The mineral composition of Fe–Mn nodules (FMNs) is closely related to the environment in which FMNs are formed. The formation mechanism of FMNs has consistently been one of the major topics in related research. In this study, the mineral composition of FMNs in soils derived from carbonate rocks in typical karst areas with high geochemical background in Guangxi, Southwest China, was investigated. The results showed that Fe₂O₃ (30.06%), SiO₂ (19.72%), Al₂O₃ (17.93%), TiO₂ (0.96%), P₂O₅ (0.78%), and MnO₂ (0.64%) were the main elemental composition, while four alkaline oxides K₂O, Na₂O, CaO, and MgO were less than 0.5% in soil FMNs. In addition, 10 mineral types were identified in soil FMNs in the study area, namely quartz, goethite, clinochlore, illite, kaolinite, boehmite, albite, microcline, lithiophorite, and hematite. There were no obvious differences in the mineral composition of soil FMNs in the study area compared with those observed in non-karst areas worldwide. The formation process of FMNs can be determined based on the surrounding environment that affects the soil mineral composition. The results suggested a relatively complex formation mechanism of soil FMNs. Moreover, both primary and secondary minerals were found in soil FMNs. However, some minerals can exist stably under normal redox conditions, while the other part of minerals can be easily weathered and dissolved, indicating a relatively high formation rate of soil FMNs and a relatively stable internal environment.

Nanoscale zero-valent iron (nZVI) has been broadly applied in the remediation of heavy metals pollution. In this research, the toxicity characteristic leaching procedure (TCLP), the in vitro gastrointestinal (IVG) method, and the diffusive gradients in thin-films (DGT) technique were used to evaluate the effects of heavy metals in soil with remediation by nZVI. The results indicate that, compared with the dose of 0.5 g·L⁻¹, the nZVI in the dose of 1.0 g·L⁻¹ can remove the heavy metals in the soil. The leaching toxicities of the heavy metals (Cr, Cu, Zn, Pb) showed apparent decreases after the remediation by nZVI. In the gastric phase, the highest bioaccessibility values of the Cr, Cu, Zn, Pb were decreased by 27.2, 31.7, 11.7, and 20.1%, respectively. Moreover, in the gastric phase, the highest bioaccessibility values of the Cr, Cu, Zn, Pb were decreased by 5.5, 1.29, 8.0, and 7.3%, respectively. The availabilities of the heavy metals were also reduced. The above results show that the nZVI effectively reduced the heavy metal pollution in the soil.

Atmospheric fine particles (PM_2.5, aerodynamic diameter ≤ 2.5 µm) have a serious effect on human health. This study combined concentration weighted trajectory (CWT) analysis with the HYSPLIT trajectory ensemble (Ens-HYSPLIT-CWT), to separate the sources of PM_2.5 transported to Beijing, and further investigate the effect of PM_2.5 originated from different sources on human health. We found that north region air masses usually come with clean events under the blessing of meteorological conditions, combined with the clean air mass transported from the north, as high wind speed near the surface promotes the horizontal diffusion of pollutants. Additionally, north region air masses contribute to the decrease in aerosol optical depth (AOD) at Beijing and surrounding areas, with AF (daily attributable fraction associated with short-term PM_2.5 exposure) values of Beijing only at 0.14. During the study period (from January to March 2024), south region air masses usually come with high PM_2.5 values, which is correlated to the meteorological conditions and pollutant spatial distribution. The air masses coming from the south region contain high temperature and relative humidity (RH), promoting the occurrence of high pollution events. AOD spatial distribution observed from satellites showed that except for the dominance of north region air mass sources, the south region presents high AOD values, further resulting in the highest AF value of 0.75 obtained at Beijing, which is 5 times higher than the north region’s dominant AF mean value. It is worth noting that the air mass originated from the east region, which originally contributed relatively clean air masses before emission reduction, increased its contribution to air mass pollution after emission reduction due to the decrease in pollution concentration in other regions. As a result, the mean PM_2.5 in this source area was second only to south region air masses and local emission sources, and the AF value even exceeded local emissions, second only to south region air mass sources, reaching 0.5. This result emphasizes that in future pollution control policy adjustments and research on human health, attention needs to be paid to the contribution of eastward air masses.

Historical chemical production sites often harbor irregularly distributed solid waste landfills, posing significant environmental risks. Traditional drilling methods, while accurate, are inefficient for comprehensive characterization due to high costs and spatial limitations. This study aims to develop an integrated geophysical drilling approach to accurately delineate the spatial distribution and volume of landfilled solid waste (predominantly organic pollutants) at two decommissioned chemical plant sites (total area: 8954 m²). Methods: We combined (1) geophysical surveys (transient electromagnetic (TEM, 50 profiles, 2936 points), high-density resistivity (HDR, 2 profiles, 192 points), and ground-penetrating radar (GPR, 22 profiles, 1072.1 m)) and (2) systematic drilling verification (136 boreholes, ≤10 m × 10 m density). Anomalies were interpreted through integrating geophysical responses, historical records, and borehole validation. Spatial modeling was conducted using Kriging interpolation in EVS software. The results show that (1) the anomalies exhibited a “sparse multi-point distribution” across zones A2 (primary waste concentration), A4, and A6, which were differentiated into solid waste, foundations, contaminated soil, voids, and cracks; (2) drilling confirmed solid waste at nine locations (A2: “multi-point, small-quantity” residues; A6: contaminated clay layers with garbage) with irregular thicknesses (0.2–1.3 m); (3) TEM identified diagnostic medium–high-resistivity anomalies (e.g., 28–37 m in A4L3), while GPR detected 17 shallow anomalies (only one validated as waste); and (4) the total waste volume was quantified as 266.9 m³. The methodology reduced the field effort by ∼35% versus drilling-only approaches, resolved geophysical limitations (e.g., HDR’s volume effect overestimating the thickness), and provided a validated framework for efficient characterization of complex historical landfills.

Through sampling and analysis of 20 groundwater monitoring wells from nine oil storage enterprises in the Jiangbei New District of Nanjing, the pollution characteristics and chemical spatial distribution of total petroleum hydrocarbons (TPH) in the groundwater of the study area were revealed. TPH was detected in all 20 groundwater samples, with concentrations ranging from 0.26 to 90.24 mg/L. A factor analysis identified two principal factors, F1 and F2, representing the biodegradation processes of iron–manganese reduction and sulfate reduction, respectively. A correlation analysis showed that TPH was significantly positively correlated with total dissolved solids (TDS), total hardness, Fe, Mn²⁺, and oxygen consumption, but its correlation with sulfides and SO₄²⁻ was not significant. A further multiple regression analysis indicated that the relative contribution rates of electron acceptors followed the order of iron reduction (90.62%) > manganese reduction (9.35%) > sulfate reduction (0.032%), suggesting that TPH biodegradation is primarily dominated by iron–manganese reduction. Additionally, the study found that microbial growth was more robust in freshwater environments, facilitating TPH degradation, whereas saline environments inhibited microbial activity, thereby hindering TPH degradation.

Groundwater contamination at active petrol stations is a global concern, yet distinguishing natural hydrogeochemical backgrounds from anthropogenic signals remains challenging. We conducted a comprehensive survey at 21 petrol stations in central China, analyzing 62 groundwater and 21 soil samples for 45 parameters, including metals, BTEX, MTBE, petroleum hydrocarbons, and conventional ions. Using Positive Matrix Factorization (PMF) coupled with spatial statistics and hydrogeological analysis, we resolved four robust sources. Factor 1 (geological background) contributed 60–70% of Mn/Al and 48–93% (mean 68%) of the individual soil heavy metals. Factor 2 (reductive pollution) contributed 75–85% of NH₄⁺-N, oxygen consumption (COD_Mn), and elevated Fe, exceeding 90% in certain hotspots. Factor 3 (petroleum hydrocarbons) contributed 75–85% to MTBE (mean 83%) and 50–65% to groundwater petroleum hydrocarbons (C₁₀–C₄₀; mean 58%), confirming point-source releases. Factor 4 (industrial solvents) dominated VOCs at an isolated site (92%). Conventional exceedance assessment misclassified geogenic Mn (26.2-fold exceedance, 62% natural) as high priority while underestimating anthropogenic NH₄⁺-N (moderate mean exceedance, 81% human-derived). The “coarse-over-fine” stratigraphy controls spatial patterns, with low-permeability clay inducing long natural-attenuation lags (8–>30 years). We propose a source-differentiated management framework, transitioning from compliance-based to risk-based regulation. This approach provides a transferable paradigm for source apportionment in urbanizing regions facing similar contamination challenges.