This study investigated the concentrations and spatial distributions, ecological risks, and potential pollution sources of potential toxic elements (PTEs) in the soils and sediments collected from the Guishui River (GSR) in Beijing, China. Multiple methods for pollution assessment and source identification of PTEs in the sediments/soils were used, including analysis of the physicochemical properties, Geo-accumulation index (I_geo), potential ecological risk index (RI), Pearson correlation, principal component analysis (PCA), and Pb isotopic ratio analysis. The results showed that PTE concentrations in the sediments/soils were similar to the soil background values (BV) of Beijing, except for Cd. Maximum Cd concentrations in soils were far below the guideline of the Environmental Quality Standard for Soils in China. PTE concentrations in the soils were slightly higher than those in the sediments. Upstream to downstream of GSR, PTEs concentrations in the soils and sediments remained stable. Pollution assessment based on I_geo and RI indicated that Cd was the main contaminant with moderate pollution levels. PCA results showed that Cd originated from anthropogenic sources, mainly including pesticide and fertilizer residues, while other metals mainly originated from natural sources. Further source identification using Pb isotopic ratios and PCA indicated that Cu, Pb, and Zn in GSR originated from anthropogenic sources (aerosols and coal combustion) and atmospheric deposition was considered as the primary input pathway.

The contamination of arsenic (As) in aqueous environments has drawn widespread attention, and iron compounds may largely alter the migration ability of As. However, the stability of As(III) in Fe-As system with the intervention of organic matter (OM) remains unclear. Herein, we had explored the co-precipitation and co-oxidation processes of As-Fe system by using batch experiments combined with Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) in this research. The precipitation quantity of As(III) increased (28.85-92.41 %) when the As/Fe ratio decreased, and increased (24.20-64.20 %) with pH increased. The main active substance for oxidizing As(III) was H₂O₂, which was produced in the As-Fe system. FTIR and XPS revealed that As(III) was first oxidized in neutral, and then absorbed and enteredthe interior of Fe(OH)₃ colloids. But under alkaline conditions, As(III) was adsorbed by Fe (Oxyhydr) oxides firstly, and then oxidized. The intervention of OM would inhibit the redistribution process of As(III) in aqueous environments. Functional groups and unsaturation of the carbon chain were the dominant factors that affected the precipitation and oxidation processes of As(III), respectively. Co-existing ions (especially PO₄^3-) also signally affected the precipitation quantity of As(Ⅲ) in the system and, when coexisting with OM, could exacerbate this process. The influence of co-existing ions on the redistributive process of As(III) in the As-Fe system with/without OM were as follows: PO₄^3- > SO₄^2- > mixed ions > SiO₃^2-. Moreover, high concentration of OM and PO₄^3- might lead to morphological alterations of As, acting as a threat to aqueous environments. In summary, the present findings were to further understand and appreciate the changes of As toxicity in the aqueous environments. Particularly, the coexistence of OM and As can potentially increase the risk to drinking water safety.

Simultaneous ecological and health risk assessments of potentially toxic elements in soils and sediments can provide substantial information on their environmental influence at the river-basin scale. Herein, soil and sediment samples were collected from the Guishui River basin to evaluate the pollution situation and the ecological and health risk of potentially toxic elements. Various indexes were utilized for quantitatively assessing their health risks. Pollution assessment by geo-accumulation index showed that Cd had “uncontaminated to moderately polluted” status in the soils and sediments. Potential ecological risk index showed that the Guishui River basin was at low risk in general, but Cd was classified as “moderate or considerable ecological risk” both in the soils and sediments. Health risk assessment calculated human exposure from soils and indicated that both non-carcinogenic and carcinogenic risks of the selected potentially toxic elements were lower than the acceptable levels. Health risks posed by potentially toxic elements bio-accumulated in fish, stemming from sediment resuspension, were also assessed. Non-carcinogenic hazard index indicated no adverse health effects on humans via exposure to sediments; however, in general, Cr contributed largely to health risks among the selected potentially toxic elements. Therefore, special attention needs to be paid to the Guishui River basin in the future.

Dramatic changes in the farmland soil–groundwater environment caused by irrigation affects the geochemical behavior of arsenic (As). However, the mechanism of As mobilization during soil–groundwater interactions remains unclear. This study explored the effects of phosphate (PO₄³⁻), fulvic acid (FA), and oxic/anoxic conditions on As mobilization through batch and column experiments. The results indicated that a saline–alkali environment and the involvement of PO₄³⁻/FA suppressed the adsorption capacity of goethite for As(III) in the water environment and that PO₄³⁻ had a primary effect. An increase in the PO₄³⁻/FA concentration further increased its inhibition. Notably, oxic/anoxic conditions did not affect the adsorption capacity of goethite for TAs in the presence of high concentrations of PO₄³⁻/FA. In the soil environment, periodic irrigation led to regular fluctuations in the As content in the soil pore water. The addition of PO₄³⁻ to irrigation water resulted in a higher content of As in the pore water in the short term. In contrast, the addition of FA greatly increased the long-term mobility of As. This study highlighted that irrigation amplifies As mobility in soil–groundwater systems, particularly in saline–alkali environments, and PO₄³⁻/FA addition exacerbates this effect, posing risks to agricultural safety. The systematic management of irrigation practices is recommended to mitigate these risks.