Natural arsenic source, migration, and flux in a catchment on the Southern Tibetan Plateau

Distribution characteristics, sources and risk assessment of heavy metals in the surface sediments from the largest tributary of the Lancang River in the Tibet Plateau, China

Angqu, positioned in the eastern expanse of the Tibet Plateau, claims the title of the largest tributary to the Lancang River. In October and December of 2018, in the sediment of Angqu, a comprehensive investigation was conducted on nine heavy metals-arsenic (As), manganese (Mn), chromium (Cr), cadmium (Cd), lead (Pb), mercury (Hg), copper (Cu), zinc (Zn), and nickel (Ni). This investigation aimed to scrutinize the spatial and temporal distribution patterns of these metals, assess the pollution status and ecological risks associated with the sediments, and delve into the sources contributing to their presence. The research results indicate that the average concentrations of As, Hg, and Cd in Angqu sediments exceed the soil background values of Tibet, while the concentrations of other heavy metals are below the soil background values of Tibet. Notably, arsenic poses potential ecological risks. In Angqu sediments, the concentrations of Mn, Cu, Ni, and Pb are generally higher in the wet season, but the seasonal variations of heavy metals in Angqu sediments are not significant. The sediments in the Angqu Basin are predominantly affected by mercury Hg, Cd, and As, with varying degrees of pollution at different sampling points. In the main stream of Angqu (City section), Hg pollution has reached above a moderate level, whereas As pollution near the tributary is only slightly polluted. The analysis of heavy metal sources reveals that there are five primary contributors to heavy metals in surface sediments of Angqu: parent material, agricultural activities, groundwater, atmospheric deposition, and other unidentified sources. Mn, Cr, Pb, and Ni are mainly derived from soil parent material, accounting for more than 50%. About 60.82% of As comes primarily from groundwater. Zn and Cd are mainly sourced from agricultural activities, accounting for 41.25% and 34.33%, respectively. Additionally, 20.6% of Hg originates from atmospheric deposition.

Novel findings from arsenic‑lead combined exposure in mouse testicular TM4 Sertoli cells based on transcriptomics

Arsenic (As) and lead (Pb) exist widespread in daily life, and they are common harmful substances in the environment. As and Pb pollute the environment more often in combination than in isolation. The TM4 Sertoli cell line is one of the most common normal mouse testicular Sertoli cell lines. In vitro, we found that the type of combined action of As and Pb on TM4 Sertoli cells was additive action by using the isobologram analysis. To further investigate the combined toxicity of As and Pb, we performed mRNA and miRNA sequencing on TM4 Sertoli cells exposed to As alone (4 μM NaAsO2) and AsPb combined (4 μM NaAsO2 and 150 μM PbAc), respectively. Compared with the control group, 1391 differentially expressed genes (DEGs) and 6 differentially expressed miRNAs (DEMs) were identified in the As group. Compared with the control group, 2384 DEGs and 44 DEMs were identified in the AsPb group. Compared with the As group, 387 DEGs and 4 DEMs were identified in the AsPb group. Through data analysis, we discovered for the first time that As caused the dysfunction of cholesterol synthesis and energy metabolism, and disrupted cyclic adenosine monophosphate signaling pathway and wingless/integrated (Wnt) signaling pathway in TM4 Sertoli cells. In addition to affecting cholesterol synthesis and energy metabolism, AsPb combined exposure also up-regulated the antioxidant reaction level of TM4 Sertoli cells. Meanwhile, the Wnt signaling pathway of TM4 Sertoli cells was relatively normal when exposed to AsPb. In conclusion, at the transcription level, the combined action of AsPb is not merely additive effect, but involves synergistic and antagonistic effects. The new discovery of the joint toxic mechanism of As and Pb breaks the stereotype of the combined action and provides a good theoretical basis and research clue for future study of the combined-exposure of harmful materials.

Insights from distribution and fractionation of the rare earth elements into As enrichment in the Singe Tsangpo River Basin

The geogenic As enrichment occurs extensively in the major river basin from the Tibetan Plateau, while the knowledge involved with the underlying mechanisms is far from completion. The present study utilized the geochemical behaviors of rare earth elements (REE) to study the hydrogeochemical evolution and As enrichment in the Singe Tsnagpo River basin, a typical As-rich river basin in the Tibetan Plateau. The river water was characterized by significant positive Eu anomalies and slight negative Ce anomalies, indicating the hydrogeochemical control of oxidative weathering of sourcing rocks and the contribution of felsic rocks. The PHREEQC modeling results suggested that the carbonate weathering contributed to the complexation of REE in the river water, where REE(CO3)+ and REE(CO3)2- were the predominant complex species. Besides, the reversing scenarios of HREE/LREE enrichment in the river water/sediments suggested a critical control of iron (hydr)oxides on the REE fractionation due to the preferential adsorption of LREE compared with HREE. Interestingly, the variations in Y/Ni and Cr/V ratios from the river sediments suggested a different contribution of sourcing rock weathering along the river flow path, where ultramafic rock showed a substantial contribution to the river sediments in the lower reaches and granite source is predominant in the upper reaches. It was also notable that the concurrent enrichment of REE and As in the river waters showed a response to the substantial enhancement of chemical weathering in the upper reaches of the STR basin, which was evidenced by the corresponding increases in the electrical conductivity and the δ18O values in the river waters. The present study thus provides new insights into utilizing REE as environmental tracers for studying hydrogeochemical evolution and As enrichment in the STR basin, which could also apply to similar alpine arid and cold river basins.

The geochemical stability of typical arsenic-bearing sinter in the Tibetan plateau: Implications from quantitative mineralogy

High‑arsenic (As) sinter deposited from geothermal water is a potentially overlooked hazardous matrix and there remain substantial gaps in our comprehension of the stability of As sequestered within it. In this study, qualitative and quantitative analysis of the mineralogy of As-bearing sinter was conducted by Mineral Liberation Analyzer (MLA) in geothermal areas of the Tibetan Plateau to reveal the geochemical stability of As. Our results indicated that the contents of As in sinter were 3 orders of magnitude higher than the local soil. The dominant host minerals of As were calcite (40.9 %), thenardite (22.5 %), calcium silicate (13.0 %), and halite (8.1 %). Additionally, it was found that a relatively higher As bioavailability was extracted by ethylene diamine tetraacetic acid (EDTA), with a leaching rate of 41.2 %. Notably, the X-ray diffraction (XRD) showed that the thenardite and halite were decomposed after the leaching. The combination of mineralogy and geochemistry data suggested that calcite and calcium silicate were a crucial mechanism for As retention in sinter, while the dissolution of saline minerals (e.g., thenardite, halite, and calcium chloride) served as the primary sources for As release. This finding unveils the potential risks and mechanisms associated with high-As sinter, providing scientific guidance for risk management of sinter.

Biowaste-based sorbents for arsenic removal from aqueous medium and risk assessment

Water contamination by arsenic (As) is widespread and is posing serious health threats globally. Hence, As removal techniques/adsorbents need to be explored to minimize potentials hazards of drinking As-contaminated waters. A column scale sorption experiment was performed to assess the potential of three biosorbents (tea waste, wheat straw and peanut shells) to remove As (50, 100, 200 and 400 µg L-1) from aqueous medium at a pH range of 5-8. The efficiency of agricultural biosorbents to remove As varies greatly regarding their type, initial As concentration in water and solution pH. It was observed that all of the biosorbents efficiently removed As from water samples. The maximum As removal (up to 92%) was observed for 400 µg L-1 initial As concentration. Noticeably, at high initial As concentrations (200 and 400 μg L-1), low pH (5 and 6) facilitates As removal. Among the three biosorbents, tea waste biosorbent showed substantial ability to minimize health risks by removing As (up to 92%) compared to peanut shells (89%) and wheat straw (88%). Likewise, the values of evaluated risk parameters (carcinogenic and non-carcinogenic risk) were significantly decreased (7-92%: average 66%) after biosorption experiment. The scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray and X-ray diffraction analyses confirmed the potential of biosorbents to remediate As via successful loading of As on their surfaces. Hence, it can be concluded that synthesized biosorbents exhibit efficient and ecofriendly potential for As removal from contaminated water to minimize human health risk.

Natural attenuation and remobilization of arsenic in a small river contaminated by the volcanic eruption of Mount Iou in southern Kyushu Island, Japan

The active volcano Mount Iou, in the southern part of Japan, erupted in 2018 for the first time in approximately 250 years. Geothermal water discharged from Mount Iou had high concentrations of toxic elements, such as arsenic (As), which could seriously contaminate the adjacent river. In this study, we aimed to clarify the natural attenuation of As in the river through daily water sampling for approximately eight months. The risk of As in the sediment was also evaluated using the sequential extraction procedures. The highest As concentration (2000 μg/L) was observed upstream but typically remained below 10 μg/L downstream. Dissolved As was the main form in the river water on non-rainy days. Arsenic concentration in the river naturally decreased through dilution and sorption/coprecipitation with Fe, Mn, and Al (hydr)oxides during flow. However, peaks in As concentration were frequently observed during rainfall events, possibly due to sediment resuspension. Furthermore, the range of pseudo-total As in the sediment was 4.62-14.3 mg/kg. Total As content was highest upstream before decreasing further along the flow. When using the modified Keon method, 44-70% of the total As existed as more reactive fractions associated with (hydr)oxides.

Phytoremediation of arsenic contaminated soil based on drip irrigation and intercropping

A directional leaching in drip irrigation along with intercropping was developed for enhanced phytoremediation of soils contaminated with arsenic (As). Spatiotemporal variations of As levels in soil and effects of irrigation eluents on As migration were analyzed in drip irrigation. Moreover, accumulated levels of As in Zea mays L. and Brassica rapa L. ssp. chinensis (the intercropping species) under drip irrigation and flood irrigation were compared to evaluate the enhancement on phytoremediation by drip irrigation. Results showed that As exhibited a directional migration in soil under drip irrigation, in which the solution of potassium dihydrogen phosphate (PDP) as the eluent significantly promoted As directional migration in soil. Compared to the flood-irrigated intercropping treatments, the As levels in crops (Brassica rapa L. ssp. chinensis) decreased significantly and that of remediating plants (Zea mays L. seedlings) increased significantly under the drip-irrigated intercropping condition. Drip irrigation coupled with intercropping dramatically reduced the risk of As contamination in crops and improved the phytoremediation of As-contaminated soil. PDP further enhanced the disparate effect of drip irrigation on As accumulation by crops and remediation plants.