Jiajia Wang

Arsenic (As) accumulation in rice presents a global health concern, yet the impacts of expanding agricultural sulfur (S) applications on As behavior in rice systems remain inadequately understood. This study integrates two-year open-air mesocosm experiments with global meta-analysis to assess S effects on soil-to-grain As transfer. Mesocosm trials showed that sulfate fertilizers significantly reduced carcinogenic inorganic As (iAs) concentrations in white rice by up to 46% compared to nonsulfur controls, across different soils, irrigation regimes, and seeding practices. Meta-analysis further revealed consistent decreases in total As in grain (37%), leaves (25%), and stems (24%), but not in roots or iron plaque. Sulfur primarily suppressed root-to-grain iAs translocation rather than enhancing direct iron-plaque binding, as indicated by unchanged plaque As/Fe and positive correlations of grain iAs with root and stem As rather than with plaque As. However, sulfate addition increased porewater methylated As and tended to elevate grain dimethylarsenate, a precursor of highly cytotoxic dimethylated monothioarsenate (DMMTA), though grain DMMTA remained unchanged. Mitigation efficacy was more strongly influenced by soil pH and organic carbon than by total soil As. These findings support the targeted use of S fertilization to lower dietary iAs exposure, while emphasizing the importance of speciation-resolved monitoring to minimize unintended toxicological risks.

Soil contamination by multiple metals is a significant concern due to the interlinked mobilization processes. The challenges in comprehending this issue arise from the poorly characterized interaction among different metals and the complexities introduced by spatial and temporal heterogeneity in soil systems. We delved into these complexities by incubating size-fractionated paddy soils under both anaerobic and aerobic conditions, utilizing a combination of techniques for aqueous and colloidal analysis. The contaminated paddy soil predominantly consisted of particles measuring <53, 250-53, and 2000-250 μm, with the <53 μm fractions exhibiting the highest concentrations of multiple metals. Interestingly, despite their higher overall content, the <53 μm fractions released less dissolved metal. Furthermore, glucose enhanced the release of arsenic while simultaneously promoting the sequestration of other metals, such as Pb, Zn, and Cu. Utilizing asymmetric flow field-flow fractionation, we unveiled the presence of both fine (0.3-130 kDa) and large (130-450 nm) colloidal pools, each carrying various metals with different affinities for iron minerals and organic matter. Our results highlighted the pivotal role of the <53 μm fraction as a significant reservoir for multiple metal contaminants in paddy soils, in which the colloidal metals were mainly associated with organic matter. These findings illuminated the size-resolved dynamics of soil metal cycling and provided insights for developing remediation strategies for metal-contaminated soil ecosystems.

Recent discoveries of methyl-coenzyme M reductase–encoding genes ( mcr ) in uncultured archaea beyond traditional euryarchaeotal methanogens have reshaped our view of methanogenesis. However, whether any of these nontraditional archaea perform methanogenesis remains elusive. Here, we report field and microcosm experiments based on ¹³ C-tracer labeling and genome-resolved metagenomics and metatranscriptomics, revealing that nontraditional archaea are predominant active methane producers in two geothermal springs. Archaeoglobales performed methanogenesis from methanol and may exhibit adaptability in using methylotrophic and hydrogenotrophic pathways based on temperature/substrate availability. A five-year field survey found Candidatus Nezhaarchaeota to be the predominant mcr -containing archaea inhabiting the springs; genomic inference and mcr expression under methanogenic conditions strongly suggested that this lineage mediated hydrogenotrophic methanogenesis in situ. Methanogenesis was temperature-sensitive , with a preference for methylotrophic over hydrogenotrophic pathways when incubation temperatures increased from 65° to 75°C. This study demonstrates an anoxic ecosystem wherein methanogenesis is primarily driven by archaea beyond known methanogens, highlighting diverse nontraditional mcr -containing archaea as previously unrecognized methane sources.

The association of arsenic (As) with colloidal particles could facilitate its transport to adjacent water systems or alter its availability in soil-rice systems. However, little is known about the size distribution and composition of particle-bound As in paddy soils, particularly under changing redox conditions. Here, we incubated four As-contaminated paddy soils with distinctive geochemical properties to study the mobilization of particle-bound As during soil reduction and subsequent reoxidation. Using transmission electron microscopy-energy dispersive spectroscopy and asymmetric flow field-flow fractionation, we identified organic matter (OM)-stabilized colloidal Fe, most likely in the form of (oxy)hydroxide-clay composite, as the main arsenic carriers. Specifically, colloidal As was mainly associated with two size fractions of 0.3-40 and >130 kDa. Soil reduction facilitated the release of As from both fractions, whereas reoxidation caused their rapid sedimentation, coinciding with solution Fe variations. Further quantitative analysis demonstrated that As concentrations positively correlated with both Fe and OM concentrations at nanometric scales (0.3-40 kDa) in all studied soils during reduction and reoxidation, yet the correlations are pH-dependent. This study provides a quantitative and size-resolved understanding of particle-bound As in paddy soils, highlighting the importance of nanometric Fe-OM-As interactions in paddy As geochemical cycling.

The association of poorly crystalline iron (hydr)oxides with organic matter (OM), such as extracellular polymeric substances (EPS), exerts a profound effect on Fe and C cycles in soils and sediments, and their behaviors under sulfate-reducing conditions involve complicated mineralogical transformations. However, how different loadings and types of EPS and water chemistry conditions affect the sulfidation still lacks quantitative and systematic investigation. We here synthesized a set of ferrihydrite-organic matter (Fh-OM) coprecipitates with various model compounds for plant and microbial exopolysaccharides (polygalacturonic acids, alginic acid, and xanthan gum) and bacteriogenic EPS (extracted from Bacillus subtilis). Combining wet chemical analysis, X-ray diffraction, and X-ray absorption spectroscopic techniques, we systematically studied the impacts of C and S loadings by tracing the temporal evolution of Fe mineralogy and speciation in aqueous and solid phases. Our results showed that the effect of added OM on sulfidation of Fh-OM coprecipitates is interrelated with the amount of loaded sulfide. Under low sulfide loadings (S(-II)/Fe < 0.5), transformation to goethite and lepidocrocite was the main pathway of ferrihydrite sulfidation, which occurs more strongly at pH 6 compared to that at pH 7.5, and it was promoted and inhibited at low and high C/Fe ratios, respectively. While under high sulfide loadings (S(-II)/Fe > 0.5), the formation of secondary Fe-S minerals such as mackinawite and pyrite dominated ferrihydrite sulfidation, and it was inhibited with increasing C/Fe ratios. Furthermore, all three synthetic EPS proxies unanimously inhibited mineral transformation, while the microbiogenic EPS has a more potent inhibitory effect than synthetic EPS proxies compared at equivalent C/Fe loadings. Collectively, our results suggest that the quantity and chemical characteristics of the associated OM have a strong and nonlinear influence on the extent and pathways of mineralogical transformations of Fh-OM sulfidation.

High concentrations of particulate matter with diameters less than 2.5 μm (PM2.5) have seriously affected the sustainable economic and social development of Henan Province. Analysis of the temporal and spatial distribution of PM2.5 and source analysis can provide a scientific basis for local pollution prevention and control. Using data from 17 atmospheric monitoring stations from 2016 to 2018, the spatiotemporal evolution of PM2.5 concentrations and source apportionment of Henan Province was explored using spatial autocorrelation analysis, empirical orthogonal function (EOF), potential source contribution factor (PSCF) analysis, and concentration weight trajectory (CWT) analysis. The PM2.5 concentration demonstrated varied annual, seasonal, monthly and daily characteristics from 2016 to 2018. The annual average concentrations decreased each year at an average rate of 5.3 μg/m3. The seasonal variation was “low in spring and summer while high in autumn and winter”. The monthly average and daily average over-standard rates exhibited a U-shaped pattern, with low values in the summer and high values in the winter. The daily average presented a pulse-type fluctuation. The areas with high concentrations of PM2.5 were primarily distributed in the central and northern parts of Henan Province, while the areas with low values were primarily distributed in the southern part of Henan Province. PM2.5 concentrations were negatively correlated with temperature, with the highest concentration at 0-5ºC, and strongly positively correlated with relative humidity in winter, with the highest PM2.5 concentrations between 80% and 90% relative humidity. Overall, the most important pollution transmission in winter came from southern Shanxi and northern Shaanxi, followed by Anhui and Shandong, again from the Beijing-Tianjin-Hebei region, and the smallest transmission came from Hubei. The area within Henan Province was also a significant contributor.