Lead bioaccumulation in Opuntia ficus-indica following foliar or root exposure to lead-bearing apatite

Bio-availability of potential trace elements in urban dust, soil, and plants in arid northwest China

Potential trace elements pollution in cities poses a threat to the environment and human health. Bio-availability affects toxicity levels of potential trace elementss on organisms. This study focused on exploring the relationship between soil, plant, and atmospheric dust pollution in Urumqi, a typical city in western China. It aims to help reduce pollution and protect residents' health. The following conclusions were drawn: 1) potential trace elementss like Cr, Pb, As, and Ni are more prevalent in atmospheric dust and soil than in plants. Chromium was in the first group, Cadmium and Mercury were in the second, and Plumb, Arsenic, and Nickel were in the third. Atmospheric dust and soil exhibit a significantly higher heavy metal content than plants. For example, The atmospheric dust summary Chromium content was up to 88 mg/kg. 2) Soil, atmospheric dust, and plants have the highest amount of residual form. Residual form had the highest percentage average of 53.3%, whereas Organic matter bound form had the lowest percentage of just 7.7%. The plants contained less residual heavy metal than the soil and atmospheric dust. 3) The correlation coefficient between the carbonated form content of Cd of soil and atmospheric dust is 0.95, which is closely related. Other potential trace elements show similar correlations in their bio-available contents in soil, plants, and atmospheric dust. This study suggests that in urban area, the focus should be on converting potential trace elements into residual form instead of increasing plants' absorption of potential trace elements.

Characterisation of Zinc-bearing sulphate phases formed during the synthesis of phosphoric acid and Zinc removal by the ligands of Opuntia ficus-indica

Phosphogypsum (PG) is a solid waste generated from phosphate fertilisers industries. It represents a serious threat to the aquatic and terrestrial environment because of its acidity and its high content in heavy metals and radionuclides. The aim of this work is to describe the formation of PG during the synthesis of the phosphoric acid, the entrapment of Zinc (Zn) in PG and its lixiviation in presence of a natural organic matter extracted as powder from the cladodes of Opuntia ficus-indica (OFI) using physical and chemical characterisation techniques such as FTIR, XRD, SEM-EDX, laser diffraction, and AAS. The formation of PG mainly occurs in the pH range between 4.6 and 3 and it accompanies the transformation of H₂(PO₄)^- into phosphoric acid H₃PO₄. The maximal Zn incorporation within the PG was reached at pH 6 and decreased progressively with pH. Zinc was found to have a great tendency to migrate from PG particles to OFI's suspensions since a maximum Zn removal percentage of 93% was achieved.

Foliar uptake, accumulation, and distribution of cadmium in rice (Oryza sativa L.) at different stages in wet deposition conditions

Atmospheric deposition of cadmium (Cd) in rice (Oryza sativa L.) has become a major global concern. Foliar uptake allows vegetables to accumulate heavy metals from the atmosphere, but this has rarely been studied in rice. Therefore, this study investigated the Cd accumulation in rice growing at different exposure periods (the tillering, booting, heading, and maturity stages) under a wet deposition of CdCl₂·2.5H₂O solution through pot experiments. The Cd concentrations in leaves, roots, husk, brown rice, and leaf structures were analyzed to explore foliar uptake, accumulation, and distribution of Cd in rice tissues at different growth stages. The results showed that wet deposited Cd can be absorbed on the rice leaf surface and remains on the leaves for a long time. The sequence of Cd accumulation in rice tissues was: leaves > brown rice > husk > roots, with leaves accounting for greater than 71.78% of the total accumulation. The accumulation of wet deposited Cd in leaves, husk, and brown rice had large temporal variations between the four typical stages. There was no significant variations in Cd content in roots between different growth stages. Correspondingly, the foliar uptake of Cd was rarely transported from the leaves via the phloem to roots. Conversely, the foliar uptake of Cd was transported upwards to grains. The accumulation of Cd fluctuated with each growth stage, initially increasing and then decreasing at the heading stage and finally reaching a peak at the maturity stage. The highest total accumulation of Cd in both the high and low wet deposition conditions occurred at maturity, resulting in 15.53 and 11.23 μg plant^-1, respectively. These results provide theoretical support for further research into identifying efficient foliar control measures to reduce Cd accumulation and maintain food safety.

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

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

Contribution of the flag leaf to lead absorption in wheat grain at the grain-filling stage

Wheat flag leaf (FL) is one of the primary sources of carbohydrates in grains; however, its role in grain lead (Pb) absorption remains unclear. A field experiment was conducted to assess the relative contribution of the FL to Pb accumulation in wheat grain by two contrasting treatments: without (CK) and with FL removal (FLR) at the grain-filling stage. The Pb concentration in leaves was closely related to leaf strata and decreased from FL to the third leaf. FLR treatment significantly reduced the yield and grain Pb concentration by 2.79% and 11.47%, respectively. The contribution of FL to grain Pb accumulation decreased gradually with the filling process, from 35.08% (at early stage) to 13.94% (at maturity stage). After FLR, the contribution proportion of atmospheric fallout to grain Pb decreased from 69.01% (CK) to 62.43% (FLR). Combined isotope analysis with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) revealed that the main contribution of FLs to grain Pb originated from Pb fallout in fine atmospheric particles. Therefore, taking measures to reduce the influence of fine atmospheric particles on wheat may be an effective way to control wheat grain Pb contamination.

Evaluation of the Mineral Content in Forage Palm (Opuntia ficus-indica Mill and Nopalea cochenillifera) Using Chemometric Tools

An acid digestion procedure of the forage palm (Opuntia ficus-indica Mill and Nopalea cochenilifera) employing a closed digestor block applied full 2⁴ factorial design was optimized. The optimal conditions were HNO₃ 5.0 mol L^-1, 2.0 mL of H₂O₂ 30% m m^-1, 120 min of digestion, and heating temperature of 180 °C. The certified reference materials of apple leaves (NIST 1515) and tomato leaves (Agro C1003a) were used to evaluate the accuracy of the analytical method. The concentrations of the macroelements were (in % m m^-1) Ca (1.32-3.71), K (0.88-5.29), Mg (0.70-1.78), and P (0.03-0.32). For the microelements, the concentrations (in μg g^-1) obtained were As (< 1.39), Cd (< 0.10), Cu (< 0.17-5.6), Fe (8.0-50.2), Na (< 1.85), Sr (41-348), and Zn (17.3-159). Essential elements such as Ca, Mg, and Zn made good contributions to daily intake, being an alternative to meet the nutritional needs of these macroelements and microelements in humans. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to evaluate the results, obtaining trends between the samples in relation to their mineral composition.

Contribution of PM2.5-Pb in atmospheric fallout to Pb accumulation in Chinese cabbage leaves via stomata

Foliar uptake of Pb is especially important when Chinese cabbage (Brassica rapa spp. pekinensis), having a large leaf surface area, is cultivated in North China during seasons with heavy haze. However, the mechanisms of foliar Pb uptake via stomata by Chinese cabbage exposed to atmospheric fallout are unclear. A field experiment was conducted to explore the impacts of Pb in particulate matter with sizes ≤ 2.5 µm (PM_2.5-Pb) from atmospheric fallout to Pb accumulation in cabbage leaves through stomata. Cabbage varieties with low-Pb-accumulation (LPA) and high-Pb-accumulation (HPA) were examined using inductively coupled plasma-mass spectrometry and scanning electron microscopy/energy-dispersive X-ray analysis. The ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios of PM_2.5, plants, and soil demonstrated that the major source of Pb in cabbage leaves was PM_2.5. The average width and length of the stomatal apertures were 7.14 and 15.61 µm for LPA cabbage and 8.10 and 16.64 µm for HPA cabbage, which are large enough for PM_2.5-Pb to enter the leaves. The HPA cabbage had significantly higher stomatal width-to-length ratios than the LPA cabbage, indicating that the former trapped much more PM_2.5-Pb and accumulated more Pb. These results clarify the contributions of the stomatal characteristics to PM_2.5-Pb accumulation in the edible parts of Chinese cabbage.

Foliar application of lead and arsenic solutions to Spinacia oleracea: biophysiochemical analysis and risk assessment

Atmospheric contamination by heavy metal(loid)s is a widespread global issue. Recent studies have shown foliar pathway of heavy metal(loid) uptake by plants, thus menacing plant productivity and threatening health risks. In contrast to root uptake of heavy metal(loid)s, there is scarce data available on heavy metal(loid) foliar uptake, accumulation in different plant parts, changes in growth and other biophysiochemical processes/reactions, detoxification mechanisms and associated health risks due to the consumption of contaminated vegetables. This study evaluated the effect of foliar application of two potentially toxic metal(loid)s (arsenic (As) and lead (Pb)) on their uptake by Spinacia oleracea, plant growth, pigment contents, physiological changes, and activation of antioxidative enzymes. Results revealed that S. oleracea seedlings can accumulate both the metal(loid)s in their leaves via foliar pathway. Arsenic was transferred from the leaves towards the roots, while Pb was mainly sequestered in S. oleracea leaves. Both the metal(loid)s significantly decreased plant growth and pigment contents, As being more toxic than Pb. Foliar application of As and Pb did not cause lipid peroxidation and overproduction of reactive oxygen species (ROS). However, both the metal(loid)s enhanced the activities of antioxidative enzymes. We also calculated possible health risks (both non-carcinogenic and carcinogenic) due to As and Pb accumulation in the edible parts for both the adults and children. It was observed that As can induce non-carcinogenic effects (HQ > 1) in children only, while both As and Pb can cause carcinogenic hazards in both adults and children under their all applied foliar levels. Therefore, it is proposed that As and Pb contents in the atmosphere must be monitored continuously for their possible foliar uptake and accumulation in edible plant parts to avoid cancer risks. Moreover, multivariate analysis traced weak-strong correlations between metal(loid) treatments and plant response variables.

Competitive binding of Cd, Ni and Cu on goethite organo-mineral composites made with soil bacteria

Soil is a heterogeneous porous media that is comprised of a variety of organo-mineral aggregates. Sorption of heavy metals onto these composite solids is a key process that controls heavy metal mobility and fate in the natural environment. Pollution from a combination of heavy metals is common in soil, therefore, understanding the competitive binding behavior of metal ions to organo-mineral composites is important in order to predict metal mobility and fate. In this study, batch experiments were paired with spectroscopic studies to probe the sorption characteristics of ternary CdNiCu sorbates to a binary organo-goethite composite made with Bacillus cereus cells. Scanning electron microscopy shows that goethite nano-sized crystals are closely associated with the bacterial surfaces. Sorption experiments show a larger adsorptivity and affinity for Cu than Cd/Ni on goethite and B. cereus, and the goethite-B. cereus composite. X-ray photoelectron spectroscopy reveals that carboxylate and phosphate functional moieties present on the bacterial cell walls are primarily responsible for metal sorption to the goethite-B. cereus composite. Synchrotron-based X-ray fluorescence shows that Cu and Ni are predominately associated with the bacterial fraction of the goethite-B. cereus composite, whereas Cd is mainly associated with the goethite fraction. The findings of this research have important implications for predicting the mobility and fate of heavy metals in soil multi-component systems.

Effect of Calcium on the Bioavailability of Dissolved Uranium(VI) in Plant Roots under Circumneutral pH

We integrated field measurements, hydroponic experiments, microscopy, and spectroscopy to investigate the effect of Ca(II) on dissolved U(VI) uptake by plants in 1 mM HCO₃^- solutions at circumneutral pH. The accumulation of U in plants (3.1-21.3 mg kg^-1) from the stream bank of the Rio Paguate, Jackpile Mine, New Mexico served as a motivation for this study. Brassica juncea was the model plant used for the laboratory experiments conducted over a range of U (30-700 μg L^-1) and Ca (0-240 mg L^-1) concentrations. The initial U uptake followed pseudo-second-order kinetics. The initial U uptake rate ( V₀) ranged from 4.4 to 62 μg g^-1 h^-1 in experiments with no added Ca and from 0.73 to 2.07 μg g^-1 h^-1 in experiments with 12 mg L^-1 Ca. No measurable U uptake over time was detected for experiments with 240 mg L^-1 Ca. Ternary Ca-U-CO₃ complexes may affect the decrease in U bioavailability observed in this study. Elemental X-ray mapping using scanning transmission electron microscopy-energy-dispersive spectrometry detected U-P-bearing precipitates within root cell walls in water free of Ca. These results suggest that root interactions with Ca and carbonate in solution affect the bioavailability of U in plants. This study contributes relevant information to applications related to U transport and remediation of contaminated sites.

Opuntia (Cactaceae) plant compounds, biological activities and prospects - A comprehensive review

Opuntia species are utilized as local medicinal interventions for chronic diseases and as food sources mainly because they possess nutritional properties and biological activities. The Opuntia plant is distributed worldwide and has great economic potential. Differences in Opuntia species phytochemical composition exist between wild and domesticated species, and within species. Opuntia aerial and underground parts exhibit beneficial properties due to their phenolic content, other antioxidants (for example ascorbate), pigments (carotenoids, betalains), and other unidentified components. This work comprehensively reviews the phytochemical composition of the different aerial and underground plant parts of Opuntia species. The applications of Opuntia compounds and their biological activities are also discussed. Other topical aspects covered include Opuntia spp. taurine composition, Opuntia side effects, Opuntia by-products valorisation and the role of Opuntia spp. in tackling antimicrobial resistance. Although biological activities have been extensively researched, much less information is available on reaction mechanisms, herbal mixtures toxicology and commercialisation prospects - aspects which should be considered for future research in this area.