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The freeze-thaw cycle is one of the important processes that affected heavy metal behaviors in soil. However, information regarding the adsorption and desorption behavior of heavy metals in soils under different freeze-thaw conditions is relatively less. Therefore, different freeze-thaw conditions including unfrozen, 15 freeze-thaw cycles at 60% water content, and 15 freeze-thaw cycles at 100% water content were investigated. Then the adsorption and desorption behaviors of Pb and Cr in freeze-thaw soils were studied. Results showed the Pb and Cr adsorption amount mostly decreased with increasing water-soil ratio, and the soil performance of Pb and Cr adsorption at same water-soil ratios showed variation under different freeze-thaw conditions. The Pb isothermal adsorption was higher for most freeze-thaw treatments compared to the control. The soil performance of Cr isothermal adsorption showed variation under different freeze-thaw conditions. Most electrostatic binding of Pb and Cr were stronger under unfrozen and freeze-thaw conditions than unfrozen conditions. Most Pb and Cr adsorption kinetics patterns of freeze-thaw treated soils were rapid than unfrozen conditions. These results implied that freeze-thaw cycles could change the soil adsorption and desorption patterns of Pb and Cr. Therefore, further studies are urgently needed to investigate Pb and Cr immobilization mechanisms in soils during freeze-thaw cycles. Hence, these findings provided useful information on Pb and Cr immobilization process in soils that underwent freeze-thaw cycles to offer an additional insight into predicting Pb and Cr behaviors in cold and freezing environments. [ABSTRACT FROM AUTHOR]

Simulation experiments were conducted using soils in the northeastern Qinghai–Tibet Plateau to explore the effects of freeze–thaw cycles on soil physicochemical properties, Pb and Cr distribution, and fraction transformation. Soils were incubated at −15°C for 24 h and at 5°C for 24 h to complete a freeze–thaw cycle. The soil physicochemical properties and fractions of Pb and Cr were analyzed after serial freeze–thaw treatments. The results showed that different freeze–thaw cycles and water content affected soil physicochemical properties and fractions of Pb and Cr to some extent. The cation exchange capacity increased significantly in agricultural and pastoral soils after five freeze–thaw cycles. The sand proportion of soil in an urban area decreased at 60 cycles. Freeze–thaw cycles did not change the functional groups and mineral constituents of the soils. The infrared peaks of soils with different freeze–thaw conditions were very similar. The freeze–thaw treatment influenced the mobility, chemical fractions of Pb and ecological risk in most of the soils. The exchangeable Pb in agricultural and pastoral areas increased from 0.19 to 1.52/0.90% after 5/10 freeze–thaw cycles with 60% water content. The ecological values of Pb in urban soil were 8.32/7.38% higher at 10/15 freeze–thaw cycles compared with the control treatment. Hence, these findings provide useful information on physicochemical properties and fraction transformation of Pb and Cr in soils undergoing freeze–thaw cycles, and offer an additional insight on Pb and Cr behaviors in cold and freezing environments. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues [ABSTRACT FROM AUTHOR]

This study investigated the pollution, potential ecological risks, and possible sources of trace elements in Gobi soils of the northeastern Qinghai-Tibet Plateau. Contents of Hg in soils were below the detection limit. The average contents of the remaining trace elements in soils ranged from 0.21 (Cd) to 2360.82 (As) mg/kg. Multiple methods were used to evaluate the soil pollution of the study area. Pb posed the most serious pollution based on geo-accumulation index evaluation. As showed the strongest enrichment feature according to enrichment factor method. Compared with pollution load index and modified contamination degree, Nemerow pollution index results obtained the most serious evaluation on pollution that 10% and 40% of sampling sites possessed moderate and high pollution, respectively. Trace elements in soils posed high ecological risks in 20% of sampling sites. Pearson's correlation matrix and principal component analysis were used to determine that anthropogenic activities such as industrial and mining activities might be the main source for several trace elements. This study will provide important information on soil quality control in the northeastern Qinghai-Tibet Plateau, especially the area with little vegetations. [ABSTRACT FROM AUTHOR]

Trace elements in soils might cause contamination and ecological risks to the environment with increasing anthropogenic disturbance. This study investigated the distribution, speciation, risks and possible sources of 28 target trace elements in soils of the northeastern Qinghai–Tibet Plateau. The average concentrations of trace elements in soils of the study area ranged from 0.25 (Hg) to 697.38 mg kg−1 (Cr). The residual fraction was the dominant host of V, Cr, Cu, Sn, Sb Hg and REEs, while Co, Ni, Zn, Mo, Cd and Pb had large proportions in the non-residual fractions. Risk assessment code analysis showed that Cd should be recognized as a priority pollutant in the study area. Correlation analysis indicated that Pb, Cu, Zn, Cd and Sn might originate from the same or similar source. The 206Pb/207Pb and 208Pb/206Pb ratios of the soils were in the range of 1.166–1.224 and 2.031–2.122, respectively. The anthropogenic Pb contribution proportion was in the range of 0–53.92% for the study area. The anthropogenic Pb contribution was higher in the areas with more intensive anthropogenic activities. Heavy metals and excessive anthropogenic disturbance should be effectively controlled in the northeastern Qinghai–Tibet Plateau to maintain the ecological sustainability and human health of this fragile area. [ABSTRACT FROM AUTHOR]

Information on rare earth elements (REEs) in soils of the Qinghai–Tibet Plateau is very limited. Therefore, this study performed field sampling to explore the concentrations, contamination degree, and potential ecological risks of REEs in soil of the northeastern Qinghai–Tibet Plateau. Concentrations of total REEs (TREEs) ranged from 95.82 to 544.01 mg/kg with average value of 241.81 mg/kg. Light REEs accounted for 72.3%–84.2% of TREEs, whereas Ce was the dominant element. Four methods were employed to evaluate the pollution of soil REEs. About 45.7% of sampling sites exhibited uncontaminated to moderately contaminated levels based on geoaccumulation index values of TREEs. Over 95.7% of sampling sites exhibited deficiency to minimal enrichment based on enrichment factor values of TREEs. The pollution load index evaluation results illustrated that about 85.7% of sampling sites possessed moderate levels of pollution, more serious than those evaluated by modified degree of contamination method. The potential ecological risk indexes of soil REEs in study area ranged from 11.02 to 40.55, showing low risk levels. This study provided important information on REEs in soils of the northeastern Qinghai–Tibet Plateau for soil pollution prevention and control at the high-elevation areas. [ABSTRACT FROM AUTHOR]

Black carbon (BC), ubiquitous in soils, plays an important role in global carbon cycles, the radiative heat balance of the Earth, pollutant fate, emissions of greenhouse gas, soil fertility, soil microbial community, and ecosystem stability. However, information on BC in topsoils of the northeastern Qinghai-Tibet Plateau is limited. Therefore, this study performed field sampling and analyzed contents of total BC and soot BC in topsoils. The results indicated that the contents of total BC in all soil samples ranged from 0.504 to 74.381 g kg−1 with an average value of 5.152 g kg−1, whereas those of soot BC were in the range of 0.400–15.200 g kg−1 with a mean value of 1.719 g kg−1. Contents of BC were significantly correlated with those of total carbon and total organic carbon. Soil types affected the distribution of soil BC. The contents of total BC in the loam soils were larger than those in the clay soils, whereas soot BC was more easily enriched in the clay soils. Total BC was negatively correlated with Ca, and soot BC was negatively correlated with Ti. The contents of soil BC in functional areas, such as agricultural and pastoral areas, industrial areas, and mining areas, were significantly higher than those in other areas, illustrating that anthropogenic activities drastically affected the distribution of soil BC. This study exhibits the fundamental information on soil BC in the northeastern Qinghai-Tibet Plateau to provide important knowledge on global soil carbon sink. [ABSTRACT FROM AUTHOR]