Previous studies have shown that significant K isotope fractionation is found in continental weathering, oceanic crust subduction, and plant growth, suggesting that K isotopes could be a potentially important tracer. However, the complicated separation method and analytical conditions limit the precise analysis of potassium isotopes via MC-ICP-MS under “cold” plasma conditions. Here, an improved separation method (single column) permits the complete purification of K from the matrix elements. This method is efficient and convenient and achieves a high yield (99.5 ± 0.6%) and low blank (<10 ng K) under complex matrix extraction conditions. The high-resolution mode with a desolvating nebulizer system was used to increase the signal intensity of ⁴¹K⁺ and ³⁹K⁺ and reduce ³⁸ArH⁺, ⁴⁰ArH⁺, and some oxide/nitride interference. To eliminate scattered ions or secondary electrons, we used a new dummy bucket to collect high intensity ⁴⁰Ar⁺ beams. Besides, potassium isotopes for the standard SRM 3141a and new geological, environmental and biological reference materials such as DNC-1a, JMS-2, and GSB-14 were determined on a Nu Plasma 3 MC-ICP-MS instrument. Overall, the reproducibility of K isotope analysis was better than ±0.06‰ (2SD) that reported in most laboratories around the world. The measured δ⁴¹K values of the rock samples are homogeneous, consistent with the previous published data. However, the K isotope composition in soils, sediments, and plants is inhomogeneous and varies greatly from −0.85‰ to −0.25‰. These results show that potassium isotopes have great application potential in the geological, environmental, and biological fields.

Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is widely used in stable and radiogenic isotope analysis of various elements because of the extremely high precision and accuracy. At present, stable K, Ca, and radiogenic Sr isotopes are increasingly used as a combined proxy of geological processes. However, time consuming and cumbersome multi-step chemical procedures hinder their development and application. This study presents a method for one-step chromatographic separation of K–Ca–Sr from matrix elements, and the purification procedure is based on AG50W-X12 cation exchange resin without any intervening evaporation step. The K fraction was first collected using 10 mL 2 M (mol L⁻¹) HCl, the Ca fraction was then collected using 18 mL 2 M HCl, and the Sr fraction was collected at last using 10 mL 3 M HCl. K–Ca–Sr isotopic ratios were measured by using MC-ICP-MS (Nu Plasma 3) with a sample–standard bracketing (SSB) method. The stability of our chemical procedure was demonstrated by replicate measurements of ten international reference materials of rocks and seawater. The analytical results obtained for these reference materials are consistent with previously reported values within analytical errors. The external reproducibility of a BCR-2 standard sample was ±0.05‰ (2SD, N = 9) for δ^41/39K, ±0.04‰ (2SD, N = 9) for δ^44/42Ca, and 0.000012 (2SD, N = 4) for ⁸⁷Sr/⁸⁶Sr. Thus, this optimal separation method improves the experimental efficiency and reduces cross-contamination.

In this study, the concentration of eight dissolved heavy metals (Ti, Cr, Mn, Fe, Ni, Mo, Sb, and Ba) in 42 water samples from the Jiulongjiang River, southeast China, were determined by inductively coupled plasma mass spectrometry (ICP-MS). Multivariate statistical methods, including correlation analysis (CA) and factor and principal component analysis (FA/PCA), were analyzed to identify the sources of the elements. Water quality index (WQI) and health risk assessment, including hazard quotient (HQ) and hazard index (HI), were used to evaluate water quality and the impacts on human health. Our results were compared with the drinking water guidelines reported by China, the World Health Organization (WHO), and the United States Environmental Protection Agency (US EPA), revealing that Ti, Mn, and Sb were not within approved limits at some sites and might be the main pollutants in the drainage basin. Based on the spatial distributions, Ti, Mn, Fe, Ni, and Mo showed good similarity, indicating that they might come from similar sources along the river. The CA results also showed that Ti, Mn, Fe, Ni, and Mo had a high correlation coefficient. The FA/PCA results identified three principal components (PC) that accounted for 79.46% of the total variance. PC 1 suggested that a mixed lithogenic and urban land source contributed to Ti, Mn, Fe, Ni, and Mo; PC 2 showed that Cr, Ni, and Mo were influenced by the discharge of industrial effluents; Sb had a strong loading on PC 3, which was controlled by mining activities. The results of the WQI indicated that the water in the Jiulongjiang River was basically categorized as excellent water, but the water quality levels in site W5 and N4 were poorer due to urban land use. Hazard quotient and HI values showed that Sb was a potential threat to human health, indicating that preventive actions should be considered in regard to mining activities in the upper reaches of Beixi stream.

Dissolved inorganic carbon isotope composition (δ¹³C_DIC), together with major ion concentrations were measured in the Mun River and its tributaries in March 2018 to constrain the origins and cycling of dissolved inorganic carbon. In the surface water samples, the DIC content ranged from 185 to 5897 μmol/L (average of 1376 μmol/L), and the δ¹³C_DIC of surface water ranged from −19.6‰ to −2.7‰. In spite of the high variability in DIC concentrations and partial pressure of carbon dioxide (pCO₂), the δ¹³C_DIC values of the groundwater were relatively consistent, with a mean value of −16.9 ± 1.4‰ (n = 9). Spatial changes occurred in the direction and magnitude of CO₂ flux through water-air interface (F_CO2). In the dry season, fluxes varied from −6 to 1826 mmol/(m²·d) with an average of 240 mmol/(m²·d). In addition to the dominant control on hydrochemistry and dissolved inorganic carbon isotope composition by the rock weathering, the impacts from anthropogenic activities were also observed in the Mun River, especially higher DIC concentration of waste water from urban activities. These human disturbances may affect the accurate estimate contributions of carbon dioxide from tropical rivers to the atmospheric carbon budgets.

River water samples between August 2017 (wet season) and March 2018 (dry season) from the Mun River Basin in northeast Thailand were collected and their dissolved heavy metals concentrations (Al, Mn, Fe, Cu, Zn, and Ba) were measured. Compared with international drinking water guidelines, Mn was the dominant pollutant in the dry season. The correlation analysis (CA) suggested that similar sources were shown in each element pair of Al-Fe, Mn-Zn, and Fe-Ba in both seasons. The principal component analysis (PCA) results showed that the dominant source of dissolved heavy metals was sedimentary inputs or colloid destabilization in the wet season, while anthropogenic inputs were the main sources in the dry season, such as agricultural runoff, industrial effluents, and domestic discharge. On the basis of water quality index (WQI), water at most sites in the wet and dry seasons can be categorized as excellent water, except for a few sites with substandard values. The river water posed no significant health risks according to the health risk assessment, but Mn, Fe, and Ba needed to be paid more attention due to the relatively high values. Al, Fe, and Ba were the main dissolved heavy metals flowing into the Mekong River, and Cu contributed to the background value in the Mekong river.