Fe-CGS Effectively Inhibits the Dynamic Migration and Transformation of Cadmium and Arsenic in Soil.

The iron-modified coal gasification slag (Fe-CGS) material has excellent performance in purifying heavy-metal-contaminated water due to its good surface properties and adsorption capacities. However, it is unclear whether it can provide long-term simultaneous stabilization of Cd and As in composite-contaminated soils in extreme environments. This study investigated the long-term stabilization of Cd and As in acidic (JLG) and alkaline (QD) soils by simulating prolonged heavy rainfall with the addition of Fe-CGS. Multiple extraction methods were used to analyze the immobilization mechanisms of Cd and As in soil and their effects on bioavailability. The results indicate that the stabilization efficiency was related to the dosage of Fe-CGS. The concentrations of Cd and As in the JLG soil leachate were reduced by 77.6% (2.0 wt%) and 87.8% (1.0 wt%), respectively. Additionally, the availability of Cd and As decreased by 46.7% (2.0 wt%) and 53.0% (1.0 wt%), respectively. In the QD soil leachate, the concentration of Cd did not significantly change, while the concentration of As decreased by 92.3% (2.0 wt%). Furthermore, the availability of Cd and As decreased by 22.1% (2.0 wt%) and 40.2% (1.0 wt%), respectively. Continuous extraction revealed that Fe-CGS facilitated the conversion of unstable, acid-soluble Cd into oxidizable Cd and acid-soluble Cd. Additionally, it promoted the transformation of both non-specifically and specifically adsorbed As into amorphous iron oxide-bound and residual As. Fe-CGS effectively improved the soil pH, reduced the bioavailability of Cd and As, and blocked the migration of Cd and As under extreme rainfall leaching conditions. It also promoted the transformation of Cd and As into more stable forms, exhibiting satisfactory long-term stabilization performance for Cd and As.

Diurnal variation in the urban thermal environment and its relationship to human activities in China: a Tencent location-based service geographic big data perspective.

The main factor of the formation and deterioration in China's urban thermal environment is human activity, which is difficult to describe and measure. A new perspective on the effect of human activity on the urban thermal environment can be obtained by examining the interaction between location-based service (LBS) data and the urban thermal environment in China. However, relevant research is still limited. In this study, we used Tencent LBS data, Terra/Aqua MODIS land surface temperature (LST) data, and land use data to investigate the relationship between LBS and the urban thermal environment, specifically the LST and surface urban heat island intensity (SUHII) across China and its provinces. Our results showed that (1) in summer, the heat island effect was an issue in 94% of the urban areas in China, which was worse during the day. The high- and low-value periods of LBS data on a given day coincided with the acquisition times of MODIS LST products during the day and at night, respectively. (2) During both the day and at night, there was a significant connection between LBS data and the urban thermal environment in China. The highest correlation coefficient (r) between LBS data and the LST could reach 0.55 (p < 0.01) at the provincial level, and the highest correlation coefficient (r) between LBS data and the SUHII could reach 0.78 (p < 0.01) at the provincial level. (3) The urban thermal environment diurnal difference and LBS data exhibited a significant relationship. The ΔLBS diurnal differences were significantly positively related to the SUHII diurnal differences in China. The overall study findings revealed that LBS data constitute an important parameter to represent the human activity intensity when investigating the formation of the urban thermal environment in China.

Application of stochastic model to assessment of heavy metal(loid)s source apportionment and bio-availability in rice fields of karst area.

Mining activities and high geological background are considered the important factors causing heavy metal(loid)s accumulation in rice fields of karst area. In this study, the contents, main sources, and the factors influencing bio-availability of heavy metal(loid)s were determined using conditional inference tree (CIT), random forest (RF), and geostatistical analyses with 105 soil samples collected from rice fields in karst area. Contamination by Cd, Hg, As, and Pb in soil was relatively serious in the study area in which the compound pollution was highly similar to that in the flooded area. CIT and RF effectively identified the contributions of natural and anthropogenic inputs of soil heavy metal(loid)s. Concentrations of Pb, As, and Hg were closely associated with human inputs whose cumulative contribution rates reached 68%, 87%, and 86%, respectively. Industrial activities (28%) and geogenic characteristics (44%) were primary sources of Cd accumulation. The soil pH, soil organic matter (SOM), distance from city center, the contents of heavy metal(loid)s in soil, and industry type were the most important factors influencing bio-availability of heavy metal(loid)s. Combined effect of multiple metals could not be ignored, in which As and Cd contributed over 80% to total non-carcinogenic risks for adults and children.

Study on molecular level toxicity of Sb(V) to soil springtails: using a combination of transcriptomics and metabolomics.

To date, numerous studies have focused on the toxicity of antimony (Sb) to soil-dwelling organisms at the individual level. However, little is known about Sb-caused molecular level toxicity. Here, an integrated transcriptomics and metabolomics approach was used to better reveal toxicity of Sb(V) to springtails Folsomia candida considering environmentally relevant speciation of Sb. No significant effects of Sb(V) on survival, reproduction and growth of springtails were observed using the ISO standard test. Transcriptomics analysis identified 1015 and 3367 differentially expressed genes (DEGs) after 2 and 7 d of exposure, indicating an increasing transcriptomal changes with time. Significantly enriched top GO (Gene Ontology) terms (chitin metabolic process, chitin binding and extracellular region) were shared between the two time exposure groups. However, no enriched KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway was shared, with fatty acid metabolism and apoptosis-fly being the most significant pathway, respectively. Metabolomics analysis identified 155 differential changed metabolites (DCMs) in springtails after 7 d of exposure. Antifolate resistance was the most significantly enriched pathway, in which dihydrofolic acid was up-regulated and three purine nucleotides (adenosine 5'-monophosphate, inosine 5'-monophosphate, guanosine 5'-monophosphate) were down-regulated. This indicated obvious repression of DNA replication, which was also observed by transcriptomics. Additionally, metabolites level related to chitin, oxidative stress, and protein metabolism significantly changed, and these metabolites could also support and confirm main transcriptomic results. Thus, the combination of multiomics facilitated better understanding of the molecular level of toxicity of Sb(V) in Collembola.

Soil migration of antimony and arsenic facilitated by colloids in lysimeter studies.

The migration behaviors of antimony (Sb) and arsenic (As) and its influence factors have not been well understood among the different soils. In this study, we used lysimeter experiments to investigate the migration behavior of Sb compared with that of As in four representative soil materials from China. All the experiments processes and management measures were conducted to simulate the actual natural environmental conditions. Results indicated that after two years of leaching, the concentrations of Sb and As at the soil surface had decreased, whereas they increased in the deep soil profiles. In the polluted soil materials, 28.5%-39.2% of Sb and 0.4%-1.3% of As existed in the stable fraction, respectively. As and Sb levels were higher in the surface soil layer, and decreased with the soil depth in the different soil profiles. In soil leachate, Sb was mainly found in particle sizes smaller than 0.45 µm with the organic colloids, which had a peak in the spring and summer. On contrast, As was found in particle sizes larger than 0.45 µm with the inorganic colloids such as iron (Fe) and aluminum (Al) oxides. Pearson correlation results showed that the concentrations of Sb in the soil leaching solution and 0.45-µm-filltered solution were all positively correlated with Fe and Al. The results confirmed that Sb was combined with Fe and Al in the solution, and As posed a greater environmental risk than Sb during the leaching process. This study will help us to describe and predict As and Sb pollution in the soil environment, providing a basis for managing soil contaminated by these pollutants.

Influences of soil properties and long-time aging on phytotoxicity of antimony to barley root elongation.

Antimony (Sb) is a toxic element of global concern. To date, the most previous researches about phytotoxicity of Sb failed to fully consider the effects of soil properties and long-time aging. To address this, the toxicity of exogenous Sb(III) and Sb(V) were studied using the standardized barley root elongation bioassay. The results indicated that in ten soils aged only for 1 d, the EC10 (concentrations causing 10% inhibition) values were 221-3164 mg kg-1 and 135-4260 mg kg-1 in Sb(III)- and Sb(V)-treated soils, respectively. The EC50 values (concentrations causing 50% inhibition) were more than the setting highest concentration of 6400 mg kg-1 in half of ten soils. The regression analysis showed that the amorphous Fe oxide and pH were the most foremost single soil factor explaining above-mentioned variance in EC10, respectively, which suggested that the dominant soil factors were related to Sb forms. The inclusion of amorphous Mn oxide in above these two simple regression model could best explain the toxicity variance. After aged for 116 and 365 d, the phytotoxicity of Sb in Sb-treated soils significantly decreased and the phytotoxicity were even not found in the majority of Sb(V)-treated soils. The extent of aging varied with soils, and correlation analysis indicated that the aging effects negatively correlated with soil pH and positively correlated with clay and amorphous Al oxide in the Sb(III)-treated test soils.

Protective Effect of foliar application of sulfur on photosynthesis and antioxidative defense system of rice under the stress of Cd.

This paper investigates the effect of foliar application of sulfur on photosynthesis and antioxidative defense system of rice under the stress of Cd. The initial field studies showed that foliar spray of S was effective for reducing Cd concentration in rice and increasing the grain yield. However, the physiological mechanisms remain less clear on how the foliar application of S alleviates Cd toxicity in rice. Chlorophyll fluorescence, as a measure of photosynthesis, was taken to estimate the efficiency of photosystem II (PSII) photochemistry after the foliar application of S. The increase of photosynthetic parameters, i.e. the maximum photochemical efficiency of PSII reaction center (Fv/Fm), the actual PSII photochemical efficiency (ΦPSII), the photochemical quenching coefficient (qP), indicated that the foliar treatment alleviated the toxicity of Cd to PSII. The decrease of non-photochemical quenching coefficient (NPQ) indicated the increase of photochemical reaction efficiency with more absorbed light energy for photochemical reactions. Fourier Transform Infrared (FTIR) spectra showed that the foliar treatment stimulated the syntheses of lignin, lipids, aliphatic acid, polysaccharides, carboxylate and proteins. Micrographs of transmission electron microscope (TEM) also revealed the reduced mobility of Cd in cells. Foliar application of S effectively reduced the damage of Cd stress by maintaining the integrity of cell structure and participating in metabolic activities such as protein synthesis.

Effects of soil properties and long aging time on the toxicity of exogenous antimony to soil-dwelling springtail Folsomia candida.

The most existing studies on the toxicity of antimony (Sb) were performed in limited types of soil and after short aging time. Effects of soil properties and long aging time on chronic toxicity of Sb(III) and Sb(V) to model organism Folsomia candida were studied in the laboratory studies. The results showed that after the Sb(V)-treated soils were aged for 365 d, the Sb exhibited no toxicity to survival and reproduction even at the nominal highest concentration of 12,800 mg kg-1 in ten types of soils with distinct differences in soil properties. In the Sb(III)-treated ten soils aged only for 30 d, the concentrations causing 50% mortality (LC50) and concentrations inhibiting 50% reproduction (EC50) were 1288-3219 mg kg-1 and 683-1829 mg kg-1, respectively. The LC50 were higher than the highest test concentration and the EC50 significantly increased by 2.24-6.16 fold after the Sb(III)-treated soils were aged for 150 d, and soil pH was the most important single factor explaining the variance in aging effects. After the aging time was 365 d, similar with Sb(V)-treated soils, no toxicity were observed in the most Sb(III)-treated soils, indicating the increasing aging effects with aging time. Regression analysis indicated that the OM and pH were the most important single factor predicting Sb toxicity to reproduction in Sb(III)-treated soils aged for 30 and 150 d, respectively.

Mitigation of Cd accumulation in rice from Cd-contaminated paddy soil by foliar dressing of S and P.

Cadmium (Cd)-contaminated paddy soil has become a global agricultural safety issue. The application of foliage dressing with mineral elements to alleviate Cd toxicity in rice might offer a cost-effective and practical strategy for safe food production. In this study, a pot experiment was conducted to optimize foliar composition and dosage. Field experiments in two consecutive rice seasons were performed to investigate the effectiveness and mechanisms of foliage dressing. Foliar spray of S, P, and a mixture of both were effective to reduce the Cd concentration in rice grain. The maximum decrease by leaf-grain translocation was achieved at 84%, and the maximum decrease of bio-concentration was 69% in the stem. The reduction of Cd concentration in rice decreased the direct damage to the photosynthetic system, and then increased the rice growth. Foliage dressing relieved the oxidative stress of Cd to rice by decreasing the MDA content, and increasing antioxidant enzyme activities. Foliar spray with S likely reduced Cd accumulation in rice by minimizing the production of reactive oxygen species, improving the activities of enzymatic and non-enzymatic antioxidant defense systems, and manipulating glutathione synthesis. The detoxification of foliar spray with P was originated from the decrease of Cd translocation and maintaining photosynthetic machinery. These results indicated that foliage dressing with S and P has great potential for the remediation of vast agricultural fields.

The toxicity thresholds of metal(loid)s to soil-dwelling springtail Folsomia candida-A review.

Increasing concentrations of metals in soil have posed a serious threat to the soil environment. The control and evaluation of soil metal hazards demand the establishment of soil ecological criteria, which is mainly based on the obtainment of toxicity thresholds. As the most typical representative of soil-dwelling springtails, Folsomia candida performs numerous essential ecological functions in soil and has been extensively used to investigate metal toxicity effects and thresholds. This review outlined the current state of knowledge on the metal toxicity thresholds to Folsomia candida, including (1) toxicity thresholds of soil metals for the different endpoints, (2) the influence factors of metal toxicity thresholds including the test conditions, the chemical forms of metal, the soil physicochemical properties, aging time and leaching, (3) the bioavailable fractions predicting metal toxicity thresholds, (4) the internal threshold of metals. To conclude, several recommendations for future research are given to obtain the more reliable toxicity thresholds and further supplement the toxicity data of metals to Folsomia candida.

The toxicity of exogenous nickel to soil-dwelling springtail Folsomia candida in relation to soil properties and aging time.

Nickel (Ni) is a toxic metal, but studies on Ni toxicity to soil-dwelling springtail are fairly limited, and did not consider the effects of various soil properties and long aging time. To address this, the chronic toxicity of Ni to model organism-Folsomia candida in relation to soil properties and aging time were evaluated in the laboratory study. The results showed that compared to the soils aged only for 7 d, the concentrations causing 50% mortality (LC50) and inhibiting 50% reproduction (EC50) basing measured total Ni in four soils aged for 120 d increased by 1.30-1.94 fold and 1.27-1.82 fold, respectively. Furthermore, the aging effects significantly correlated with soil pH. The toxicity values of Ni differed in ten soils aged for 120 d, the LC50 values were 279-4025 mg/kg and the EC50 values were 133-1148 mg/kg. When calculating the toxicity values basing water soluble and CaCl2 extracted Ni, the variations in LC50 values between ten soils decreased, while the variations in EC50 values increased. Regression analysis indicated that soil pH was the most important single factor predicting soil Ni toxicity to springtail, the combination of soil pH and OM could best explain Ni toxicity variance in ten soils (89.1% of the variance in LC50 values and 89.6% of the variance in EC50 values).

Toxicity of exogenous hexavalent chromium to soil-dwelling springtail Folsomia candida in relation to soil properties and aging time.

Chromium (Cr) is a well-known toxic metal, but studies on Cr toxicity to soil-dwelling springtails are fairly limited, and did not consider the effects of various soil properties and long aging time. To address this, the chronic toxicity of Cr(VI) to survival and reproduction of model organism-Folsomia candida were evaluated in the laboratory studies. The results showed that compared to the soils aged only for 2 and 21 d, the concentrations inhibiting 50% reproduction (EC50) significantly increased by 2.8-5.2 fold and 1.7-2.6 fold, the concentrations causing 50% mortality (LC50) were higher than the highest test concentration in four soils aged for 150 d. Furthermore, the aging effects correlated significantly with soil amorphous Fe oxides. The EC50 values of Cr significantly differed in ten soils aged for 150 d, ranging from 27 to 512 mg kg-1, which were associated with the variations in reduction and sorption capacity in different soils. Regression analysis indicated that soil clay was the most important single factor predicting soil Cr toxicity to reproduction, and the inclusion of cation exchange capacity in the clay regression could best explain the toxicity variance (87.2%). Additionally, soil pH, organic matter and amorphous Fe oxides could also well explain the toxicity variance (>55%).

The toxicity of exogenous arsenic to soil-dwelling springtail Folsomia candida in relation to soil properties and aging time.

Arsenic (As) is a toxic metalloid, but studies on As toxicity to soil-dwelling springtails are fairly limited, and did not consider the effects of various soil properties and long aging time. To address this, the toxicity of As to model organism-Folsomia candida were evaluated in the laboratory studies. The results showed that compared to the soils aged only for 15 d, the concentrations inhibiting 50% reproduction (EC50) significantly increased by 1.3- to 2.0-fold in four soils aged for 150 d, the concentrations causing 50% mortality (LC50) were higher than the highest test concentration in the most soils. Furthermore, the aging effects correlated significantly with soil free Fe oxides contents. The toxicity of As differed in ten soils aged for 150 d, the LC50 were 320-> 1280 mg/kg in acute test and the EC50 were 67-580 mg/kg in chronic test. Regression analysis indicated that soil clay was the most important single factor predicting soil As toxicity to reproduction, explaining 89% of the variance in EC50 values. Soil pH, free Fe oxides and Al oxides could also well explain the toxicity variance (> 65%), indicating that As sorption was a key factor controlling its toxicity.

Toxicity of exogenous antimony to the soil-dwelling springtail Folsomia candida.

Antimony (Sb) is a toxic pollutant, but data for Sb toxicity to springtails in soil are limited, and the effects of Sb speciation, soil physiochemical properties, and aging time on Sb toxicity have not been investigated. To address this, the effects of Sb on Folsomia candida were evaluated in laboratory studies. The results demonstrated that compared with Sb(III), no significant change in mortality was observed in Sb(V)-treated soil, but the EC50 value for the reproduction was 28-fold higher than that of Sb(III). Sb(III) toxicity was very different in four soils. The LC50 values for the survival were 2325-5107 mg kg-1 in the acute test and 605-2682 mg kg-1 in the chronic test, and the EC50 values for the reproduction were 293-2317 mg kg-1. The toxicity discrepancies were associated with the variations in oxidation potential and sorption capacity among corresponding soils. Toxicity significantly positively correlated with the clay and amorphous iron content but significantly negatively correlated with pH. Long-term aging markedly decreased Sb(III) toxicity, and the EC50 and LC50 values were unexpectedly higher than the highest test concentration in soil aged for 180 days. Sb(III) toxicity was probably modified more by oxidation than by changes in the available Sb fraction during aging.

Linkage between human population and trace elements in soils of the Pearl River Delta: Implications for source identification and risk assessment.

The human population is both an emitter and receptor of metals. This study aims to clarify how the relationship of metals and metalloids to human populations influences their source characterization and health risk, based on metal concentrations in 298 soil samples in the Pearl River Delta (PRD) and the corresponding zip-code level population. Nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), mercury (Hg), and lead (Pb), but not chromium (Cr) and arsenic (As), were significantly correlated with population (p<0.01), suggesting potential anthropogenic sources. A principal component analysis (PCA) revealed three factors (i.e., F1, F2, and F3) contributing to metal levels in the PRD: (1) metal transport from rivers (F1), which explained the high levels of Cr, Ni, Cu, Zn, As, and Cd in downstream areas; (2) industrial sources (F2), mainly contributing to Ni, Cu, Zn, Cd, Hg, and Pb; and (3) natural and agricultural sources (F3), mainly contributing to As and Pb. F2 was significantly correlated with population, while F3 was not, indicating that an analysis of the correlation with population could be used to identify industrial sources of metals. Compared with directly calculated risks, the population-weighted non-carcinogenic and carcinogenic risks were increased by 4.2-4.9% and 7.7-9.2%, respectively. A unit increase in the concentration of industrial metals led to higher extra risks than a corresponding increase in natural metals due to the proximity to human populations.

Application of a self-organizing map and positive matrix factorization to investigate the spatial distributions and sources of polycyclic aromatic hydrocarbons in soils from Xiangfen County, northern China.

The concentrations of 16 priority polycyclic aromatic hydrocarbons (PAHs) were measured in 128 surface soil samples from Xiangfen County, northern China. The total mass concentration of these PAHs ranged from 52 to 10,524ng/g, with a mean of 723ng/g. Four-ring PAHs contributed almost 50% of the total PAH burden. A self-organizing map and positive matrix factorization were applied to investigate the spatial distribution and source apportionment of PAHs. Three emission sources of PAHs were identified, namely, coking ovens (21.9%), coal/biomass combustion (60.1%), and anthracene oil (18.0%). High concentrations of low-molecular-weight PAHs were particularly apparent in the coking plant zone in the region around Gucheng Town. High-molecular-weight PAHs mainly originated from coal/biomass combustion around Gucheng Town, Xincheng Town, and Taosi Town. PAHs in the soil of Xiangfen County are unlikely to pose a significant cancer risk for the population.

DDT, DDD, and DDE in soil of Xiangfen County, China: Residues, sources, spatial distribution, and health risks.

We collected and analyzed 128 surface soil samples from Xiangfen County for dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE). Total DDT concentrations (DDTs; sum of p,p'-DDD, p,p'-DDE, and p,p'-DDT) ranged from ND to 427.81 ng g(-1) (dry weight, dw), with a mean of 40.26 ng g(-1) (dw). Among the three compounds, p,p'-DDD was the most dominant. The DDTs in Xiangfen County soils mainly originated from historical DDT use, but there were also new inputs likely related to dicofol use. The DDTs in Xiangfen County soils were mainly degraded under anaerobic conditions, and direct degradation to DDD was the main degradation route. Regions with relatively high concentrations of DDTs were mainly located in North and South Xiangfen County. In these regions, many soil samples contained p,p'-DDT as the predominant pollutant, suggestive of extensive new inputs of DDT. A health risk assessment revealed that there are no serious long-term health impacts of exposure to DDTs in soil, for adults or children.