Novel Chemical Routes for Carbon Dioxide and Methane Production from Lignin Photodegradation: The Role of Environmental Free Radicals.

Sunlight irradiation significantly mediates plant litter's carbon dynamics and volatile carbon release in semi-arid and arid ecosystems. In this process, carbon loss is controlled by lignin, but the mechanisms of production of CO2 and CH4 during lignin photolysis are ambiguous. In this study, the photomineralization of plant litter and the lignocellulosic component collectively indicate that lignin is a major source of CO2 and CH4 emissions. Characterization and free radical analysis reveal that the production of CO2 is due to the oxidation and ring-opening reaction of the coniferyl alcohol unit, with the subsequent decarboxylation of carboxylic acid as an oxidation product. This reaction involves o-quinone formation by the reactions between O2, superoxide radical (O2·-), and persistent free radicals (PFRs)-bearing lignin. Of this, O2·- contributes to 43.2% of the photogenerated CO2, as a new pathway, derived from the electron transfer from PFRs to O2. Interestingly, photoinduced demethylation of the dimethoxybenzene-type compounds as the photolysis products of lignin results in a never-before-reported CH4 formation chemical route independent of that of O2. This mechanistic insight into the role of lignin in volatile carbon production from the irradiative plant litter will contribute to a deeper understanding of carbon balance in water-limited ecosystems.

Seasonal and Spatial Fluctuations of Reactive Oxygen Species in Riparian Soils and Their Contributions on Organic Carbon Mineralization.

Reactive oxygen species (ROS) are ubiquitous in the natural environment and play a pivotal role in biogeochemical processes. However, the spatiotemporal distribution and production mechanisms of ROS in riparian soil remain unknown. Herein, we performed uninterrupted monitoring to investigate the variation of ROS at different soil sites of the Weihe River riparian zone throughout the year. Fluorescence imaging and quantitative analysis clearly showed the production and spatiotemporal variation of ROS in riparian soils. The concentration of superoxide (O2•-) was 300% higher in summer and autumn compared to that in other seasons, while the highest concentrations of 539.7 and 20.12 µmol kg-1 were observed in winter for hydrogen peroxide (H2O2) and hydroxyl radicals (•OH), respectively. Spatially, ROS production in riparian soils gradually decreased along with the stream. The results of the structural equation and random forest model indicated that meteorological conditions and soil physicochemical properties were primary drivers mediating the seasonal and spatial variations in ROS production, respectively. The generated •OH significantly induced the abiotic mineralization of organic carbon, contributing to 17.5-26.4% of CO2 efflux. The obtained information highlighted riparian zones as pervasive yet previously underestimated hotspots for ROS production, which may have non-negligible implications for carbon turnover and other elemental cycles in riparian soils.

Unlocking high-efficiency decontamination by building a novel heterogeneous catalytic reduction system of thiourea dioxide/biochar.

Herein, we reported a new contaminant purification paradigm, which enabled highly efficient reductive denitration and dechlorination using a green, stable reducing agent thiourea dioxide (TDO) coupled with biochar (BC) over a wide pH range under anoxic conditions. Specifically, BC acted as both activators and electron shuttles for TDO decomposition to achieve complete anoxic degradation of p-nitrophenol (PNP), p-nitroaniline, 4-chlorophenol and 2,4-dichlorophenol within 2 h. During this process, multiple strongly reducing species (i.e., SO22-, SO2•- and e-/H•) were generated in BC/TDO systems, accounting for 13.3%, 9.7% and 75.5% of PNP removal, respectively. While electron transfer between TDO and H+ or contaminants mediated by BC led to H• generation and contaminant reduction. These processes depended on the electron-accepting capacity and electron-conducting domains of biochar. Significantly, the BC/TDO systems were highly efficient at a pH of 2.0-8.0, especially under acidic conditions, which performed robustly in common natural water constituents.

Toxic effects and primary source of the aged micro-sized artificial turf fragments and rubber particles: Comparative studies on laboratory photoaging and actual field sampling.

Numerous micro-sized artificial turf fragments (MATF) and rubber particles (MRP) are generated and accumulated during the use of the artificial playing field. However, attention has rarely been paid to the potential toxic effects of MATF and MRP on sportsmen. In this study, the active components and chemical composition of aged MATF and MRP derived from laboratory photoaging and actual field sampling were detected, and their effects on cytotoxicity were examined correspondingly. Laboratory photoaging significantly increased environmental persistent free radicals (EPFRs), reactive oxygen species (ROS) abundances and oxidative potential (OP) levels on MATF and MRP, but they have limited cytotoxicity. Unfortunately, in the actual field, aged MATF and MRP with higher heavy metals and polycyclic aromatic hydrocarbons (PAHs) contents exhibited markedly higher cytotoxicity with the survival rate of cells of 78 % and 26 % (p < 0.05), although they had lower EPFRs and ROS yields. Correlation analysis revealed that the cell viability was closely linked to heavy metals of MATF (p < 0.05), and to organic hydroperoxide (OHP), PAHs and heavy metals of MRP (p < 0.05). By systematically considering the above results, heavy metals and PAHs enriched on MATF and MRP from the surrounding environment played the important role in the cytotoxicity, which was different from conventional perspectives. Our findings demonstrate that MATF and MRP associated with an artificial turf field contain potent mixtures of pollutants and can, therefore, be relevant yet underestimated factors contributing to the health risks.