Heavy metals and trace elements in atmospheric fall-out: their relationship with topsoil and wheat element composition

Enhancing soil health to minimize cadmium accumulation in agro-products: the role of microorganisms, organic matter, and nutrients

Agro-products accumulate Cd from the soil and are the main source of Cd in humans. Their use must therefore be minimized using effective strategies. Large soil beds containing low-to-moderate Cd-contamination are used to produce agro-products in many developing countries to keep up with the demand of their large populations. Improving the health of Cd-contaminated soils could be a cost-effective method for minimizing Cd accumulation in crops. In this review, the latest knowledge on the physiological and molecular mechanisms of Cd uptake and translocation in crops is presented, providing a basis for developing advanced technologies for producing Cd-safe agro-products. Inoculation of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi, application of organic matter, essential nutrients, beneficial elements, regulation of soil pH, and water management are efficient techniques used to decrease soil Cd bioavailability and inhibiting the uptake and accumulation of Cd in crops. In combination, these strategies for improving soil health are environmentally friendly and practical for reducing Cd accumulation in crops grown in lightly to moderately Cd-contaminated soil.

Limestone and yellow gypsum can reduce cadmium accumulation in groundnut (Arachis hypogaea): A study from a three-decade old landfill site

Cadmium (Cd) toxicity has cropped up as an important menace in the soil-plant system. The use of industrial by-products to immobilise Cd in situ in polluted soils is an interesting remediation strategy. In the current investigation, two immobilizing amendments of Cd viz., Limestone (traditionally used) and Yellow gypsum (industrial by-product) have been used through a green-house pot culture experiment. Soil samples were collected from four locations based on four graded levels of DTPA extractable Cd as Site 1 (0.43 mg kg-1), Site 2 (0.92 mg kg-1), Site 3 (1.77 mg kg-1) and Site 4 (4.48 mg kg-1). The experiment was laid out in a thrice replicated Factorial Complete Randomized Design, with one factor as limestone (0, 250, 500 mg kg-1) and the other being yellow gypsum (0, 250, 500 mg kg-1) on the collected soils and groundnut was grown as a test crop. Results revealed that the DTPA-extractable Cd content in soil and Cd concentration in plants decreased significantly with the increasing doses of amendments irrespective of initial soil available Cd and types of amendment used. The effect of amendment was soil specific and in case of Site 1 (low initial Cd) the effect was more prominent. The reduction in DTPA-extractable Cd in combined application of limestone and yellow gypsum @500 mg kg-1 over the absolute control in soil under groundnut for the sites was by far the highest with the values of 83.72%, 77.17%, 48.59% and 40.63% respectively. With the combined application, Target Cancer Risk (TCR) of Cd was also reduced. Hence, combined application of limestone and yellow gypsum can be beneficial in the long run for mitigating Cd pollution.

Transcriptome and ultrastructural analysis revealed the mechanism of Mercapto-palygorskite on reducing Cd content in wheat

Large areas of crop yields in northern China have faced with cadmium (Cd) contamination problems. Mercapto-modified palygorskite (MP), as a highly efficient immobilization material, could reduce Cd absorption in wheat and alleviate its biotoxicity. However, the molecular mechanism underlying MP-mediated Cd reduction and detoxification processes in wheat is not well understood. This aim of this study was to investigate the biochemical and molecular mechanisms underlying the reduction in Cd accumulation in wheat (Triticum aestivum L.). The results showed that MP application decreased the Cd concentration by 68.91-74.32% (root) and 70.68-77.2% (shoot), and significantly increased the glutathione (GSH) and phytochelatins (PCs) contents in root and shoot. In addition, with the application of MP, the percentage of Cd in the cell walls and organelles of wheat decreased, while that of Cd in soluble components was increased. The content of Cd in all components was significantly reduced. Ultrastructural analysis revealed that MP thickened the cell wall, promoted vesicle formation in the membrane and protected the integrity of intracellular organelles in wheat. Transcriptome analysis further confirmed the above results. MP upregulated the expression of several genes (CCR, CAD COMT and SUS) involved in cell wall component biosynthesis and promoted vesicle formation on cell membranes by upregulating the expression of PLC and IPMK genes. In addition, genes related to antioxidant synthesis (PGD, glnA and GSS) and photosynthesis (Lhca, Lhcb) were altered by MP to alleviate Cd toxicity in wheat. This present work will help to more thoroughly elucidate the molecular mechanism by which wheat defends against Cd contamination under MP application and provide and important research basis for the application of this material in the future.

More effective than direct contact: Nano hydroxyapatite pre-treatment regulates the growth and Cd uptake of rice (Oryza sativa L.) seedlings

Cd contamination in rice urgently needs to be addressed. Nano hydroxyapatite (n-HAP) is an eco-friendly material with excellent Cd fixation ability. However, due to its own high reactivity, innovative application of n-HAP in the treatment of Cd contamination in rice is needed. In this study, we proposed a new application, namely n-HAP pre-treatment, which can effectively reduce Cd accumulation in rice and alleviate Cd stress. The results showed that 80 mg/L n-HAP pre-treatment significantly reduced Cd content in rice shoot by 35.1%. Biochemical and combined transcriptomic-proteomic analysis revealed the possible molecular mechanisms by which n-HAP pre-treatment promoted rice growth and reduced Cd accumulation. (1) n-HAP pre-treatment regulated gibberellin and jasmonic acid synthesis-related pathways, increased gibberellin content and decreased jasmonic acid content in rice root, which promoted rice growth; (2) n-HAP pre-treatment up-regulated gene CATA1 expression and down-regulated gene OsGpx1 expression, which increased rice CAT activity and GSH content; (3) n-HAP pre-treatment up-regulated gene OsZIP1 expression and down-regulated gene OsNramp1 expression, which reduced Cd uptake, increased Cd efflux from rice root cells.

Temporal and Spatial Variations of Potentially Toxic Elements in PM10 Collected in Jeddah City, Saudi Arabia

Air pollution causes environmental and health problems around the world. In this study, ambient particulate matter with an aerodynamic diameter equal to or less than 10 microns (PM10) has been collected at three different locations in Jeddah city, Saudi Arabia. The locations are characterized by differences in terms of traffic, residential intensity, industrial, and non-road mobile machinery activities. The monthly and annual mass concentration of the PM10 exceeds the recommended annual limit of the World Health Organization (15 µg/m3) and the European air quality standard (40 µg/m3) at the three locations. The collected PM10 samples as well as a certified reference material of atmospheric particulates (NIST 1678a) were digested in aqua regia using microwave digestion. The quantitative elemental analysis was carried out using inductively coupled plasma mass spectrometry. The variations of the elemental concentration in terms of workdays, weekends, seasons, and annual were determined at the three locations. The spatial and temporal elemental variations were found to be different between the three sites, pointing to local influences that should be further evaluated. The concentration of Cd was found to be high and may cause health problems.

Risk assessment of toxic and hazardous metals in paddy agroecosystem by biochar-for bio-membrane applications

Toxic and carcinogenic metal (loid)s, such arsenic (As) and cadmium (Cd), found in contaminated paddy soils pose a serious danger to environmental sustainability. Their geochemical activities are complex, making it difficult to manage their contamination. Rice grown in Cd and As-polluted soils ends up in people's bellies, where it can cause cancer, anemia, and the deadly itai sickness. Solving this issue calls for research into eco-friendly and cost-effective remediation technology to lower rice's As and Cd levels. This research delves deeply into the origins of As and Cd in paddy soils, as well as their mobility, bioavailability, and uptake mechanisms by rice plants. It also examines the current methods and reactors used to lower As and Cd contamination in rice. Iron-modified biochar (Fe-BC) is a promising technology for reducing As and Cd toxicity in rice, improving soil health, and boosting rice's nutritional value. Biochar's physiochemical characteristics are enhanced by the addition of iron, making it a potent adsorbent for As and Cd ions. In conclusion, Fe-BC's biomembrane properties make them an attractive option for remediating As- and Cd-contaminated paddy soils. More efficient mitigation measures, including the use of biomembrane technology, can be developed when sustainable agriculture practices are combined with these technologies.

GhCYS2 governs the tolerance against cadmium stress by regulating cell viability and photosynthesis in cotton

Cysteine, an early sulfur-containing compound in plants, is of significant importance in sulfur metabolism. CYS encodes cysteine synthetase that further catalyzes cysteine synthesis. In this investigation, CYS genes, identified from genome-wide analysis of Gossypium hirsutum bioinformatically, led to the discovery of GhCYS2 as the pivotal gene responsible for Cd2+ response. The silencing of GhCYS2 through virus-induced gene silencing (VIGS) rendered plants highly susceptible to Cd2+ stress. Silencing GhCYS2 in plants resulted in diminished levels of cysteine and glutathione while leading to the accumulation of MDA and ROS within cells, thereby impeding the regular process of photosynthesis. Consequently, the stomatal aperture of leaves decreased, epidermal cells underwent distortion and deformation, intercellular connections are dramatically disrupted, and fissures manifested between cells. Ultimately, these detrimental effected culminating in plant wilting and a substantial reduction in biomass. The association established between Cd2+ and cysteine in this investigation offered a valuable reference point for further inquiry into the functional and regulatory mechanisms of cysteine synthesis genes.

Impacts of a lead smelter in East Java, Indonesia: degree of contamination, spatial distribution, ecological risk, and health risk assessment of potentially toxic elements in soils

This study investigates the characteristics of potentially toxic elements in soils collected from the vicinity of a lead smelter in East Java, Indonesia. The objective is to assess the impact of the lead smelter on the surrounding soil. The study involves chemical composition analysis, spatial distribution mapping, and potential ecological and health risk assessments. Soil samples were collected from the surface area (0-10 cm) and subsurface (15-30 cm) within radii of 1.5 km, 3 km, and 5 km from the lead smelter. The samples were analyzed for As, Cr, Cu, Ni, Pb, and Zn using energy-dispersive X-ray fluorescence. Principal component analysis (PCA) was performed to identify the sources of potentially toxic elements in the soil. The results indicate severe Pb contamination within a 1.5 km radius of the smelter, with an average contamination factor (Cf) value of 22.0, posing a high potential health risk. The contamination factor indicated that the soils were heavily polluted by As and Pb and moderately polluted by Cu, Ni, and Zn. The results of PCA showed that smelter releases are the main source of potentially toxic element contamination in the soil, accounting for 66.2%. The health risk assessment suggested that the children and adults in the study region were exposed to non-carcinogenic risks caused by As and Pb. Oral ingestion was identified as the primary exposure route impacting health risks. The carcinogenic risk from potentially toxic elements in soil was found to exceed the acceptable level for children and adults in the study region. Therefore, it is necessary for the government to take effective measures, including designing regulations and interventions, and improving lead smelter management to mitigate potential contamination and minimize the impact of lead smelter releases on the surrounding environment, especially to protect human health, particularly that of children.

Multi-year monitoring of atmospheric dust fall as a sink for lead in an agro-industrial and petrochemical city of Argentina. Geo-accumulation and ecological risk assessment

A multi-year monitoring data set of potentially harmful elements (PHEs), which are present in the chemical composition of atmospheric settleable particulate matter (SPM) in the urban, industrial and port areas in Bahía Blanca, was studied in order to assess potential ecological risk. The selected PHEs were metal elements of local and regional environmental importance (Cd, Cr, Cu, Ni, Pb, and Zn). Seventeen sampling campaigns were carried out between April 2013 and September 2019. After the microwave-assisted acid digestion of samples, the total contents of the PHEs were determined by ICP-OES. The annual dry deposition rate, the indexes associated with the potential ecological risk (RI) and the degree of geo-accumulation (Igeo) of each PHE were calculated. The results indicated that: (a) there are 3 groups (I, II, III) of PHEs with differentiated concentration levels, ranked I (Pb > Zn > Cu) > II (Cr ≈ Ni) > III (Cd) (p < 0.01) in all the studied areas; (b) the median of the total deposition rate was 1 mg cm-2. month-1 with a significant relative contribution of Pb; (c) a considerable increase in geo-accumulation of Pb indicated that SPM was functioning as a sink for Pb, and also reflected a significant progressive increase in the potential ecological risk in all sites (p < 0.01); and (d) there were chemometrically identified potential sources of Pb, Cu and Zn emissions that would be associated mainly to the resuspension of dust from geogenic, industrial and urban origin, and to a lesser extent, to other gaseous emissions of the industrial sector. This work highlights three major aspects of environmental assessment: (a) the value of continuous monitoring as an important tool to detect long-term trends; (b) the importance of the role of dust fall as a useful environmental indicator of lead geo-accumulation; and (c) the great utility of geo-accumulation and potential ecological risk indices as rapid quantitative assessment tools of environmental pollution.

Agronomic and ionomics indicators of high-yield, mineral-dense, and low-Cd grains of wheat (Triticum aestivum L.) cultivars

The accumulation of toxic and essential nutrient elements in wheat grain influences wheat yield, grain nutritional quality, and human health. Here, we assessed the potential for breeding wheat cultivars to combine high yield with low cadmium and high iron and/or zinc concentrations in grains, and we screened appropriate cultivars. A pot experiment was conducted to explore differences in grain cadmium, iron, and zinc concentrations among 68 wheat cultivars, as well as their relationships with other nutrient elements and agronomic characters. The results showed 2.04-, 1.71-, and 1.64-fold differences in grain cadmium, iron, and zinc concentrations, respectively, among the 68 cultivars. Grain cadmium concentration was positively correlated with grain zinc, iron, magnesium, phosphorus, and manganese concentrations. Grain copper concentration was positively correlated with grain zinc and iron concentrations, but not with grain cadmium concentration. Therefore, copper has a potential role in regulating grain iron and zinc accumulation without influencing cadmium concentration in wheat grain. There were no significant relationships between grain cadmium concentration and four important wheat agronomic characters (i.e., grain yield, straw yield, thousand kernel weight, and plant height), indicating that the breeding of low-cadmium-accumulating cultivars with dwarfism and high yield characteristics is possible. On cluster analysis, four cultivars (Ningmai11, Xumai35, Baomai6, and Aikang58) exhibited low-cadmium and high-yield characteristics. Among them, Aikang58 contained moderate iron and zinc concentrations, while Ningmai11 had relatively high iron but low zinc concentrations in the grain. These results imply that it is feasible to breed high-yield dwarf wheat with low cadmium and moderate iron and zinc concentrations in the grain.

Effects of atmospheric deposition on heavy metals accumulation in agricultural soils: Evidence from field monitoring and Pb isotope analysis

Atmospheric deposition is an essential pathway of heavy metals (HMs) from the atmosphere to soils, while few studies assess the effects and contributions of atmospheric deposition on HMs accumulations in agricultural soils from the field and regional scales. In this study, eleven representative field monitoring sites from industrial areas, agricultural areas, and reference site in a typical rapid industrial development region were selected to determine the effects of atmospheric deposition on soil HMs accumulation. Industrial activities significantly increased the deposited particles flux from atmospheric deposition, with annual particles fluxes in industrial areas being 1.83 and 1.90 times higher than in agricultural areas and reference site, respectively. Although the HMs deposition fluxes had decreased significantly with time by literature comparison, the deposition fluxes of Cd and Pb were still at high levels in this study area. Precipitation was the key factor affecting seasonal variations of atmospheric HMs deposition. Lead isotope analysis indicated that atmospheric Pb originated from coal combustion, and atmospheric deposition was the primary source of Pb contamination in agricultural soil adjacent to industries. This study provided insight into the effects of atmospheric deposition on agricultural soil HMs accumulations at the regional scale and an important theoretical basis for source-preventing soil HMs contamination in industrial developed and other similar areas.

Towards the carbon neutrality of sludge treatment and disposal in China: A nationwide analysis based on life cycle assessment and scenario discovery

Motivated by the carbon neutrality target, strategic planning for a low-carbon transition of sludge treatment and disposal in China is challenging due to the unpredictability of technical, regional, socioeconomic, and political factors affecting greenhouse gas (GHG) emissions. This study combines the use of a Life Cycle Assessment and the Patient Rule Induction Method, accounting for possibilities that could achieve net-zero carbon emissions by exploring multiple plausible future profiles of sludge treatment and disposal. Results show that reducing sludge landfill and increasing anaerobic digestion are effective methods to facilitate GHG reduction. Achieving carbon neutrality is closely linked to developing a cleaner electricity mix. Based on a cascaded scenario analysis considering regional differences for 31 Chinese provinces, results demonstrated a maximum cumulative reduction potential of 371 Mt CO₂ equivalents from 2020 to 2050, equal to 59.84% of the business-as-usual scenario. Together with GHG reductions, terrestrial acidification and ecotoxicity as well as freshwater ecotoxicity are synergistically reduced. However, the shifting environmental burden results in freshwater eutrophication, human toxicity, marine ecotoxicity, marine eutrophication, and photochemical oxidant formation. This study presents a novel method for systematically identifying possible future development paths toward carbon neutrality. The findings may support policy designs for achieving target carbon reduction effects for sludge disposal.

Research on health risk assessment of heavy metals in soil based on multi-factor source apportionment: A case study in Guangdong Province, China

Environmental problems caused by heavy metal pollution in soil have attracted widespread attention worldwide. Identifying and quantifying the heavy metal pollution sources and risks is crucial for subsequent soil management. In this study, an integrated source-risk method for source apportionment and risk assessment based on the PMF model, the geodetector model and the health risk assessment model (HRA) was proposed and applied. Analysis of Hg, As, Pb, Cd, Cu, Ni, Cr, and Zn in 208 topsoils showed that the average contents of eight heavy metals were 1.87-5.86 times greater than corresponding background values, among which Cd and As were relatively high, which were higher than the specified soil risk screening values, high-value areas of heavy metals are mainly concentrated in the central part of the study area. The source apportionment showed that the accumulation of heavy metals was affected by five sources: atmospheric deposition (16.3 %), natural sources (33.1 %), industrial activities dominated by metal mining (15.1 %), industrial activities dominated by metal smelting (12.6 %) and traffic sources (22.9 %). The results of the health risk assessment showed that the carcinogenic risks (adult: 4.74E-05, children: 7.41E-05) of heavy metals in soil to the study population were both acceptable, the non-carcinogenic risk of adult (THI = 0.277) was within the limit, while the non-carcinogenic risk of children (THI = 1.70) was higher than the limit value. Ingestion (89.5 %-95.9 %) contributed the greatest health risk among all exposure routes. Source 3 (arsenic-related industrial activities dominated by metal mining) contributed the most to the HI and CRI of adults and children (all above 50 %), therefore, in the formulation stage of soil management strategy in this area, priority should be given to the control and management of this pollution source. These results can provide more detailed support for environmental protection departments to propose targeted soil pollution control measures.

Sodium alginate-based composite microspheres for controlled release of pesticides and reduction of adverse effects of copper in agricultural soils

Excessive copper (Cu) concentrations pose significant health risks to both plants and humans. In this study, sodium alginate (SA)-gelatin (GEL)-polyvinyl pyrrolidone (PVP)- embedded dinotefuran (DIN) microspheres were prepared using spray-drying technology. The loading content and encapsulation efficiency of optimal microspheres determined by physical modifications were 19.77% and 99.32%, respectively. In addition, the microspheres showed variable stimuli-responsive controlled release capacities in different temperatures and types of soil, as well as showed better control efficiency of larvae of Protaetia brevitarsis at pesticide application in the early stage, with the potential ability to control pest outbreaks at high temperatures. In addition, blank microspheres improved the growth and physiological activity of cucumber seedlings, reduced copper content in leaves, increased soil nutrient content, and prevented soil acidification. Further, the use of blank microspheres increased the relative abundance of soil beneficial functional bacteria communities, which mediate heavy metal (HM) immobilization/tolerance and promote plant growth. Redundancy analysis (RDA) and Spearman correlation analysis showed that these beneficial functional bacteria were mainly positively correlated with soil EC, A-N, and N-N. In summary, this study showed that the technique of combining physically modified carrier materials with pesticides has the potential to reduce Cu contamination in the surrounding agricultural soil during pesticide application, thereby reducing Cu uptake by crops.

Molecular mechanisms of Chromium(III) sorption by organo-ferrihydrite coprecipitates induced by crop straws

Agricultural organo-ferrihydrite (Fh) coprecipitates (OFCs), resulting from the coprecipitation of Fe(III) and dissolved organic carbon (DOC) from returned straws, significantly affect the bioavailability of heavy metals in farmland. However, the molecular sorption mechanisms of Cr(III) by the OFCs remain unclear. Here, we explored the sorption behaviors of Cr(III) by the OFCs formed with wheat or maize straws derived-DOC (wheat-DOC or maize-DOC) under various environmental conditions, and further underlying molecular sorption mechanisms using Cr K-edge X-ray absorption near edge structure (XANES) spectroscopy. Results showed that high C loadings reduced the specific surface areas (SSAs) and Cr(III) sorption capacities of the OFCs, implying the blockage of binding sites by C loading. Additionally, although the wheat-DOC induced OFC had a smaller SSA than the maize-DOC induced OFC, their Cr(III) sorption were comparable, which was likely to be compensated by the more carboxyl in the wheat-DOC. Moreover, at a higher ionic strength, the increased or slightly decreased Cr(III) sorption indicated that the inner-sphere sorption was dominant regardless of high or low C loadings, which was also supported by the extremely low Cr(III) extraction percentage. The Cr K-edge XANES spectroscopy suggested that Cr(III) could be immobilized by both the Fh and organic fractions, with the Fh fractions playing a significant role. These findings contribute to a molecular-level mechanistic understanding of Cr(III) sorption by the OFC, which will aid in the prevention and control of Cr-contaminated agricultural soils.

Agro-environmental sustainability of using digestate fertilizer for solanaceous and leafy vegetables cultivation: Insights on fertilizer efficiency and risk assessment

Digestate generated from anaerobic digestion (AD) has been widely used as digestate fertilizer (DF) for plant growth, but its application should be comprehensively investigated. This study evaluates the effects of different amounts of DF on crop growth, nutrient use efficiency (NUE), soil properties, and potential negative impacts of DF application (salinity and heavy metals (HMs)) with two different crops (Eggplant and Shanghai cabbage). In eggplant cultivation, the yield increased with the increase of DF amount, and the yield of the DF-680 group was the highest (65.4 t/ha) under the highest fertilizer amount. However, due to high ammonia volatilization loss and excessive application, the NUE of DF was only about half of that of chemical fertilizer (CF). Significantly different from eggplant, the high application amount of DF resulted in yield reduction in Shanghai cabbage cultivation. The yield and NUE of the DF-170 group were the highest, the yield was 46.5 t/ha, and the NUE was more than twice compared to CF. Moreover, DF can raise soil nitrogen storage and alleviate soil acidification caused by fertilization in both batches of cultivation. Nevertheless, the electrical conductivity (EC) value of the soil was increased by 2-3 times, and the long-term application may lead to soil salinization. On the other hand, the increase of DF application elevated the content of copper (Cu), zinc (Zn), and cadmium (Cd) in soil significantly but did not cause HMs contamination in crops and tillage soil. In summary, reasonable application amounts and methods should be considered when applying DF.

Deposition of trace metals associated with atmospheric particulate matter: Environmental fate and health risk assessment

Anthropogenic and natural sources influence trace metals (TMs) bound to different sized particulate matter (PM) in dry and wet atmospheric deposition, which can create ecosystem and human health issues in the long run. Limited reviews are available summarizing worldwide concentrations in TMs in atmospheric PMs, their sources and pathways. Simultaneously, quantitative assessment of the potential human and ecosystem health risks imposed by the atmospheric particulate matter has not been adequately reviewed. Addressing this gap, here we review, the concentration of TMs in dry deposition mainly varies with the responsible sources, whereas, in wet deposition, it depends on the solubility of TMs. Other than deposition on impervious surfaces, the TMs incorporated PM can be deposited on biological agents. Health risk assessments show that ingestion and dermal contact pathways are more likely to cause health issues, however, the probability of occurring ingestion and dermal contact pathways is limited. Attention must be paid to the contribution from non-exhaust and exhaust vehicular emissions for TMs in atmospheric deposition, understanding their impact on stormwater management and urban agriculture. Behaviors of TMs in the atmosphere depends on many complex factors including origin, wind patterns, and weather conditions. Therefore, future research needs to be carried to model and predict the fate and transfer of TMs once they are generated through natural and anthropogenic sources. We believe that such research would allow establishing pollution control policies and measures in urban environments which will be critical to reduce the levels of TMs associated with atmospheric deposition in the environment.

Phosphorus fertilization regimes and rates alter Cd extractability in rhizospheric soils and uptake in maize (Zea mays L.)

Understanding cadmium (Cd) extractability and transfer in soil-plant system is crucial for the evaluation of the remediation effect of Cd-contaminated soils. However, knowledge on the effects of different phosphorus (P) fertilizers on Cd uptake in plants, root morphology, and Cd extractability in rhizosphere soils remains very limited. In this study, a five-year field experiment was conducted to evaluate the impacts of four P fertilizers (i.e. calcium superphosphate, calcium magnesium phosphate, monopotassium phosphate, and compound fertilizer) on Cd uptake in maize (Zea mays L.), root morphology, and Cd extractability in rhizospheric acidic soils contaminated with Cd. The results showed that compared to the control, the contents of rhizospheric DTPA-Cd were respectively 18-40% and 8-29% lowered by the calcium magnesium phosphate and monopotassium phosphate, but 21-59% and 10-36% elevated by the calcium superphosphate and compound fertilizer. Similar effects of P fertilizers were observed on exchangeable Cd. Furthermore, the altered levels of the DTPA-Cd and exchangeable Cd in the rhizospheric soils were greater than those in the non-rhizospheric soils. Moreover, different P fertilization regimes altered the contents of Cd in maize tissues (roots, stems, leaves, and grains), and the alterations were closely related to the variation of DTPA-Cd and exchangeable Cd in the rhizospheric soils. Meanwhile, different P fertilization regimes enhanced root morphological parameters (root length, surface area, and volume), and the activities of urease and surcase. In general, the lowest concentrations of soil DTPA-Cd and Cd in maize tissues were found in the treatments with calcium magnesium phosphate. This study has demonstrated that the calcium magnesium phosphate can be used as a potential amendment agent for the acidic Cd-contaminated soils cultivated with maize.

Research Progress on Heavy Metals Pollution in the Soil of Smelting Sites in China

Contamination by heavy metals is a significant issue worldwide. In recent decades, soil heavy metals pollutants in China had adverse impacts on soil quality and threatened food security and human health. Anthropogenic inputs mainly generate heavy metal contamination in China. In this review, the approaches were used in these investigations, focusing on geochemical strategies and metal isotope methods, particularly useful for determining the pathway of mining and smelting derived pollution in the soil. Our findings indicate that heavy metal distribution substantially impacts topsoils around mining and smelting sites, which release massive amounts of heavy metals into the environment. Furthermore, heavy metal contamination and related hazards posed by Pb, Cd, As, and Hg are more severe to plants, soil organisms, and humans. It's worth observing that kids are particularly vulnerable to Pb toxicity. And this review also provides novel approaches to control and reduce the impacts of heavy metal pollution. Hydrometallurgy offers a potential method for extracting metals and removing potentially harmful heavy metals from waste to reduce pollution. However, environmentally friendly remediation of contaminated sites is a significant challenge. This paper also evaluates current technological advancements in the remediation of polluted soil, such as stabilization/solidification, natural attenuation, electrokinetic remediation, soil washing, and phytoremediation. The ability of biological approaches, especially phytoremediation, is cost-effective and favorable to the environment.

Heavy Metal Pollution Analysis and Health Risk Assessment of Two Medicinal Insects of Mylabris

Mylabris is the dried body of the Chinese blister beetle (Mylabris sp.), which has been used in traditional Chinese medicine and achieved significant positive effects in the treatment of cancer including liver cancer, lung cancer, and rectal cancer. However, heavy metal pollution and accumulation of Mylabris insects could pose threat to human health. This study was carried out to assess levels of different heavy metals like Cu, As, Cd, Hg, and Pb, along with soil-plant-insect system and health risks using two representative Mylabris insects from the Hasi Mountains of Gansu Province, China. The results showed that the heavy metal concentration of plants and insects followed the order Cu > Pb > As > Hg > Cd. Compared with soil and plants, the content of Cu in insects was the highest, reaching 45.65 mg/kg. Cu was the main element that caused insects to absorb and accumulate. The quantitative risk analysis implied the two Mylabris insects had carcinogenic risks, with the contribution of As providing 63% and 60.7%, respectively. This kind of carcinogenic risk that the human body could bear was not easy to cause side effects to normal people, but it was difficult and dangerous for cancer patients. Thus, the evaluation of health risk lays the foundation for pollutant risk monitoring.

Comprehensive assessment of harmful heavy metals in contaminated soil in order to score pollution level

Soil-related problems have grown up to be a major threat to human society. Scientific evaluation is helpful to understand the status of soil pollution and provide reference to further work. In this situation, Liaoning Province, a typical industrial and agricultural province in Northeast China, was selected as a case study region. It reviewed 200 studies published between 2010 and 2020 and recorded related data of soil heavy metal. It used model method and index method to evaluate the agricultural region. The comprehensive assessment score of Liaoning pollution level was 0.8998. Dalian was 0.9536, ranking first among the 14 cities. Huludao and Jinzhou were 0.7594 respectively, ranked the last. Heavy metal accumulation in different cities stemmed from different sources, including weathering of parent materials, industrial wastes, sewage irrigation, and mining activities. In general, the pollution level of heavy metal in Liaoning was at low risk level, but it still needs to pay attention to the health risk of heavy metal and the input of heavy metal into the soil, especially cadmium (Cd). This study provides a comprehensive assessment of soil heavy metal pollution in Liaoning, while identifying policy recommendations for pollution mitigation and environmental management.

Bioimaging of Pb by LA-ICP-MS and Pb isotopic compositions reveal distributions and origins of Pb in wheat grain

Atmospheric heavy metal deposition in agroecosystems has increased recently, especially in northern China, which poses serious risks to crop safety and human health via food chain. Wheat grains can accumulate high levels of Pb even when wheat is planted in soils with low levels of Pb. However, the influence of atmospheric deposition on the accumulation and distribution of Pb in wheat grain is still unclear. A field survey was conducted in three districts (A: a district with industrial and traffic pollution; B: a district with traffic pollution; and C: an unpolluted district) in Hebei Province, North China. The grain of wheat cultivated in district A accumulated more Pb from soil and atmospheric deposition than those in other districts, and the bran from district A contained 3.50 and 2.04 times more Pb than those from districts B and C, respectively. The Pb distribution pattern in wheat grain detected by laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was characterized by accumulation mostly in the pericarp and seed coat rather than in the crease, embryo and endosperm. Furthermore, Pb isotopic data showed that airborne Pb was the major source (>50%) of Pb in wheat grain. Interestingly, average contributions of Pb from atmospheric deposition to white flour (78.22%) were higher than its contributions to bran (56.27%). In addition, wheat flag leaves were exposed to PbSO₄ at the booting stage, and much greater Pb accumulation (0.33-0.48 mg/kg) was observed in exposed wheat grain than in the control (P < 0.05), PbSO₄ constituted most (82.80-100%) of the Pb in the wheat grain. In summary, the results confirmed the efficient foliar Pb uptake and transfer from atmospheric deposition into wheat grain. It would be a new sight for understanding the contribution of airborne Pb to Pb accumulation in wheat grains.

Natural and anthropogenic sources of solutes in the wet precipitation of a densely populated city of Southern South America

The chemistry of rainwater is controlled by the interaction among water, airborne particles and gas sources, whether natural or human-made. This article analyzes the chemical composition dynamics of individual rainfall events collected over a three-year period in the densely populated city of Córdoba (Argentina). The main purpose is to identify the natural and/or anthropogenic sources, and the extent to which they determine the seasonal chemical signature exhibited by wet precipitation in the heart of the South Eastern South America. The results reveal that, despite geogenic components are only minor constituents of the airborne particles in downtown Córdoba, they appear to be the main source of solutes in rainwaters, also responsible for the alkaline water pH that predominates most of the year. This fraction mostly corresponds to wind-blown soil particles transported either from local or distant sources, with rare earth elements (REE) patterns similar to those of rainwaters produced during the dry season. Anthropogenic contributions are only evident during the wet season, when rainwater shows REE patterns similar to those of industrial emissions and exhibits moderate enrichment of heavy metals such as Cu and Zn, derived from soluble compounds used in agricultural activities (e.g, sowing, fertilizing). With the exception of these two metals, the remaining heavy metals are depleted in rainwater suggesting that the airborne conveying compounds (mostly anthropogenic) are barely soluble.

Research trends and frontiers on source appointment of soil heavy metal: a scientometric review (2000-2020)

In recent years, source appointment of soil heavy metal has attracted growing attention. However, few studies have attempted to make a comprehensive and systematical review on this topic. For this reason, a total of 1051 publications were retrieved from the Web of Science (WOS) database between 2000 and 2020. A scientometric analysis was carried out to reveal the characteristics of publications, research power, and research hotspots. CiteSpace was used to visualize and summarize the information about the development in this field. The results showed that (1) the number of publications in source appointment of soil heavy metal had increased rapidly; Environmental science and ecology and environmental sciences were top 2 most popular subject categories; (2) Research power was mainly distributed in Asia, Europe, and North America. China and Chinese Academy of Sciences were the most productive country and institution in terms of publications in this field. Biao Huang (China) was the most productive author. However, Hakanson L (Sweden) was the most influential author in terms of citation frequency; (3) Heavy metal, source identification, and contamination were the most frequent keywords. Keyword clustering analysis showed that the research hotspots mainly concentrated on air pollution, bioremediation, spatial distribution, soil, PCA, and so on; (4) Keyword bursts analysis showed that the research frontiers mainly focused on spatial analysis of soil heavy metal and exposure risk to human health.

Aging and phytoavailability of newly introduced and legacy cadmium in paddy soil and their bioaccessibility in rice grain distinguished by enriched isotope tracing

Phytoavailability of Cadmium (Cd) plays a critical role in its accumulation in soil-rice systems. However, differential aging and phytoavailability of newly introduced Cd (Cd_N) and legacy Cd (Cd_L) in the soil-rice system remains unknown. Moreover, distinguishing their aging and phytoavailability is challenging. Enriched ¹¹²Cd isotope was introduced into a series of pot experiments, combined with sequential extraction and isotope dilution (¹¹⁰Cd isotopic spike), to investigate the aging and distribution of Cd_N and Cd_L under different treatments. The treatments included simulated acid rain, slaked lime, and biochar. Cd_N aged quickly than Cd_L in flooded soil and its availability was similar to that of Cd_L after tillering stage. The grain Cd contents were positively correlated to Cd concentrations in the overlying water. Acid rain reduced the soil pH, increasing the grain Cd, while slaked lime reduced grain Cd content. The acidic biochar used in this study increased grain Cd, possibly through soil acidification-induced Cd release. The differences in bioaccumulation and translocation factors between Cd_N and Cd_L in rice plants under slaked lime and biochar treatments suggested their different in vivo complexations and translocations. Analysis of bioaccessibility of Cd_N and Cd_L in rice grains provided valuable insights regarding human Cd exposure.

Effect of urea fertilization on growth of broad bean (Vicia faba L.) under various nickel (Ni) levels with or without acetic acid addition, using 15N-labeled fertilizer

Although nickel (Ni) has direct relationship with nitrogen metabolism of plants, the high dose of Ni fertilizer in broad bean plants may affect the nitrogen use efficiency (NUE), impair plant development and even cause Ni pollution in soil. Thus, a pot experiment was set up to study the effect of urea fertilization on N-uptake, root and shoots' Ni content as well as growth of broad bean plants under different levels of Ni, using ¹⁵N tracer technique. ¹⁵N-labeled urea (5% ¹⁵N atom excess) was added at three doses (0, 30 and 60 mg N kg^-1 soil). Nickel sulfate (NiSO₄) was also applied at three levels (0, 50 and 100 mg Ni kg^-1 soil). The experiment was laid out with or without acetic acid in randomized complete block design in three replicates. Treatment with the addition of 60 mg N + 50 mg Ni showed the highest values in dry weights of root and shoots, N-uptake by shoots, nitrogen derived from fertilizer (Ndff %) and NUE % by shoots in both with or without acetic acid solution. Higher rate of Ni addition can decrease shoot and root biomass by inhibiting the ability of the plant to uptake the nitrogen efficiently. However, addition of acetic acid solution induced the improvement of NUE % and Ndff % by shoot and root of broad bean plants. This study provides insight into how to improve plant yield without damaging the soil health and will be helpful to create a better world with sustainable agriculture.

Reference gene identification for gene expression analysis in rice under different metal stress

Real-time quantitative polymerase chain reaction (RT-qPCR) is the most common approach to quantify changes in gene expression. Appropriate internal reference genes are essential for normalization of data of RT-qPCR. In the present study, we identified suitable reference genes for analysis of gene expression in rice seedlings subjected to different heavy metal stresses such as deficiencies of iron and zinc and toxicities of cobalt, cadmium and nickel. First, from publically available RNA-Seq data we identified 10 candidate genes having stable expression. We also included commonly used house-keeping gene OsUBQ5 (Ubiquitin 5) in our analysis. Expression stability of all the 11 genes was determined by two independent tools, NormFinder and geNorm. Our results show that selected candidate reference genes have higher stability in their expression compared to that of OsUBQ5. Genes with locus ID LOC_Os03g16690, encoding an oxysterol-binding protein (OsOBP) and LOC_Os01g56580, encoding Casein Kinase_1a.3 (OsCK1a.3) were identified to be the most stably expressed reference genes under most of the conditions tested. Finally, the study reveals that it is better to use a specific reference gene for a specific heavy metal stress condition rather than using a common reference gene for multiple heavy metal stress conditions. The reference genes identified here would be very useful for gene expression studies under heavy metal stresses in rice.

Cadmium induced inflammation and apoptosis of porcine epididymis via activating RAF1/MEK/ERK and NF-κB pathways

Cadmium (Cd) was a serious heavy metal pollutant. Cd exposure will cause damage to reproductive organs. It was largely unknown whether Cd exposure caused inflammation and apoptosis in epididymis. In this study, we established models of Cd exposure in swine, and the apoptotic level of epididymis was detected by in situ TUNEL fluorescence staining assay, the results showed that Cd exposure significantly increased TUNEL-apoptosis index. Furthermore, the results of qRT-PCR and Western blot showed that Cd activated the proto-oncogenic serine/threonine kinase-1 (RAF1)/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) signal pathway (RAF1/MEK/ERK) and led to the subsequent up-regulation of the nuclear factor-κB (NF-κB), tumor necrosis factor α (TNF-α), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), caused inflammation in epididymis. NF-κB inflammation pathway also mediated the tumor protein P53 (P53) and indirectly activated the Cytochrome c (Cytc), B-cell lymphoma-2 (Bcl-2), Bcl-2-Associated X protein (Bax), Caspase 3, Caspase 9. In summary, we believed that the RAF1/MEK/ERK pathway came into play in the apoptosis of epididymal tissues exposed to Cd by activating the NF-κB Inflammation pathway, followed by activation of the mitochondrial apoptotic pathway. This study provides more abundant data for exploring the reproductive toxicity of Cd.

Cadmium stress in paddy fields: Effects of soil conditions and remediation strategies

Cadmium (Cd) toxicity in paddy soil and accumulation in rice plants and grains have got global concern due to its health effects. This review highlights the effects of soil factors including soil organic matter, soil pH, redox potential, and soil microbes which influencing Cd uptake by rice plant. Therefore, a comprehensive review of innovative and environmentally friendly management practices for managing Cd stress in rice is lacking. Thus, this review discusses the effect of Cd toxicity in rice and describes management strategies to offset its effects. Moreover, future research thrusts to reduce its uptake by rice has also been highlighted. Through phytoremediation, Cd may be extracted and stabilized in the soil while through microbes Cd can be sequestrated inside the microbial bodies. Increased Cd uptake in hyperaccumulator plants to remediate and convert the toxic form of Cd into non-toxic forms. While in chemical remediation, Cd can be washed out, immobilized and stabilized in the soil through chemical amendments. The organic amendments may help through an increase in soil pH, adsorption in its functional groups, the formation of complexations, and the conversion of exchangeable to residual forms. Developing rice genotypes with restricted Cd uptake and reduced accumulation in grain through conventional and marker-assisted breeding are fundamental keys for safe rice production. In this regard, the use of molecular techniques including identification of QTLs, CRISPR/Cas9, and functional genomics may be quite helpful.

Spatial assessment models to evaluate human health risk associated to soil potentially toxic elements

Quantifying source apportionment of potentially toxic elements (PTEs) in soils and associated human health risk (HHR) is essential for soil environment regulation and pollution risk mitigation. For this purpose, an integrated method was proposed, and applied to a dataset consisting of As, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Zn in 273 soil surface samples. Positive matrix factorization (PMF) was used to quantitatively examine sources contributions of PTEs in soils; and the HHR arising from the identified source was determined by combining source profiles and health risk assessment; at last, sequential Gaussian simulation (SGS) was used to identify the areas with high HHR. Four sources were identified by PMF. Natural and agricultural sources affected all 9 PTEs contents with contributions ranging from 19.2% to 62.9%. 41.9% of Cd, 40.8% of Pb, 58.6% of Se, and 29.8% of Zn were controlled by industrial and traffic emissions. Metals smelting and mining explained 35.5%, 30.5%, and 24.9% of Cr, Cu, and Ni variations, respectively. Hg was dominated by atmospheric deposition from coal combustion and coking (58.7%). The mean values of the total non-carcinogenic risks of PTEs were 1.55 × 10^-1 and 9.40 × 10^-1 for adults and children, and the total carcinogenic risk of PTEs had an average value of 8.86 × 10^-5. Based on source-oriented HHR calculation, natural and agricultural sources were the most important factor influencing HHR, explaining 51.0% and 49.1% of non-carcinogenic risks for children and adults, and 44.2% of carcinogenic risk. SGS indicated that 1.1% of the total area was identified as hazardous areas with non-carcinogens risk for children.

Input-output balance of cadmium in typical agriculture soils with historical sewage irrigation in China

The gradual increase of cadmium (Cd) in soils has caused environmental and health risk, and it's important to study the accumulation trend to evoke the awareness of farmland safety management. This research during the period of March in 2017-2018 evaluated the input (irrigation, atmospheric deposition, fertilizer and pesticide application) and the output (runoff and seepage, grain and straw uptake) of Cd in contaminated farmland irrigated with sewage water in Hebei Province. The experimental results indicated sewage irrigation (51.03%), and atmospheric deposition (46.35%) were the main input pathways; Grain uptake (42.72%) and straw removal (50.71%) played a major role in output fluxes. The input-output balance (net transport fluxes) of Cd in the farmland were estimated to be +3621.68 ~ +8899.78 mg·(ha·yr)^-1 under different conditions (sewage irrigation with straw returning/straw removal, clean water irrigation with straw returning/straw removal), representing there was a Cd inputting in the farmland during the study. Even in the case of the lowest net transport fluxes, the annual increase of Cd concentration in soils reached to 0.0014 mg/kg. Therefore, it's necessary to take action that cutting off those pathway inputs into farmland ecosystems, such as monitoring the water quality of irrigation water sources, applying fertilizer and pesticide properly. Furthermore, attentions need to be paid to the Cd input into the farmland and environmental risks that may arise while returning straw to the field for improving soil fertility and crop production.

Physiological Response and Multi-Elemental Content in Lichens Growing on Agricultural Fences: A Pilot Study Comparing No-Tillage and Organic Cropping

The objective of this study is to compare the physiological response (content and degradation of photosynthetic pigments, membrane oxidation products and soluble proteins) and multi-element content of Ramalina celastri (lichenized fungi) growing on agricultural fences with no-tillage (associated with transgenic crops and agrochemical application), organic cropping and a non-cultivated area. We found that R. celastri did not differ in its physiological response to agricultural practices, except for the contents of chlorophyll b and phaeophytin a which were high in both cultivated areas. Lichens growing in organic cropping fields have higher arsenic, chromium, uranium and internal transition elements common in the earth's crust, possibly due to the greater resuspension of the material during soil tillage. Lichens that grow on posts close to no-tillage field had higher bromine contents (present in numerous pesticides). We found evidence that R. celastri behaves as a tolerant species to air pollution in agricultural environments.

Heavy metal concentration, potential ecological risk assessment and enzyme activity in soils affected by a lead-zinc tailing spill in Guangxi, China

In 1976, a tailing dam collapse accident at the Xingping Lead-Zinc Mine in Guangxi Province, China, led to the spillage of mining wastewater and sludge into downstream agricultural lands in Side Village. Heavy metal concentrations, soil pollution and soil enzyme activity were analysed to understand the pollution characteristics of the agricultural lands along the Side stream by this accident. The tailing soil (TS), natural forest soil without spill contamination (NFS) and four representative agricultural soils were selected. The four agricultural soil sites located at the entrance of the stream to the agricultural soil (EnS), the upstream region (US), the middle stream (MS) and at the exit of the stream (ExS) from the village, respectively. The results showed that the soil pH values and heavy metal concentrations were in the order of tailing soil TS > ExS > MS > US > EnS > NFS. The concentration of Pb ranked highest among the analysed elements followed by Zn, Cd, Mn and Cu. The concentrations of Pb, Zn, Cd Mn and Cu 10530.41, 1708.58, 8.32, 885.61 and 104.51 mg kg^-1, respectively. Soil pollution assessments by single pollution index, synthesis pollution index and individual/comprehensive potential ecological risk analysis explicated all the soils reached the heavily polluted level and presented extremely high ecological risk grades. Pb, Zn and Cd were the dominant pollutants. The soil enzyme activities of invertase, protease and urease exhibited the opposite distribution pattern as those of the heavy metal concentrations, while the inversely results were observed for the activity of catalase.

A dynamic model to evaluate the critical loads of heavy metals in agricultural soil

Estimation of critical load (CL) is important for soil environmental management and pollution prevention. We developed a mass balance-based dynamic critical load (DCL) model, which improved the model performance, applicability and functionality compared with the traditional one. Paddy soils in two typical fields in central south China and two scenarios were chosen as case studies. The result of case study showed that atmospheric deposition was the main source of Cd, Cu, Pb, and Zn in the soils, with percentage contributions ranging from 59.9 to 79.8%. Crop uptake, particularly the rice straw harvest, was the primary output pathway, accounting for 35.1-71.2% of the total output flux. The critical loads also known as annual input limits (I_max) of heavy metals in the paddy soils were calculated by the developed DCL model. For example, the Imax of Cd was recommended as 0.05 kg ha^-1 in the paddy soils under the default scenario for a protection period of 40 years, and that became 0.12 kg ha^-1 and 0.17 kg ha^-1 under the straw removal scenario in the two typical fields, respectively. The scenario simulation suggested that the straw removal strategy reduced the total concentrations of heavy metals (C_t) in the soils and notably increased the I_max. Meanwhile, the sensitivity analysis indicated that the changes of C_t and I_max can be controlled by adjusting the partition coefficient (K_d), plant uptake factor (PUF) and input flux. The mass balance-based DCL model provides a reference method to establish the standard for controlling heavy metal inputs to agricultural soil, this will be helpful to develop strategies for the prevention of soil contamination.

Brown gold of marginal soil: Plant growth promoting bacteria to overcome plant abiotic stress for agriculture, biofuels and carbon sequestration

Marginal land is defined as land with poor soil characteristics and low crop productivity with no potential for profit. Poor soil quality due to the presence of xenobiotics or climate change is of great concern. Sustainable food production with increasing population is a challenge which becomes more difficult due to poor soil quality. Marginal soil can be made productive with the use of Plant Growth Promoting Bacteria (PGPB). This review outlines how PGPB can be used to improve marginal soil quality and its implications on agriculture, rhizoremediation, abiotic stress (drought, salinity and heavy metals) tolerance, carbon sequestration and production of biofuels. The feasibility of the idea is supported by several studies which showed maximal increase in the growth of plants inoculated with PGPB than to uninoculated plants grown in marginal soil when compared to the growth of plants inoculated with PGPB in healthy soil. The combination of PGPB and plants grown in marginal soil will serve as a green technology leading to the next green revolution, reduction in soil pollution and fossil fuel use, neutralizing abiotic stress and climate change effects.

Atmospheric deposition of cadmium in an urbanized region and the effect of simulated wet precipitation on the uptake performance of rice

Excessive inputs of potentially toxic elements (PTEs) into the surface environment as a consequence of atmospheric deposition, imposes long-term burdens on agricultural ecosystems. Studying the spatial and temporal variation in PTEs in atmospheric deposition and their effects on plant shoot accumulation are important in understanding the sources and contributions of PTEs in soils and agricultural products. Here, the spatial and temporal variations in cadmium (Cd) concentration and atmospheric deposition fluxes were investigated in five rice-producing areas of the urbanized Chang-Zhu-Tan region over two years. Then, the effects of simulated wet precipitation on the uptake of Cd in rice seedlings in hydroponic culture was explored. The results showed substantial spatial variability in Cd concentrations and atmospheric deposition fluxes in this region. The Cd concentration of atmospheric deposition ranged from 0.07 to 114 μg L^-1, and the annual Cd fluxes in the industrial area reached 61.0 g ha^-1 but all were <10.0 g ha^-1 in the rural areas. Rice seedling growth became significantly inhibited with increasing concentrations of Cd. Cadmium content in the shoots and white roots and dithionite-citrate-bicarbonate (DCB) extractable Cd on root surfaces were significantly and positively correlated with the concentration of Cd in the nutrient solution. Shoot Cd concentrations increased significantly (p < 0.05) when the annual Cd precipitation flux was ≥50 g ha^-1 compared to the control with no Cd precipitation, and the concentration in the shoot was higher than that in roots of rice cultivar A159, when the annual simulated wet precipitation flux of Cd was 400 g ha^-1. Thus, shoot Cd was directly related to the simulated wet precipitation when the flux exceeded 50 g ha^-1a^-1, indicating that air pollution is an important source factor affecting crop Cd uptake.

Toxicity of enrofloxacin and cadmium alone and in combination to enzymatic activities and microbial community structure in soil

Antibiotics and heavy metals have long-term potential toxicity to the environment, and their residuals in agricultural soils are receiving more and more attention. To evaluate the ecotoxicological effects of enrofloxacin and cadmium on soil enzymatic activities and microbial community structure, soil samples were exposed to individual and combined contaminants over 28 days. The results indicated that the toxic effects of enrofloxacin alone on soil enzymatic activities were relatively small and showed no concentration dependence. In contrast, significant inhibition of soil enzymatic activities was observed upon cadmium contamination by itself. Overall, the combination of two contaminants also has toxic effect on enzymatic activities; an antagonism between enrofloxacin and cadmium was observed. On 14 and 21 days, individual enrofloxacin and cadmium reduced average well color development (AWCD), Shannon, McIntosh, Simpson indices, and substrate utilization, except for Shannon, McIntosh, Simpson indices of the cadmium 0.4 mmol/kg treatment were higher than the control on 21 days. In general, combined treatments led to higher value of these microbial diversity indicators than those found under separate contamination, although there were some exceptions. With the increase in enrofloxacin concentration, the utilization of any carbon source by the microorganisms gradually decreased. In addition, the AWCD value and substrate utilization decreased as time increased. In the separate and combined contaminant treatments, the order of substrate utilization by soil microorganisms was aliphatics > amino acids > saccharides > metabolites. Thus, enrofloxacin and cadmium had a variable but generally negative influence on soil enzymatic activities and microbial community structure.

Pollution characteristics and health risk assessment of heavy metals in dry atmospheric deposits from Sfax solar saltern area in southeast of Tunisia

Concentrations of six heavy metals such as Fe, Pb, Cu, Cd, Ni and Zn in dry atmospheric deposits weekly collected through 20 sample sites from Sfax solar saltern during two successive sampling campaigns, selected from a long time monitoring, have been examined in order to evaluate their contamination levels as well as their human health risk; such concentrations (expressed in mg/kg) have shown that Fe varied from 7006.24 to 7856.45, Pb from 8.64 to 344.45, Cu from 9.33 to 298.67, Cd from 0.16 to 85.24, Ni from 6.02 to 150.02, and Zn from 12.23 to 624.57. During the study period, average concentrations (mg/kg) have been 7315.99, 103.08, 82.34, 15.93, 46.21 and 142.39, for Fe, Pb, Cu, Cd, Ni and Zn, respectively. Except for Fe, the other concentrations in dry atmospheric deposits have recorded the highest level during the first campaign especially in the sites which are close and more exposed to emissions of local pollutant industries, as well as nearby main road, resulting from high exposure frequencies. Statistical approaches, such as principal component analysis and hierarchical cluster analysis have been applied to all data, revealing an affinity between analyzed metals resulting from their origins, and confirming the influence of exposure frequencies on the spatial variability of heavy metal concentrations. Human health risk assessment has revealed that ingestion of heavy metals is the main exposure pathway for the local population. Computed Hazardous Quotient and Hazardous Index have been higher for children than for adults, thus indicating that the former may be subjected to potentially higher health risk than the latter especially during the first campaign. Calculated carcinogenic risks through ingestion and dermal contact, as well as the total carcinogenic risk for the selected heavy metals, have shown that cancer could occur more probably through ingestion than dermal contact, for children than adult, and during the first campaign (during C1: average values CRing = 8.72 × 10^-4 and CRder = 1.40 × 10^-6 for child; average values CRing = 5.61 × 10^-5 and CRder = 2.84 × 10^-6 for adult) than the second one (during C2: average values CRing = 1.59 × 10^-4 and CRder = 2.54 × 10^-7 for child; average values CRing = 1.02 × 10^-5 and CRder = 5.19 × 10^-7 for adult). The total calculated carcinogenic risk through all the sites have infrequently signaled high to very high carcinogenic risk in the first campaign (average CRA = 8.73 × 10^-4 for child and CRA = 5.89 × 10^-5 for adult) and occasionally exceeded the safe range for the local population in the second one (average CRA = 1.59 × 10^-4 for child and CRA = 1.07 × 10^-5 for adult).

Hepatic alterations associated with fine particulate matter exposure

Several studies have pointed to fine particulate matter (PM_2.5) as the main responsible for air pollution toxic effects. Indeed, PM_2.5 may not only cause respiratory and cardiovascular abnormalities but it may also affect other organs such as the liver. Be that as it may, only a few studies have evaluated the PM_2.5 effects on hepatic tissue. Moreover, most of them have not analyzed the relationship between particles composition and toxicological effects. In this study, healthy rats were subjected to urban levels of PM_2.5 particles in order to assess their structural and functional effects on the liver. During the exposure periods, mean PM_2.5 concentrations were slightly higher than the value suggested by the daily guideline of the World Health Organization. The exposed rats showed a hepatic increase of Cr, Zn, Fe, Ba, Tl and Pb levels. This group also showed leukocyte infiltration, sinusoidal dilation, hydropic inclusions and alterations in carbohydrates distribution. These histologic lesions were accompanied by serological changes, such as increase of total cholesterol and triglycerides, as well as genotoxic damage in their nuclei. We also observed significant associations between several biomarkers and PM_2.5 composition. Our results show that exposure to low levels of PM_2.5 might cause histologic and serological changes in liver tissue, suggesting that PM_2.5 toxicity is influenced not only by their concentration but also by their composition and the exposure frequency.

Atmospheric deposition as a source of cadmium and lead to soil-rice system and associated risk assessment

Atmospheric deposition of heavy metals is widely documented and has been connected to adverse ecological and health impacts. The influence of atmospheric deposition on the soil-rice system in a typical urban agglomeration region was studied continuously through a field contrast experiment for two years. The results showed that the Cd and Pb in rice grains is mainly from soil, but Cd and Pb from the atmospheric deposition should be a focus of attention. The bioavailable content of heavy metals in atmospheric deposition is higher than that in corresponding surface soil. Atmospheric deposition contributed 10.8-47.7% of the Cd and Pb in brown rice, and 13.7-60.3% of the Cd and Pb in rice leaves was from atmospheric deposition. In the traffic area, a high deposition site, the contributions of atmospheric depositions to heavy metals in rice plants were higher than those from abandoned mine area and suburban area. Atmospheric deposition also consistently decreased the pH (0.17-0.66) and increased the exchangeable Cd (27.1-62.1%) and Pb (3.3-26.1%) in surface soil. In addition, the health risk index (HRI) of rice consumption was also increased as a result of the different atmospheric depositions of heavy metals, which accounted for 40.0% and 35.5% of Cd and Pb at the high deposition site, respectively. These findings demonstrate the potential influences of atmospheric deposition on the soil-crop system and human health, and can also provide a useful reference for developing the emission control strategies.

Physiological responses and accumulation characteristics of turfgrasses exposed to potentially toxic elements

The tolerance and enrichment of potentially toxic elements (PTEs) in plants are the most important basis of phytoremediation technology for mining area soils. The aim of this research was to study PTEs tolerance, translocation and accumulation differences in three turfgrass species and the biochemical changes of plants and soils. Three turfgrass species were cultured on soils contaminated by single and compound PTEs. Pb, Zn, Cd and As concentrations and biochemical indicators in plant (root and shoot) and soil were determined. Moreover, the microbial communities in rhizosphere soil were analyzed. The studied plants showed strong tolerance and high enrichment ability to Pb, Zn, Cd and As in soil under different PTE concentration gradient stress. Festuca arundinacea had the strongest tolerance to PTEs, whereas Medicago sativa L. had the best tolerance to PTEs. Among all the measured growth or biochemical indicators, the relative growth rate and enzymatic activity of Orychophragmus violaceus were most sensitive to stress. The bioconcentration and translocation factors of Medicago sativa L. for Cd were 1.60 and 1.17, respectively, indicating that it was the most suitable plant for extracting Cd. Compared with other plants, Festuca arundinacea had the most significant effect on soil environment improvement, increasing the soil enzyme activities and microbial community after phytoremediation. This study indicates that Medicago sativa L. can be a potential phytoextraction plant to remove Cd, whereas Festuca arundinacea is more suitable as a cover plant to prevent the dispersion of contaminants in polluted soil.

Soil physiochemical properties and landscape patterns control trace metal contamination at the urban-rural interface in southern China

This study examined the influences of three subsets of environmental factors (i.e. soil physicochemical properties including pH, organic matters and soil texture, landscape patterns, and parent materials) on the spatial variations and sources of soil trace metal contamination across an urban-rural environmental gradient in Guangzhou City, southern China. We collected 318 surface soil samples from forests, orchards, farmlands, and urban lawns using a random tessellation design for selecting sample sites. The geo-accumulation indices showed that 18%-88% of soil samples were contaminated: moderate to high contamination with Cd and Hg, low to moderate contamination with Cu, Pb, Zn and Ni, and low contamination with As and Cr. However, less than 13% of soil samples were considered to have exceeded the national standards causing environmental and human health concerns. The mean geo-accumulation indices increased in the order of forest, paddy field/orchard, vegetable, road/residential, and park/residential areas for As, Cd, Ni, Pb, Zn, closely following a land disturbance gradient. Spearman Correlation and Cluster Analyses showed that Pb-Cu-Zn had traffic-related origins, Cd-Hg were mainly influenced by fertilization or industrial emissions, and As-Cr-Ni had geogenic origins for agricultural soils. In contrast, the Ni, Hg and Cd contamination sources for urban soils included both anthropogenic and geogenic origins. The Stepwise Regression and Partial Redundancy Analyses showed that three subsets of environmental factors explained 43%-87% of variations of soil contamination for both agricultural and urban soils. We concluded that soil contamination was mainly controlled by soil physiochemical properties followed by landscape patterns. Soil absorption of aerial loads of trace metal pollutants dominated the soil contamination processes. Our findings implied that improving soil physiochemical properties and landscape designs can strengthen environmental buffering and carrying capacity, thus alleviating soil contamination and reducing non-point-source pollution in the study region.

Transgenerational memory of gene expression changes induced by heavy metal stress in rice (Oryza sativa L.)

BACKGROUND

Heavy metal toxicity has become a major threat to sustainable crop production worldwide. Thus, considerable interest has been placed on deciphering the mechanisms that allow plants to combat heavy metal stress. Strategies to deal with heavy metals are largely focused on detoxification, transport and/or sequestration. The P_1B subfamily of the Heavy Metal-transporting P-type ATPases (HMAs) was shown to play a crucial role in the uptake and translocation of heavy metals in plants. Here, we report the locus-specific expression changes in the rice HMA genes together with several low-copy cellular genes and transposable elements upon the heavy metal treatment and monitored the transgenerational inheritance of the altered expression states. We reveal that plants cope with heavy metal stress by making heritable changes in gene expression and further determined gene-specific responses to heavy metal stress.

RESULTS

We found most HMA genes were upregulated in response to heavy metal stress, and furthermore found evidence of transgenerational memory via changes in gene regulation even after the removal of heavy metals. To explore whether DNA methylation was also altered in response to the heavy metal stress, we selected a Tos17 retrotransposon for bisulfite sequencing and studied its methylation state across three generations. We found the DNA methylation state of Tos17 was altered in response to the heavy metal stress and showed transgenerational inheritance.

CONCLUSIONS

Collectively, the present study elucidates heritable changes in gene expression and DNA methylation in rice upon exposure to heavy metal stress and discusses implications of this knowledge in breeding for heavy metal tolerant crops.

Atmospheric bulk deposition of heavy metal(loid)s in central south China: Fluxes, influencing factors and implication for paddy soils

The depositions of heavy metal(loid)s (HMs) were measured in an urban agglomeration of China to investigate the fluxes, influencing factors, sources, and potential effects of these HMs. Our results showed that the deposition fluxes of As and Cd were higher in this area than in other regions. In the area, 59.63% of the total deposition fluxes of the Cr, Cu, Ni, Pb and Zn were observed in the wet season (March to July). Lower total fluxes of HMs were observed at the rural site. Principal component analysis (PCA) results showed that the As, Cd, Pb, and Zn might originate from the same anthropogenic sources, including traffic and industrial sources, and that the Cr, Cu, and Ni might come from natural sources. Correlation analysis and redundancy analysis (RDA) showed that rainfall, wind speed, and PMs were critical factors influencing the atmospheric bulk deposition of HMs. For the paddy soil, the input fluxes of HMs by deposition, accounted for 38.66-84.57% (except for Cr) of the total input fluxes. The prediction indicated that the accumulation of HMs in surface soil will notably increase over the next decades due to the influence of atmospheric deposition.

An explanation of soil amendments to reduce cadmium phytoavailability and transfer to food chain

Cadmium contamination in soil, water and food has become a global problem since last century's industrial and agricultural revolution. It is a highly toxic metal with serious consequences on human and animal health. Different natural and anthropogenic sources are responsible for Cd release in the soil which ultimately leads to the food chain. Cd persists in soil for long durations due to its minimal microbial or chemical loss. There are various physical, chemical or biological techniques which are helpful to minimize Cd risk in food chain. Among them, in-situ immobilization with organic, inorganic or clay amendments is a cost-effective and an environment friendly strategy to remediate Cd polluted sites. Lime, biochar, organic wastes, phosphorus fertilizers, sepiolite, zeolite, hydroxyapatite and bentonite are commonly used amendments for amelioration of Cd contaminated soils. These amendments reduce Cd uptake and enhance immobilization by adsorption, complexation, and precipitation processes. This review is aimed to provide a comprehensive note on Cd toxicity in humans and environment, its immobilization by different agents through variety of processes, and comparison of technologies for Cd removal from contaminated sites.

Impact of Non-Agricultural Employment and Environmental Awareness on Farmers’ Willingness to Govern the Heavy Metal Pollution of Farmland: A Case Study of China

Heavy metal pollution of farmland is a significant issue affecting the quality of agricultural products and human health. Farmers’ behaviors can have a direct impact on the level of heavy metal pollution affecting farmland in China. Whether the heavy metal pollution of farmland can be effectively governed at a low cost depends on the farmers. This paper analyzes the mechanism by which the extent of non-agricultural employment and environmental awareness influences farmers’ willingness to govern the heavy metal pollution of farmland using microdata for farmers in China and conducts an empirical analysis via a logit model. The results show that farmers in China display low willingness to govern the heavy metal pollution of farmland and that the increase in non-agricultural income will not significantly improve this willingness. Environmental awareness and farmers’ willingness to govern the heavy metal pollution of farmland are closely related: the higher the environmental awareness of farmers is, the stronger their willingness to govern heavy metal pollution, and the higher the probability of their participating in fallow land treatment. The government can introduce incentives to improve farmers’ environmental awareness of the heavy metal pollution of farmland. In addition, the government should strengthen publicity about the positive effects of fallow land treatment and encourage farmers to participate in the governance of heavy metal pollution of farmland. Given increasing non-agricultural employment opportunities and the transformation of agricultural production modes, agricultural technical training provided by governmental departments can enable them to be more scientific and rational in their agrochemical selection and application, thus reducing or avoiding the heavy metal pollution of farmland at the source. Attention should be paid to the differences between farmers to ultimately reduce the cost and improve the efficiency of treatment.

Effect of Landscape Changes on Water Quality and Health Status of Heptapterus mustelinus (Siluriformes, Heptapteridae)

Substances derived from anthropogenic activities induce changes in the physical and chemical characteristics of the aquatic environment. Physicochemical and biological studies are necessary to understand how changes in landscape affect the health of the aquatic environment. The main goal of this study was to evaluate how the landscape at different spatial scales affects (1) water quality and (2) the health status of Heptapterus mustelinus, based on several biomarkers. During the dry season, individuals were caught in three sites with different degrees of anthropogenic activity. The quality of the terrestrial environment was assessed using the Riparian Quality and Land Use Indices. The water quality condition was evaluated using a water quality index, and pesticides and pharmaceuticals were measured in water. The following biomarkers were analyzed in the fish: general health status (Condition Factor, Hepatosomatic index and energetic costs), enzymatic activity (GST, CAT, AchE), carbonyl content in proteins and histopathological responses in liver and gills. The most impacted sites by the presence of pesticides showed more alterations in the surrounding landscape; specially, changes in the riparian area. In this area, biomarkers denoted more damage than in sites with protected riparian zone. Conservation status of riparian ecosystems is crucial in the determination of rivers ecological quality. Our results demonstrate the importance of monitoring the environmental quality through an integrated analysis, using native fish to understand the effects of human activities on the biota.

Immutable heavy metal pollution before and after change in industrial waste treatment procedure

This study compared state of pollution around an intermediate treatment plant of industrial wastes before and after the change of its treatment procedure. Bulk atmospheric deposition, surface soil, suspended particulate matter and groundwater were collected after the plant changed main operation to waste crushing and volume reduction. Their heavy metals content were comparatively investigated with the previous results obtained when it was burning wastes. The bulk heavy metals deposition showed a clear distance-related attenuation both in burning and crushing periods, indicating that the plant was the main emissions source in either case. High concentrations of heavy metals in suspended particles, soil, and groundwater during the crushing period indicated their diffusion to water environment over time. The bulk atmospheric heavy metals deposition decreased significantly, 0.20~ 0.49 times for Cu, Zn, Cd and Pb and 0.69~0.94 times for Cr, during the crushing period than burning period. However, change of their enrichment factors was not significant. It may indicate that the pollution state did not change qualitatively in a bulk deposition basis and quantitatively in a depositing particle basis. The results showed that heavy metals deposition is dominated by suspended and precipitated particulate matters that adsorb and transport the metals.

Health implication of heavy metals exposure via multiple pathways for residents living near a former e-waste recycling area in China: A comparative study

Herein, crop (vegetables and rice, n = 30), soil (n = 14), dust (n = 12), and PM10 (n = 25) samples were collected to assess the environmental quality of a former e-waste recycling area and evaluate the related health risks. In dust and PM₁₀, the concentrations of heavy metals (Cd, Cu, Ni, Pb, and Zn) were lower than previously reported values, although the numbers for soil, vegetables, and rice remained high. The average accumulation factors of heavy metals in crops decreased in the order of Zn > Cd > Ni > Cu > Pb, and soil was identified as the largest contributor to crop pollution. Heavy metal ingestion largely occurred via rice consumption, which accounted for a significant fraction of the total average daily dose (ADD; 75.2-86.7% in children and 78.0-91.7% in adults), especially for Cd, Cu, Ni, and Zn. However, in the case of Pb, soil ingestion accounted for 48.9% of the ADD in adults, while in children, vegetable, rice, and dust ingestion accounted for 44.7%, 28.6%, and 23.7% of the ADD, respectively. The combined exposure hazard indices at the fifth, median, and 95th percentiles for all heavy metals were determined as 2.54, 9.40, and 40.1 for adults and as 3.75, 13.7, and 58.4 for children, respectively. In terms of health risk, crop consumption was identified as the major exposure pathway for both children and adults, featuring a contribution of 99.9%. In addition, the 95th percentile carcinogenic risks for Pb exceeded the acceptable level. Thus, this work shows that to reduce the health risk for local residents in the former e-waste area, more attention should be paid to soil repair.