Arsenic accumulation in maize crop (Zea mays): a review

Flavonoid metabolism plays an important role in response to lead stress in maize at seedling stage

BACKGROUND

Pb stress, a toxic abiotic stress, critically affects maize production and food security. Although some progress has been made in understanding the damage caused by Pb stress and plant response strategies, the regulatory mechanisms and resistance genes involved in the response to lead stress in crops are largely unknown.

RESULTS

In this study, to uncover the response mechanism of maize to Pb stress phenotype, physiological and biochemical indexes, the transcriptome, and the metabolome under different concentrations of Pb stress were combined for comprehensive analysis. As a result, the development of seedlings and antioxidant system were significantly inhibited under Pb stress, especially under relatively high Pb concentrations. Transcriptome analysis revealed 3559 co-differentially expressed genes(co-DEG) under the four Pb concentration treatments (500 mg/L, 1000 mg/L, 2000 mg/L, and 3000 mg/L Pb(NO3)2), which were enriched mainly in the GO terms related to DNA-binding transcription factor activity, response to stress, response to reactive oxygen species, cell death, the plasma membrane and root epidermal cell differentiation. Metabolome analysis revealed 72 and 107 differentially expressed metabolites (DEMs) under T500 and T2000, respectively, and 36 co-DEMs. KEGG analysis of the DEMs and DEGs revealed a common metabolic pathway, namely, flavonoid biosynthesis. An association study between the flavonoid biosynthesis-related DEMs and DEGs revealed 20 genes associated with flavonoid-related metabolites, including 3 for genistin and 17 for calycosin.

CONCLUSION

In summary, the study reveals that flavonoid metabolism plays an important role in response to Pb stress in maize, which not only provides genetic resources for the genetic improvement of maize Pb tolerance in the future but also enriches the theoretical basis of the maize Pb stress response.

Suppression of OsSAUR2 gene expression immobilizes soil arsenic bioavailability by modulating root exudation and rhizosphere microbial assembly in rice

One of the factors influencing the behavior of arsenic (As) in environment is microbial-mediated As transformation. However, the detailed regulatory role of gene expression on the changes of root exudation, rhizosphere microorganisms, and soil As occurrence forms remains unclear. In this study, we evidence that loss-of-function of OsSAUR2 gene, a member of the SMALL AUXIN-UP RNA family in rice, results in significantly higher As uptake in roots but greatly lower As accumulation in grains via affecting the expression of OsLsi1, OsLsi2 in roots and OsABCC1 in stems. Further, the alteration of OsSAUR2 expression extensively affects the metabolomic of root exudation, and thereby leading to the variations in the composition of rhizosphere microbial communities in rice. The microbial community in the rhizosphere of Ossaur2 plants strongly immobilizes the occurrence forms of As in soil. Interestingly, Homovanillic acid (HA) and 3-Coumaric acid (CA), two differential metabolites screened from root exudation, can facilitate soil iron reduction, enhance As bioavailability, and stimulate As uptake and accumulation in rice. These findings add our further understanding in the relationship of OsSAUR2 expression with the release of root exudation and rhizosphere microbial assembly under As stress in rice, and provide potential rice genetic resources and root exudation in phytoremediation of As-contaminated paddy soil.

Lead, Cadmium, and Arsenic in Raw Milk Produced in the Vicinity of a Mini Mineral Concentrator in the Central Andes and Health Risk

The bovine milk quality, safety, and security are of great concern mainly due to the dispersion of toxic substances from various anthropogenic activities and poor practices for organophosphates in agriculture use. This study evaluated the potential risk to human health from lead (Pb), cadmium (Cd), and arsenic (As) from the consumption of milk produced in an area of the Central Andes valley near a mini mineral concentrator by estimating the weekly intake (WI), dietary risk quotient (DRC), hazard quotient (THQ), and hazard index (HI) for the Peruvian population aged 2 to 85 years, in three scenarios of milk consumption by age (minimum, average, and maximum). Toxic element quantification was performed by flame atomic absorption spectrometry following standardized procedures. The mean amount ± standard deviation of Pb, Cd, and As in soils was 292±60.90, 3.54±1.58, and 5.60±2.20 mg/kg, the order of importance being Pb>As>Cd. The contents of Pb, Cd, and As in pastures were 23.17±10.02, 0.25±0.57, and 0.06±0.09 mg/kg, being from highest to lowest Pb>Cd>As. The means of Pb, Cd, and As content in 19 milk samples were 0.029±0.022, 0.007±0.006, and 0.010±0.004 mg/kg. Pb and Cd exceeded the maximum permissible limits (MPL), and the As was below the MPL. At all ages and milk consumption levels, the WI for Pb and Cd were below the estimated tolerable intake (TWI). The WI for As in < 19 years was higher than the TWI. The DRC for Pb and Cd at all three milk intake levels and all ages was < 1, and for As, it was > 1 in < 19 years, being the risk group. The TQH and HI for Pb and Cd were also > 1, signifying no health risk, and for As, the values were > 1 in < 11 years. Our results are valuable for preventing adverse health impacts from safe and innocuous milk consumption.

Biospectroscopic fingerprinting phytotoxicity towards environmental monitoring for food security and contaminated site remediation

Human activities have resulted in severe environmental pollution since the industrial revolution. Phytotoxicity-based environmental monitoring is well known due to its sedentary nature, abundance, and sensitivity to environmental changes, which are essential preconditions to avoiding potential environmental and ecological risks. However, conventional morphological and physiological methods for phytotoxicity assessment mainly focus on descriptive determination rather than mechanism analysis and face challenges of labour and time-consumption, lack of standardized protocol and difficulties in data interpretation. Molecular-based tests could reveal the toxicity mechanisms but fail in real-time and in-situ monitoring because of their endpoint manner and destructive operation in collecting cellular components. Herein, we systematically propose and lay out a biospectroscopic tool (e.g., infrared and Raman spectroscopy) coupled with multivariate data analysis as a relatively non-destructive and high-throughput approach to quantitatively measure phytotoxicity levels and qualitatively profile phytotoxicity mechanisms by classifying spectral fingerprints of biomolecules in plant tissues in response to environmental stresses. With established databases and multivariate analysis, this biospectroscopic fingerprinting approach allows ultrafast, in situ and on-site diagnosis of phytotoxicity. Overall, the proposed protocol and validation of biospectroscopic fingerprinting phytotoxicity can distinguish the representative biomarkers and interrogate the relevant mechanisms to quantify the stresses of interest, e.g., environmental pollutants. This state-of-the-art concept and design broaden the knowledge of phytotoxicity assessment, advance novel implementations of phytotoxicity assay, and offer vast potential for long-term field phytotoxicity monitoring trials in situ.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

The behavior of arsenic accumulation in onion (Allium cepa) structures by irrigation water: effect of phosphates and arsenic on the total bioactive compounds and antioxidant capacity

The presence of arsenic (As) in irrigation water is a threat to agricultural crops as well as human health. The presence of arsenic and phosphorous in irrigation water influences the behavior of bioaccumulation, biotransfer, and total bioactive compounds in the distinct parts of the onion structure. The present work evaluates the behavior of the bioaccumulation and biotransfer of As in the structures of onion (Allium cepa) through a composite central design and response surface method. The factors employed include the concentration of arsenic (V) and phosphate (V) in the nutritive solution. Additionally, this study analyzes the behavior of the effect that the induced stress has on the total bioactive compounds (phenols and flavonoids) and antioxidant capacity (ABTS and DPPH) in the onion roots. The results showed that the physiological properties, bioaccumulation factors, As transference, and the total bioactive compounds in the onion structure are affected by the competition of As and phosphates (P(V)) in the irrigation water. For concentrations of As and phosphorous of 450 μg L-1 and 0.30 mg L-1 respectively in irrigation water, there are negative effects on the equatorial diameter of the bulb (DE), length, weight of the leaf, and weight of the bulb. Besides, the transference and bioaccumulation factors range from 0.02 to 0.22 and from 2.15 to 7.81, respectively, suggesting that the plant has the ability to accumulate As but exhibits a low translocation ability of As from the root to aerial organs. Besides, it is found for central concentrations of As and phosphorous (450 μg L-1 and 0.30 mg L-1, respectively) in irrigation water, a greater production occurs in total phenolic compounds and antioxidant capacity (ABTS and DPPH) as a response to the stress generated by As.

Regulating sludge composting with percarbonate facilitated the methylation and detoxification of arsenic mediated via reactive oxygen species

This study purposed to demonstrate the impact of reactive oxygen species (ROS) on arsenic detoxification mechanism in sludge composting with percarbonate. In this study, sodium percarbonate was used as an additive. Adding sodium percarbonate increased the content of H2O2 and OH, which the experimental group (SPC) was higher than the control group (CK). In addition, it decreased the bioavailability of arsenic by 19.10%. Metagenomic analysis found that Firmicutes and Pseudomonas took an active part in the overall compost as the dominant bacteria of arsenic methylation. ROS positively correlated with arsenic oxidation and methylation genes (arsC, arsM), with the gene copy number of arsC and arsM increasing to 7.74 × 1012, 5.24 × 1012 in SPC. In summary, the passivation of arsenic could be achieved by adding percarbonate, which promoted the methylation of arsenic, reduced the toxicity of arsenic, and provided a new idea for the harmless management of sludge.

Arsenic in the hyperaccumulator Pteris vittata: A review of benefits, toxicity, and metabolism

Arsenic (As) is a toxic metalloid, elevated levels of which in soils are becoming a major global environmental issue that poses potential health risks to humans. Pteris vittata, the first known As hyperaccumulator, has been successfully used to remediate As-polluted soils. Understanding why and how P. vittata hyperaccumulates As is the core theoretical basis of As phytoremediation technology. In this review, we highlight the beneficial effects of As in P. vittata, including growth promotion, elemental defense, and other potential benefits. The stimulated growth of P. vittata induced by As can be defined as As hormesis, but differs from that in non-hyperaccumulators in some aspects. Furthermore, the As coping mechanisms of P. vittata, including As uptake, reduction, efflux, translocation, and sequestration/detoxification are discussed. We hypothesize that P. vittata has evolved strong As uptake and translocation capacities to obtain beneficial effects from As, which gradually leads to As accumulation. During this process, P. vittata has developed a strong As vacuolar sequestration ability to detoxify overloaded As, which enables it to accumulate extremely high As concentrations in its fronds. This review also provides insights into several important research gaps that need to be addressed to advance our understanding of As hyperaccumulation in P. vittata from the perspective of the benefits of As.

Insight into the plant-associated bacterial interactions: Role for plant arsenic extraction and carbon fixation

This study investigated the interactions between rhizosphere and endosphere bacteria during phytoextraction and how the interactions affect arsenic (As) extraction and carbon (C) fixation of plants. Pot experiments, high-throughput sequencing, metabonomics, and network analysis were integrated. Results showed that positive correlations dominated the interconnections within modules (>95 %), among modules (100 %), and among keystone taxa (>72 %) in the bacterial networks of plant rhizosphere, root endosphere, and shoot endosphere. This confirmed that cooperative interactions occurred between bacteria in the rhizosphere and endosphere during phytoextraction. Modules and keystone taxa positively correlating with plant As extraction and C fixation were identified, indicating that modules and keystone taxa promoted plant As extraction and C fixation simultaneously. This is mainly because modules and keystone taxa in plant rhizosphere, root endosphere, and shoot endosphere carried arsenate reduction and C fixation genes. Meanwhile, they up-regulated the significant metabolites related to plant As tolerance. Additionally, shoot C fixation increased peroxidase activity and biomass thereby facilitating plant As extraction was confirmed. This study revealed the mechanisms of plant-associated bacterial interactions contributing to plant As extraction and C fixation. More importantly, this study provided a new angle of view that phytoextraction can be applied to achieve multiple environmental goals, such as simultaneous soil remediation and C neutrality.

Contradictory Impacts of Nitrate on the Dissimilatory Arsenate-Respiring Prokaryotes-Induced Reductive Mobilization of Arsenic from Contaminated Sediments: Mechanism Insight from Metagenomic and Functional Analyses

Dissimilatory arsenate-respiring prokaryotes (DARPs) are considered to be a key impetus of the reductive dissolution of solid-phase arsenic. However, little is known about the interaction between nitrate and DARPs so far. In this study, we showed that nitrate either inhibited or promoted the DARP population-catalyzed reductive mobilization of As in sediments. Metagenomic analysis of the microbial communities in the microcosms after seven days of As release assays suggested that microbes mainly consisted of: Type-I DARPs having potential to reduce NO3- into NO2- and Type-II DARPs having potential to reduce NO3- to NH4+. We further isolated two cultivable DARPs, Neobacillus sp. A01 and Paenibacillus sp. A02, which represent Type-I and -II DARPs, respectively. We observed that nitrate suppressed A01-mediated release of As(III) but promoted A02-mediated release of As(III). Furthermore, we demonstrated that this observation was due to the fact that nitrite, the end product of incomplete denitrification by Type-I DARPs, suppressed the arrA gene expression per cell and growth of all DARPs, whereas ammonium, the end product of dissimilatory nitrate reduction to ammonium (DNRA) by Type-II DARPs, enhanced the arrA gene expression per cell and significantly promoted the growth of all DARPs. These findings suggest that the actual effects of nitrate on DARP population-catalyzed reductive mobilization of arsenic, largely depend on the ratio of Type-I to Type-II DARPs in sediments.

Improved EfficientNet for corn disease identification

Introduction

Corn is one of the world's essential crops, and the presence of corn diseases significantly affects both the yield and quality of corn. Accurate identification of corn diseases in real time is crucial to increasing crop yield and improving farmers' income. However, in real-world environments, the complexity of the background, irregularity of the disease region, large intraclass variation, and small interclass variation make it difficult for most convolutional neural network models to achieve disease recognition under such conditions. Additionally, the low accuracy of existing lightweight models forces farmers to compromise between accuracy and real-time.

Methods

To address these challenges, we propose FCA-EfficientNet. Building upon EfficientNet, the fully-convolution-based coordinate attention module allows the network to acquire spatial information through convolutional structures. This enhances the network's ability to focus on disease regions while mitigating interference from complex backgrounds. Furthermore, the adaptive fusion module is employed to fuse image information from different scales, reducing interference from the background in disease recognition. Finally, through multiple experiments, we have determined the network structure that achieves optimal performance.

Results

Compared to other widely used deep learning models, this proposed model exhibits outstanding performance in terms of accuracy, precision, recall, and F1 score. Furthermore, the model has a parameter count of 3.44M and Flops of 339.74M, which is lower than most lightweight network models. We designed and implemented a corn disease recognition application and deployed the model on an Android device with an average recognition speed of 92.88ms, which meets the user's needs.

Discussion

Overall, our model can accurately identify corn diseases in realistic environments, contributing to timely and effective disease prevention and control.

Remediation of arsenic-contaminated calcareous agricultural soils by iron-oxidizing bacteria combined with organic fertilizer

In arid soil with low-iron and high-calcium carbonate contents, the fate of arsenic (As) is mainly controlled by the contents of calcium and organic matter in the soil. However, there is still a lack of knowledge about their interaction and that effect on their absorption by maize. The purpose of this study was to explore the long-term immobilization and repair mechanism of in situ As-contaminated farmland. We designed three treatments: iron-oxidizing bacteria (FeOB), organic fertilizer, FeOB and organic fertilizer added in combination. After 140-day field farmland remediation trial, the results showed that the FeOB can effectively immobilize the water-soluble As (F_S1) in soil, and the organic fertilizer promoted the remediation of FeOB. In addition, the content of As in maize grains was reduced after treatment by FeOB and organic fertilizer. The XRD and XPS analysis of the topsoil showed that the combined treatment of FeOB and organic fertilizer promoted the formation of calcium arsenate mineral with low solubility and high stability; As(III) would gradually transform into As(V). The biological iron (hydr)oxide can increase the contents of Fe and As in the rhizosphere and form iron plaques on the surface of the roots by SEM-EDS analysis of maize root. Collectively, these results clarify the main biogeochemical ways to control the fate of As in calcareous soils with low-iron and low-organic matter contents and provide a basis for in situ remediation of As.

Relations between personal exposure to elevated concentrations of arsenic in water and soil and blood arsenic levels amongst people living in rural areas in Limpopo, South Africa

Exposure to arsenic even at low levels can lead to adverse health outcomes, however, there is a paucity of research from South Africa in relation to human exposure to arsenic. We investigated long-term exposure of residents in Limpopo province, South Africa, in a cross-sectional study by analysing water, soil and blood arsenic concentrations from two arsenic-exposed (high and medium-low exposure) villages and one non-exposed (control) village. There were statistically significant differences in the distribution of arsenic in water, soil and blood amongst the three sites. The median drinking water arsenic concentration in the high-exposure village was 1.75 µg/L (range = 0.02 to 81.30 µg/L), 0.45 µg/L (range = 0.100 to 6.00 µg/L) in the medium- / low-exposure village and 0.15 µg/L (range =  < limit of detection (LOD) to 29.30 µg/L) in the control site. The median soil arsenic concentration in the high-exposure village was 23.91 mg/kg (range =  < LOD to 92.10 mg/kg) whilst arsenic concentrations were below the limit of detection in all soil samples collected from the medium-/low-exposure and control villages. In the high-exposure village, the median blood arsenic concentration was 1.6 µg/L (range = 0.7 to 4.2 µg/L); 0.90 µg/L (range =  < LOD to 2.5 µg/L) in the medium-/low-exposure village and 0.6 µg/L (range =  < LOD to 3.3 µg/L) in the control village. Significant percentages of drinking water, soil and blood samples from the exposed sites were above the internationally recommended guidelines (namely, 10 µg/L, 20 mg/kg and 1 µg/L, respectively). Majority of participants (86%) relied on borehole water for drinking and there was a significant positive correlation between arsenic in blood and borehole water (p-value = 0.031). There was also a statistically significant correlation between arsenic concentrations in participants' blood and soil samples collected from gardens (p-value = 0.051). Univariate quantile regression found that blood arsenic concentrations increased by 0.034 µg/L (95% CI = 0.02-0.05) for each one unit increase in water arsenic concentrations (p < 0.001). After adjusting for age, water source and homegrown vegetable consumption in multivariate quantile regression, participants from the high-exposure site had significantly higher blood concentrations than those in the control site (coefficient: 1.00; 95% CI = 0.25-1.74; p-value = 0.009) demonstrating that blood arsenic is a good biomarker of arsenic exposure. Our findings also provide new evidence for South Africa on the association between drinking water and arsenic exposure, emphasising the need for the provision of potable water for human consumption in areas with high environmental arsenic concentrations.

Effects of polyethylene and biodegradable microplastics on photosynthesis, antioxidant defense systems, and arsenic accumulation in maize (Zea mays L.) seedlings grown in arsenic-contaminated soils

Arsenic (As) and microplastic (MP) co-exposure is a major environmental problem in terrestrial ecosystems. Polyethylene and biodegradable plastics decompose into MP particles under microbial-mediated and weathering conditions. However, the effects of MP particles on physiological responses and As accumulation in maize have not been thoroughly explored. In this study, the effects of polyethylene microplastic particles (PEMPs) and biodegradable microplastic particles (BPMPs) on As accumulation, growth and physio-biochemical performance of maize seedlings (Zea mays L.) in As-contaminated soil were investigated. Our study showed that 10 % PE reduced As content in maize seedlings leaves (roots) by 41.19(34.53) μg kg^-1, compared to the control. The 10 % BP reduced As content in maize seedlings leaves (roots) by 64.24 (57.27) μg kg^-1. 10 % PE (10 % BP) reduced maize seedlings leaf area, total chlorophyll content and photosynthetic rate by 5.05 % (21.68 %), 44.98 % (57.12 %) and 65.29 % (77.89 %) and increased H₂O₂ content by 38.04 % (179.6 %), respectively. The antioxidant defense system of maize seedlings leaves was damaged by PEMPs and As co-exposure. Maize seedlings has adapted to stress by regulating antioxidant enzyme activity and the AsA-GSH cycle under BPMPs and As co-exposure. This study provides new insights into the effects of PEMPs and BPMPs on phytotoxicity and As accumulation in As-contaminated soils. Preliminarily data suggests that BPMPs may exhibit greater toxic effects on maize seedlings than PEMPs, which warrants further exploration.

Microbial remediation and plant-microbe interaction under arsenic pollution

Arsenic contamination in aquatic and terrestrial ecosystem is a serious environmental issue. Both natural and anthropogenic processes can introduce it into the environment. The speciation of the As determine the level of its toxicity. Among the four oxidation states of As (-3, 0, +3, and + 5), As(III) and As(V) are the common species found in the environment, As(III) being the more toxic with adverse impact on the plants and animals including human health. Therefore, it is very necessary to remediate arsenic from the polluted water and soil. Different physicochemical as well as biological strategies can be used for the amelioration of arsenic polluted soil. Among the microbial approaches, oxidation of arsenite, methylation of arsenic, biosorption, bioprecipitation and bioaccumulation are the promising transformation activities in arsenic remediation. The purpose of this review is to discuss the significance of the microorganisms in As toxicity amelioration in soil, factors affecting the microbial remediation, interaction of the plants with As resistant bacteria, and the effect of microorganisms on plant arsenic tolerance mechanism. In addition, the exploration of genetic engineering of the bacteria has a huge importance in bioremediation strategies, as the engineered microbes are more potent in terms of remediation activity along with quick adaptively in As polluted sites.

Whole-crop biorefinery of corn biomass for pullulan production by Aureobasidium pullulans

In the present study, corn starch, cob, and straw were biorefined and used as feedstocks for the production of pullulan. The titer and molecular weight (Mw) of pullulan significantly decreased when corn cob and straw hydrolysates were utilized by the parental strain Aureobasidium pullulans CCTCC M 2012259 (PS). Based on adaptive laboratory evolution of PS, an evolved strain A. pullulans EV6 with strong adaptability to the whole corn biomass hydrolysate and high capability of pullulan biosynthesis was screened. Batch pullulan fermentation results indicated that EV6 produced an increased titer of pullulan with a higher Mw than PS. The underlying reasons for these increases were revealed by assaying key enzymes activities and measuring intracellular uridine diphosphate glucose levels. Subsequently, whole-crop biorefinery of corn biomass was conducted, and the results confirmed that whole corn crop has immense potential for efficient pullulan production.

Involvement of exogenous arsenic-reducing bacteria in root surface biofilm formation promoted phytoextraction of arsenic

Root surface biofilm (RSB) is the last window for pollutants entering plant roots and thus plays a critical role in the phytoextraction of pollutants. Exogenous arsenic-reducing bacteria (EARB) have been adopted to enhance the phytoextraction of arsenic (As). However, whether EARB would be involved in RSB formation together with indigenous bacteria and the role of EARB involvement in As phytoextraction are still unknown. Herein, two EARB strains and two phytoextractors (wheat and maize) were selected to investigate the involvement of EARB in RSB formation and its role in As phytoextraction. Results showed that EARB successfully participated in RSB formation together with indigenous bacteria, attributing to their strong chemotaxis and biofilm formation abilities induced by root exudates. The involvement of EARB in RSB formation significantly enhanced As accumulation in plant roots, since more arsenite (As(III)) caused by arsenate (As(V)) reduction in RSB was absorbed by roots. Its underlying mechanism was further elucidated. EARB involvement increased phylum Proteobacteria to produce more siderophores in RSB. Siderophores then improved photosynthesis by increasing catalase and peroxidase activities and decreasing the malondialdehyde of plants. These actions further raised the shoot fresh weight to enhance As accumulation in plant roots. Moreover, mesophyll cell in wheat has a stronger As(V) reduction ability than that in maize, resulting in opposite distribution patterns of As(III) and As(V) in wheat and maize shoots. This study provides a new understanding of phytoextraction enhanced by exogenous bacteria and fills the gap in the role of EARB in As phytoextraction from the perspective of the RSB microregion.

Assessment of the Hormetic Effect of Arsenic on Growth and Physiology of Two Cultivars of Maize (Zea mays L.)

Although growth stimulation at low arsenic doses was observed in several plants, few studies have focused on this phenomenon in more detail. The effects of different concentrations of arsenic (0-50 mg kg-1 of soil: As0-As50) on the growth and selected physiological parameters of two maize cultivars (Zea mays L. cvs. Chapalu and MvNK 333) were tested. Cultivar MvNK 333 manifested a generally higher tolerance to As than cv. Chapalu, which may be related to the lower content of As in the tissues. The highest stimulatory effect of As was recorded at doses of As1 and As2 (cv. Chapalu), and at the As5 dose (MvNK 333), there was an increase in shoot elongation, biomass, and relative water content (RWC), as well as the content of photosynthetic pigments. The stimulatory effect of lower doses of As apparently represents an adaptation mechanism that is associated with water content regulation in the given conditions. The stomata of the studied cultivars were involved in this regulation in different ways. While cv. Chapalu exhibited increased numbers of stomata on both sides of leaves, cv. MvNK 333 instead responded to the given conditions with decreased stomata size. Although hormetic manifestations closely related to changes in stomatal number and size were observed, a typical stomatal hormetic response was not observed in the given range of As doses.

Phytoremediation of arsenic contaminated soil based on drip irrigation and intercropping

A directional leaching in drip irrigation along with intercropping was developed for enhanced phytoremediation of soils contaminated with arsenic (As). Spatiotemporal variations of As levels in soil and effects of irrigation eluents on As migration were analyzed in drip irrigation. Moreover, accumulated levels of As in Zea mays L. and Brassica rapa L. ssp. chinensis (the intercropping species) under drip irrigation and flood irrigation were compared to evaluate the enhancement on phytoremediation by drip irrigation. Results showed that As exhibited a directional migration in soil under drip irrigation, in which the solution of potassium dihydrogen phosphate (PDP) as the eluent significantly promoted As directional migration in soil. Compared to the flood-irrigated intercropping treatments, the As levels in crops (Brassica rapa L. ssp. chinensis) decreased significantly and that of remediating plants (Zea mays L. seedlings) increased significantly under the drip-irrigated intercropping condition. Drip irrigation coupled with intercropping dramatically reduced the risk of As contamination in crops and improved the phytoremediation of As-contaminated soil. PDP further enhanced the disparate effect of drip irrigation on As accumulation by crops and remediation plants.

Heavy Metal Pollution and Risk Assessment of Surface Dust in the Arid NW China

High concentrations of heavy metals (HMs) in urban surface dust (USD) can be extremely hazardous to urban ecology and human health. Oasis cities are located at the edge of deserts and are more exposed to salt/sandstorms, and they face a significantly higher accumulation of USD than wet or semi-humid areas. However, systematic studies on the pollution and risk assessment of HMs in USD in oasis cities have rarely been conducted. This study systematically analyzed the enrichment status, spatial distribution, pollution levels, health risks, and sources of HMs in USD in a typical oasis city (Changji city). The results showed that the average concentrations of Pb, Ni, As, Cd, Hg, and Cu in the USD of Changji city were 46.83, 26.35, 9.92, 0.21, 0.047, and 59.33 mg/kg, respectively, and the results of the pollution index evaluation showed moderate Pb, Hg, and Cu pollution, mild Cd pollution, and no Ni or As pollution. The spatial distribution of HM concentrations in the USD was substantially heterogeneous. High values of Pb, Hg, and Cu concentrations were mainly observed in areas with relatively intensive transportation and commercial activities, and high values of Cd and Ni were observed in industrial areas. The health risk assessment showed that HMs do not pose non-carcinogenic risks to humans at their current level, but they pose a carcinogenic risk to children, with As contributing the largest carcinogenic and non-carcinogenic risks. The source identification of HMs showed that the main pollution of HMs were traffic sources for Pb and Cu, industrial sources for Ni and Cd, natural sources for As, and coal-fired sources for Hg. According to the results of the quantitative analysis with the positive matrix factorization, the contribution of pollution sources followed this order: industrial sources (31.08%) > traffic sources (26.80%) > coal-fired sources (23.31%) > natural sources (18.81%).

Silicon-Induced Tolerance against Arsenic Toxicity by Activating Physiological, Anatomical and Biochemical Regulation in Phoenix dactylifera (Date Palm)

Arsenic is a toxic metal abundantly present in agricultural, industrial, and pesticide effluents. To overcome arsenic toxicity and ensure safety for plant growth, silicon (Si) can play a significant role in its mitigation. Here, we aim to investigate the influence of silicon on date palm under arsenic toxicity by screening antioxidants accumulation, hormonal modulation, and the expression profile of abiotic stress-related genes. The results showed that arsenic exposure (As: 1.0 mM) significantly retarded growth attributes (shoot length, root length, fresh weight), reduced photosynthetic pigments, and raised reactive species levels. Contrarily, exogenous application of Si (Na₂SiO₃) to date palm roots strongly influenced stress mitigation by limiting the translocation of arsenic into roots and shoots as compared with the arsenic sole application. Furthermore, an enhanced accumulation of polyphenols (48%) and increased antioxidant activities (POD: 50%, PPO: 75%, GSH: 26.1%, CAT: 51%) resulted in a significant decrease in superoxide anion (O₂^•−: 58%) and lipid peroxidation (MDA: 1.7-fold), in silicon-treated plants, compared with control and arsenic-treated plants. The Si application also reduced the endogenous abscisic acid (ABA: 38%) under normal conditions, and salicylic acid (SA: 52%) and jasmonic acid levels (JA: 62%) under stress conditions as compared with control and arsenic. Interestingly, the genes; zeaxanthin epoxidase (ZEP) and 9-cis-epoxycarotenoid dioxygenase (NCED-1) involved in ABA biosynthesis were upregulated by silicon under arsenic stress. Likewise, Si application also upregulated gene expression of plant plasma membrane ATPase (PMMA-4), aluminum-activated malate transporter (ALMT) responsible for maintaining cellular physiology, stomatal conductance, and short-chain dehydrogenases/reductases (SDR) involved in nutrients translocation. Hence, the study demonstrates the remarkable role of silicon in supporting growth and inducing arsenic tolerance by increasing antioxidant activities and endogenous hormones in date palm. The outcomes of our study can be employed in further studies to better understand arsenic tolerance and decode mechanism.

Dietary contribution to total urinary arsenic in Mexican women

Exposure to inorganic arsenic (iAs) damages health in many ways. The main routes of human exposure are consumption of contaminated water and diet, but evidence regarding the dietary contribution of iAs is limited. The objective of this work was to determine the foods and beverages that contribute to urinary total arsenic levels (TAs). This is a secondary analysis of an original study of breast cancer cases and population controls carried out in northern Mexico during the period 2007-2011, from which 1,462 women without a history of diabetes were selected. We estimated the consumption of the food and beverage groups with a frequency questionnaire. We measured the concentrations of urinary iAs metabolites by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Total arsenic ranged from 0.5 to 2,360 µg/g creatinine. After adjusting for covariates, we observed a positive association between TAs (with arsenobetaine) with non-bottled drinking water intake, as well as the consumption of root vegetables, vegetables and fruits rich in water, eggs, fish and shellfish. Our findings highlight the relevance of water consumption and some foods for TAs exposure. Food quality monitoring deserves attention in high-risk regions of arsenic contamination.

Co application of biofertilizer and zinc oxide nanoparticles upregulate protective mechanism culminating improved arsenic resistance in maize

During this study, the bioremediation potential of zinc-oxide nanoparticles (ZnO-NPs) and PGPR mixed biofertilizer (BF) on maize plants under induced arsenic (As) stress of 50 ppm and 100 ppm was investigated. The treated plants showed increased As resistance to mitigate the adverse effects of stress by enhancing fresh and dry biomass, relative water content, protein content, soluble sugars, proline content, enzymatic antioxidant defense mechanisms including activities of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), and malondialdehyde (MDA) content. In the pot experiment, the parameters studied have shown that the integrated treatments of ZnO-NPs and BF cause a notable enhancement in relative water content 43%-50% and plant biomass. Moreover, the same treatment showed a marked upregulation in enzymes activity (APX, SOD, APX, and CAT) which oxidized the cell-damaging ROS, produced in response to As stress. Likewise, the combined treatment showed a maximum reduction in MDA content 46%-57% and electrolyte leakage in As treated plants as compared to stressed plants. On the other hand, total soluble sugar 114%-170% and total protein content 117%-241% escalated. SEM analysis revealed marked damage reduction in the treated cells caused by arsenic toxicity. Thus, the use of BF comprised of rhizobacteria along with ZnO-NPs could be a very effective bio source for improving maize plant growth under As stress. In in silico study, As mediated network of proteins showed positive and negative regulation of As activity that leads to stress generation for housekeeping genome.

Risk management for arsenic in agricultural soil-water systems: lessons learned from case studies in Europe

Chronic exposure to arsenic may be detrimental to health. We investigated the behaviour, remediation and risk management of arsenic in Freiberg, Germany, characterized by past mining activities, and near Verdun in France, where World War I ammunition was destroyed. The main results included: (1) pot experiments using a biologically synthesized adsorbent (sorpP) with spring barley reduced the mobility of arsenic, (2) the Omega-3 Index ecotoxicological tests verified that sorpP reduced the uptake and toxicity of arsenic in plants, (3) reverse osmosis membrane systems provided 99.5% removal efficiency of arsenic from surface water, (4) the sustainability assessment revealed that adsorption and coagulation-filtration processes were the most feasible options for the treatment of surface waters with significant arsenic concentrations, and (5) a model was developed for assessing health risk due to arsenic exposure. Risk management is the main option for extensive areas, while remediation options that directly treat the soil can only be considered in small areas subject to sensitive use. We recommend the risk management procedure developed in Germany for other parts of the world where both geogenic and anthropogenic arsenic is present in agricultural soil and water. Risk management measures have been successful both in Freiberg and in Verdun.

Ferrihydrite enrichment in the rhizosphere of unsaturated soil improves nutrient retention while limiting arsenic and uranium plant uptake

Improvement of nutrient use efficiency and limiting trace elements such as arsenic and uranium bioavailability is critical for sustainable agriculture and food safety. Arsenic and uranium possess different properties and mobility in soils, which complicates the effort to reduce their uptake by plants. Here, we postulate that unsaturated soil amended with ferrihydrite nanominerals leads to improved nutrient retention and helps reduce uptake of these geogenic contaminants. Unsaturated soil is primarily oxic and can provide a stable environment for ferrihydrite nanominerals. To demonstrate the utility of ferrihydrite soil amendment, maize was grown in an unsaturated agricultural soil that is known to contain geogenic arsenic and uranium. The soil was maintained at a gravimetric moisture content of 15.1 ± 2.5%, typical of periodically irrigated soils of the US Corn Belt. Synthetic 2-line ferrihydrite was used in low doses as a soil amendment at three levels (0.00% w/w (control), 0.05% w/w and 0.10% w/w). Further, the irrigation water was fortified (~50 μg L^-1 each) with elevated arsenic and uranium levels. Plant dry biomass at maturity was ~13.5% higher than that grown in soil not receiving ferrihydrite, indicating positive impact of ferrihydrite on plant growth. Arsenic and uranium concentrations in maize crops (root, shoot and grain combined) were ~ 20% lower in amended soils than that in control soils. Our findings suggest that the addition of low doses of iron nanomineral soil amendment can positively influence rhizosphere geochemical processes, enhancing nutrient plant availability and reduce trace contaminants plant uptake in sprinkler irrigated agroecosystem, which is 55% of total irrigated area in the United States.

Predictive model for cadmium uptake by maize and rice grains on the basis of bioconcentration factor and the diffusive gradients in thin-films technique

It is possible for heavy metals in soils to be adsorbed by crop roots and then accumulated in crops, which eventually causes great health risk when the crops are ingested by humans. Thus, it is valuable to understand the enrichment model of heavy metals in crops. Diffusive gradients in thin-films (DGT) technique, as an in-situ passive sampling method, can be used to evaluate the bioavailable heavy metals contents in soils. In this study, data of the bioavailable cadmium (Cd) in soils determined by DGT and Cd contents uptake in rice and maize grains in Tianjin, Zhejiang and Guangxi provinces of China were collected from previous references in Web of Science. By comparing bioconcentration factors, it was found that the heavy metal concentrations accumulated in rice and maize followed a general order roots > stems or leaves > grains. An accurate and robust model for the prediction of Cd content in maize and rice grains was established based on bioconcentration factor (BCF) and the bioavailable Cd content determined by DGT method, with R² 0.986 and root mean square error (RMSE) 0.128. This result suggests that the DGT method can be good tool for predicting heavy metals uptake in crops.

Comparative physiological and transcriptomic analyses illuminate common mechanisms by which silicon alleviates cadmium and arsenic toxicity in rice seedlings

The inessential heavy metal/loids cadmium (Cd) and arsenic (As), which often co-occur in polluted paddy soils, are toxic to rice. Silicon (Si) treatment is known to reduce Cd and As toxicity in rice plants. To better understand the shared mechanisms by which Si alleviates Cd and As stress, rice seedlings were hydroponically exposed to Cd or As, then treated with Si. The addition of Si significantly ameliorated the inhibitory effects of Cd and As on rice seedling growth. Si supplementation decreased Cd and As translocation from roots to shoots, and significantly reduced Cd- and As-induced reactive oxygen species generation in rice seedlings. Transcriptomics analyses were conducted to elucidate molecular mechanisms underlying the Si-mediated response to Cd or As stress in rice. The expression patterns of the differentially expressed genes in Cd- or As-stressed rice roots with and without Si application were compared. The transcriptomes of the Cd- and As-stressed rice roots were similarly and profoundly reshaped by Si application, suggesting that Si may play a fundamental, active role in plant defense against heavy metal/loid stresses by modulating whole genome expression. We also identified two novel genes, Os01g0524500 and Os06g0514800, encoding a myeloblastosis (MYB) transcription factor and a thionin, respectively, which may be candidate targets for Si to alleviate Cd and As stress in rice, as well as for the generation of Cd- and/or As-resistant plants. This study provides valuable resources for further clarification of the shared molecular mechanisms underlying the Si-mediated alleviation of Cd and As toxicity in rice.

Arsenic Toxicity-Induced Physiological and Metabolic Changes in the Shoots of Pteris cretica and Spinacia oleracea

Arsenic is a ubiquitous toxic element that can be accumulated into plant parts. The present study investigated the response of Pteris cretica and Spinacia oleracea to As treatment through the analysis of selected physiological and metabolic parameters. Plants were grown in pots in As(V) spiked soil (20 and 100 mg/kg). Plants’ physiological condition was estimated through the determination of elements, gas-exchange parameters, chlorophyll fluorescence, water potential, photosynthetic pigments, and free amino acid content. The results confirmed differing As accumulation in plants, as well as in shoots and roots, which indicated that P. cretica is an As-hyperaccumulator and that S. oleracea is an As-root excluder. Variations in physiological and metabolic parameters were observed among As treatments. Overall, the results revealed a significant effect of 100 mg/kg As treatment on the analysed parameters. In both plants, this treatment affected growth, N, Mg, S, Mn, and Zn content, as well as net photosynthetic rate, chlorophyll fluorescence, and total free amino acid content. In conclusion, the results reflect the similarity between P. cretica and S. oleracea in some aspects of plants’ response to As treatment, while physiological and metabolic parameter changes related to As treatments indicate the higher sensitivity of S. oleracea.

The combination of phytoremediation and electrokinetics remediation technology on arsenic contaminated remediation in tailing storage facilities from gold mine

This research aims to study the effects of combining Mott dwarf Napier grass cultivation and electrokinetic (EK) treatment on arsenic (As) mobility and remediation of As-contaminated mine tailings. Experimental groups were treated with 0, 1, 2, and 4 V/cm for 15 days–120 days. Groups treated with 1 and 2 V/cm electromagnetic field had better As remediation efficiency than the control group with no electromagnetic field treatment. However, electromagnetic field treatment at 4 V/cm inhibited plant growth and had an effect on As uptake in the form of solution at a low level. Plants in experimental group treated with 1 V/cm electromagnetic field for 90 days had significantly high As accumulation (7.69 ± 0.16 mg/kg) in their roots. Their relative growth rate was close to that of the control group with the highest biomass (15.09 ± 0.65 g) recorded on day 120. Mobility and accumulation of As and other elements in the plants were investigated using micro-X-ray fluorescence technique (Beamline BL6b). It was found that very low As concentrations could not be detected although energy emitted from its innermost electron shell (K alpha (Kα1&2) and K beta (Kβ1)) were equal to 10.54 and 11.72 keV. In general, As accumulation in plants occurs primarily in the roots and stems, with greater accumulation around the cortex, epidermis, and xylem. This is similar to the patterns of iron and phosphate accumulation, which occurs through phosphate transporters. In addition, high aluminum mobility and accumulation were found in the stems and leaves of Mott dwarf Napier grass. However, As accumulation in the roots of Mott dwarf Napier grass was higher than in the stem and leaves.

•

Plants treated with 1 V/cm electromagnetic field for 120 days had the highest arsenic accumulation.

•

Treatment with 4 V/cm electromagnetic field can inhibit plant growth.

•

Napier grass accumulated more arsenic in its roots than in its stems and leaves.

•

Treatment with 1 V/cm electromagnetic field stimulated toxin uptake by plants.

Screening maize (Zea mays L.) varieties with low accumulation of cadmium, arsenic, and lead in edible parts but high accumulation in other parts: a field plot experiment

To find maize varieties with both safe production and soil remediation, 11 maize varieties were planted in field soil which was combinedly polluted by cadmium (Cd), arsenic (As), and lead (Pb). The plant growth, accumulation, phytochemical forms, and translocation of Cd, As, and Pb in different tissues were examined. Furthermore, maize varieties with low metal accumulation in their edible parts but high accumulation in other parts were selected as remediation candidates and pollution-safe varieties. The results showed that the growth of varieties Yayu69, Longhuang2502, and Shennongyu10 were the least affected by heavy metals. The concentrations of Cd, As, and Pb in all of the tested maize grains met the national feed hygiene standards, and the grain concentrations of the three metals in Yayu69, Shengnongyu10, and Yunrui62 all met the national food safety standards. According to the extraction efficiency of Cd, As, and Pb and heavy metal concentrations in grains, four types of maize were classified as follows: (1) the first category was suitable for both soil remediation and safe production, including the varieties Yayu69 (Cd, Pb), Jinyi418 (As, Cd), and Shengnongyu10 (Pb); (2) the second category had a high concentration of metals in edible part but did not exceed the limiting value in national feed hygiene standards, and the metal extraction efficiency was also high, including Beiyu1521 (Cd) and Longhuang2502 (Cd, As, Pb); (3) the third category included heavy metal exclusion varieties with low metals accumulation, such as Yayu749 (Cd), Yunrui62 (As, Pb), and Yunrui8 (As); and (4) the fourth type covered risk maize varieties with food safety risks and unsuitable cultivation at sites polluted with toxic metals, including Chuangui1586 (Pb) and Enyu69 (As). The variety Yayu69 (a Cd/Pb low accumulator in grain) contained a low percentage of inorganic (FE) and water-soluble (FW) Cd (4%) and Pb (6%) in roots, respectively, but the percentage of FE and FW Cd and Pb in the variety Beiyu1521 (a Cd/Pb high accumulator in grain) was up to 29% and 13%. Our results provided a new perspective in applying maize varieties with different metal-accumulating ability in their different parts to achieve the remediation of metal-polluted soil and the sustainable development of agricultural production.

Salicylic acid-induced nitric oxide enhances arsenic toxicity tolerance in maize plants by upregulating the ascorbate-glutathione cycle and glyoxalase system

The role of nitric oxide (NO) in salicylic acid (SA)-induced tolerance to arsenic (As) stress in maize plants is not reported in the literature. Before starting As stress (AsS) treatments, SA (0.5 mM) was sprayed to the foliage of maize plants. Thereafter, AsV (0.1 mM as sodium hydrogen arsenate heptahydrate) stress (AsS) was initiated and during the stress period, sodium nitroprusside (SNP 0.1 mM), a NO donor, was sprayed individually or in combination with SA. Furthermore, cPTIO (0.1 mM) was also applied as a NO scavenger during the stress period. Arsenic stress led to significant reductions in plant growth, photosynthesis, water relation parameters and endogenous NO content, but it increased hydrogen peroxide, malondialdehyde, electrolyte leakage, methylglyoxal, proline, the activities of major antioxidant enzymes, and leaf and root As content. The combined treatment of SA+SNP was more effective to reverse oxidative stress related parameters and reduce the As content in both leaves and roots, with a concomitant increase in antioxidant defense system, the ascorbate-glutathione (AsA-GSH) cycle-related enzymes, glyoxalase system enzymes, plant growth, and photosynthetic traits. The beneficial effects of SA were completely abolished with cPTIO supply by blocking the NO synthesis in AsS-maize plants, indicating that NO effectively participated in SA-improved tolerance to AsS in maize plants.

Ferrihydrite Reduction Increases Arsenic and Uranium Bioavailability in Unsaturated Soil

Redox driven mobilization and plant uptake of contaminants under transiently saturated soil conditions need to be clarified to ensure food and water quality across different irrigation systems. We postulate that solid-phase iron reduction in anoxic microsites present in the rhizosphere of unsaturated soil is a key driver for mobilization and bioavailability of contaminants under nonflooded irrigation. To clarify this, two major crops, corn and soybean differing in iron uptake strategies, were grown in irrigated synthetic soil under semiarid conditions with gravimetric moisture content ∼12.5 ± 2.4%. 2-line ferrihydrite, which was coprecipitated with uranium and arsenic, served as the only iron source in soil. Irrespective of crop type, reduced iron was detected in pore water and postexperiment rhizosphere soil confirming ferrihydrite reduction. These results support the presence of localized anoxic microsites in the otherwise aerobic porous bulk soil causing reduction of ferrihydrite and concomitant increase in plant uptake of comobilized contaminants. Our findings indicate that reactive iron minerals undergo reductive dissolution inside anoxic microsites of primarily unsaturated soil, which may have implications on the mobility of trace element contaminants such as arsenic and uranium in irrigated unsaturated soils, accounting for 55% of the irrigated area in the US.

Elemental composition of teff (a gluten-free grain), maize and wheat: Staple crops in the Main Ethiopian Rift Valley

Teff, maize, and wheat are the major cereals grown in volcanic ash-rich soils of the Main Ethiopian Rift (MER) Valley. Teff is a gluten-free cereal native to Ethiopia, used for making a local flat bread called injera, and is getting popularity globally due to its nutritional value (gluten-free and high fiber content). Teff can thus be an alternative diet for the treatment of celiac disease, a lifelong intolerance to gluten. This study aims to assess the distribution of toxic and essential elements in these staple cereals using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and compare with mineral composition of wheat, and maize consumed in the Main Ethiopian Rift Valley. We found significantly higher mean concentrations (in mg/kg) of Mg (1400), Ca (1210), Na (33), Fe (159), Mn (71), Sr (5.6), and Cu (4.8) in teff compared to wheat and maize. Maize had the lowest concentrations of these essential elements. Mean concentrations (in μg/kg) of As (24.7) and Pb (70) in teff were relatively higher compared to wheat and maize, which had similar values of As (4.5) and Pb (8.9). Teff and wheat had similar Cd concentrations (in μg/kg) of 4.8 and 5.4 respectively compared to maize (1.5). Cadmium concentrations were below the Codex standard established for Cd in cereal grains (100 μg/kg). Only one teff sample exceeded the Codex standard set for Pb (200 μg/kg) in cereal grains. This study provides information on nutritional values and food safety of maize, wheat, and teff; the latter is becoming an alternative gluten-free diet for celiac patients in countries where wheat is commonly a staple food.

Heavy metal assimilation in maize (Zea mays L.) plants growing near mine tailings

Mining is one of the main economic activities in Mexico, and Hidalgo State is one of the main areas; however, this activity produces wastes, such as mine tailings, that are disposed in deposits and may be dispersed on the soils (e.g., agricultural soils). In this study, the concentrations of As and heavy metals in maize plants cultivated in a greenhouse in two soils influenced by tailings were evaluated. Plants were grown for 165 days in the soils (one of them more polluted due to a closer distance to the tailings) and one control soil close to the study zone. Plants' growth was evaluated, and after harvesting, they were divided in six parts: root, stalk, plant leaves, cob sheath, corncob and grains. Plants showed depressed development: small height, slow growth and physiological cob immaturity. Assimilation of As and heavy metals by plants was influenced by the concentration of the contaminants but also by the availability of nutrients. Important concentrations of the metals were recorded in the harvestable parts (grain, stalk and cob sheath). The order of accumulation was Zn > Fe > Pb > As > Cd. Cadmium was not detected in grains, but a maximum concentration of As at 1.02 mg/kg and Pb at 3.9 mg/kg was measured in the dry grain. These As and Pb concentrations do not comply with CODEX Alimentarius standards for maize, which states that the cob must be free of heavy metals. In addition, Pb also exceeds the limits established by the Mexican NOM-247-SSA1-2008 regulation.

Compositional and health risk assessment of drinking water from health facilities of District Vehari, Pakistan

Arsenic (As) is a potentially toxic and carcinogenic metalloid. It has gained considerable attention owing to its high ecotoxic nature. High As contamination of groundwater in scattered areas is the current status of Pakistan. A number of assessments exist for the As contamination of the drinking water in District Vehari, Pakistan. However, there is scarcity of data about As contents in drinking water of health facilities and healthcare centers in District Vehari. The current study, therefore, was carried out to assess As concentration and associated health risk in the drinking water of three health facilities (district head quarter, rural health center and basic health unit) of District Vehari. In total, 75 drinking water samples were collected and examined for As contents in addition to physicochemical characteristics such as electrical conductivity, pH, total soluble salts, chloride, carbonates, bicarbonates, fluoride, nitrate, nitrite, calcium, magnesium and iron. Results indicated that the groundwater samples are not fully fit for drinking purposes with respect to several parameters, especially the alarming levels of As. It was found that 52% of drinking water samples of Vehari have As concentration greater than WHO permissible limit (10 µg/L) and 17% have As concentration greater than Pak-EPA permissible limit (50 µg/L). The risk assessment parameters (average daily dose, hazard quotient and carcinogenic risk) showed possible carcinogenic and non-carcinogenic risks associated with ingestion of As-contaminated drinking water in the healthcare facilities. Based on the results of the present study, it is anticipated that hospitals and health centers in Vehari are in need of safe drinking water. The implementation of national/international standards for drinking water in healthcare facilities is a necessary measure to improve the services and increase local access to safe drinking water. The same may be applied to other public offices and organizations such as educational institutes and district government offices.

Variation in arsenic accumulation and translocation among 74 main rice cultivars in Jiangsu Province, China

Arsenic (As) is a ubiquitous carcinogen and environmental toxin. In China, rice consumption is a major dietary source of inorganic As. Thus, the development of strategies to decrease As accumulation in rice is of considerable importance. In this study, we investigated variation in As accumulation and translocation among 74 hydroponically grown rice cultivars in Jiangsu Province, China. We also examined the relationships between As accumulation and translocation, and the uptake of elements such as silicon (Si), phosphorus (P), iron (Fe), and manganese (Mn). Our results showed 3.43-, 2.7-, and 6.34-fold variations in shoot As concentration, root As concentration, and root-to-shoot As translocation factors (TFs), respectively, among 74 cultivars, indicating that cultivar genotype significantly affected As accumulation and translocation. Redundancy analysis revealed that As uptake and transport were more closely related to P and Mn uptake than to Si and Fe uptake, for all 74 rice genotypes. In addition, the 20 cultivars that accumulated the least shoot As (low-As), and those that accumulated the most shoot As (high-As), exhibited different strategies in response to As exposure. The As TFs were key factors influencing shoot As concentrations in high-As cultivars, but this was not the case in low-As cultivars. In the latter, more accumulated As were sequestered in roots, which restricted As translocation to shoots, thus leading to lower shoot As concentrations. In addition, the shoot As concentrations of various rice cultivars and their parents differed. The low-As rice cultivar YJ2 exhibited a significantly lower shoot As concentration than its parents, suggesting that it is possible to breed low-As rice cultivars from parents that also exhibit low-As characteristics.

Combined toxicity and detoxification of lead, cadmium and arsenic in Solanum nigrum L

A 3-factor-5-level central composite design was conducted to investigate the combined toxicity and detoxification mechanisms of lead (Pb), cadmium (Cd) and arsenic (As) in Solanum nigrum L. The three metal(loid)s exhibited low-dose stimulation and high-dose inhibition on plant length. Analyses of eleven oxidative stress and antioxidant parameters showed all Pb, Cd and As induced oxidative damages, and the co-exposure further enhanced their toxic effects. Pb, Cd and As were mainly accumulated in plant roots and poorly translocated to shoots, being beneficial for metal(loid) detoxification. The results of subcellular fractionation showed that Pb, Cd and As in plant leaves, stems and roots were mainly localized in the cell wall and soluble fractions. Most of Pb and As in soils occurred in residual fraction while Cd in exchangeable fraction. Although single Pb, Cd and As in all plant tissues existed predominantly in 1 M NaCl-soluble form, the d-H₂O and 80 % ethanol-soluble forms were increased under the binary or ternary combinations. This study will conduce to the potential use of S. nigrum L. in the phytostablization of soil co-contaminated with Pb, Cd and As.

Assessing the most sensitive and reliable endpoints in plant growth tests to improve arsenic risk assessment

Arsenic (As) is toxic to humans and the environment. Its toxicity has been assessed in many ways, including plant growth tests integrated in As risk assessments (RA). The tiered approach used in RA schemes assumes that lower tiers are more conservative than higher tiers. Plant growth tests may comprise lower tier of a RA and include the measurement of several endpoints. However, only few of these endpoints are highly sensitive and reliable, which makes them more appropriate to comprise lower tiers. Therefore, the selection of those endpoints is needed. The present study aimed to evaluate the most appropriate endpoints of plant growth tests to use in lower tier As RA schemes. This selection of endpoints was based on their sensitivity and reliability, using different tropical soils and plant species. In order to achieve this objective, six plant species were exposed to eight levels of As contamination (0; 8; 14.5; 26; 46.5; 84; 150; 270 mg kg^-1), in three different tropical soils (Oxisol, Inceptisol, and tropical artificial soil). The endpoints measured were: first germination count (FrC), plant height (PH), relative leaf area (RLA), stem diameter (SD), total germination (TG), germination speed index (GSI), dry mass (DM), number of completely expanded leaves (CEL), plant survival (PS), soil plant analysis development chlorophyll level (SPAD), and the final germination count (FnC). Toxic values for 50% of effect were estimated for each endpoint within each species and test soil, to rank them according to their sensitivity and reliability. The most sensitive endpoints were: FrC, RLA, DM, GSI, PH, and FnC, while the most reliable endpoints were: FrC, DM, GSI, DM, PH, FnC, and TG. Our findings suggest that FrC, DM, GSI, PH, and FnC are the most adequate endpoints to be used in plant growth tests as lower tiers of As RA in tropical regions.

Effects of environmental governance in mining areas: The trend of arsenic concentration in the environmental media of a typical mining area in 25 years

China has considered different environmental management measures (EMMs) in mining areas. However, their effects remain unclarified. In this study, the achievements and limitations of different EMMs of a typical mining area-Huangchang realgar mine-located in Hunan province were explored. The variations in the arsenic concentrations in the soil, agricultural products, drinking water, and atmosphere in 25 years of EMM implementation were investigated. Source control measures, such as ceasing mining and smelting activities, disposal of waste residues, and purifying wastewater, significantly reduced the arsenic concentrations in the atmosphere and surface water by more than 99%-from 68 μg m^-3 and 0.42 mg L^-1 to 3.63 ng m^-3 and 4.31 μg L^-1, respectively. The arsenic concentrations in agricultural products decreased by more than 78.8%-from 1.32 mg kg^-1 in wheat to 0.28 mg kg^-1 in vegetable and 0.13 mg kg^-1 in maize-after the planting structure adjustment (PSA). However, the chronic daily intake of arsenic via product ingestion was 1.5 times higher than the benchmark dose lower confidence limit. Natural attenuation measures exerted limited effects on soil remediation; the arsenic concentration in the soil decreased insignificantly from 291.9 mg kg^-1 to 213.3 mg kg^-1. With the current attenuation rate, decreasing the soil arsenic concentration to under 30 mg kg^-1 would require 47,900 years. The exceeding contaminant concentration in the resuspended dust, surface runoff, and agricultural products from the contaminated soil must be considered. China's EMMs in mining areas have achieved significant results, but the contaminated soil requires more attention and the PSA should accommodate the dietary habits and economic limits.

Trace element content in cereals from a gold mining site in Burkina Faso and intake risk assessment

Cereals grown close to mining sites could contain high levels of trace elements which could jeopardize local population health through intake of those crops. This study investigated for the first time the concentration of trace elements, namely arsenic, cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead and zinc in four types of cereals (two of maize and two of sorghum) grown within the perimeter of a gold mine and at three surrounding villages in Burkina Faso. A total of 47 samples were taken. Cereal consumption surveys in those villages were undertaken to evaluate the intake hazard. Average arsenic content trend was Site (0.31 ± 0.56 mg kgdw^-1) > Songo (0.18 ± 0.17 mg kgdw^-1) > Sighnoguin (0.15 ± 0.10 mg kgdw^-1) > Youga (0.10 ± 0.00 mg kgdw^-1); subsequently, the average estimated daily intake of Arsenic followed this pattern: Site > Songo > Sighnoguin > Youga with 1.93, 1.08, 0.89 and 0.63 μg kgbw^-1 day^-1 respectively which all fall below a target hazard quotient of 1. Non-parametric Kruskal-Wallis tests confirmed significant difference of Co, Cu, Fe, Mn and Ni between locations whilst not significant differences were found for As, Cd, Pb and Zn. Considering cereals types, yellow corn from the mine site exhibited As value higher than the Referential dose (2.14 μg kgbw^-1 day^-1) and consequently a target hazard quotient of 1.97. This finding indicates that there is an intake risk to the local population from dietary intake. Contamination by As could be linked to mining activities on parent rocks that contain As with spread by wind to Songo and Youga. Sighnoguin village is more subject to contamination by agricultural practices. Decontamination of the site and selection of cereals with low uptake capability and some changes to agricultural practices could reduce the hazards.

A deterministic and stochastic assessment for exposure and risk of arsenic via ingestion of edible crops

Natural arsenic contamination is a critical problem for various places around the world. Simav Plain (Kutahya, Turkey) is one such area that was shown to have natural arsenic contamination in its waters and soils. Arsenic exposure through ingestion of edible crops cultivated in Simav Plain and associated health risks were assessed in this study. To achieve this objective, arsenic levels in 18 crop species were estimated based on measured soil arsenic concentrations. Individual and aggregate non-carcinogenic and carcinogenic risks associated with ingestion of arsenic-contaminated crops were then assessed with scenario-based deterministic point estimates and stochastic population estimates. Monte Carlo simulation was used for the estimation of population health risks. Accordingly, wheat was found as the highest-ranked crop specie for the both types of health risks, followed by tomato and potato, which are three of the most consumed crops in the region. The risk levels estimated in this study were relatively high, indicating consumption of crops grown in the plain may be posing significant health risks even at lower-bound estimates. Consuming wheat, tomato, potato, and their products from uncontaminated sources was found to reduce the aggregate risks up to 88% implicating the importance of proposing suitable management measures for similar risk-prone areas.

Bioconcentration, Potential Health Risks, and a Receptor Prediction Model of Metal(loid)s in a Particular Agro-Ecological Area

To investigate the bioconcentration and potential health risks of metal(loid)s in a particular agro-ecological area, 230 pairs of soil and corresponding crop grain samples were collected from typical corn and wheat plants. The geo-accumulation index (Igeo), bioconcentration factors (BCF), health risk assessment (the target hazard quotient), and Receptor Prediction Model (PCS-SMLR) analysis were adopted to study the spatial distribution, assess the health risks, and predict the relationship between metal(loid)s and soil properties. It was found that the mean concentrations of Cu, Zn, Pb, Hg, and Cd in the study area’s agricultural soils exceeded the background soil concentrations, especially for Cd (0.2 mg/kg), Meanwhile, the corresponding Cd concentration in wheat samples was higher than the food quality limit. The results of the Igeo showed that the samples with a value higher than 0 for Cd and Hg accounted for 47.83% and 33.48%, respectively. The results of BCF of Cu, Zn, Cd, and As were higher in wheat than in corn, except for Ni. The target hazard quotient (TTHQ) of health risk of wheat, corn, and soil were higher for children (2.48) than adults (1.78), showing a potential health risk for individuals who mostly consume wheat. In addition, the PCS-SMLR analysis of the BCF prediction model for Cu, Zn, As, and soil properties showed differences in terms of the influences from wheat and corn. These results provide valuable information that not only can help local residents improve the staple food structure, but also can get provide a reference metal(loid)s concentration level for agricultural soils in the study area and restore a sustainable agro-ecological environment.

Arsenate phytoextraction abilities of one-year-old tree species and its effects on the nutritional element content in plant organs

The aim of the study was to evaluate the As phytoextraction potential of four tree species: Acer pseudoplatanus L., Betula pendula Roth., Quercus robur L., and Ulmus laevis Pall. in light of their prospective use in the phytoremediation of arsenate [As(V)] contaminated soils. The content of nutritional elements: B, Ca, K, Mg, Na, Si, P, and S was also analyzed. The trees were grown for 1 month in hydroponic cultures (Knop medium) supplemented with As(V), (1 mM). The results showed that the highest As accumulation efficiency was characterized by B. pendula (BCF = 0.87) and Q. robur (BCF = 0.5). Betula pendula accumulated about 80% of As in its roots (TF = 0.22) whereas Q. robur accumulated more than 60% of As in its shoots (TF = 1.60). The other tree species accumulated significantly lower amounts of As, more than 60% of which collected in their shoots. As(V) phytoextraction led to a significantly lower level of P and S in the roots of all tested tree species. Betula pendula seems promising for phytostabilisation and Q. robur for phytoextraction of As(V) from contaminated soils. The obtained results confirm the accumulation and translocation of As(V), as well as the acquisition of nutritional elements by the selected tree species.

Arsenic content in two-year-old Acer platanoides L. and Tilia cordata Miller seedlings growing under dimethylarsinic acid exposure-model experiment

The presence of cacodylic acid (dimethylarsinic acid, DMA) can be an important factor in limiting the abilities of young tree seedlings to adapt to unfavorable environmental conditions. For this reason, the aim of the study was to estimate the influence of different DMA additions (from 0.01 to 0.6 mM) to modified Knop solution to arsenic (As) and selected forms of this metalloid (As(III), As(V), DMA) phytoextraction by two-year-old Acer platanoides L. and Tilia cordata Miller seedlings. Additionally, the biomass and other elements important in As transport in plants were analyzed. Seedlings of both tree species were able to grow in all experimental systems except the one with the highest DMA concentration (0.6 mM). Exposure of tree seedlings was related to a general decrease in plant biomass. Phytoextraction of As in roots, stems, and leaves increased with a rise of DMA concentration in solution to the highest content of As in A. platanoides and T. cordata roots growing under 0.3 mM (135 ± 13 and 116 ± 14 mg kg^-1 dry weight). Arsenic was accumulated mainly in roots, thereby confirming bioconcentration factor values BCF > 1 for all tree seedlings treated with DMA. Exposure of plants to low DMA concentrations (0.01 and 0.03 mM) was related to the transport of this element to aboveground parts, while increased DMA concentration in other experimental systems led to the limitation of As transport to stems, as confirmed by translocation factor values TF < 1. Changes in many other elements such as boron, silicon, phosphorus, or sulfur concentration indicated the possible influence of DMA on the transport of As from roots to leaves. The obtained results show that DMA can be an important factor in modulating As phytoextraction in the studied tree species.

Alleviative role of exogenously applied mannitol in maize cultivars differing in chromium stress tolerance

A pot experiment was performed to examine the role of foliar applied mannitol (M) in chromium (Cr) stress alleviation in different maize cultivars. Two maize cultivars, one tolerant (6103) and one sensitive (9108) to chromium stress, were grown in soil treated with three concentrations of Cr (0, 5, and 10 mg kg^-1) and three levels of mannitol (0, 50, and 100 mg L^-1). Chromium stress decreased the overall growth of plants by reducing the plant height, root/shoot dry weight, chlorophyll contents, and enzymatic activities, while exacerbated the severity of reactive oxygen species in both maize cultivars. Chromium-induced reduction in growth attributes of maize plants was relatively higher in sensitive cultivar than that of tolerant one. Uptake of Cr by the plants and its translocation from roots to shoots increased with increasing concentration in the soil. However, foliar application of mannitol significantly alleviated the Cr stress and improved growth, biomass, and photosynthetic pigments of maize plants. Mannitol also considerably reduced Cr contents in leaves and roots of both cultivars. Hence, it is concluded that mannitol can be helpful for crops grown on heavy metal, especially Cr, contaminated soils for remediation purpose.

Spatio-Temporal Analysis of Natural and Anthropogenic Arsenic Sources in Groundwater Flow Systems

The presence of arsenic in groundwater constitutes a hazard for the environment and human health, and the determination of its source has become a global challenge, which can be approached by defining the natural background levels (NBL) in conjunction with the indicator kriging method, with the aim of delineating anthropogenically contaminated areas. However, having a unique value of NBL for large areas can generate interpretation errors. This research integrates the determination of the flow systems present in the Calera Aquifer, and the definition of the natural background levels in each flow system by making estimation maps in ArcGIS using two databases, 10 years apart, to evaluate the spatio-temporal variation of arsenic in groundwater. The results indicate a notable increase in the probability of exceeding the arsenic NBL, mainly in the intermediate flow, which may be due to movement resulting from mining activities as well as a mixture of regional and intermediate flows caused by the extraction of water for agriculture and drinking water supplies. The presented values exceed the maximum limits allowed for human consumption, as stated by the World Health Organization.

Arsenic forms in phytoextraction of this metalloid in organs of 2-year-old Acer platanoides seedlings

The aim of the study was to estimate the significance of the role of arsenite (As(III)), arsenate (As(V)), and dimethylarsinic acid (DMA) presence in modified Knop medium in the efficiency of phytoextraction of arsenic (As) in Acer platanoides root, stem, and leaves. The addition of particular As forms in single, double, and triple experimental systems was associated with a lower increase of seedling biomass compared to control plants (system free of As forms addition). Depending on As forms and their concentration in solution, negative symptoms from slight visible changes (inorganic forms separately or jointly), through smaller and discolored leaves (after DMA addition), and finally to their withering (after high DMA addition) were observed. Changes of color and shape for root systems exposed to particular As forms separately or jointly were also observed, in spite of the fact that there were no significant changes in biomass of seedlings growing in all experimental systems. The highest mean concentrations of As in root, stem, and leaves (590, 70, and 140 mg kg^-1 dry weight (DW), respectively) were observed in plants growing under different experimental systems. The highest bioconcentration factor values were 10.8 for plants exposed to 0.06 mM of As(III) and DMA, while the highest translocation factor (1.0) was recorded for plants growing under the same As forms (0.6 and 0.06 mM, respectively). The obtained results indicate that the presence of particular As forms not only determines As phytoextraction and transport of this metalloid form but also has a decisive influence on plant morphology and survivability. As regards the practical aspects of phytoremediation, the kind of As forms present in substrate are more important than their total concentration.