Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation.

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., "circular" shaped in the talc group, "fine-grained" shaped in the chlorite group, and "donut" shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

Microplastics in plateau agricultural areas: Spatial changes reveal their source and distribution characteristics.

The Huangshui catchment on the northeastern Qinghai-Tibet Plateau (QTP) was selected as the study area to investigate the abundance, distribution characteristics, and influencing factors of microplastics (MPs) in surface agricultural soils (0-20 cm). The MP levels ranged from 6 to 444 items/kg, with an average of 86 items/kg. The relative abundance of small-sized MPs (<2 mm) was higher than that of large-sized MPs (2-5 mm). Polyethylene was the most common, and residual mulching film in farmland was the main source of MPs. The spatial distribution characteristics of MPs were analyzed through inverse distance weight interpolation, and MP abundance in agricultural soils in neighboring urban areas was significantly higher than that in other areas. Further analysis found that population density was significantly positively correlated with MP abundance (R2 = 0.9090, p < 0.01), indicating that human activities play a key role in MP pollution even in remote areas. In addition, the effects of irrigation, land use type, and soil physicochemical properties on the abundance of MPs were analyzed. Atmospheric transport and irrigation with surface water contribute to soil MP pollution. The direct effects of soil properties on MP abundance are still largely unclear, requiring further studies.

Distribution of pesticide residues in agricultural topsoil of the Huangshui catchment, Qinghai Tibet Plateau.

This study presents monitoring data on the spatial distribution and occurrence of pesticide residues of cultivated soil in the Huangshui catchment in the northeastern part of the Qinghai Tibet Plateau. We also provide factors that influence the distribution of pesticides, such as the properties of pesticides and soil and crop types. A total of 110 soil samples were collected in early April 2021, and 49 pesticides were analyzed. Only 3.6% of the samples contained no pesticide residues (concentrations < limit of quantitation or not detected [ND]), and the total pesticide concentration ranged from ND to 0.925 mg/kg. Most commonly, two to five pesticides were found in the soil samples (> 70.9%), and up to 10 pesticide residues were present in some samples. A total of 85 different pesticide combinations were observed in all the soil samples. Chlorpyrifos and difenoconazole were the dominant compounds. The levels of pesticide residues were mainly driven by their half-life values. Bulk density, along with soil water content and pH, also affected the retention of pesticides in the soil. The crop type played no role in the distribution of pesticides.