Lead and cadmium contamination and exposure risk assessment via consumption of vegetables grown in agricultural soils of five-selected regions of Pakistan

Optimization of polyamine and mycorrhiza in sorghum plant for removal of hazardous cadmium

Eco-friendly and sustainable practices must be followed while using the right plants and microbes to remove harmful heavy metals from the soil. The goal of the current study was to ascertain how effectively sorghum plants removed cadmium (Cd) from the soil using polyamines and mycorrhiza. Plant-biochemicals such as free amino acids, ascorbic acids, anthocyanin, proline, and catalase, APX, peroxidase activities were considered as markers in this study which revealed the adverse plant growth performance under 70 and 150 ppm of Cd concentration (w/w) after 30,60, and 90 days of treatment. The plants showed a mitigating effect against high Cd-concentration with exogenous use of mycorrhiza and putrescine. The treatment T17 (mycorrhiza +5 mM putrescine) showed a substantial decrease in the content of total free amino acid, ascorbic acid, catalase, APX, peroxidase by 228.36%, 39.79%, 59.06%, 182.79% 106.97%, respectively after 90 days as compared to T12 (150 ppm Cd). Anthocyanin content was negatively correlated (-0.503, -0.556, and -0.613) at p < 0.01 with other studied markers, with an increase by 10.52% in T17 treated plant as compared to T12. The concentration of Cd in root increased by 49.6% (141 ppm) and decreased in the shoot by 71% (17.8 ppm) in T17 treated plant as compared to T12 after 90 days. The application of mycorrhiza and putrescine significantly increased BCF (>1) and decreased TF (<1) for Cd translocation. The administration of mycorrhiza and putrescine boosted the Cd removal efficiency of sorghum plants, according to FTIR, XRD, and DSC analysis. As a result, this study demonstrates novel approaches for induced phytoremediation activity of plants via mycorrhiza and putrescine augmentation, which can be a promising option for efficient bioremediation in contaminated sites.

Comparative assessment of pantothenic, aspartic, ascorbic and tartaric acids assisted Pb-phytoextraction by sunflower (Helianthus annuus L.)

Phytoextraction of lead (Pb) is a challenging task due to its extremely low mobility within soil and plant systems. In this study, we tested the influence of some novel chelating agents for Pb-phytoextraction using sunflower. The Pb was applied at control (0.0278 mM) and 4.826 mM Pb as Pb(NO3)2 through soil-spiking. After 10 days of Pb addition, four different organic ligands (aspartic, ascorbic, tartaric, and pantothenic acids) were added to the soil at 1 mM concentration each. respectively. In the absence of any chelate, sunflower plants grown at 4.826 mM Pb level accumulated Pb concentrations up to 104 µg g-1 DW in roots, whereas 64 µg g-1 DW in shoot. By contrast, tartaric acid promoted significantly Pb accumulation in roots (191 µg g-1 DW; + 45.5%) and shoot (131.6 µg g-1 DW; + 51.3%). Pantothenic acid also resulted in a significant Pb-uptake in the sunflower shoots (123 µg g-1 DW; + 47.9%) and in roots (177.3 µg g-1 DW; + 41.3%). The least effective amongst the chelates tested was aspartic acid, but it still contributed to + 40.1% more Pb accumulation in the sunflower root and shoots. In addition, plant growth, biochemical, and ionomic parameters were positively regulated by the organic chelates used. Especially, an increase in leaf Ca, P, and S was evident in Pb-stressed plants in response to chelates. These results highlight that the use of biocompatible organic chelates positively alters plant physio-biochemical traits contributing to higher Pb-sequestration in sunflower plant parts.

Accumulation and translocation of lead in vegetables through intensive use of organic manure and mineral fertilizers with wastewater

In many countries with wastewater irrigation and intensive use of fertilizers (minerals and organics), heavy metal deposition by crops is regarded as a major environmental concern. A study was conducted to determine the impact of mineral fertilizers, cow manure, poultry manure, leaf litter, and sugarcane bagasse on soil's trace Pb content and edible parts of vegetables. It also evaluated the risk of lead (Pb) contamination in water, soil, and food crops. Six vegetables (Daucus carota, Brassica oleracea, Pisum sativum, Solanum tuberosum, Raphanus sativus, and Spinacia oleracea) were grown in the field under twelve treatments with different nutrient and water inputs. The lead concentrations in soil, vegetables for all treatments and water samples ranged from 1.038-10.478, 0.09346-9.0639 mg/kg and 0.036-0.26448 mg/L, The concentration of lead in soil treated with wastewater in treatment (T6) and vegetable samples was significantly higher, exceeding the WHO's permitted limit. Mineral and organic fertilizers combined with wastewater treatment reduced lead (Pb) concentrations in vegetables compared to wastewater application without organic fertilizers. Health risk indexes for all treatments except wastewater treatment (T6) were less than one. Pb concentrations in mineral fertilizers, cow manure, poultry manure, leaf litter, and sugarcane bagasse treated were determined to pose no possible risk to consumers.

Evaluation of the concentration and human health risk of nitrate and potentially toxic elements (PTEs) in melons from a southern region of Iran: Identification of pollution sources

Decentralized agriculture, improper monitoring of cultivation conditions, and leaching of contaminants into lands led to the contamination of crops with various potentially toxic elements (PTEs). However, it is essential to know more about the profile level and associated risk of these contaminants and their origin, especially in high-water content crops. This study aimed to investigate the concentration of PTEs in melons of one of Iran's southern cities and follow that health risk assessment in the target population for the first time. Results of the present study confirmed that although the mean concentration of some metals was lower than the safety standard (Cr: 4.6 ± 2 mg/kg and Pb: 7.4 ± 4 mg/kg), their nutritional value was unfavorable regarding some micronutrients (Cu: 88.8 ± 27 mg/kg and Zn: 480 ± 275 mg/kg). The highest metal concentration in cantaloupe was iron (1706.47 mg/kg, p-value<0.05), and nitrate concentration in all melon types was 2.59-524.54 mg/kg (p-value<0.05). Principal component analysis (PCA) with K-means clustering and the Positive Matrix Factorization (PMF) model have shown that contaminants in melons originated from human activities. So, excessive use of agricultural fertilizers is a possible source of nitrates in melons, which have 93 % of factor loading values. The health risk assessment also showed that melons' carcinogenic and non-carcinogenic risk using the deterministic method was lower than the permissible limit (HQ < 1, ILCR 1 in the children group for the 95th percentile. Furthermore, the level of certainty in the carcinogenesis risk for children, women, and men was estimated at 86.48 %, 64.67 %, and 61.30 %, respectively. Also, the consumption rate was determined as the most important parameter in the sensitivity analysis. As a consequence, there is a potential health risk for Iranians after the consumption of melon due to PTEs and nitrate levels that also originated from anthropogenic sources.

Heavy metals and potential health risk assessment of Lactuca sativa and Daucus carrota from soil treated with organic manures and chemical fertilizer

The large-scale production of food crops with heavy application of chemical fertilizers in the effort to meet the astronomical increase in food demands may be counterproductive to the goal of food security. This study investigated the effect of different soil treatments on the levels of heavy metals (Cr, Cu, Fe, Ni, Pb, and Zn) in two types of vegetables Lactuca sativa (lettuce) and Daucus carrota (carrot). The potential carcinogenic and non-carcinogenic health risks from their consumption were also evaluated. Planting experiment was set up in a randomized block design, with different soil treatments of soil + cow dung (CD), soil + sewage sludge (SS), soil + chemical fertilizer (nitrogen-phosphorus-potassium (NPK)), and untreated soil (UNTRD). The vegetables were harvested at maturity, washed with distilled water, and subjected to an acid digestion process before the levels of heavy metals were measured by inductively coupled plasma spectrometry (ICP-MS). The mean concentrations of the metals in the vegetables across all treatments were below the maximum permissible limits. The pattern of heavy metal accumulation by the vegetables suggested that the lettuce from SS treatment accumulated higher concentrations of heavy metals like Cr (0.20 mg/kg), Cu (3.91 mg/kg), Ni (0.33 mg/kg), and Zn (20.44 mg/kg) than carrot, with highest concentrations of Fe (90.89 mg/kg) and Pb (0.16 mg/kg) recorded in lettuce from NPK treatment. The bioaccumulation factor (BAF) showed that lettuce, a leafy vegetable, has bioaccumulated more heavy metals than carrot, a root vegetable. The BAF was generally below the threshold value of 1 in both vegetables, except in lettuce from NPK and CD treatments and carrot from NPK treatments, with BAF values of 1.6, 1.69, and 1.39, respectively. The cancer risk assessment factors were well below the unacceptable maximum range of 10-4 suggesting that consuming these vegetables might not expose an individual to potential risk of cancer development. The hazard quotient estimations were below the threshold values of 1 for all heavy metals; however, the hazard index (HI) values of 1.27 and 1.58 for lettuce from NPK and SS treatments indicate a potential non-carcinogenic health risk to consumers from intake of all the heavy metals.

Exogenous methyl jasmonate enhanced kenaf (Hibiscus cannabinus) tolerance against lead (Pb) toxicity by improving antioxidant capacity and osmoregulators

In this study, the effects of exogenous methyl jasmonate (MeJA) on metal uptake and its ability to attenuate metal toxicity in kenaf plants under Pb stress were investigated. The experiment was conducted with five different MeJA concentrations (0, 40, 80, 160, and 320 μM) as a foilar application to kenaf plants exposed to 200 μM Pb stress. The results revealed that pretreatmen of MeJA significantly increased plant dry weight, plant height, and root architecture at all concentrations tested, with the most significant increase at 320 μM. Foliar application of MeJA at 160 μM and 320 μM increased the Pb concentrations in leaves and stems as well as the translocation factor (TF) from root to leaf. However, the bioaccumulation factor in the shoot initially decreased and then increased with increasing MeJA concentration. By increasing enzymatic (SOD, POD, and CAT) and non-enzymatic (AsA and non-protein thiols) antioxidants, MeJA pretreatment decreased lipid peroxidation, O2- and H2O2 accumulation and recovered photosynthetic pigment content under Pb stress. Increased osmolytes (proline, sugar, and starch) and protein content after MeJA pretreatment under Pb stress restore cellular homeostasis and improved kenaf tolerance. Our results suggest that MeJA pretreatment modifies the antioxidant machinery of kenaf and inhibits stress-related processes that cause lipid peroxidation, hence enhancing plant tolerance to Pb stress.

New-style electrokinetic-adsorption remediation of cadmium-contaminated soil using double-group electrodes coupled with chitosan-activated carbon composite membranes

Global soil cadmium (Cd(II)) contamination threatens the soil environment, food safety, and human health. Conventional electrokinetic remediation (EKR) and enhancement methods usually operate in strong electric fields, leading to strong side reactions and uneven removal. In this work, to remove Cd(II) from soil effectively in a low-voltage electric field, a new-style electrokinetic-adsorption remediation using double-group electrodes coupled with chitosan-activated carbon composite membranes (DE-EKR-CAC) was developed. Chitosan-activated carbon (CAC) composite membranes were synthesized for easy recovery and reuse of adsorbents. The effects of pH, contact time, initial concentration, and foreign ions on the removal of Cd(II) by the CAC composite membranes were determined. The CAC composite membranes performed well except in a strongly acidic environment (pH = 2.0). The soil pH varied between 3.4 and 5.0 in DE-EKR-CAC, where the CAC composite membranes were applicable. High concentrations of Ca2+ interfered with the adsorption of Cd(II), which means that the selectivity of CAC composite membranes for Cd(II) is not high enough. The Langmuir (R2 = 0.999) and pseudo-second-order kinetic (R2 = 1.0) models revealed the monolayer coverage and chemisorption mechanism, and the maximum adsorption capacity was 40.81 mg/g. Furthermore, SEM, FTIR, and XPS analyses suggest that physical adsorption, complexation of oxygen-containing functional groups, chelation of amino groups, and ion exchange are potential mechanisms for the adsorption of Cd(II) on CAC. DE-EKR-CAC performed better than the group remediated with one set of electrodes, with higher removal efficiencies and more uniform removal. The lowest energy consumption was 3.33 kWh/m3, which is lower than other enhancement methods. Separation of CAC composite membranes from soil is easy, and reuse performance is good. DE-EKR-CAC provides a potential option for Cd(II) removal from soil because of its better performance using low-voltage direct current, low energy consumption, and ease of recycling the adsorbent.

Organic amendments perform better than inorganic amendments in reducing the absorption and accumulation of cadmium in lettuce

The main purpose of applying organic or inorganic amendments is to guarantee crop safe production in heavy metal contaminated soil. However, previous studies showed that the effects of organic or inorganic composite amendments on the cadmium (Cd) concentration of lettuce (Lactuca sativa var. ramosa Hort) were inconsistent. Accordingly, a sixty-day pot experiment was carried out to examine the impacts of the inorganic materials (lime, L and zeolite, Z), organic materials (biochar, B and compost, C), and their combination on the immobilization of Cd in soil and its uptake by lettuce. The objective was to identify the most suitable soil amendment combination that promotes safe lettuce production. The results revealed that the combined application of BC, LZC, and LBC significantly increased the plant height by 11.09-28.04% and fresh weight by 183.47-207.67%. This improvement can be attributed to enhanced soil quality, such as increased dissolved organic carbon (DOC) by 70.19-80.42%, soil respiration (SR) by 29.04-38.46%, and soil microbial carbon content (SMC) by 36.94-46.63%. Compared to inorganic fertilizers and their combination with organic amendments, organic amendments had a significant impact on reducing shoot Cd concentration by 33.93%-56.55%, while increasing the activity of catalase by 138.87-186.86%. And soil available Cd measured by diffusive gradients in thin-films (DGT-Cd) decreased 24.73-88.13% in all treatments. Correlation analysis showed that plant Cd concentration was significantly correlated with soil pH, SR, cation exchange capacity (CEC), DOC and SMC. These results demonstrated that organic amendments, especially the combination of biochar and compost, have greater potential than inorganic amendments and inorganic-organic combinations for realizing safe production of lettuce and improving soil quality in the Cd moderately contaminated acid farmland.

Aquaculture sediments amended with biochar improved soil health and plant growth in a degraded soil

Sustainable and safe management of aquaculture sediments is of great concern. Biochar (BC) and fishpond sediments (FPS) are rich in organic carbon and nutrients and thus can be used as soil amendments; however, it is not fully explored how the biochar amended fishpond sediments can affect soil properties/fertility and modulate plant physiological and biochemical changes, particularly under contamination stress. Therefore, a comprehensive investigation was carried out to explore the effects of FPS and BC-treated FPS (BFPS) on soil and on spinach (Spinacia oleracea L.) grown in chromium (Cr) contaminated soils. Addition of FPS and BFPS to soil caused an increase in nutrients content and reduced Cr levels in soil, which consequently resulted in a significant increase in plant biomass, chlorophyll pigments, and photosynthesis, over the control treatment. The most beneficial effect was observed with the BFPS applied at 35 %, which further increased the antioxidant enzymes (by 2.75-fold, at minimum), soluble sugars by 24.9 %, and upregulated the gene expression activities. However, the same treatment significantly decreased proline content by 74.9 %, Malondialdehyde by 65.6 %, H₂O₂ by 65.1 %, and Cr concentration in spinach root and shoot tissues. Moreover, the average daily intake analysis showed that BFPS (at 35 %) could effectively reduce human health risks associated with Cr consumption of leafy vegetables. In conclusion, these findings are necessary to provide guidelines for the reutilization of aquaculture sediments as an organic fertilizer and a soil amendment for polluted soils. However, more future field studies are necessary to provide guidelines and codes on aquaculture sediments reutilization as organic fertilizer and soil amendment for polluted soils, aiming for a more sustainable food system in China and globally, with extended benefits to the ecosystem and human.

Evaluation of Essential, Toxic and Potentially Toxic Elements in Leafy Vegetables Grown in the Canary Islands

Forty-seven elements in leafy green vegetables were studied to estimate the daily intakes from this food category in different scenarios (average and high consumers) and age groups of the Canary Islands population. The contribution of the consumption of each type of vegetable to the reference intakes of essential, toxic and potentially toxic elements was assessed and the risk-benefit ratio was evaluated. The leafy vegetables that provide the highest levels of elements are spinach, arugula, watercress and chard. While spinach, chard, arugula, lettuce sprouts and watercress were the leafy vegetables with the highest concentrations of essential elements (38,743 ng/g of Fe in spinach, 3733 ng/g of Zn in watercress), the high levels of Mn in chard, spinach and watercress are noteworthy. Among the toxic elements, Cd is the element with the highest concentration, followed by As and Pb. The vegetable with the highest concentration of potentially toxic elements (Al, Ag, Be, Cr, Ni, Sr and V) is spinach. In average adult consumers, while the greatest contribution of essential elements comes from arugula, spinach and watercress, insignificant dietary intakes of potentially toxic metals are observed. Toxic metal intakes from the consumption of leafy vegetables in the Canary Islands do not show significant values, so the consumption of these foods does not pose a health risk. In conclusion, the consumption of leafy vegetables provides significant levels of some essential elements (Fe, Mn, Mo, Co and Se), but also of some potentially toxic elements (Al, Cr and Tl). A high consumer of leafy vegetables would see their daily nutritional needs regarding Fe, Mn, Mo, and Co covered, although they are also exposed to moderately worrying levels of Tl. To monitor the safety of dietary exposure to these metals, total diet studies on those elements with dietary exposures above the reference values derived from the consumption of this food category, mainly Tl, are recommended.

A Dark Septate Endophyte Improves Cadmium Tolerance of Maize by Modifying Root Morphology and Promoting Cadmium Binding to the Cell Wall and Phosphate

Dark septate endophytes (DSEs) can improve the performance of host plants grown in heavy metal-polluted soils, but the mechanism is still unclear. A sand culture experiment was performed to investigate the effects of a DSE strain (Exophiala pisciphila) on maize growth, root morphology, and cadmium (Cd) uptake under Cd stress at different concentrations (0, 5, 10, and 20 mg·kg^-1). The results indicated that the DSE significantly improved the Cd tolerance of maize, causing increases in biomass, plant height, and root morphology (length, tips, branch, and crossing number); enhancing the Cd retention in roots with a decrease in the transfer coefficient of Cd in maize plants; and increasing the Cd proportion in the cell wall by 16.0-25.6%. In addition, DSE significantly changed the chemical forms of Cd in maize roots, resulting in decreases in the proportions of pectates and protein-integrated Cd by 15.6-32.4%, but an increase in the proportion of insoluble phosphate Cd by 33.3-83.3%. The correlation analysis revealed a significantly positive relationship between the root morphology and the proportions of insoluble phosphate Cd and Cd in the cell wall. Therefore, the DSE improved the Cd tolerance of plants both by modifying root morphology, and by promoting Cd binding to the cell walls and forming an insoluble phosphate Cd of lower activity. These results of this study provide comprehensive evidence for the mechanisms by which DSE colonization enhances Cd tolerance in maize in root morphology with Cd subcellular distribution and chemical forms.

Pseudomonas aeruginosa improved the phytoremediation efficiency of ryegrass on nonylphenol-cadmium co-contaminated soil

The effect of Pseudomonas aeruginosa (P. aeruginosa) on the phytoremediation efficiency of ryegrass on soil contaminated with nonylphenol (NP) and cadmium (Cd) was investigated by pot experiments. Pseudomonas aeruginosa application stimulated the adsorption of Cd by ryegrass and facilitated the biodegradation of NP in the soil. Exogenous P. aeruginosa inoculation increased the activities of urease, dehydrogenase, and polyphenol oxidase in the soil of the T4 treatment by 38.5%, 50.0%, and 56.5% compared to that of the T2 treatment, respectively. There was a significant positive correlation between the activities of dehydrogenase and polyphenol oxidase and the NP removal rate (P < 0.001). The relative abundances of beneficial microorganisms (such as Sphingomonas, Lysobacter, Streptomyces, Chloroflexia, Deltaproteobacteria, and Alphaproteobacteria) were increased as a result of P. aeruginosa inoculation. These microorganisms play important roles in nutrient cycling, Cd adsorption, and NP degradation. Additionally, P. aeruginosa was not the dominate bacterial species at the end of the experiment. According to this study, P. aeruginosa application improved the phytoremediation efficiency of ryegrass on soil contaminated with NP and Cd, with a minimal risk of alien microbial invasion.

Potentially toxic elements in iron mine tailings: Effects of reducing soil pH on available concentrations of toxic elements

Tailings from iron mining are characterized by high concentrations of iron and manganese oxides, as well as high pH values. With these characteristics, most of the potentially toxic elements (PTE) contained in the tailings are somewhat unavailable. The aim of the present study was to evaluate how a reduction in the pH of iron mine tailings may affect PTE availabilities. The tailings were collected on the banks of the Gualaxo do Norte River (Mariana, MG, Brazil), one of the main areas impacted by the rupture of the Fundão Dam (Barragem de Fundão). A completely randomized experimental design was used, including five pH values (6.4, 5.4, 4.3, 3.7, and 3.4) and five replications. The concentrations of the PTE (Ba, Cr, Cd, Co, Cu, Fe, Mn, Pb, Ni, and Zn) were determined after extraction following different methodologies: USEPA 3051A, DTPA, Mehlich-1, Mehlich-3, and distilled water. A comparison of the available concentrations of the elements in the tailings with those in a soil not impacted by tailings shows that Cr, Cd, Cu, Fe, Mn, Ni, Ba, and Co were higher in the soil impacted by the tailings. The different methods used for evaluating the availability of PTE in the tailings at various pH exhibited the following decreasing order in relation to the quantity extracted: Mehlich-3 > Mehlich-1 > DTPA > distilled water. However, regarding sensitivity to change in pH, the order was DTPA > water > Mehlich-1 > Mehlich-3. The increases in the concentrations of PTE due to the reduction in the pH of the tailings did not lead to concentrations that exceed the limits of Brazilian regulations. The DTPA extractant exhibited higher coefficients of correlation between the PTE concentrations and the pH of the tailings, proving to be suitable for use in areas affected by the deposition of iron mine tailings.

Collinear double-pulse laser-induced breakdown spectroscopy based Cd profiling in the soil

Cadmium (Cd) can migrate in the soil and is readily absorbed by crops. High Cd accumulated in grains poses a huge threat to human health by inhibiting the function of the kidney system. Thus, it is crucial to reveal the content of soil Cd in vertical-depth series using a fast, real-time, and reliable method. For this purpose, laser-induced breakdown spectroscopy (LIBS) combined with multivariate chemometrics was developed to analyze Cd content in the soil with vertical-depth series. Soil samples spiked with different levels of Cd were prepared, and LIBS spectra were obtained by single-pulse LIBS (SP-LIBS) and collinear double-pulse LIBS (CDP-LIBS) with wavelengths of 532 nm and 1064 nm. With appropriate parameters, CDP-LIBS showed better performance in detecting Cd than SP-LIBS. Partial least squares regression (PLSR), genetic algorithm (GA)-optimized back propagation artificial neural network (BP-ANN), and particle swarm optimization (PSO)-optimized least squares-support vector machine (LS-SVM) were tested for quantitative analysis of the spectra after median absolute deviation (MAD), multiple scattering correction (MSC), wavelet transform (WT), spectral averaging, and normalization. PSO-optimized LS-SVM yielded an ideal result, with a coefficient of determination (R², 0.999) and root mean square error (RMSE, 0.359 mg/Kg) in the prediction dataset. Finally, CDP-LIBS coupled with PSO-optimized LS-SVM was employed to analyze soil Cd content in vertical-depth series to reveal the migration pattern of Cd. Our results indicated that soil Cd had a significant positive relationship with the inverse of soil depth. However, Cd was mainly concentrated in 0-20 cm and rarely leached below 45 cm in the soil. This study suggests that LIBS and its enhancement techniques provide a reliable method for revealing the content of soil Cd in vertical-depth series.

Differential toxicity of potentially toxic elements to human gut microbes

Specific microorganisms in the human gut (i.e., gut microbes) provide mutually beneficial outcomes such as microbial balance by inhibiting the growth of pathogenic organisms, immune system modulation, fermentation of ingested products, and vitamin production. The intake of contaminants including potenially toxic elements (PTEs) can occur through food, air, water and some medicines. The gut microbes not only can be affected by environmental contaminants but they themselves can alter the speciation and bioavailability of these contaminants. This research work was designed to demonstrate the relationship between increasing level of selected PTEs including As, Cd, Pb and Hg on the growth of selected gut microbes. The toxicity of above mentioned PTEs to three gut bacteria (Lactobacillus rhamnosus, Lactobacillus acidophilus and Escherichia coli) was examined. While the toxicity of all the cationic PTEs including Cd, Pb and Hg towards gut bacteria decreased with increasing pH, the anionic As species exhibited an opposite effect. The order of toxicity was Hg > Cd > Pb > As(III)>As(V) for E. coli; and Hg > Cd > As(III)>Pb > As(V) for the two Lactobacillus sp. Arsenite (AsIII) showed higher toxicity than arsenate (AsV) to gut bacteria. While As is an anion, Cd, Pb and Hg are cations and hence their binding capacity to the bacterial cell wall varied based on the charge dependent functional groups. However, the toxic effects of PTEs for a bacteria are controlled by their speciation and bioavailability.

Crop selection reduces potential heavy metal(loid)s health risk in wastewater contaminated agricultural soils

Vegetable crops have varied heavy metal(loid)s accumulation rates from soils to their edible tissues. However, crop selection has been seldom evaluated as a strategy for reducing the health risks of ingesting vegetables grown in soils contaminated by treated wastewater (TWW) irrigation. We cultivated twenty commonly grown vegetables using soils with an approximately 50-year history of TWW irrigation, and their ingestion risks were evaluated by the health risk index (HRI). Results showed that twenty vegetable species had varied abilities in accumulating heavy metal(loid)s from soils to their edible parts (e.g., >100 times of difference for Cd). We found higher potential health risks (HRI > 1) due to As, Cd, and Pb for adults ingesting few vegetable species and all the studied vegetables had negligible health risks (HRI < 1) for Cr, Cu, and Zn. These results suggest that remediation strategies should be targeted towards As, Cd, and Pb removal in agricultural soils in this region. Total HRI > 5 was obtained for ingesting spinach, Chinese lettuce, and Chinese chives, suggesting a high potential of severe health risks. Negligible risks (total HRI < 1) were found for tomato, kidney bean, potato, and cabbage. Our study highlights crop selection as a feasible strategy for ensuring food safety in TWW contaminated farmlands.

Evaluating a Sampling Regime for Estimating the Levels of Contamination and the Sources of Elements in Soils Collected from a Rapidly Industrialized Town in Guangdong Province, China

Gaogang Town, a typical urban center within the Pearl River Delta region of China, suffers contamination of soils with metals/metalloids due to rapid development of industrial activities and agriculture. Few studies have been conducted to systematically describe the main sources, influencing factors, and ecological risks of metals/metalloids in soils in China. In this study, 312 surface soil samples were collected, and 15 elements were detected by plasma emission spectroscopy, atomic fluorescence spectroscopy, and atomic emission spectrometry. Element content features were analyzed by index of geo-accumulation (I_geo), pollution load index (PLI), potential ecological risk index (RI), positive matrix factorization model (PMF), and geostatistical analysis. The PLI value is between 0 and 1, indicating that the whole study area is lightly polluted. Combining PMF model and geostatistical analysis, soil elements in surface soils of Gaogang town were quantitatively apportioned into four sources: parent material and basic substances (23.5%), natural sources (32.2%), agricultural activities and industrial pollution (22.9%), and transportation (21.4%). The comprehensive analysis results show that polluted areas are mainly distributed on roads, rivers, and industrial and human activity areas. The main sources of ecological risks are factory pollution and human activity. Finally, we found that a quarter of the sampling density was the best sample size for this study.

Distribution of heavy metals in surface soil near a coal power production unit: potential risk to ecology and human health

Coal thermal power plants are the dominant factor in producing various hazardous elements in surrounding surface soil, resulting in a significant human health hazard. In the current study, the seasonal (pre- and post-monsoon) concentration of As, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb, and Zn in surface soil around coal power production unit was analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). The possible health risks throughout multiple exposure routes, i.e., ingestion, dermal, and inhalation were estimated for adult and children. Furthermore, geo-accumulation index (Igeo), enrichment factor (EF), pollution factor (CF), ecological risk index, and pollution load index (PLI) were applied to interpret the environmental pollution in the study area. The geospatial distribution pattern was computed to understand the trace and hazardous element distribution in the surface soil. As a result, the concentration of Fe (mg/kg) in pre-monsoon (15,620) and post-monsoon (27,180), Ni (mg/kg) in pre-monsoon (19.8), and post-monsoon (81.7) was found above the standard limits of soil prescribed by the WHO and FAO. Enrichment factor was observed between 0.95-6948 (pre-monsoon) and 0.53-116.09 (post-monsoon). The ecological risk index was found moderate to considerable for As and Cd metals during both seasons. In addition, the average PLI value was observed high for both seasons indicating the contamination of the study area with heavy metals. Moreover, Igeo values for Fe, Mg, and As were found relatively high. Conversely, health risks to the human population were found within the USEPA acceptable limits.

Toxic element contents and associated multi-medium health risk assessment in an area under continuous agricultural use

Soils and contaminated plants are in the group of significant environmental pathways of human exposure to toxic elements (TEs). This study aimed to assess the soil-to-plant transfer of TEs (Pb, As, Cd, Hg), as well as the plausible health risks via different exposure pathways in the Armavir region of Armenia. The contents of TEs were determined in soil, fruit and vegetable samples using X-ray fluorescence and atomic absorption spectroscopy, respectively, and the soil-to-plant transfer of TEs and induced chronic non-carcinogenic risks were evaluated. The detected TE contents did not exceed the available national and international regulatory levels. Moreover, the evaluated soil-to-plant transfer of these TEs was negligible. The obtained results indicated the absence of a single-element non-carcinogenic risk via one single ingestion pathway. Meanwhile, in the case of multi-food and multi-soil ingestion, the combined non-carcinogenic risk estimates for Pb and As exceeded the precautionary level of 0.1 indicating a low health risk. Similarly, the multi-element hazard index (HI) showed a low level of non-carcinogenic risk through a multi-pathway ingestion. Thus, the outcomes highlighted that there was a need for precautionary measures to prevent plausible health issues for the adult population in Armavir.

Deciphering Cadmium (Cd) Tolerance in Newly Isolated Bacterial Strain, Ochrobactrum intermedium BB12, and Its Role in Alleviation of Cd Stress in Spinach Plant (Spinacia oleracea L.)

A cadmium (Cd)-tolerant bacterium Ochrobactrum intermedium BB12 was isolated from sewage waste collected from the municipal sewage dumping site of Bhopal, India. The bacterium showed multiple heavy metal tolerance ability and had the highest minimum inhibitory concentration of 150 mg L-1 of Cd. Growth kinetics, biosorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy studies on BB12 in the presence of Cd suggested biosorption as primary mode of interaction. SEM and TEM studies revealed surface deposition of Cd. FTIR spectra indicated nitrogen atom in exopolysaccharides secreted by BB12 to be the main site for Cd attachment. The potential of BB12 to alleviate the impact of Cd toxicity in spinach plants (Spinacia oleracea L.) var. F1-MULAYAM grown in the soil containing Cd at 25, 50, and 75 mg kg-1 was evaluated. Without bacterial inoculation, plants showed delayed germination, decrease in the chlorophyll content, and stunted growth at 50 and 75 mg kg-1 Cd content. Bacterial inoculation, however, resulted in the early germination, increased chlorophyll, and increase in shoot (28.33%) and root fresh weight (72.60%) at 50 mg kg-1 of Cd concentration after 75 days of sowing. Due to bacterial inoculation, elevated proline accumulation and lowered down superoxide dismutase (SOD) enzyme activity was observed in the Cd-stressed plants. The isolate BB12 was capable of alleviating Cd from the soil by biosorption as evident from significant reduction in the uptake/translocation and bioaccumulation of Cd in bacteria itself and in the plant parts of treated spinach. Potential PGP prospects and heavy metal bioremediation capability of BB12 can make the environmental application of the organism a promising approach to reduce Cd toxicity in the crops grown in metal-contaminated soils.

Metal-tolerant Pantoea sp. WP-5 and organic manures enhanced root exudation and phytostabilization of cadmium in the rhizosphere of maize

This study investigated the phytoremediation potential of maize (Zea mays L.) in Cd-contaminated soil through co-inoculation of metal-tolerant plant beneficial rhizobacteria (MtPBR: Pantoea sp. strain WP-5) with organic manures (PM, poultry manure, and BGR, biogas residues). The objectives of this study were to (i) examine comparative efficiency of MtPBR, PM and BGR alone or in combined form to improve maize biomass and physiology and (ii) understand the role of organic acid production in root exudates of maize for Cd accumulation and translocation. Pantoea sp. WP-5 showed organic acid production and tolerance to high Cd concentration (1000 mg L^-1), thereby inoculated to maize seeds sown in soil spiked with 75 mg Cd kg^-1 soil and 500 g each of the organic manures per pot. The co-inoculation of MtPBR + BGR significantly (P<0.05) increased chlorophyll contents, root/shoot dry weight, photosynthetic rate, stomatal conductance, and relative water contents and decreased electrolyte leakage, malondialdehyde contents, ascorbate peroxidase, and catalase activity in maize over the control treatment. The co-inoculation of MtPBR + BGR produced significantly (P<0.05) higher concentrations of acetic and citric acid (52.7±0.5 and 22.8±0.08 μg g^-1 root fwt, respectively) in root exudates of maize, which immobilized Cd within plant roots inferred by the positive relation (root Cd vs. organic acids; R² = 0.80-0.92) and reduced Cd translocation to shoots inferred by the negative relation (shoot Cd vs. organic acids; R² = 0.81-0.90). It is concluded that the application of MtPBR + BGR enhanced organic acid induced phytostabilization and accumulation of Cd in roots and restricted its translocation to shoots.

The effects of a combined amendment on growth, cadmium adsorption by five fruit vegetables, and soil fertility in contaminated greenhouse under rotation system

Cadmium (Cd) exposure is related to a multitude of adverse health outcomes because food crops grown on Cd-polluted soil are widely consumed by the public. The present study investigates the different application techniques of a combined amendment (lime + zeolite + biochar + compost, LZBC) for soil Cd immobilization effect on growth performance, Cd uptake by the second season crops, and soil quality in greenhouse vegetable production (GVP) under a rotation system. Five fruit vegetables were cultivated as the second season crop in the same plots which have been used for pakchoi as the first season crop (with or without LZBC application). The results indicated that LZBC with the consecutive application (T3) promoted crops biomass and fruit yield the most, followed by LZBC with the second crop application (T2) and LZBC with the first crop application (T1). LZBC application showed increasing rhizosphere soil pH and improvement in soil fertility of all crops including available nitrogen, available phosphorus, available potassium, organic matter, and cation exchange capacity. LZBC had positive influences on soluble sugar, soluble protein, and vitamin C in edible parts of 5 vegetables. Cd contents in fruit, shoot, and root of eggplant, pimento, cowpea, and tomato except cucumber were reduced by adding LZBC. As for the economic performance, T3 had the highest output/input ratio in general. Overall, these results demonstrated that T3 was dramatically more effective for minimizing health risk, increasing production, and facilitating sustainable utilization of soil under the Cd-contaminated GVP system.

Selenium improved the combined remediation efficiency of Pseudomonas aeruginosa and ryegrass on cadmium-nonylphenol co-contaminated soil

Most chemical plant wastewater contains both organic and inorganic pollutants, which are easy to diffuse along with surface runoff. The combined pollution of nonylphenol (NP) and cadmium (Cd) in soil is a serious problem that has not attracted enough attention. Based on the effects of selenium (Se) and Pseudomonas aeruginosa (P. aeruginosa) on plant and soil microbial communities, we speculated that the application of Se and P. aeruginosa in soil could improve the phytoremediation efficiency of ryegrass on contaminated soil. In this study, pot experiments with Cd and NP co-contaminated soil were conducted, and the results showed that application of P. aeruinosa alone could improve the removal rates of NP and Cd by ryegrass, and the supplementary of Se further enhanced the effect of micro-phyto remediation, with the highest removal rates of NP and Cd were 79.6% and 49.4%, respectively. The application of P. aeruginosa plus Se reduced the adsorption of Cd and NP through C-O and Si-O-Fe of the soil, changed the enzyme activity, and also affected the changing trend of the microbial community in soil. Pseudomonas, Sphingomonadales, Nitrospira, and other beneficial bacteria were enriched after a 60-day period with P. aeruginosa and Se treatment, thus promoting the removal of NP and Cd. In light of the above results, we suggest that P. aeruginosa application can efficiently facilitate the phytoremediation of ryegrass on Cd-NP co-contaminated soil, and Se supplementation in soil showed the synergistic effect on the remediation.

Challenges in microbially and chelate-assisted phytoextraction of cadmium and lead - A review

Cadmium (Cd) and lead (Pb) are ubiquitously present in surface soils, due to anthropogenic activities, causing threat to ecological and human health because of their carcinogenic nature. They accumulate in large quantities in the environment and affect negatively soil microbiota, plants, animals, and humans. For the cleanup of Cd/Pb polluted soils, different plant species have been studied. Many plants have shown the potential to hyperaccumulate Cd/Pb in their above-ground tissues. These plants decrease soil pH by root exudation or by releasing H⁺ ions, and this, in turn, increases the bioavailability of Cd/Pb for plant uptake. Different environmental processes related to soil organic matter, microorganisms, pH, genetic modifications, and various soil-borne chelating agents affect the potential of phytoremediation technology. Review papers trying to identify a single factor influencing the phytoremediation of heavy metals are available in the literature. However, an integrated approach dealing with different factors involved in the remediation of both metals is scarcely discussed. The main focus of this review is to discuss the phytoextraction technique for Cd/Pb removal from contaminated sites along with detoxification mechanisms. Further, the challenges in the Cd/Pb phytoextraction and different options available to cope with these challenges are also discussed. The update on the relevant findings on the use of microorganisms and amendments in enhancing the Cd/Pb phytoextraction is also provided. Finally, the areas to be explored in future research for the removal of Cd/Pb by integrated strategies have been discussed.

Portulaca oleracea L. for phytoremediation and biomonitoring in metal-contaminated environments

In phytoremediation and biomonitoring, plants are used to clean and monitor contaminated environments, respectively. Thus, scientists are searching for ideal plants, i.e., those that rapidly uptake and accumulate a considerable quantity of contaminants in their tissues, with or without toxicity symptoms. All these aspects are satisfied by the annual herbaceous plant Portulaca oleracea L. P. oleracea L. is ranked eighth as "most common plant in the world" and twelfth as "non-cultivating species well colonise[d] in new areas." Because of its fast regeneration of shoots and roots from leaves and roots and leaves from the stem and its tolerance capacity for metal stress, this plant has been used for phytoremediation and biomonitoring studies in the field, as well as in pot and hydroponics studies. The growth attributes of this plant in metal-stressed environments and the uptake of metals from its growth media (via the root), which is followed by the accumulation of the metals in its tissues, have been studied. Metal is translocated from the root into the shoot and is calculated as the translocation factor, TF; the metal taken from the soil into the plant is calculated as the bioaccumulation factor, BAF. These measures have been used to determine the hyperaccumulation (uptake and storage of unusually large amounts of metals) potential of the plant. This review article critically evaluates the literature studies to increase the practicability of phytoremediation and biomonitoring approaches using various life stages of P. oleracea.

Cadmium (Cd) and zinc (Zn) accumulation by Thai rice varieties and health risk assessment in a Cd-Zn co-contaminated paddy field: Effect of soil amendments

Zinc mining and smelting activities result in cadmium (Cd) and zinc (Zn) contamination in rice grains, causing deleterious impacts on human health and local economies. Here, we investigated the effects of soil amendments, including mixtures of dicalcium phosphate with cattle manure (T1) and leonardite (T2), on soil physicochemical properties as well as growth performance and accumulation of Cd and Zn among three commercial Thai rice varieties: Khao Dok Mali 105 (KDML105), Phitsanulok2 (PSL2) and RD3, grown in a Cd-Zn co-contaminated paddy field. Human health risk was assessed using the health risk index (HRI) and Daily Intake of Metal (DIM). Application of the amendments, particularly T1, decreased Cd and Zn bioavailability by 60% and 39%, respectively, increased biomass production in PSL2 and RD3 varieties, and substantially reduced Cd uptake in the KDML105 variety by 47%. While levels of Zn in whole plant tissues of all treatments did not exceed maximum levels of undesirable substances in fodder, Cd contents in grain of PSL2 and RD3 exceeded the maximum allowable concentration of 0.2 mg kg^-1. The HRI values for Cd of PSL2 and RD3 varieties were relatively high and are considered to pose a potential risk to human health. KDML105 in the T1 treatment had the lowest HRI value (0.05 ± 0.03), which was within acceptable limits. Our results suggest that Cd and Zn accumulation in rice and associated human health risks could be reduced by application of amendments to paddy soils, but the effectiveness depends on amendment types, rice varieties and soil physicochemical properties.

Lead acetate ecotoxicity in tropical soils

Lead acetate (AcPb) is an important raw material used in chemical industries worldwide. The potential toxicity of AcPb is generally attributed to the presence of Pb. However, the effect of AcPb on the environment as a whole is still poorly known. This study aimed to evaluate AcPb toxicity on three standard species of soil invertebrates and two plant species using ecotoxicology tests. Three tropical soils (Oxisol, Inceptisol, and Tropical Artificial Soil (TAS)) were contaminated with different concentrations of AcPb and one dose of K-acetate (positive control). These soils were used in tests with Eisenia andrei (earthworm), Folsomia candida (springtail), Enchytraeus crypticus (enchytraeid), Zea mays (maize), and Phaseolus vulgaris (common bean). Dose-response curves obtained in the laboratory tests were used to estimate the EC₅₀ values for each species. Among invertebrates, the highest sensitivity to AcPb was observed for E. crypticus in the TAS (EC₅₀ = 29.8 mg AcPb kg^-1), whereas for E. andrei and F. candida the highest sensitivity was observed in the Oxisol (EC₅₀ = 141.9 and 1835 mg AcPb kg^-1, respectively). Folsomia candida was the least sensitive invertebrate species to AcPb in all soils. Among plant species, Z. mays was less sensitive (EC₅₀ = 1527.5 mg AcPb kg^-1) than P. vulgaris (EC₅₀ = 560.5 mg AcPb kg^-1) in the Oxisol. The present study evidenced that the toxicity of AcPb should not be attributed uniquely to the presence of Pb, as the treatment containing uniquely Ac provoked the same toxicity as the highest dose of AcPb.

Health risks connected with ingestion of vegetables harvested from heavy metals contaminated farms in Western Nigeria

Investigation of lead (Pb), cadmium (Cd), zinc (Zn) and chromium (Cr) in soils and vegetables; and the consequent health risks connected with ingestion of the vegetables was conducted at Agbabu farm (F) settlement close to bitumen mining area of Ondo State, Nigeria. Soil and eleven vegetables were sampled from ten farms (Fs) and analyzed for Pb, Cd, Zn and Cr concentrations. Health risk parameters such as daily intake of metal (DIM), health risk index (HRI), target health quotient (THQ), and total diet target health quotient (TTHQ) were evaluated. Except Cd, other metals in soils were below their respective maximum allowable concentrations (MACs) set for agro soils. Only Cd and Pb were higher in vegetables than their respective MACs. Bioconcentration factors (BCFs) of the metals were higher in Talinum triangulare but lower for Cd, Zn, Cr and Pb in Solanum macrocarpon, Vernonia amygdalina, Ocimum gratissimum, and Taraxacum officinale respectively. DIMs of Cd, Zn and Pb for adults and children were higher than 0.0035, 0.001 and 0.300 mg/kg/day respective values of oral reference doses (RfD). The DIMs of Cr ingestion by children were above the RfD of Cr for all vegetables, while DIMs of ingesting Cr by adults were above Cr RfD for some vegetables. The (HRI >1) for Pb, Cd and Zn; (THQ >1) for Pb, Cd; and (TTHQ >1) indicated health risks in connection with the ingestion of these vegetables. These health risks were higher for children.

Application of DGT/DIFS to assess bioavailable Cd to maize and its release in agricultural soils

Tianjin, as an important maize production region in China, has a long history of sewage irrigation resulting in the soil cadmium (Cd) contamination. In this study, single extractions of CaCl₂ and HNO₃, BCR sequential extraction and the diffusive gradients in thin films technique (DGT) were used to measure the bioavailable Cd content in soils. The Cd content in soil samples all exceeded the background values, with 14.3% and 33.3% of sites in the Baodi District (BDD) and Jinghai District (JHD) exceeding the risk control values, respectively. The average content of Cd in maize samples is lower than the pollution control values, which may be related to the higher pH (8.53) and organic matter (OM) content (15.01 g kg^-1) in soils. Bioavailable Cd measured by DGT correlated well with Cd in maize grains (R² =0.92). The DGT and DIFS model predicted the metals release from the agricultural lands, the total concentration of Cd in soil was relatively low, but the labile Cd in the soils has adequate metal release capability. This study shows that DGT is efficient in predicting Cd accumulation in grains from contaminated soils.

Lead and cadmium exposure network in children in a periurban area in India: susceptibility and health risk

To investigate the complex Pb-Cd exposure network in school-going children, a thorough investigation of the probable exposure means (diet, water, and school micro-environments such as paint dust and school courtyard soil) and exposure route (ingestion, inhalation and dermal) was carried out in a periurban area spanning three districts in southern Assam, India. Multivariate statistical analysis was carried out to understand the complex data matrices, and the health risk assessments (carcinogenic and non-carcinogenic) based on US EPA Risk Assessment models were also made. We found the median values to be 0.9-4.0 mg Pb/kg and 0.21-6.2 mg Cd/kg in various food items. Groundwater also had Pb (0.13-0.48 mg/L) and Cd (0.11-0.29 mg/L). Pb levels in paint dust were within the permissible limits, but 50% of the samples had higher than permissible levels of Cd. Approximately 23% of the school courtyard soil had Pb above the global background levels, but all the samples had 4-27 times elevated levels of Cd in them. School micro-environment contributed significantly to the metal load in children due to their typical hand-to-mouth behavior and dietary intake (food and water) via ingestion was the most prominent route of exposure in children. The evaluation of the estimated chronic daily intake and the hazard quotient indicated hazardous exposure over a lifetime to both Pb and Cd, but only Cd posed a prominent cancer risk. It could be concluded that chronic insidious effects of metals would be a noteworthy toxicological threat to children when exposed early on.

Recycling of bottom ash derived from combustion of cattle manure and its adsorption behaviors for Cd(II), Cu(II), Pb(II), and Ni(II)

Bottom ash generated by the combustion of cattle manure (BA-CCM) was investigated as an adsorbent for the removal of heavy metals such as Cd(II), Cu(II), Pb(II), and Ni(II) from aqueous solutions. When cattle manure was used as fuel, the thermal efficiency of the boiler was 88.7%, and the CO and CO₂ concentrations in the exhaust gas were 2.3 ppm and 12.1%, respectively. The percentage of remaining solids was 31 wt.% after combustion at 900 °C. X-ray fluorescence analyses showed that the elemental composition of the BA-CCM was mainly CaO (43.3%), SiO₂ (15.8%), CO₂ (13.0%), and P₂O₅ (10.3%). The kinetic adsorption of Cd(II), Cu(II), Pb(II), and Ni(II) by BA-CCM reached equilibrium after 12 h, and the pseudo-second-order model fitted the experimental data well. The maximum amount of Cd(II), Cu(II), Pb(II), and Ni(II) adsorbed by the bottom ash was 5.4, 72.6, 88.2, and 24.6 mg/g, respectively. The equilibrium adsorption of metals onto BA-CCM was well-described by the Freundlich model. Thermodynamic analysis showed that the adsorption onto the bottom ash was endothermic and that the Gibbs free energy decreased as the temperature increased. The presence of cations such as Na⁺, Ca²⁺, and Al³⁺ was found to reduce the amount of metals adsorbed onto the BA-CCM, and Cd(II) adsorption was found to be more dependent on ionic strength than adsorption of Cu(II), Pb(II), and Ni(II). This study demonstrates the feasibility of producing heat energy by burning cattle manure and removing heavy metals from aqueous solutions using the generated bottom ash as an adsorbent.

Zinc oxide nanocatalyst mediates cadmium and lead toxicity tolerance mechanism by differential regulation of photosynthetic machinery and antioxidant enzymes level in cotton seedlings

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ZnONPs enhanced plant growth and biomass by alleviation of heavy metal toxicity.

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Increased level photosynthetic pigments, MDA and protein contents recorded in cotton leaves in co-presence of ZnONPs.

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The activity of antioxidative enzymes was promoted significantly in the presence of ZnONPs under Cd and Pb induced stress.

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No distinct genomic alterations were recorded in the RAPD banding pattern.

Cadmium (Cd) and Lead (Pb) heavy metal pollution induced toxicity severely affects the plant growth and yield of various agriculutral crops worldwide. The present study discuss the prime role of phycomolecules coated zinc oxide nanoparticles (ZnONPs) application on development of heavy metal tolerance mechanism in cotton (Gossypium hirsutum L.) seedlings better than exposed to Cd and Pb treatments alone. Co-exposure of ZnONPs along with heavy metal treatments significantly promoted the shoot, and root growth as well as biomass compared to control, while it was down-regulated in Cd and Pb exposed seedlings. The intervention of ZnONPs had up-regulated the level of chlorophyll a, b and carotenoid contents in leaves grown under Cd and Pb treatments than the untreated control. Similarly, the level of total soluble protein and malondialdehyde (MDA-lipid peroxidation) contents was significantly increased in the co-presence of ZnONPs along with Cd and Pb treatments over their respective control. Accumulation of antioxidant defense enzymes viz., superoxide dismutase (SOD), catalase (CAT), peroxidase (POX) and ascorbate peroxidase (APX) was up-regulated significantly in seedlings upon co-exposure of ZnONPs with Cd and Pb treatments. Random amplified polymorphic DNA (RAPD) fingerprinting analysis exhibited no genomic changes/alterations in seedlings by co-existence of ZnONPs with heavy metals. Overall, the present results indicate that the addition of ZnONPs with Cd and Pb ion exposure protects cotton seedlings by alleviating heavy metal induced phytotoxicity and promoted physiochemical characteristics via differential regulation of photosynthetic machinery as well as antioxidative defense mechanisms in cotton seedlings. Results strongly suggest that phycomolecule coated ZnO nanoparticles could be effectively used as nanofertilizer to cultivate agronomically important crops in heavy metal polluted soil in the future.

Effect of different industrial activities on soil heavy metal pollution, ecological risk, and health risk

Soil heavy metal (Cr, Cu, Zn, Pb, Cd, V, As) concentrations in different areas were analyzed to investigate the effects of different industrial activities on heavy metal pollution status, potential ecological risk, and human health risk in Panzhihua. Our results showed that Cu and V enrichment in soil was due to ore smelting. Soil Cr accumulation was related to coal ore mining. Soil Cd, Zn, As, and Pb enrichment was attributed to high-temperature coal combustion. Under the effect of industrial activities, soils were moderately contaminated with Cd, uncontaminated to moderately contaminated with As and Zn, and uncontaminated with Cr, Cu, V, and Pb. Soil heavy metal potential ecological risk was considerable, and non-carcinogenic risks and carcinogenic risks of soil heavy metals were acceptable for adults but unacceptable for children. Thermal power generation was the dominated industrial activity that influence the soil heavy metal concentrations and environmental risks in Panzhihua, which posed considerable potential ecological risks and unacceptable heavy metal non-carcinogenic risks and As carcinogenic risk to both adults and children. This study indicates that industrial activities have great effects on heavy metal pollution, ecological risks, and health risk, and more attention should be paid to the ecological risk and health risks brought by thermal power generation.

Follow-Up of Elevated Blood Lead Levels and Sources in a Cohort of Children in Benin

Lead exposure is associated with poor cognitive development in children. Very few studies in sub-Saharan Africa (SSA) have studied blood lead levels (BLLs) and non-gasoline sources of exposure in children. Data from a birth cohort in Benin (2011-2013) suggested that 58% of 1-year-old children had BLLs > 50 ug/L. We aimed to investigate the prevalence of elevated BLLs (>50 µg/L and >100 µg /L) among 425 of these children at 6 years of age in 2016-2018 and to compare BLLs between age 1 and 6 years, and study sources of lead at age 6 years. BLLs were analysed by inductively coupled plasma mass spectrometry. Multiple linear regression and quantile regressions were used to study potential sources of lead. The prevalence of BLLs > 50 µg/L in children was 59.5% (Geometric Mean (GM) 56.4 µg/L, 95% CI: 54.1-58.7) at 6 years of age compared to 54.8% (GM 56.5 µg/L, 95% CI: 53.4-59.6) at 1 year of age. The prevalence of children with BLLs > 100 µg/L decreased from 14.4% at 1 year of age to 8.2% at 6 years of age. After adjustment for all other covariates, consumption of peanuts more than once per month was significantly associated with a 22.0% (95% CI: 4.6, 42.5) increment in BLLs at age 6 years compared with no consumption. Consumption of bushmeat killed by lead bullets at age 6 years was associated with an increase in the higher percentiles of BLLs (P75) compared with the absence of this source. Other potential sources of lead associated with BLLs with marginal significance were consumption of rice, paternal occupational exposure, and the presence of activity with the potential use of lead. This prospective cohort confirms the persistently high prevalence of elevated BLLs in children residing in a rural region in the south of Benin, as well as the presence of multiple and continuous sources of lead. These results highlight the need for prevention programs to reduce and eliminate lead exposure in children.

Environmental and health risk assessment of agricultural areas adjacent to uranium ore fields in Brazil

To investigate the risks posed by trace and rare earth elements (REEs) in two tropical uranium ore fields, metal concentrations from 50 vegetable samples (corn and soybean) and their corresponding agricultural soils were evaluated in a U mining area and a U-rich coal mining area in Brazil. Samples from both areas had metal concentrations (REE: La to Lu, and trace elements: As, Pb, Cd, Ni, Cu, Cr, Mn, Zn, Ba, U, Sr) that were higher than the guidelines proposed by the Brazilian environmental agency. Soils from the U mining area (Poços de Caldas) generally had higher contents of trace elements than the coal mining area (Figueira), with the exception of Ni and Cr, indicating a higher risk of pollution, which was confirmed by a pollution load index that was greater than unity. For both sites, concentrations of uranium in the soil and plants, its hazard quotients and the soil contamination factor were higher in agricultural fields closer to the mines, indicating that contamination and the consequent risks to human health were distance dependent. REE concentrations averaged 52.8 mg kg^-1 in the topsoils and 0.76 mg kg^-1 in the grains for Figueira, whereas higher values of 371 mg kg^-1 (topsoils) and 0.9 mg kg^-1 (grains) were found in Poços de Caldas. Based upon corn and soybean consumption, the estimated intake dose of the REE was lower than the intake dose predicted to be problematic for human health for both sites, indicating limited risk related to the ingestion of REE.

Evaluation of risk levels of trace elements in walnuts from China and their influence factors: Planting area and cultivar

The potential health risk of trace elements in nut foods has been widely concerned. The accumulations of trace elements by plants in the environment are disturbed by multiple factors. The objective of this work was to investigate the risk levels of trace elements in walnuts and their influence factors (planting area and cultivar). A total of 228 walnut samples were collected from four major walnut producing areas of China. The contents of essential elements for Fe, Cu, Zn, Mo and Se were 35.8, 21.9, 14.8, 0.3 and 0.04 mg/kg, respectively. The contribution of Cu for dietary reference intake was as high as 82.22%. The risk levels of potential toxicological elements and toxic elements within the acceptable limits. Significantly, the hazard quotients (HQs) of Ba and Co were up to 26.14% and 25.31%, respectively. The effect of planting area on trace elements was determined from the aspects of regional distribution and urbanization. Significant differences of essential elements were found between northeast and northwest areas. The urbanization directly influenced toxic elements, which could cause variation up to 85.0% (Pb) and 42.9% (As). Finally, cultivar effect was confirmed that all walnut cultivars were divided into four categories with different trace element characteristics.

Popular wood and sugarcane bagasse biochars reduced uptake of chromium and lead by lettuce from mine-contaminated soil

As a result of metal mining activities in Pakistan, toxic heavy metals (HMs) such as chromium (Cr) and lead (Pb) often enter the soil ecosystem, accumulate in food crops and cause serious human health and environmental issues. Therefore, this study examined the efficacy of biochar for contaminated soil remediation. Poplar wood biochar (PWB) and sugarcane bagasse biochar (SCBB) were amended to mine-contaminated agricultural soil at 3% and 7% (wt/wt) application rates. Lactuca sativa (Lettuce) was cultivated in these soils in a greenhouse, and uptake of HMs (Cr and Pb) as well as biomass produced were measured. Subsequently, health risks were estimated from uptake data. When amended at 7%, both biochars significantly (P<0.01) reduced plant uptake of Cr and Pb in amended soil with significant (P<0.01) increase in biomass of lettuce as compared to the control. Risk assessment results showed that both biochars decreased the daily intake of metals (DIM) and associated health risk due to consumption of lettuce as compared to the control. The Pb human health risk index (HRI) for adults and children significantly (P<0.01) decreased with sugarcane bagasse biochar applied at 7% rate relative to other treatments (including the control). Relative to controls, the SCBB and PWB reduced Cr and Pb uptake in lettuce by 69%, 73.7%, respectively, and Pb by 57% and 47.4%, respectively. For both amendments, HRI values for Cr were within safe limits for adults and children. HRI values for Pb were not within safe limits except for the sugarcane bagasse biochar applied at 7%. Results of the study indicated that application of SCBB at 7% rate to mine impacted agricultural soil effectively increased plant biomass and reduced bioaccumulation, DIM and associated HRI of Cr and Pb as compared to other treatments and the control.

The Recovery of Soybean Plants after Short-Term Cadmium Stress

BACKGROUND

Cadmium is a non-essential heavy metal, which is toxic even in relatively low concentrations. Although the mechanisms of Cd toxicity are well documented, there is limited information concerning the recovery of plants after exposure to this metal.

METHODS

The present study describes the recovery of soybean plants treated for 48 h with Cd at two concentrations: 10 and 25 mg/L. In the frame of the study the growth, cell viability, level of membrane damage makers, mineral content, photosynthesis parameters, and global methylation level have been assessed directly after Cd treatment and/or after 7 days of growth in optimal conditions.

RESULTS

The results show that exposure to Cd leads to the development of toxicity symptoms such as growth inhibition, increased cell mortality, and membrane damage. After a recovery period of 7 days, the exposed plants showed no differences in relation to the control in all analyzed parameters, with an exception of a slight reduction in root length and changed content of potassium, magnesium, and manganese.

CONCLUSIONS

The results indicate that soybean plants are able to efficiently recover even after relatively severe Cd stress. On the other hand, previous exposure to Cd stress modulated their mineral uptake.

Aging and trace elements in human coronal tooth dentine

Teeth are a fundamental tool in forensic odontology for identification in a legal context of those individuals who cannot be identified visually or by other means. Dentine presents physiological exchanges of in trace elements after a period of mineralization and several factors can affect its concentration. The aim of this study was to investigate the concentration of 25 trace elements in the coronal dentine according to sex and type of tooth to determine their relationship with age. A total of 25 trace elements were analyzed in 150 human coronal dentine. Teeth were classified into three age groups, sex and tooth type. The trace elements were grouped as potentially toxic or essential. Inductively Coupled Plasma-Mass Spectrometry and Atomic Emission Spectroscopy were used. The toxic and essential elements were detected in the following order of concentration: Al > Pb > Sn > Li > As > Cd and Ca > P > Mg > Na > S > K > Sr > Zn > Ba > Fe > B > Ti > Mn > Cr > Ni > Cu > Co > Se > V. Our findings show an increase in the concentration of toxic (Pb, Li and Sn) and essential (B, Ba, K, Sr, S and Mg) elements in coronal dentin related to the age of the teeth, regardless of sex. The concentrations of Pb and K in dentin of molars and premolars are the elements that best relate their variations with age. In view of our results, the analysis of these trace elements in dentin in combination with other types of techniques could be established as an element to consider in age dating studies in different forensic situations.

The hybridization between Sphagneticola trilobata (L.) Pruski and Sphagneticola calendulacea (L.) Pruski improved the tolerance of hybrid to cadmium stress

Hybridization is common between invasive and native species and may be accompanied by invasive evolution. The hybrid of Sphagneticola trilobata (alien invasive species) and Sphagneticola calendulacea (indigenous congener) was found in South China. According to previous studies, the hybrid performed weak environmental adaptability in comparison with parents. However, based on the results from this study, the hybridization significantly improved the tolerance of the hybrid to cadmium (Cd) stress (200 μmol L^-1). Under Cd stress, the hybrid lines showed lowest level of oxidative damage and the highest level of photosynthetic efficiency. Compared with the parents, the hybrid utilized more active detoxification strategies, such as the cell walls of the leaves and roots adsorbed 88% and 95% Cd, respectively, reducing the amount of Cd entering cells; moreover, most of the Cd that entered cells was transformed into less toxic chemical forms through the reduction of the highly toxic chemical forms; furthermore, it accumulated a large number of phytochelatins to bind Cd²⁺ and reduced the damage of organelles by Cd²⁺. The results demonstrate that hybridization between S. trilobata and S. calendulacea improved the adaptability of the new hybrid species to Cd stress and may pose a greater threat to the survival of the native parent species in the presence of serious water and soil pollution.

The high levels of heavy metal accumulation in cultivated rice from the Tajan river basin: Health and ecological risk assessment

Consumption of food crops contaminated with heavy metals (HMs) is a significant risk factor for human health and safety. We evaluated the health risks of HMs in contaminated food crops irrigated with surface water. Results showed there is a substantial buildup of HMs in rice, collected from the Tajan river basin, Iran. The transfer factor (TF) value for toxic elements Cd (3.6-12.4) and Pb (4.9-23.6) were significantly high and exceeded the permissible limits for crops set by WHO. The principal component analysis was used to analyze the relevance of different metals and identify the primary sources. The results showed that two factors dominated the metals variability (94.10% of total variance) that Cr, Fe, Cd, and Pb were dominated by PC1 whereas another factor charged Zn and Cu. The average total hazard quotient (THQ) values for Pb, Fe, Cr, and Cd were 13.8, 7.7, 5.5, and 1.5, respectively, that suggest a considerable risk to the health of regular rice consumers. The high hazard index (HI) value (29.2) demonstrated that the exposure concentration was very high compared to the effective threshold, and it may have potentially harmful implications for human health. To sum up, these results proved that rice from this basin could be a serious dietary source of Pb and Cd exposure to the consumer population.

The compound effects of biochar and iron on watercress in a Cd/Pb-contaminated soil

Pot experiment was conducted to evaluate the effect of two types of biochar (2% (w/w)), Pennisetum sinese Roxb biochar (PB) and coffee grounds biochar (CB), combined with iron fertilizer (1.3 g kg^-1 Fe) on the growth, quality, Cd/Pb accumulation in watercress, soil physicochemical properties, soil fertility, soil enzyme activities, and fraction distribution of Cd/Pb in soil. The results showed that the two types of biochar combined with iron fertilizer (BC-Fe) amendments could increase the shoot height, root length, plant biomass, soluble sugar and soluble protein of watercress, soil pH value, soil organic matter (SOM), ammonium nitrogen (NH₄⁺-N), available phosphorus, and available potassium. CB-Fe amendment enhanced soil urease, sucrose, and catalase activities, while PB-Fe amendment only enhanced soil urease activity among the three enzymes. The two BC-Fe amendments decreased exchangeable-Cd/Pb and reducible-Cd/Pb concentrations, while enhanced oxidizable-Cd/Pb and residual-Cd/Pb concentrations. Furthermore, the two BC-Fe amendments decreased significantly Cd and Pb accumulation in watercress root and shoot. The reduction rate for Cd and Pb in shoot by 42.9%, 20.0%, and 68.2%, 58.4% under PB-Fe and by 38.1%, 20%, and 62.5%, 48.8% under CB-Fe, respectively, for the first crop and the second crop. In conclusion, BC-Fe amendment could improve soil physicochemical properties and soil fertility, promote Cd and Pb transfer to the stable form, thus, reduce the bioavailability and mobility of Cd and Pb, and further, decrease Cd and Pb ecotoxicity and its accumulation in watercress and improve watercress quality.