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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]

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]

Abstract Environmental quality of the northeastern Qinghai-Tibet Plateau has attracted more attention due to increasing anthropogenic disturbance. Therefore, this study investigated the distribution, pollution, ecological risks, and bioaccumulation of 12 target heavy metals and 16 rare earth elements (REEs) in soils of this area. The average concentrations of target trace elements in soils ranged from 0.16 (Hg) to 500.46 (Cr) mg/kg. Pb caused more serious pollution than the other elements based on geo-accumulation index evaluation. Hg exhibited the strongest enrichment feature with the average enrichment factor of 8.41. Compare with modified contamination degree and pollution load index, Nemerow pollution index method obtained the most serious evaluation results that 45.67% and 16.54% of sampling sites possessed high and moderate pollution. Evaluation results of potential ecological risk index showed that trace elements in soils posed very high and considerable ecological risks in 34.65% and 7.09% of sampling sites, respectively. Mining area was the region with the most serious pollution and ecological risks. Average bioaccumulation factor (BCF) values of target trace elements ranged from 0.05 (REEs) to 2.67 (Cr). Cr was the element that was easier to bio-accumulate in plants of the study area than the other target elements. It is in urgent need to take effective measures for controlling current pollution and potential ecological risks of trace elements in soils of the northeastern Qinghai-Tibet Plateau. Graphical abstract fx1 Highlights • Approximately 45.67% of sampling sites possessed high pollution by trace elements. • Trace elements in soils posed very high ecological risks in 34.65% of sampling sites. • REEs contributed to pollution and ecological risks far less than heavy metals. • The maximal BCF value of target trace elements reached 17.87 (Cr). • Mining area was the region with the most serious pollution and ecological risks. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibet Plateau, especially the northeastern region, is not a pure land any more due to recently increasing anthropogenic activities. This study collected soil samples from 70 sites of the northeastern Qinghai-Tibet Plateau to evaluate pollution, ecological-health risks, and possible pollution sources of heavy metals. The concentrations of heavy metals in soil were relatively high. Values of geo-accumulation index exhibited that Hg pollution was the most serious meanwhile Hg possessed the strongest enrichment feature based on enrichment factor values. The modified degrees of contamination showed that about 54.3% and 17.1% of sampling sites were at moderate and high contamination degree while pollution load indexes illustrated that 72.9% and 27.1% of sampling sites possessed moderate and high contamination level, respectively. Ecological risk indexes of heavy metals in soil ranged from 234.6 to 3759.0, suggesting that most of sites were under considerable/very high risks. Cancer risks for adults and children were determined as high and high-very high levels while non-cancer risks for children were high although those for adults were low. Industrial source contributed to the main fraction of ecological and health risks. Summarily speaking, heavy metals in soil of the study area has caused significantly serious pollution and exerted high potential ecological and health risks, especially for children who are more susceptible to hurt from pollutants. Therefore, more efficient and strict pollution control and management in study area should be put out as soon as possible. [ABSTRACT FROM AUTHOR]