Pyrolysis temperature and biochar redox activity on arsenic availability and speciation in a sediment

Influence of biochar on the partitioning of iron and arsenic from paddy soil contaminated by acid mine drainage

Paddy fields contaminated by arsenic-containing acid mine drainage (AMD) may also have rich iron in soil. Whether this iron can be loaded onto biochar to passivate the dissolved arsenic is worth further exploration. Soil was mixed with biochar prepared at 400, 550, and 700 °C and incubated under alternating anaerobic and aerobic conditions. Soil, soil solution and biochar samples were analysed using ICP-MS, FTIR, SEM, XPS, etc. The results showed that biochar prepared at lower pyrolysis temperatures contained a higher number of functional groups. Under the combined action of microorganisms, primarily from the Firmicutes phylum, biochar promoted the dissolution of arsenic-containing iron oxides in soil, with the residual arsenic also undergoing transformation. The biochar rapidly loaded dissolved iron onto its surface, likely in the form of Fe3O4 and FeOOH, and adsorbed arsenic primarily as As(III). Although the iron oxides detached over time, they were more stable on the biochar prepared at 400 °C compared to those prepared at higher pyrolysis temperatures. Meanwhile, the arsenic content on the biochar increased, raising the As/Fe molar ratio to above that of the soil. This study lays the foundation for further exploring the long-term use of biochar in AMD-contaminated paddy fields.

Effects of Biochar on Arsenic-Contaminated Soil: Chemical Fractionation, Vegetation Growth, and Oral Bioaccessibility

Contamination by arsenic (As) is a pressing environmental and public health issue requiring urgent remediation strategies. One cost-effective and eco-friendly method involves adding stabilizing agents to soils to reduce As mobility. However, remediation projects must also address potential ecotoxicological effects. These effects may include harmful impacts on both aquatic and terrestrial organisms, including plants, disruption of ecosystem balance, and the potential bioaccumulation of toxic substances in the food chain. Biochar from organic fraction of municipal solid waste (OFMSW) shows promise for As-contaminated soil remediation. Pot experiments were conducted with soil contaminated with As (100 mg kg-1) and amended with biochar produced at three different temperatures (300, 500, and 700 °C) and addition rates (1 and 5%, w/w). Chemical fractionation showed higher As concentration in a less accessible fraction (F4). Biochar amendments did not significantly differ from the control in As immobilization, but enhanced maize (Zea mays) growth and reduced As uptake, with the most promising results seen with 1% of biochar produced at 700 °C. The bioaccumulation factor (BCF) and translocation factor (TF) were both lower than 1, indicating a low absorption of As and minimal translocation from the root to the shoot. The bioaccessible percentage was higher in the samples treated with biochar compared to the control. According to the results, biochar showed no satisfactory potential for As immobilization and its approach of pretreatment/modification should be tested regarding possible improvements in the immobilization performance of As. Since most contaminations involve multiple contaminants simultaneously, it is essential to test the interactions between arsenic and other pollutants to understand the effects of biochar in such complex scenarios, which will be explored in future studies. Graphical abstract.

Well-managed grass is a key strategy for carbon storage and stabilization in anthropized Amazon soils

Soils under anthropic use in the Amazon region are often associated with soil carbon (C) stock losses. More recently, the restoration of degraded pastures and the introduction of integrated systems have changed this pattern, and soil C accumulation is often observed. This study evaluated an 11-year field experiment to quantify soil C changes and elucidate C stabilization mechanisms in areas under anthropic uses in the southern Amazon of Brazil. Four land use systems were evaluated: crop succession (CS), integrated crop-livestock (ICL), integrated crop-livestock-forest (ICLF), and a well-managed pasture (MP). Land uses with a greater presence of well-managed grass increased soil C stocks, especially in the top 10 cm, with values of 30.9, 29.7, 36.5, and 39.4 Mg ha-1 in the CS, ICLF, ICL, and MP systems, respectively. Compared to the baseline, ICL and MP systems showed soil C accumulation rates of 0.68-0.95 Mg C ha-1 yr-1. Greater aggregate stability and higher mineral-associated organic carbon (MAOC) were observed in both MP and ICL. X-ray photoelectron spectroscopy verified 11%, 38%, and 32% more recalcitrant C groups (aliphatic/aromatic) in the MP system than ICL, ICLF, and CS at 0-5 cm. In the ICLF system, the eucalyptus row showed 15% lower soil C stocks, less MAOC, and less abundance of recalcitrant groups than the inter-row position. Land use systems with long-term spatial-temporal use of grass in well-managed pastures or ICL promoted greater C stabilization through intra-aggregate occlusion, mineral sorption, and chemical recalcitrance, representing a good strategy to enhance C storage in Amazon anthropized soils.

The Mechanism of Arsenic Release in Contaminated Paddy Soil with Added Biochar: The Role of Dissolved Organic Matter, Fe, and Bacteria

The addition of biochar inevitably modifies the acidity (pH), redox potential (Eh), and dissolved organic matter (DOM) level in the soil. These alterations also have coupled effects on the cycling of iron (Fe) and the composition of bacterial communities, thereby impacting the speciation and availability of arsenic (As) in the soil. This study explored the potential mechanisms through which biochar affects As in paddy soil during flooded cultivation with different pyrolysis temperature biochars (300 °C, 400 °C, and 500 °C) added. The results revealed that the TAs concentration increased in the initial 15 days of soil cultivation with SBC300 or SBC400 addition because increasing the concentration of DOM induced the mobility of As though the formation of As-DOM complexes. Meanwhile, biochar addition elevated the pH, decreased the Eh, and promoted the transformation of specific adsorbed As (A-As) and amorphous iron oxide-bound As (Amo-Fe-As) to supernatant As through enhancing the reductive dissolution of Fe(oxy)(hydr)oxides. Moreover, the biochar altered the relative abundance of As (V)-reducing bacteria (such as Firmicutes) and As (III)-oxidizing bacteria (such as Chloroflex), thereby affecting As speciation. However, these mechanistic effects varied depending on the pyrolysis temperature of the biochar. The microbial composition of SBC300 and SBC400 were similar, with both containing larger populations of Enterobacteriaceae (AsRB) and pseudomonas (FeRB) compared to CK and SBC500. It was proposed that lower pyrolysis temperatures (300 °C and 400 °C) are more favorable for the dissolution of Fe(oxy)(hydr)oxides and the reduction of As (V). However, the biochar from the higher pyrolysis temperature (500 °C) showed environmental impacts akin to the control group (CK). This study demonstrated potential mechanisms of biochar's effect on As and the role of pyrolysis temperature.

Redox conditions and biochar pyrolysis temperature affecting As and Pb biogeochemical cycles and bacterial community of sediment from mining tailings

Despite the widespread use of biochar for soil and sediment remediation, little is known about the impact of pyrolysis temperature on the biogeochemistry of arsenic (As) and lead (Pb) and microorganisms in sediment under reducing conditions. In this study, we investigated the effects of pyrolysis temperature and the addition of glucose on the release and transformation of As and Pb, as well as their potential effects on the bacterial community in contaminated sediments. The addition of biochar altered the geochemical cycle of As, as it favors specific bacterial groups capable of changing species from As(V) to As(III) through fermentation, sulfate respiration and nitrate reduction. The carbon quality and content of N and S in solution shaped the pH and redox potential in a way that changed the microbial community, favoring Firmicutes and reducing Proteobacteria. This change played a fundamental role in the reductive dissolution of As and Pb minerals. The addition of biochar was the only efficient way to remove Pb, possibly as a function of its sorption and precipitation mechanisms. Such insights could contribute to the production or choice of high-efficiency biochar for the remediation of sediments subjected to redox conditions.

Magnetic phytic acid-modified kapok fiber biochar as a novel sorbent for magnetic solid-phase extraction of antidepressants in biofluids

BACKGROUND

Therapeutic drug monitoring (TDM) of antidepressants is essential for monitoring patient medication to avoid drug toxicity, complications, or nonadherence. Chromatographic techniques with high sensitivity and reproducibility are the main detection method for antidepressants. Effective pretreatment of biological sample processes is necessary prior to instrumental analysis. Magnetic solid-phase extraction (MSPE) has received much attention for its advantages of simple operation, rapidity, cost-effectiveness and low organic solvent consumption. Therefore, the development of a suitable and green magnetic sorbent for the detection of antidepressants in plasma and urine is apparently necessary. (88) RESULTS: A magnetic phytic acid-modified kapok fiber biochar sorbent (Fe3O4/PAKFBC) was successfully synthesized by pyrolytic impregnation and physical milling methods. Fe3O4/PAKFBC exhibited a large specific surface area (214 m2 g-1) and a rich pore structure (5-10 nm). The extraction equilibrium, using 10 mg Fe3O4/PAKFBC, can be completed in about 1 min. The density functional theory (DFT) results showed that the adsorption mechanism of Fe3O4/PAKFBC on the six antidepressants mainly included electrostatic interactions, van der Waals interactions, π-π interactions and weak hydrogen bonding. Examination using the greenness assessment tools showed that the developed method exhibited excellent greenness. By combining with liquid chromatography-ultraviolet (LC-UV), a quantitative method with good linearity (R2 > 0.993) and relative recoveries (92.4-107.7%) and negligible matrix effect (-11.5-6.0%) was developed. The Fe3O4/PAKFBC successfully detected six antidepressants in plasma and urine samples, requiring no pH adjustment with buffer salts. (142) SIGNIFICANCE: The environmental sustainability of the proposed methods was affirmed by six greenness evaluation tools, all indicating exceptional eco-friendliness. The Fe3O4/PAKFBC demonstrated outstanding greenness in both its creation and analytical application, proving highly effective in real sample applications and showcasing potential for broader use. This study contributes to a deeper and broader understanding of the microscopic adsorption mechanism, which can help in the optimization and development of more green sorbents. (69).