Typical heavy metals accumulation, transport and allocation in a deglaciated forest chronosequence, Qinghai-Tibet Plateau

An integrated evaluation of potentially toxic elements and microplastics in the highland soils of the northeastern Qinghai-Tibetan Plateau

As gateways to the scenic Qinghai-Tibetan Plateau (QTP), some underexplored five grassland (GLs) and three farmland (FLs) soil locations of northeastern counties were investigated. Preliminary detection showed that in the grazing and agricultural soils, elemental concentrations (Fe>Zn>Cr>Cu>Pb>Co>As>Cd) were up to 37 and 10 mg/g, but within the China soil standards, except Cd, while microplastics (MPs) abundances were 200-3640 and 280-973 particles/kg, respectively. Polypropylene (PP: 40-55 %) dominated in GLs mostly as fragments, whereas polyethylene (PE: 72-92 %) in FLs as films. Adsorption results demonstrated that potentially toxic elements (PTEs)-MPs' interaction may chiefly depend on their types and speciation in soils, the physiochemical structure of MPs, and surrounding conditions. The integrated two-dimensional risk assessment categorized three of five GLs under Risk Level VI (high pollution), whereas one of three FLs displayed Risk Level III (moderate pollution). Correlation analysis revealed that altitude, organic matter, soil clay content, and precipitation significantly affected PTEs (p ≤ 0.01), whereas MPs were influenced by altitude, soil clay content, precipitation (p ≤ 0.001), and population density (p ≤ 0.05). Comparison with low-land soils globally designated QTP as a vulnerable region to MPs due to the expanding development. Overall, our study provides a data set to understand the pollution scenario of highlands for its targeted management.

Spatial differentiation of metallic micronutrients in soil-plant systems along an altitudinal gradient in the Fanjing Mountain, Southwestern plateau of China

Metallic micronutrients (Cu, Fe, etc.) play a crucial role in plant growth, but limited research has explored the distribution patterns and determinants of these elements within the soil-plant system along elevation gradients in highland alpine forest ecosystems. In this study, we focused on Fanjing Mountain, a highland forest ecosystem in Southwest China, to examine the distribution and partitioning of metal micronutrients (Cu, Fe, Zn, Mo, Ni) within the soil-plant system along an altitudinal gradient, and to identify factors influencing micronutrient dynamics in plants across varying elevations. The results showed that the average contents of Cu, Fe, Zn, Mo, and Ni in soil (plant) were 24.64 (11.96), 28784.38 (1185.17), 659.57 (60.23), 0.97 (0.77), and 25.42 (5.41) mg/kg, respectively. Micronutrient elements exhibited varied trends along the altitudinal gradient; notably, Zn content in both soil and plants increased with elevation. The enrichment capacity of plant branches and leaves for metal micronutrients also shifted with altitude, with Cu and Mo showing significantly higher enrichment levels compared to other elements. Metal micronutrient content of plants was influenced by environmental factors such as soil properties and location, where the effect of soil environmental factors on plant micronutrient content decreases with increasing altitude. These findings enhance our understanding of the biogeochemical cycling of metal micronutrients in highland alpine forest ecosystems and provide valuable insights for improving forest soil quality and vegetation conservation.

Climate and vegetation controlling accumulation and translocation of heavy metals in water tower regions of Qinghai-Tibet Plateau

Understanding how climate and vegetation influencing accumulation and translocation of heavy metals (HMs) in soils and vegetation in the Qinghai-Tibet Plateau (QTP) is critical to assess the ecological risk induced by HMs under the global warming. To accompany this goal, we comprehensively determined the accumulation and translocation of HMs within the interface of soil-vegetation in water tower regions of the QTP. The PMF model results show that 54 %-86 % of cobalt (Co), nickel (Ni), arsenic (As), zinc (Zn) and lead (Pb) in the surface soil are mainly from rock weathering and 54 % of cadmium (Cd) comes from effect of litter return. The increase of vegetation biomass significantly promotes the accumulation of HMs in the surface soil. The increase of root biomass significantly enhances the uptake of Co, Ni, As, Cd and Pb by roots, due to the increasing availability of these HMs in surface soil, but reduces the translocation from roots to shoots. The precipitation and temperature influence HMs translocation by controlling the root biomass. Hence, we speculate that the further global warming in the QTP would enhance HMs accumulation in surface soil, but would not significantly increase HMs accumulation in ground vegetation biomass.

Quantifying Altitudinal Mercury Accumulation in Biomonitors along Himalayan Valleys Using Mercury Isotopes

The Himalayan valleys are important transport channels of atmospheric pollutants from South Asia to the Tibetan Plateau. This study aims to demonstrate the use of biomonitors (i.e., tree foliage, bark, mosses, and lichens) in the Himalayas to understand the sources and accumulation of mercury (Hg), including the transboundary atmospheric Hg transport across the Himalayas. Results showed that the significant variability in the physiological characteristics and nutrient uptake pathways, coupled with rapid changes in topography and climate-forced precipitation, led to significant differences in concentrations and isotopic compositions among biomonitor species. Δ199Hg values (-0.32 to -0.10‰) at the lower altitudes were slightly more positive than values at upper altitudes, likely reflecting signals of transboundary transport of anthropogenic Hg from South Asia. The isotope mixing model determined atmospheric Hg0 as the main source of Hg in most biomonitors (67 ± 13% to 88 ± 13%), except for Usnea longissimas (i.e., a unique type of lichen) with 61 ± 16% contribution of atmospheric Hg2+. Additionally, the morphological structure and epiphytic environment of U. longissimas facilitate aqueous Hg secondary reactions. Our results suggest that the Hg cycling in the Himalayan valleys could mix multiple impacts from montane environments and signals of transboundary transport of anthropogenic Hg from South Asia.

A portable solid sampling visualization nano-sensor for soil Cd based on "three-phase transforming" technique

Direct analysis of solid samples is always challenging for ionic sensors due to solidified elemental presence and matrix interference. In this work, a "three-phase transforming" technique was first established to make solid sampling elemental sensors and visual detection possible in the future. For Cd transforming from soil samples, a metal ceramic heater (MCH) electrothermal vaporizer (ETV) coupled with a dielectric barrier discharge quartz trap (DBD-QT) was first utilized to fulfill the solid sampling and preconcentration of Cd in soil; for on-site analysis, a colorimetric sensor based on the trithiocyanuric acid (TMT) functionalized gold nanoparticles (AuNPs) was chosen as a chromogenic analysis model. The portable and miniature ETV-DBD apparatus directly introduced Cd from soil and then captured Cd, consuming only <130 W and 4.5 kg weight; finally, only 200 μL water was injected as eluent to dissolve Cd for the following colorimetric detection. Herein, the Cd analyte underwent a "three-phase transforming" from solid (Cd compounds in soil), to aerosol (vaporization and transportation), to solid (Cd oxides trapped on quartz surface) and to liquid (Cd2+ in eluate). Under optimized conditions, the method limit of detection (LOD) reached 0.04 mg/kg Cd (50 mg sample), fulfilling fast monitoring of Cd contamination in soil, with <20 % relative standard deviations (RSDs). The analysis time was <10 min excluding sample digestion and acid application, as well as the interference of Pb2+ on the AuNPs sensor can be eliminated via the "three-phase transforming" process, proving an excellent anti-interference for solid analysis. This "three-phase transforming" processing technique coupled with colorimetric sensor holds a great potential for direct and on-site analysis in solid samples without complicated handling, providing a fantastic methodology for the application of ionic sensors and making solid sampling elemental sensor and visual detection possible.