Arsenic In Soils Research Articles

Arsenic Uptake and Distribution in Green Pea Plants Under Arsenite and Arsenate Treatments

Soil arsenic (As) contamination is a global issue affecting regions worldwide. As in the soil is primarily present in inorganic forms, such as arsenite [As(III)] and arsenate [As(V)]. As is a microelement that is toxic to plants grown in As-contaminated soil. The aim of our study was to investigate the effects of increasing concentrations (0, 3, 10, 30, 90, and 270 mg kg−1) of As(III) and As(V) on the As content in green pea (Pisum sativum L.) and the distribution of As among different plant parts at four phenophases (the four-node stage, beginning of flowering, green ripening, and mature stage). Another aim was to determine the percentage of total soil As available to plants under different treatments. The results indicate that the developmental stage of the pea and treatment concentration significantly influence the distribution of As among plant organs. However, the differences between the effect of inorganic As forms were less pronounced. The amount of As absorbed by the whole test plant increased with higher treatment concentrations. In the case of As(III)-treatment, As amount in the whole plant increased from 0.170 µg to 7.31 µg (I. Phenophase); from 0.294 µg to 10.1 µg (II. Phenophase); from 0.435 µg to 31.6 µg (III. Phenophase); and from 0.697 µg to 36.1 µg (IV. Phenophase). As a result of As(V)-treatment, the whole plant’s As content increased from 0.170 µg to 8.94 µg (I. Phenophase); from 0.294 µg to 17.4 µg (II. Phenophase); from 0.435 µg to 29.7 µg (III. Phenophase); and from 0.697 µg to 58.5 µg (IV. Phenophase). The concentration of As accumulated by the plant also increased over time. The proportion of As absorbed by generative parts was much smaller than that absorbed by vegetative organs. The pea seeds generally accumulated less As (maximum 7%) than the pea pods (in some cases, this reached the 10%). As the total amount of As taken up by the plant increased, the proportion of As reaching the seeds generally decreased (from 5% to 0.3% in the case of As[III]-treatment, and from 5% to 0.1% in the case of As[V]-treatment). At treatment levels where the ability of the stem to retain As increased, a maximum of 1% of the total As absorbed by the plant was found in the seeds. Depending on the treatment, 3.82–5.69% [As(V)-treatments] and 3.9–6.07% [As(III)-treatments] of the total soil As were available to the plants. The difference in the ratio of the total As content to the soluble As content was more evident at higher treatment levels (≥30 mg kg−1). This value was typically lower for the As(V)-treatments.

Accumulation of heavy metals (Cr, Cu, As, Cd, Pb, Zn, Fe, Ni, Co) in the water, soil, and plants collected from Edayar Region, Ernakulam, Kerala, India

The accumulation of heavy metals in the environment is a significant concern due to their potential toxicity and persistence. This study investigates the levels of heavy metal contamination in the water, soil, and plants of the Edayar region in Ernakulam, Kerala, India. The region has experienced industrialization and urbanization, leading to concerns about heavy metal pollution. The study aims to assess the concentrations of chromium (Cr), copper (Cu), arsenic (As), cadmium (Cd), lead (Pb), zinc (Zn), iron (Fe), nickel (Ni), and cobalt (Co) in water, soil, aquatic and terrestrial plants. Samples were collected from various locations within the Edayar region, and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was conducted to quantify heavy metal concentrations. The findings of this study will contribute to the assessment of heavy metal pollution in the Edayar region. Plants with a high diversity index were taken for analysis from both aquatic and terrestrial habitats. Scoparia dulcis L. seems to specialize in metal accumulation, possibly for protective purposes. Synedrella nodiflora Gaertn demonstrates adaptability to metal-rich environments through robust metal uptake and tolerance mechanisms. Alternanthera philoxeroides (Mart.) Griseb, on the other hand, appears to have developed mechanisms to manage heavy metal exposure. The results indicate significant levels of heavy metal contamination across all samples, with the highest concentrations detected in soil, followed by water and plants. Chromium and lead levels in soil exceeded the permissible limits set by international standards, posing potential risks to human health and the ecosystem. The accumulation patterns in plants varied, with higher bioaccumulation factors observed for zinc and copper, suggesting their preferential uptake. This study highlights the urgent need for remediation strategies and continuous monitoring to mitigate the impact of heavy metal pollution in the Edayar region. The results will help in understanding the environmental impact of human activities.

Fe3O4/Mulberry Stem Biochar as a Potential Amendment for Highly Arsenic-Contaminated Paddy Soil Remediation

Magnetite-loaded biochar has recently received attention owing to its ability to remove arsenic from contaminated soil. In this study, mulberry stem biochar (MBC) and Fe3O4-loaded mulberry stem biochar (Fe3O4@MBC) were produced and used in a 100-day incubation experiment to investigate their performance in the stabilization of arsenic in paddy soil severely polluted by the As (237.68 mg·kg−1) mechanism. Incubation experiments showed that Fe3O4@MBC was more effective in immobilizing As after incubation for 100 days. Moreover, adding Fe3O4@MBC facilitated the transformation of exchangeable heavy metals into organic-bound and residual forms, thereby reducing As available concentrations, mobility, and bioavailability in the soil, and elevating slightly the soil pH and dissolved organic carbon (DOC). The concentration of TCLP-extractable As (AsTCLP) in contaminated soil was reduced from 93.85 to 7.64 μg·L−1 within 10 d, below the safety limit for drinking water set by the World Health Organization (WHO). The characterization results of Fe3O4@MBC after incubation indicated that the mechanisms for As passivation are linked to redox reactions, complexation, electrostatic attraction, surface adsorption, and coprecipitation. Conclusively, Fe3O4@MBC is a promising amendment in highly As-contaminated soil and provides a theoretical reference in such polluted paddy soil remediation.

Distribution patterns, health hazards, and multivariate assessment of contamination sources of As, Pb, Ni, Zn, and Fe in agricultural soils

Soil heavy metal contamination is a worldwide environmental concern that presents considerable risks to ecosystems, agricultural progress, and human health. This study aims to evaluate the potential environmental and health hazards linked to the presence of arsenic (As), lead (Pb), nickel (Ni), zinc (Zn), and iron (Fe) in agricultural soil in Al Majma’ah governorate, Saudi Arabia. The contamination factor (CF), pollutant load index (PLI), chronic daily intake (CDI), hazard index (HI), and total lifetime cancer risk (LCR) were calculated for 34 soil samples. The results from the CF and PLI analysis demonstrate that the examined soil has a low contamination factor and is free from heavy metal pollution. The average CDI values for adults and children exhibited the following descending order: Fe > Zn > Cu > Pb > As. The highest HI values observed in adults ranged from 0.0375 (Fe) to 0.00019 (Zn), but in children, the range was from 0.3497 (Fe) to 0.0018 (Zn). The hazard index values for heavy metal(loid)s (HMs) in the Al Majma’ah area were all below 1.0, suggesting that residents in the area are not exposed to a significant non-carcinogenic risk. The LCR values ranged from 8.37E−06 to 7.80E-05 for As in both adults and children, and from 7.50E−08 to 6.98E-07 for Pb. The findings indicated a level of risk that was deemed acceptable or tolerable, without any significant adverse health effects

Industrial by-products (ferrous sulfate minerals and stone powder) can serve as amendments to remediate Cd-As paddy soil, alleviating Cd-As accumulation in rice

Our previous research has shown that industrial by-products such as ferrous sulfate mineral and stone powder as amendments can remediate Cadmium (Cd) and arsenic (As) soil. However, their role in the soil-rice system is unknown. Therefore, this article explored the effects of the combined use of industrial by-products and commercial conditioners on the accumulation of Cd-As in weakly alkaline and acidic soil-rice systems. Potted experiments shown that SL (stone powder+ferrous sulfate mineral) and SLW (stone powder+ferrous sulfate mineral+Weidikang conditioner) could reduce the availability of Cd-As in soil by adjusting soil pH and CEC, increase iron film content on the root surface, strengthening the “barrier” for fixing Cd-As. Brown rice Cd was lower than the national food safety standard of 0.20 mg kg−1 (GB2762–2022). 1 % SLW could reduce brown rice As from 1.24 mg kg−1 to 0.83 mg kg−1. The results of field experiments confirmed the conclusion of pot experiments. SL and SLW not only reduced the accumulation of Cd-As in rice but also significantly increased rice yield by 16.58 % and 11.68 %, respectively. Compared to the two types of conditioning agents sold in the market, the material costs have been reduced by 79.1 % -86.5 % and 12.4 % -43.3 %, respectively. In summary, this study demonstrates that ferrous sulfate minerals and stone powder could efficiently remediate Cd-As pollution in paddy soil under different acid-base conditions, providing an application example for the resource utilization of industrial by-products for the remediation of Cd-As pollution in paddy soil.

Time-dependent redistribution of soil arsenic induced by transformation of iron species during zero-valent iron biochar composites amendment: Effects on the bioaccessibility of As in soils

Zero-valent iron biochar composites (ZVI/BC) are considered as effective amendments for arsenic (As)-contaminated soils. However, the mechanisms of transformation of various soil As species during ZVI/BC amendments remain unclear. This study investigated As transformation in four soils (namely, GX, ZJ, HB, and HN) treated with ZVI/BC for 65 days under two soil moisture conditions, unsaturated and oversaturated. Results showed that the 65-day treatment was divided into two stages based on the variation of labile As content. Within 2 days (stage 1), ZVI/BC addition quickly reduced labile As content by 5.91–90.3 % in soils under unsaturated conditions. During days 2–65 (stage 2), labile As ultimately decreased by 0.06–0.31 mg/kg in GX, ZJ, and HB while increasing by 22.1 mg/kg in HN soil, due to its lower pH value and Fe content. The variations of labile As were attributed to changes in multiple Fe minerals and associated As species. In stage 1, the corrosion of ZVI/BC generated amorphous Fe oxides to immobilize labile As, resulting in the accumulation of meta-stable As. In stage 2, amorphous Fe oxides were transformed into crystalline Fe oxides, resulting in the release and re-precipitation of As along with transformation, thus redistributing immobilized As into labile and stable As, which was evidenced by multiple methods, including chemical extraction, XRD, and TEM-EDX. The elevated soil moisture condition would enhance the corrosion of ZVI/BC in stage 1, further forming a reductive environment to facilitate the transformation of Fe minerals in stage 2. Besides, As bioaccessibility in soils was reduced by 10.8–38.7 % after ZVI/BC treatment in in-vitro gastrointestinal simulations. Overall, our study revealed the time-dependent transformation mechanism of soil As species and associated Fe minerals under different soil moisture with ZVI/BC treatments, and highlighted the effectiveness of ZVI/BC as a long-term amendment for As-contaminated soils.

EVALUATION OF THE SPATIAL DISTRIBUTION AND ACCUMULATION OF ARSENIC IN SOIL AT THE CORNER OF THE RUNWAY AT BIEN HOA AIRBASE, VIET NAM

The primary source of arsenic in soil is a combination of anthropogenic and natural weathering processes. The increased concentration of arsenic is a major issue due to its possible negative impacts on both ecosystems and human health. Considering these issues, this work conducts a rigorous and extensive investigation into the intricate dynamics of arsenic accumulation and contamination levels within soil matrices. The focus of this investigation is especially urgent, particularly in the context of the dioxin-contaminated environment. Specifically, the soil environment at Bien Hoa Airbase exhibits high levels of dioxin contamination.A look at the values of the contamination factor, which ranges from 2.8 to 17.3, suggests indicators of a non-natural origin for the arsenic found in the soils. In addition, the arsenic quantities measured vary significantly, ranging from 9.9 mg/kg to 66.2 mg/kg, and the high accumulation distributed almost the Northeast of the study site. This observed range exceeds the World Health Organization's (WHO) and Viet Nam's regulatory guidelines. The contamination level is much higher than the background arsenic concentration. These results emphasize how critical it is to address and lessen the effects of anthropogenic arsenic pollution on the ecosystem and public health.

Identifying the habitat suitability of Pteris vittata in China and associated key drivers using machine learning models

Pteris vittata (P. vittata) possesses significant potential in remediating arsenic (As) soil pollution. Understanding the habitat suitability of P. vittata in China and pinpointing the key drivers that influence its distribution can facilitate the identification of optimal areas for using P. vittata as a remediation tool for As-polluted soils. In this study, a comparative analysis was conducted using ten machine learning models to assess the habitat suitability of P. vittata based on 744 specimen records and 20 environmental factors. The key drivers affecting the distribution of P. vittata were also investigated based on the optimal model. The results indicate that the XGBOOST model was the most reliable and stable, achieving a coefficient of determination of 0.95. Approximately 24.47 % of China's land area was identified as suitable for P. vittata. Particularly, it was predominantly found in Hainan (45.9 %), Guangxi (92.96 %), Guangdong (91.68 %), Hunan (91.26 %), Guizhou (90.83 %), Chongqing (88.17 %), Fujian (85.70 %), Yunnan (77.44 %), Jiangxi (73.99 %) and Zhejiang (57.05 %). Furthermore, this study pinpointed the lowest temperature, annual temperature range, and mining density as key drivers, contributing 45.9 %, 31.9 %, and 7.2 %, respectively. Spatial correlation analysis revealed a significant correlation between mining density and the habitat distribution of P. vittata (Moran' I = 0.519). This study confirmed that both natural factors and anthropogenic activities affect the distribution of P. vittata and provided valuable insights for optimizing the application of P. vittata in soil phytoremediation and reclamation.

Magnetic porous functional material from coal mine waste for simultaneous removal of cadmium and arsenic in water and soil: Synergistic effect of iron-containing minerals and porous structure

Heavy metals such as cadmium and arsenic (Cd/As) can cause harmful effects on human health. Coal mine waste (coal gangue) is a solid waste residue without commercial values produced abundantly in the coalfield. Hence, treating Cd and As concurrently with reutilizing coal gangue (CG) is critical to ecologically sustainable growth. This work successfully synthesized the magnetic porous functional materials (MPCG) based on CG using a two-step method for the simultaneous removal of Cd and As in water and soil. First, MPCG exhibited an irregular network porous structure. Then, it consisted of iron (Fe), mainly in magnetite, hematite, and pyrite forms. Such properties also exhibited excellent pH adaptability and coadsorption capacity by removing up to 103.79 mg g−1 and 579.43 mg g−1 for Cd(II) and As(V), respectively. There is a synergistic effect between the iron-containing minerals and porous structure to enhance the adsorption capacity of MPCG for Cd(Ⅱ) and As(Ⅴ). Several primary potential adsorption mechanisms by MPCG for Cd(Ⅱ) and As(Ⅴ) were identified. The potential mechanisms of Cd(II) adsorption mainly include ion exchange, electrostatic attraction, surface complexation and precipitation/co-precipitation, and the potential mechanisms of As(V) adsorption mainly include electrostatic attraction, surface complexation and precipitation. In addition, the removal rates of MPCG for Cd and As in soil were as high as 44.78 and 38.44 %, respectively. In conclusion, MPCG has excellent potential as an efficient and environmentally compatible functional material, which provides a potential way to realize efficient heavy metal removal from our ecosystems.

Predicting the risk of arsenic accumulation in soil-rice system in Asian monsoon region

Rice is a staple food for a significant portion of the global population. Arsenic (As) accumulated in rice grains influences rice quality which threatens human health. In this study, we used three machine learning models to predict arsenic accumulation in rice based on over 300 surveys. The prediction results of soil arsenic indicate that high-arsenic soil areas are mainly distributed in South and Southeast Asia such as India, China, and Thailand. In addition, higher bioaccumulation factors (BAF), associated with higher temperature, are predominantly observed in eastern India and southern Myanmar. However, arsenic content in soil is relatively lower in these areas. About 5.5 billion population may be threatened by the consumption of high-arsenic rice. It can be concluded that temperatures may influence the BAF except for soil arsenic, and soil physicochemical properties. Further research on the relationship between climate parameters and BAF should be conducted to address and adapt to future climate change. Additionally, understanding the mechanism of arsenic accumulation under different climatic conditions is crucial for developing agricultural technologies to reduce arsenic accumulation in rice.

Effect of the combined treatment of red mud and gypsum on plant-available arsenic in acidic and alkaline soils

Effect of the combined treatment of red mud and gypsum on plant-available arsenic in acidic and alkaline soils

Adding mineral-enriched biochar to the rhizosphere reduces heavy metal toxicity on plants and soil microbes

In this study, a mineral-enriched (Ca and P) bagasse biochar was synthesized and characterized. The formulation of Ca and P-enriched bagasse biochar (CPB) was examined for immobilizing arsenic (As), cadmium (Cd), and lead (Pb) in rhizospheric soil. The potential of CPB to alleviate heavy metal stress on plants and soil microbial communities was also investigated. The Ca and P-enriched bagasse biochar demonstrated loading of 88 % Ca and 86 % P with improved pore volume, cation exchange capacity, and water-holding capacity. The FTIR and morphology studies demonstrated an increase in surface functionalities on biochar surface and porous morphology. CPB had 1089±21 µm particle size, 1.1 µm pore size, 0.35±0.01 mv PDI, and 20.8±0.2 mv zeta potential, and displayed no phytotoxicity. The application of the CPB in the soil significantly reduced the availability of As, Cd, and Pb in the soil and their uptake in A. paniculata. CPB application altered the subcellular distribution of As, Cd, and Pb in plant tissues. The CPB spray significantly enhanced the biomass (16–27 %), protein (8–44 %), and chlorophyll (15–61 %) contents of A. paniculata. The application of CPB in metal-contaminated soil resulted in an increased relative abundance of the phylum Proteobacteria and the genera Bacillus, Gemmata, and Sphingobium in the microbial community structure of the rhizospheric soil. The study suggested that CPB formulation can be used as a potential solution to alleviate different metal uptake and toxicity of crops planted in contaminated soil, improve rhizospheric soil quality, and reconstruct the microbial community structure.

The degree of soil arsenic background enrichment by carbonate weathering is mainly controlled by climate in large spatial scale

Spatial distribution of soil arsenic (As) is heterogeneous. Making clear the dominant factor(s) controlling its spatial variation contributes to the differentiation of its natural background from anthropogenic pollution. Recent studies have found that the “high background” of soil heavy metals may be induced by the process of carbonate weathering. However, the extent, process, and factors that controls the degree of this enrichment, is still unclear, especially in large spatial scales. In this study, this problem is to be revealed by a compilation and spatial data mining of soil geochemical data for Australia, North America, Europe, and China with a collection and chemical analysis of bedrock and soil profiles in a typical region. The results indicated that the process of carbonate weathering strengthened the As enrichment in the soil; therefore, the carbonate rock underlaid regions could be distinguished from those of other bedrocks in the soil As maps. In the southwest region of China, an area larger than 12,000 km2 exceeding the intervention value of 100 mg/kg could be produced according to the national standard. Iron minerals play an important role for this enrichment as they serve as carriers for As during the stages of both carbonate leaching and the decomposition of silicate minerals. Geodetector results indicated a significant dependence on climate for the degree of enrichment, and both higher temperature and precipitation were necessary, which caused a decreasing trend of soil As on carbonate region from the warm and humid south to the cold and dry north in China. The dependence of soil As concentration on the mean average precipitation (MAP) and mean average temperature (MAT) was formulated using the data of the wider geographical regions across the world, and a theoretically predicted map has been produced to show the extent caused by this causation.

Evaluation of nutrients effect on the arsenic bioaccessibility of contaminated soil

Soil is considered the primary source of heavy metals. Even at very low concentrations, chronic exposure to harmful heavy metal (arsenic) has a significant negative impact on human health. In this study, we evaluated the effect of nutrients including glucose, proteins, calcium and control (fasted condition) on soil arsenic (As) bioaccessibility by PBET (Physiologically Based Extraction Test) technique with SHIME (simulator of the human intestinal microbial ecosystem). As bioaccessibility of the NJY soil sample was 4.43 to 8.28%, 2.56 to 8.55% and 5.66 to 23.49% in gastric phase, intestine phase and colon phase respectively with different nutrients. CFI soil sample’s As bioaccessibility varied depending on the nutrients used, and was 5.78 to 23.86%, 2.32% to 12.54% and 1.06 to 13.85% in gastric phase, intestine phase and colon phase correspondingly. As bioaccessibility of the ZZH soil sample was 2.26 to 25.16%, 24.38% to 57.27% and 9.92 to 23.10% in gastric phase, intestine phase and colon phase with varying nutrients. The outcomes showed that, As bioaccessibility of the soil samples was greatly influenced with plant protein, animal protein, calcium and glucose in the three phases of the digestive system. Therefore, nutrients have a considerable effect on As bioaccessibility and assessment of human health risk.

Adsorption and migration behaviors of heavy metals (As, Cd, and Cr) in single and binary systems in typical Chinese soils

In this study, the competitive adsorption and migration behaviors of arsenic (As), cadmium (Cd), and chromium (Cr) in typical Chinese soils were investigated. It was observed that Hainan, Shanxi, and Zhejiang Mengjiadai soils exhibited the highest adsorption capacities for As (563 μg/g), Cd (653 μg/g), and Cr (383 μg/g), respectively. Heavy metals (HMs) adsorption capacities were predicted by Extreme gradient boosting (XGBoost) models, and the Shapley additive explanation (SHAP) was employed to elucidate the effect of soil physicochemical properties on target values. Due to redox and complexation reaction, the primary factor affecting adsorption has changed from free state manganese (Mn) in single As system to antimony (Sb) in As/Cd and As/Cr systems. Furthermore, the maximum adsorption capacity (Qm) of As increased by 49.4 % with the addition of Cd into Heilongjiang soil. Finally, the migration process of HMs in Heilongjiang, Hebei, and Hainan soils was simulated by column experiments. With a relatively large dispersion coefficient (D = 29.630 cm2/h) and small retardation factor (Rh = 0.030), Cr penetrated fastest in Heilongjiang soil. This research demonstrates that both the types and coexistence of HMs may affect the HMs behaviors in soil.

Research progress on environmental behavior of arsenic in Qinghai-Tibet Plateau soil

The Qinghai-Tibet Plateau, with its high altitude and cold climate, is one of the most fragile ecological environments in China and is distinguished by its naturally elevated arsenic (As) levels in the soil, largely due to its rich mineral and geothermal resources. This review provides a comprehensive analysis of As content, focusing on its distribution, environmental migration, and transformation behavior across the plateau. The review further evaluates the distribution of As in different functional areas, revealing that geothermal fields (107.2 mg/kg), mining areas (53.8 mg/kg), and croplands (39.3 mg/kg) have the highest As concentrations, followed by river and lake sediments and adjacent areas (33.1 mg/kg). These elevated levels are primarily attributed to the presence of As-rich minerals, such as arsenopyrite and pyrite. Additionally, human activities, including mining and geothermal energy production, exacerbate the release of As into the environment. The review also highlights the role of local microorganisms, particularly those from the phyla Proteobacteria and Actinobacteria, which possess As metabolic genes that facilitate As translocation. Given the unique climatic conditions of the plateau, conventional methods for As control may not be fully effective. However, the review identifies promising remediation strategies that are environmentally adaptable, such as the use of local microorganisms, specific adsorbents, and integrated technologies, which offer potential solutions for managing and utilizing As-contaminated soils on the plateau.

Cumulative characteristics and ecological risk source analysis of soil potentially toxic elements in the northern margin of the Tibetan Plateau.

To understand the soil toxic and hazardous elements content, pollution level, and ecological risk status in the northern margin of the Tibetan Plateau, we collected and analyzed 8273 sets of surface soil samples. Evaluations were conducted using the single-factor pollution index, geo-accumulation, pollution load, and potential ecological risk indices, and source identification correlation and principal component analysis. The results revealed that, compared with the background levels in China, the accumulation of soil arsenic, cadmium, nickel, and chromium was greater in the surface soil of the study area. Additionally, in comparison with Qinghai Province, more mercury accumulated in the surface soil of the study area and owing to the influence of anthropogenic activities. Benchmarking against soil environmental quality standards, the study area exhibited pollution control zones primarily dominated by arsenic and cadmium (3.9%). The spatial distribution revealed distinct zones: a ridge mountain type characterized by arsenic-cadmium-chromium-nickel, a Daban mountain type with solely cadmium presence, and a Longyangxia-Jianzha South type dominated by arsenic. Compared with the Qinghai Province soil background values, evaluations using the Pollution loading index, Geological Cumulative Index, and Potential Ecological Risk Index methods revealed varying degrees of potentially toxic element content exceedance. From an ecological risk perspective, the individual element with the highest potential ecological risk coefficients were mercury, followed by cadmium and arsenic; however, the region's overall ecological risk index was classified as low. Three distinct sources were identified: natural sources leading to high background levels of chromium, nickel, copper, zinc, and mercury; mixed natural and industrial/agricultural sources contributing to elevated cadmium levels; and human activity-related mercury enrichment. Based on the evaluation results, synergistic monitoring of soil and biota in naturally occurring risk zones is recommended to ensure the safety of agricultural and pastoral products. Additionally, ecological impact assessments and pollution source mitigation studies should be conducted in regions influenced by human activities to curb the further degradation of soil ecological quality.

Prediction of As and Cd dissolution in various soils under flooding condition

Although the mobility of arsenic (As) and cadmium (Cd) in soils during the flooding-drainage process has been intensively studied, predicting their dissolution among various soils still remains a challenge. After comprehensively monitoring multiple parameters related to As and Cd dissolution in 8 soils for a 60-day anaerobic incubation, the redundancy analysis (RDA) and structural equation model (SEM) were employed to identify the key factors and influencing pathways controlling the dynamic release of As and Cd. Results showed that pH alone explained 90.5 % Cd dissolution, while the dissolved-Fe(II) and 5 M-HCl extractable Fe(II) jointly only explained 50.6 % As dissolution. After data normalization, the ratio of Fe(II) to 5 M-HCl extracted total Fe (i.e. FetotII/Fetot) significantly improved the correlation to R2 = 0.824 (p < 0.001) with a fixed slope of 0.393 among the 8 soils. Our results highlight the crucial role played by the reduction degree of total iron contents in determining both the reduction and dissolution of As during flooding. In contrast, dissolved-Fe(II) was too vulnerable to soil properties to be a stable indicator of As dissolution. Therefore, we propose to replace the dissolved-Fe(II) with this novel ratio as the key index to quantitatively assess the kinetic change of As solubility potential across various soils under flooding conditions.

Carrier-Gas free arc igniter microplasma optical emission spectrometry for the determination of arsenic in soil

Rapid on-site assessment of arsenic contamination in soils is crucial for environmental protection and human health. In order to build an effective and affordable device for the determination of arsenic, the use of carrier gas supplies and high power energy consumption largely limit the miniaturization of microplasma-based optical emission spectrometry (OES). An arc igniter microplasma (AIM) can be powered by a low DC power supply and operated in the atmosphere of air without gas infusion, which is beneficial to construct a carrier-gas free and low power supply setup. Hydride generation (HG) can improve sample transport efficiency and reduce matrix effects, but the generated by-product hydrogen has not been explored as a sole working gas for plasma excitation. In this work, a hydride generation arc igniter microplasma optical emission spectrometer (HG-AIM-OES) was fabricated for detecting arsenic in soils. H2 derived from HG was served as a working gas to transport AsH3 to excite, eliminating the use of a carrier gas unit. Under the optimized operating conditions, the limit of detection (LOD) for arsenic was 164 μg/L (the analytical line at 234.98 nm), and good linearity of the method was achieved in the range of 0.5–20 mg/L with a precision of 3.14 % (the concentration of arsenic at 1 mg/L). In addition, the influence of H2 on AIM physical properties was carefully studied in the air and Ar discharge atmospheres. The accuracy of the proposed device was validated by the analysis of certified reference materials (CRMs) and a real soil sample, resulting in good agreement with the obtained results by air and Ar as working gas. This HG-AIM-OES system provides a miniaturized, carrier gas-free and low power consuming tool for monitoring and assessment of arsenic-contaminated soils.

Phase transformation of schwertmannite in paddy soil under different water management regimes and its impact on the migration of arsenic in soil

Schwertmannite (Sch) holds a great promise as an iron material for remediating Arsenic (As)-contaminated paddy soils, due to its extremely high immobilization capacities for both arsenate [As(V)] and arsenite [As(III)]. However, there is still limited knowledge on the mineral phase transformation of this metastable iron-oxyhydroxysulfate mineral in paddy soils, particularly under different water management regimes including aerobic, intermittent flooding, and continuous flooding, and how its phase transformation impacts the migration of As in paddy soils. In this study, a membrane coated with schwertmannite was first developed to directly reflect the phase transformation of bulk schwertmannite applied to paddy soils. A soil incubation experiment was then conducted to investigate the mineral phase transformation of schwertmannite in paddy soils under different water management regimes and its impact on the migration of As in paddy soil. Our findings revealed that schwertmannite can persist in the paddy soil for 90 days in the aerobic group, whereas in the continuous flooding and intermittent flooding groups, schwertmannite transformed into goethite, with the degree or rate of mineral phase transformation being 5% Sch >1% Sch > control. These results indicated that water management practices and the amount of schwertmannite applied were the primary factors determining the occurrence and degree of mineral transformation of schwertmannite in paddy soil. Moreover, despite undergoing phase transformation, schwertmannite still significantly reduced the porewater As (As(III) and As(V)), and facilitated the transfer of non-specifically adsorbed As (F1) and specifically adsorbed As (F2) to amorphous iron oxide-bound As (F3), effectively reducing the bioavailability of soil As. These findings contribute to a better understanding of the mineralogical transformation of schwertmannite in paddy soils and the impact of mineral phase transformation on the retention of As in soil, which carry important implications for the application of schwertmannite in remediating As-contaminated paddy soils.