, respectively; and the Pb content decreased by 31.03% and 20.00%, respectively. The results showed that the application of biochar combined with calcium magnesium phosphate fertilizer had a better effect in terms of reducing the available Cd and Pb content in the soil and the Cd and Pb content in the potato flesh compared to their individual application. Biochar and calcium magnesium phosphate fertilizer can synergistically increase the content of soil available nutrients and reduce the activity of heavy metals in the soil to prevent the transfer and accumulation of cadmium and lead to potatoes, as well as improve their yield and quality. The results of this study provide technical support for safe potato planting and agricultural soil management.

Understanding of manganese-sulfur functionalized biochar: Bridging effect enhanced specific passivation of lead in soil

Widespread contamination of soils by neurotoxic lead ions (Pb) posed a serious risk to food security, but efficient treatment in soil remained a challenge. For the adsorption of Pb, DFT calculations were firstly performed to predict the synergistic effect of sulfhydryl-hydroxyl groups as well as the ability of sulfur ions to strengthen Pb-OH bonding. Consequently, Mn-S functionalized coffee ground biochar (MSBC) was then synthesized utilizing precipitation and impregnation methods. In the soil experiment, the removal efficiency of Pb reached 82.92%, exceeding the previous research results. In addition, it successfully restored the polluted farmland near the mining area and increased the plant height of Swiss chard by 186.23%. Subsequently, synergistic effect of sulfhydryl-hydroxyl groups was confirmed by XPS, FT-IR, and DFT calculations. Furthermore, the factors affecting the structural stability of O-Pb-S were discussed by regression analysis. These reflected that MSBC can enhance the removal efficiency of Pb in soil by mitigating the competition of impurity ions to adsorption sites. These findings may provide new insights into the development of the specific passivation materials for other heavy metals.

Sustainable soil rehabilitation with multiple network structures of layered double hydroxide beads: Immobilization of heavy metals, fertilizer release, and water retention

The remediation of heavy metal-contaminated soils necessitated a holistic approach that encompassed water and fertilizer conservation alongside soil property restoration. This study introduced the synthesis of (poly)acrylamide-layered double hydroxide gel spheres (PAM-LDH beads), which were designed to simultaneously immobilize heavy metals, control the release of fertilizers, and enhance soil water retention. Laboratory soil experiments under diverse conditions highlighted the superior performance of PAM-LDH beads in the immobilization of hexavalent chromium (Cr(VI)). The layered double hydroxide (LDH) component was identified as the key player in Cr(VI) immobilization, with anion exchange being the predominant mechanism. Notably, the encapsulated urea within the beads was released independently of environmental influences, governed by a concentration gradient across the beads surface. This release process was characterized by an initial phase of absorptive swelling followed by a diffusive phase. The impact on plant growth was assessed, revealing that PAM-LDH beads significantly curtailed Cr(VI) accumulation and alleviated its phytotoxic effects. Changes in the carbon (C) and nitrogen (N) content of the plants suggested that the urea encapsulated within the beads served as a nutrient source, contributing to soil fertility. Moreover, the water-holding capacity and soil-water characteristic curves of PAM-LDH beads suggested that these superabsorbent beads could delay soil water evaporation. The observed shifts in microbial community structure provided evidence for the enhancement of soil carbon and nitrogen cycles, indicative of improved soil properties.

The application of P-modified biochar in wastewater remediation: A state-of-the-art review

Phosphorus modified biochar (P-BC) is an effective adsorbent for wastewater remediation, which has attracted widespread attention due to its low cost, vast source, unique surface structure, and abundant functional groups. However, there is currently no comprehensive analysis and review of P-BC in wastewater remediation. In this study, a detailed introduction is given to the synthesis method of P-BC, as well as the effects of pyrolysis temperature and residence time on physical and chemical properties and adsorption performance of the material. Meanwhile, a comprehensive investigation and evaluation were conducted on the different biomass types and phosphorus sources used to synthesize P-BC. This article also systematically compared the adsorption efficiency differences between P-BC and raw biochar, and summarized the adsorption mechanism of P-BC in removing pollutants from wastewater. In addition, the effects of P-BC composite with other materials (element co-doping, polysaccharide stabilizers, microbial loading, etc.) on physical and chemical properties and pollutant adsorption capacity of the materials were investigated. Some emerging applications of P-BC were also introduced, including supercapacitors, CO2 adsorbents, carbon sequestration, soil heavy metal remediation, and soil fertility improvement. Finally, some valuable suggestions and prospects were proposed for the future research direction of P-BC to achieve the goal of multiple utilization.

Effects of three plant growth-promoting bacterial symbiosis with ryegrass for remediation of Cd, Pb, and Zn soil in a mining area

The quality of soil containing heavy metals (HMs) around nonferrous metal mining areas is often not favorable for plant growth. Three types of plant growth promoting rhizobacteria (PGPR)-assisted ryegrass were examined here to treat Cd, Pb, and Zn contaminated soil collected from a nonferrous metal smelting facility. The effects of PGPR-assisted plants on soil quality, plant growth, and the migration and transformation of HMs were evaluated. Results showed that inter-root inoculation of PGPR to ryegrass increased soil redox potential, urease, sucrase and acid phosphatase activities, microbial calorimetry, and bioavailable P, Si, and K content. Inoculation with PGPR also increased aboveground parts and root length, P, Si, and K contents, and antioxidant enzyme activities. The most significant effect was that the simultaneous inoculation of all three PGPRs increased the ryegrass extraction (%) of Cd (59.04-79.02), Pb (105.56-157.13), and Zn (27.71-40.79), compared to CK control (without fungi). Correspondingly, the inter-root soil contents (%) of total Cd (39.94-57.52), Pb (37.59-42.17), and Zn (34.05-37.28) were decreased compared to the CK1 control (without fungi and plants), whereas their bioavailability was increased. Results suggest that PGPR can improve soil quality in mining areas, promote plant growth, transform the fraction of HMs in soil, and increase the extraction of Cd, Pb, and Zn by ryegrass. PGPR is a promising microbe-assisted phytoremediation strategy that can promote the re-greening of vegetation in the mining area while remediating HMs pollution.

Chemical and mechanical coating of sulfur on baby corn biochar and their role in soil Pb availability, uptake, and growth of tomato under Pb contamination

In recent ages, industrial revolution and natural weathering processes have been increasing lead (Pb) contamination in agricultural soils, therefore, green remediation technologies are becoming attractive and cost-effective. In the current pot study, 1% and 2% (w/w) application rates of sulfur (S) alone and novel chemo-mechanically S-modified baby corn biochars (CSB and MSB) were applied in a Pb-contaminated (500 mg/kg) soil to evaluate tomato (Lycopersicon esculentum L.) growth, Pb uptake and its soil availability. The results from SEM-EDS and XRD patterns confirmed the S enrichment on the surface of baby-corn biochar. Further, Pb treatment alone imposed a significant reduction in biomass accumulation, photosynthetic pigments, antioxidative mechanism, root traits, and Pb-tolerance index because of increased soil Pb availability and its uptake, translocation and biological accumulation in various tissues of tomato. However, incorporation of lower rate of elemental S (1%) and higher rates of biochars, especially chemically S-modified biochar, CSB (2%) significantly improved dry biomass production, Pb-tolerance index, physiological attributes and antioxidative defense system of tomato plants. These results might be due to a prominent decrease in soil Pb availability by 37.5%, Pb concentration in shoot by 66.7% and root by 58.3%, soil to root transfer by 33.8%, and root to shoot transfer by 20.2% in tomato plants under 2% application rate of CSB, as compared with the Pb treatment without any amendment. Moreover, sulfur treatment induced a significant impact in reduction of soil pH (from 8.97-7.47) as compared to the biochar treatments under Pb-toxicity. The current findings provided an insight that 2% chemically S-modified biochar (CSB) has significant potential to improve the tomato growth by reducing Pb bioavailability in the Pb-contaminated soil, compared to the S alone and MSB amendments.