Williamson Gustave

Biochar is no longer considered merely a substitute for conventional fillers in asphalt materials; rather, it represents a multifunctional modifier that aligns with the goals of sustainable road design and urban mobility in smart cities. Its application now extends to the rheological modification of asphalt binders, mitigation of asphalt fume emissions, improvement in aging resistance and interfacial adhesion, and assessment of carbon sequestration potential. Biochar can improve the high-temperature stability, rutting and aging resistance, and asphalt–aggregate adhesion of asphalt materials in a suitable dosage, and at the same time reduce emissions of volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), hydrogen sulfide (H₂S), and other fumes. However, the above effects are highly dependent on the biochar feedstock, production process, physicochemical properties, particle size, dosage and degree of dispersion. An excess amount or uneven distribution will reduce the crack resistance and fatigue life at low temperatures; phase separation may also occur and VOC emissions will increase. Therefore, the main problem in this area has shifted from whether biochar is effective to when it can be applied for particular pavement performance goals, what pollutant control targets are aimed for, and over what life-cycle periods. This review integrates evidence obtained at the binder, mastic, and mixture scales and critically evaluates the influence of biochar on pavement performance, fume emissions, aging, interfacial adhesion, and environmental safety. It also argues that empirical dosage selection should be replaced by coordinated optimization of biochar structure, material performance, emission mitigation, and life-cycle impacts. Verification of the low-carbon benefits and environmental safety of biochar-modified asphalt will ultimately require standardized assessment frameworks and consistently defined system boundaries. Ultimately, this work provides a foundation for integrating biochar-modified asphalt into eco-friendly and resilient road infrastructures, aligning with the goals of smart urban mobility and sustainable transportation.

Eutrophication is a major threat to freshwater ecosystems, leading to harmful algal blooms, biodiversity loss, and hypoxia. Excessive nutrient loading, primarily from nitrates and phosphates, is driven by fertilizer runoff, sewage discharge, and agricultural practices. Sediment microbial fuel cells (sMFCs) have emerged as a potential bioremediation strategy for nutrient removal while generating electricity. Although various studies have explored ways to enhance sMFC performance, limited research has examined the relationship between external resistance, electricity generation, and nutrient removal efficiency. This study demonstrated effective nutrient removal from overlying water, with 1200 Ω achieving the highest nitrate and phosphate removal efficiency at 59.0% and 32.2%, respectively. The impact of external resistances (510 Ω and 1200 Ω) on sMFC performance was evaluated, with the 1200 Ω configuration generating a maximum voltage of 466.7 mV and the 510 Ω configuration generating a maximum current of 0.56 mA. These findings show that external resistance plays a major role in both electrochemical performance and nutrient-removal efficiency. Higher external resistance consistently resulted in greater voltage output and improved removal of nitrate and phosphate. The findings also indicate that sMFCs can serve as a dual-purpose technology for nutrient removal and electricity generation. The power output may be sufficient to support small, eco-friendly biosensing devices in remote aquatic environments while mitigating eutrophication.

Soils are critical regulators of elemental cycling, mediating interactions among carbon (C), iron (Fe), and arsenic (As) that influence ecosystem function, climate regulation, and environmental health. Soil organic carbon (SOC) represents the largest terrestrial carbon reservoir and is often considered a natural solution for mitigating climate change. However, the stability of SOC is strongly mediated by its interactions with Fe oxides and hydroxides, which can either protect organic matter through mineral associations or promote its loss under reducing conditions (Xu and Tsang, 2024; Hu et al., 2025). The transformation of Fe, in turn, directly governs the fate of As, one of the most hazardous environmental contaminants, through adsorption, reduction, and microbial methylation pathways (Gao et al., 2024; Tang et al., 2024). The complex interplay of these processes highlights the need for integrative approaches that couple soil chemistry, microbial ecology, and environmental engineering. While Fe minerals provide protective surfaces that stabilize SOC, their reductive dissolution can release both C and As into more labile pools, with microorganisms playing central roles in mediating redox transformations (Yao et al., 2025; Wang et al.,, 2024). Horizontal gene transfer and viral interactions further add layers of complexity (Wang et al., 2024; Liang et al., 2025). Yet, despite growing evidence for these interconnections, major knowledge gaps remain, particularly in predicting the dynamics of C–Fe–As coupling under fluctuating redox conditions and in understanding the roles of less-studied microbial groups. To address these challenges, this Research Topic brings together six contributions spanning mechanistic, methodological, and applied perspectives. Collectively, they shed light on the stabilizing functions of minerals, the roles of microbes in soil health and disease, the use of engineered amendments and bioreporters, and innovative bioelectrochemical approaches to pollution management. One set of studies focuses on the mineralogical and structural controls of soil processes. Li and Guo revealed how soil microaggregates vary along an elevation gradient in Tongbai Mountain, with Mn-and Fe-rich microaggregates at low elevations promoting metal mobility, while high elevations favored the formation of organo-mineral complexes that stabilized C, N, and Fe. This highlights how landscape position can mediate elemental coupling and provides a framework for anticipating how mountain soils may respond to climate change. In parallel, Chen and colleagues explored engineered soil amendments, showing that silicon– iron modified biochars effectively reduced the bioavailability of Cd and As in paddy soils by altering speciation pathways. Their work emphasizes the potential for Fe-and Si-based additives to immobilize contaminants while simultaneously influencing microbial functional genes involved in As oxidation and Cd precipitation. Together, these studies highlight the central role of Fe mineral phases, whether natural or engineered, in regulating C–Fe–As transformations and contaminant dynamics. A second theme centers on microbial tools and ecological perspectives. Zhang and co-authors provided an opinion on whole-cell bioreporter (WCBs) technology as an emerging tool for assessing As risk in soils. Unlike traditional chemical assays, WCBs can differentiate As species and measure bioavailable fractions, offering ecologically relevant insights into toxicity. Complementing this, Tong and colleagues reviewed the persistence and pathogenicity of Fusarium oxysporum in watermelon soils. Although focused on plant pathology, their review illustrates how soil microbial communities and environmental factors interact to sustain long-term pathogen survival, mirroring the challenges of predicting microbial mediation in C–Fe–As cycles. Both contributions underscore the value of microbial systems, whether as tools or as agents, for monitoring and managing soil processes. Technological innovation emerges as another unifying thread. Zhang and collaborators synthesized over 10,000 cases of microbial fuel cells' (MFCs) studies to identify the strongest drivers of performance. Their analysis showed that cathode chamber volume and surface area are key predictors of power density, while biological pretreatment of substrates significantly enhances efficiency. Importantly, MFCs are not only promising for energy generation but also for pollutant removal, including heavy metals and organics. Meanwhile, Tian and colleagues identified a new soilborne pathogen, Ilyonectria robusta, causing basal stem rot in Schisandra chinensis. Their study demonstrates how integrating molecular tools with field surveys can rapidly identify emerging risks to soil–plant systems, further reinforcing the importance of innovation in soil biogeochemistry and health research. Collectively, these contributions illustrate the interconnectedness of mineral, microbial, and technological dimensions in advancing soil science. Mineral studies demonstrate how natural and engineered Fe associations mediate contaminant dynamics; microbial perspectives highlight the dual roles of soil organisms as both sentinels and stressors; and technological innovations, from MFCs to WCBs, open new pathways for monitoring and remediation. Together, they provide a multifaceted view of the challenges and opportunities in managing C–Fe–As interactions in soils. While the studies in this Research Topic significantly broaden our understanding of soil biogeochemistry, they also point to critical areas for future research. There is a pressing need to integrate mineralogical, microbial, and engineering perspectives into predictive frameworks that can capture soil heterogeneity and dynamic redox processes. Future work should explore the underappreciated roles of viruses, archaea, fungi, and microplastics in shaping...

Soil and sediment contamination with heavy metals (HMs) is a critical environmental issue, posing significant risks to both ecosystems and human health. Whole-cell bioreporter (WCB) technology offers a promising alternative to traditional detection techniques due to its ability to rapidly assess the bioavailability of pollutants. Specifically, lights-on WCBs quantify pollutant bioavailability by measuring bioluminescence or fluorescence in response to pollutant exposure, demonstrating comparable accuracy to traditional methods for quantitative pollutant detection. However, when applied to soil and sediment, the signal intensity directly measured by WCBs is often attenuated due to interference from solid particles, leading to the underestimation of bioavailability. Currently, no standardized method exists to correct for this signal attenuation. This review provides a critical analysis of the benefits and limitations of traditional detection methods and WCB technology in assessing HM bioavailability in soil and sediment. Based on the approaches used to address WCB signal attenuation, correction methods are categorized into four types: the assumed negligible method, the non-inducible luminescent control method, the addition of a standard to a reference soil, and a pre-exposure bioreporter. We provide a comprehensive analysis of each method’s applicability, benefits, and limitations. Lastly, potential future directions for advancing WCB technology are proposed. This review seeks to establish a theoretical foundation for researchers and environmental professionals utilizing WCB technology for pollutant bioavailability assessment in soil and sediment.

In recent years microbial fuel cells have been studied for their biosensing properties. Consequently, sediment microbial fuel cells (sMFCs) have been found to be able to detect minor oil spills in freshwater. However, it was previously unknown whether sMFC properties as a biosensor would be able to produce the same results in a saltwater environment. Therefore, sMFCs at various external resistances (220 Ω, 300 Ω, 430 Ω, 510 Ω, 1000 Ω and 2000 Ω) were assembled to assess their ability to detect oil in seawater. The results indicated that an ER of 1k Ω is optimal for sMFC power generation, and that as oil was added to the cathode of the sMFCs, there was a clear and gradual decrease in the voltage output due to the oil’s interference with oxygen dissolvability in seawater; However, the relationship between the change in voltage and change in time was less linear than the change observed in previous studies, and inconsistent across the different voltages. The variation observed may be due to the absence of a catalyst, such as platinum, which would have sped up the rate of the decrease in voltage. This study illustrates that sMFCs provide a cost effective and environmentally friendly method to detect minor oil spills in seawater.

Editorial: Soil pollution, risk assessment and remediation

Background Macroalgae blooms (Sargassum sp.) occur annually in the Bahamas due to the integration of various events related to human intercession with the roles of algae in biogeochemical cycles. These blooms are of great concern, as they are associated with many negative effects; thus, the primary aims of this study were to assess the quality of soils collected from South, Central, and North Long Island, and to determine if Sargassumsp. can be used as a biofertilizer for soils on Long Island. A 60-day pot trial method was established to determine the efficacy of different concentrations (1%, 5%, and 10%) of Sargassum sp. as a biofertilizer on cherry tomato cultivation. Additionally, the soil quality prior and after fertilizer amendment was evaluated. Results The results show that Sargassum sp. increased nutrient content of the soil, specifically nitrate nitrogen and phosphorus; however, plant growth performance parameters (plant height, leaf number, bud number, flower number, and root and shoot weights) were negatively impacted. Conclusions Due to the obtained results, it is recommended that serious consideration be taken when utilizing Sargassum sp. as a biofertilizer because the pH and type of soil in Long Island, Bahamas affects the bioavailability of the nutrients in algae.

Heavy metal pollution in soils threatens food safety and human health. Calcium sulfate and ferric oxide are commonly used to immobilize heavy metals in soils. However, the spatial and temporal variations of the heavy metals’ bioavailability in soils regulated by a combined material of calcium sulfate and ferric oxide (CSF) remain unclear. In this work, two soil column experiments were conducted to investigate the spatial and temporal variations of CSF immobilized Cd, Pb, and As. In the horizontal soil column, the results showed that CSF’s immobilization range for Cd increased over time, and adding CSF in the center of the soil column decreased the concentrations of bioavailable Cd significantly, up to 8 cm away by day 100. The CSF immobilization effect on Pb and As only existed in the center of the soil column. The CSF’s immobilization depths for Cd and Pb in the vertical soil column increased over time and extended to 20 cm deep by day 100. However, the CSF’s immobilization depths for As only extended to between 5 and 10 cm deep after 100 days of incubation. Overall, the results from this study can serve as a guide to determine the CSF application frequency and spacing distance for the in-situ immobilization of heavy metals in soils.

Water contaminated with emerging pollutants has become a serious environmental issue globally. Biochar is a porous and carbon-rich material produced from biomass pyrolysis and has the potential to be used as an integrated adsorptive material. Many studies have shown that biochar is capable to adsorb emerging pollutants from aquatic systems and could be used to solve the water pollution problem. Here, we provided a dual perspective on removing emerging pollutants from aquatic systems using biochar and analyzed the emerging pollutant removal efficiency from the aspects of biochar types, pollutant types and coexistence with heavy metals, as well as the associated mechanisms. The potential risks and future research directions of biochar utilization are also presented. This review aims to assist researchers interested in using biochar for emerging pollutants remediation in aquatic systems and facilitate research on emerging pollutants removal, thereby reducing their environmental risk.