Migration patterns of heavy metals from solid waste stockpile soils by native plants for ecological restoration in arid and semi-arid regions of Northwest China

Ecological remediation with native plants is the main measure to control the pollution of solid waste in Northwest China. However, the heavy metal transport characteristics of these native plants are still unidentified. This study analyzed the distribution of 16 heavy metals in native plants in the desulfurization gypsum yard (DGY), the gangue yard (GY) and the fly ash yard (FAY). The results showed that the soil contained many heavy metals in high concentrations. For instance, As concentrations were comparable to the global soil background values, whereas Cr and Mn concentrations in the area were 2-3 times greater than the global soil background values. The content of heavy metals in the plant root system increased first, then decreased as the distance from the yard increased. Ni, Pb, and Cd migrated well in Artemisia frigida Willd and Artemisia sieversiana Ehrhart ex Willd, with A. sieversiana showing a particularly strong migration in GY. A. sieversiana, on the other hand, was more successful at migrating Cd at DGY and had a similar capability for Mg migration in all three locations. Festuca rubra L was potentially suitable for planting in GY for Ni removal. In conclusion, the migration patterns of different heavy metals were not alike for plants in the three landfills. The results provided a basis for plant selection for ecological restoration in arid and semi-arid regions.

Impacts of irrigation with treated livestock wastewater on the accumulation characteristic of ARGs in the farmland soil: a case study in Hohhot, China

Irrigation with treated livestock wastewater (TWW) is a promising strategy for reusing resources. However, TWW irrigation might introduce antibiotic resistant genes (ARGs) into the soil, posing environmental risks associated with antibiotic resistance. This study focuses on investigating the influence of irrigation amounts and duration on the fate of ARGs and identifies key factors driving their changes. The results showed that there were 13 ARGs in TWW, while only 5 ARGs were detected in irrigated soil. That is some introduced ARGs from TWW could not persistently exist in the soil. After 1-year irrigation, an increase in irrigation amount from 0.016 t/m2 to 0.048 t/m2 significantly enhanced the abundance of tetC by 29.81%, while ermB and sul2 decreased by 45.37% and 76.47%, respectively (p < 0.01). After 2-year irrigation, the abundance of tetC, ermB, ermF, dfrA1, and total ARGs significantly increased (p < 0.05) when the irrigation amount increased. The abundances of ARGs after 2-year irrigation were found to be 2.5-34.4 times higher than 1 year. Obviously, the irrigation years intensified the positive correlation between ARGs abundance and irrigation amount. TetC and ermF were the dominant genes resulting in the accumulation of ARGs. TWW irrigation increased the content of organic matter and total nitrogen in the soil, which affected microbial community structure. The changes of the potential host were the determining factors driving the ARGs abundance. Our study demonstrated that continuous TWW irrigation for 2 years led to a substantial accumulation of ARGs in soil.

Cadmium distribution and transformation in leaf cells involved in detoxification and tolerance in barley

Barley is a diagnostic plant that often used in the research of soil pollution by heavy metals, our research explored the detoxification and tolerance mechanism of cadmium(Cd) in barley through pot experiment. We investigated subcellular distribution, chemical forms and oxidative damage of Cd in barley leaves, combing with the transmission electron microscopy and Fourier-transform infrared spectroscopy(FT-IR) to further understand the translocation, transformation characteristics and toxic effect of Cd in cells. The results showed that, the bioaccumulation factors in roots and shoots of barley were ranged of 4.03-7.48 and 0.51-1.30, respectively. Barley reduces the toxic effects by storing Cd in the roots and reducing its transport to the shoots. Compared to the control treatment (0 mg/kg), the percentage of Cd in the cell wall fractions of leaves in 300 mg/kg Cd treatment increased from 34.74 % to 38.41 %; the percentage of the organelle fractions increased from 24.47 % to 56.02 %; and the percentage of soluble fraction decreased from 40.80 % to 5.57 %. We found that 69.13 % of the highly toxic inorganic Cd and water-soluble Cd were converted to less toxic pectates and protein-integrated Cd (50.20 %) and undissolved Cd phosphates (18.93 %). This conversion of Cd was mainly due to its combination with -OH, -NH, -CN, -C-O-C, and -C-O-P groups. Excessive Cd induced a significant (P < 0.05) increase in the levels of peroxidase, malondialdehyde, and cell membrane permeability, which damaged the cell membrane and allowed Cd to enter the organelles. The chloroplasts and mitochondria were destroyed, and eventually the metabolism of intracellular substances was affected, resulting in symptoms of toxicity. Our research provides cellular-scale insight into the mechanisms of Cd tolerance in barley.

Toxic effects of microplastics in plants depend more by their surface functional groups than just accumulation contents

Differentially charged microplastics (MPs) engendered by plastic aging (e.g., plastic film) widely existed in the agricultural ecosystem, yet minimal was known about the toxic effects of MPs on plants and their absorption and accumulation characteristics. Root absorption largely determined the migration and accumulation risks of MPs in the soil-crop food chain. Here, five types of MPs exposure experiments of leaf lettuce were implemented to simulate root absorption by hydroponics. MPs exposure caused different degrees of growth inhibition, root lignification, root cell apoptosis, and oxidative stress responses; accelerated chlorophyll decomposition and hampered normal electron transfer within the PSII photosystem. Moreover, the uptake of essential elements by roots was inhibited to varying degrees due to the pore blockage in the cell wall and the hetero-aggregation of opposite charges after MPs exposure. MPs exposure observably up-regulated the organic metabolic pathways in roots, thus affecting MPs mobility and absorption through the electrostatic and hydrophobic interactions between the root exudations and MPs. Importantly, MPs penetrated the root extracellular cortex into the stele and were transported to the shoots by transpiration through xylem vessels based on confocal laser scanning microscopy and scanning electron microscopy images. Quantitative analysis of MPs indicated that their toxic effects on plants were determined to a greater extent by the types of surface functional groups than just their accumulation contents, that is, MPs were confirmed edible risks through crop food chain transfer, but bioaccumulation varied by surface functional groups.

Effects of urbanization on Cd accumulation in agricultural soils: From the perspective of accessibility gradient

Road accessibility clearly reflects the spatial heterogeneity of urbanization. This study therefore adopted accessibility gradient to analyze the effects of urbanization on Cadmium (Cd) accumulation in agricultural soils. In total, 212 soil samples were collected along the accessibility gradient from agricultural soils in the Guangzhou-Foshan metropolitan region. Cd concentration showed a clearly decreasing pattern in agricultural soils with a decrease in accessibility level. The decreasing patterns varied in different accessibility ranges. The urban-rural ecotone (accessibility range 10-15) was the region with the most drastic changes in Cd accumulation. The influencing factors of Cd accumulation in agricultural soils mainly include industrial pollutants, agriculture chemicals, mining activities, domestic wastes, and soil properties. The importance of these factors varies across different accessibility ranges. Our findings imply that the characteristic variation of Cd accumulation with the road accessibility gradient must be considered in the formulation of targeted policies for controlling Cd contamination in agricultural soils.

Soil characterization and differential patterns of heavy metal accumulation in woody plants grown in coal gangue wastelands in Shaanxi, China

Soil contamination by heavy metals in coal mine wastelands is a significant environmental issue in most developing countries. The purpose of this study is to evaluate contamination characteristics in the coal mine wastelands of Sanlidong coal mine, Tongchuan, China. To achieve this goal, we conducted field sampling work, followed by further analysis of the properties of soil contamination and accumulation characteristics in woody plants. At this site, the pH value ranged from 4.41 to 7.88, and the nutrient content of the soil rose gradually with the time after deposition due to the weathering effect improving the soil quality. Meanwhile, the levels of Cd, Cr, Cu, Ni, and Zn gradually decreased with the passage time. Generally, heavy metal contamination was found to be more serious in the discharge refuse area, with Cd contamination at moderate or heavy levels; Ni, Zn, and Cu contamination at light levels; and with no Cr contamination. The geoaccumulation index (I geo) was highest for Cd (2.38-3.14), followed by Ni, Zn, Cu, and Cr. Heavy metals accumulated on the lower slopes and spread to the surrounding areas via hydrodynamic effects and wind. According to transfer and enrichment coefficient analyses, Robinia pseudoacacia, Ulmus pumila, and Hippophae rhamnoides with considerable biomass could be used as pollution-resistant tree species for vegetation restoration. This study provided a theoretical basis for the restoration of the ecological environment in the mining area. This report described a link between heavy metal contamination of soils and growth dynamics of woody plants in China.