Biosorption of arsenic from groundwater using Vallisneria gigantea plants. Kinetics, equilibrium and photophysical considerations

Chlorophyll fluorescence in sentinel plants for the surveillance of chemical risk

This research aimed to develop natural plant systems to serve as biological sentinels for the detection of organophosphate pesticides in the environment. The working hypothesis was that the presence of the pesticide in the environment caused changes in the content of pigments and in the photosynthetic functioning of the plant, which could be evaluated non-destructively through the analysis of reflected light and emitted fluorescence. The objective of the research was to furnish in vivo indicators derived from spectroscopic parameters, serving as early alert signals for the presence of organophosphates in the environment. In this context, the effects of two pesticides, Chlorpyrifos and Dimethoate, on the spectroscopic properties of aquatic plants (Vallisneria nana and Spathyfillum wallisii) were studied. Chlorophyll-a variable fluorescence allowed monitoring both pesticides' presence before any damage was observed at the naked eye, with the analysis of the fast transient (OJIP curve) proving more responsive than Kautsky kinetics, steady-state fluorescence, or reflectance measurements. Pesticides produced a decrease in the maximum quantum yield of PSII photochemistry, in the proportion of PSII photochemical deexcitation relative to PSII non photochemical decay and in the probability that trapped excitons moved electrons into the photosynthetic transport chain beyond QA-. Additionally, an increase in the proportion of absorbed energy being dissipated as heat rather than being utilized in the photosynthetic process, was notorious. The pesticides induced a higher deactivation of chlorophyll excited states by photophysical pathways (including fluorescence) with a decrease in the quantum yields of photosystem II and heat dissipation by non-photochemical quenching. The investigated aquatic plants served as sentinels for the presence of pesticides in the environment, with the alert signal starting within the first milliseconds of electronic transport in the photosynthetic chain. Organophosphates damage animals' central nervous systems similarly to certain compounds found in chemical weapons, thus raising the possibility that sentinel plants could potentially signal the presence of such weapons.

Controlling factors of heavy metal(loid) accumulation in rice: Main and interactive effects

Identifying the key determinants of heavy metal(loid) accumulation in rice and quantifying their contributions are critical for precise prediction of heavy metal(loid) concentrations in rice and the formulation of effective pollution control strategies. The accumulation of heavy metal(loid)s in rice can be influenced by both natural and anthropogenic factors, which may interact with each other. However, distinguishing the independent roles (main effects) from interactive effects and quantifying their impacts separately pose challenges. To address this knowledge gap, we employed TreeExplainer-based SHAP and random forest algorithms in this study to quantitatively estimate the primary influencing factors and their main and interactive effects on heavy metal(loid)s in rice. Our findings reveal that soil cadmium (SCd) and rice cultivation time (C_TIME) were the primary contributors to rice cadmium (RCd) and rice arsenic (RAs), respectively. Soil lead (SPb) and sampling distances from roads significantly contributed to rice lead (RPb). Additionally, we identified significant interactive effects of SCd and C_TIME, C_TIME and RCd, and RCd and rice variety on RCd, RAs, and RPb, respectively, emphasizing their significance. These insights are pivotal in improving the accuracy of heavy metal(loid) concentration predictions in rice and offering theoretical guidance for the formulation of pollution control measures.

Sustainable Chromium Recovery From Wastewater Using Mango and Jackfruit Seed Kernel Bio-Adsorbents

Wastewater is a rich source of valuable chemicals of industrial importance. However, their economic recovery is crucial for sustainability. The objective of the present work is to recover hexavalent chromium (Cr VI) as a value-added transition metal from wastewater cost-effectively; the biosorbent derived from seed kernels of mango (M) and jackfruit (JF) were applied for removing the metal from simulated wastewater. The functional groups of the biomass were analysed with the help of Fourier transform infrared (FTIR) spectroscopy, micrographs were generated using a scanning electron microscope, and crystallinity was determined by an x-ray diffractometer (XRD). The concentration of Cr VI in wastewater was analysed by an inductively coupled plasma optical emission spectrometer (ICP-OES). Process parameters (pH, dose, contact time, temperature, and initial concentration) were optimized for efficient Cr VI adsorption using a response surface methodology-based Box-Behnken design (BBD) employing Design-software 6.0.8. The batch experiment at room temperature at pH 4.8 and Cr VI removal ∼94% (M) and ∼92% (JF) was achieved by using a 60-mg dose and an initial Cr (VI) concentration of 2 ppm in 120 min. The equilibrium Cr binding on the biosorbent was well explained using Freundlich isotherm (R ² = 0.97), which indicated the indirect interactions between Cr (VI) and the biosorbent. Biosorption of Cr (VI) followed the pseudo-order and intra-particle diffusion models. The maximum adsorption capacity of the M and JF bio-adsorbent is 517.24 and 207.6 g/mg, respectively. These efficient, cost-effective, and eco-friendly biosorbents could be potentially applied for removing toxic Cr (VI) from polluted water.

Reclamation competence of Crotalaria juncea with the amalgamation and influence of indigenous bacteria on a waste dump of bauxite mine

The accumulated bauxite mine soil had an acidic pH of 5.52 ± 0.12 and more heavy metals such as Cr, Cd, Zn, and Pb, which can cause severe soil and water pollution to the nearby farmlands and water reservoirs. Hence, the work was designed to find the possibility of reclamation of bauxite mine soil through Crotalaria juncea with the amalgamation of native metal degrading bacterial isolates. Out of 15 bacterial cultures, only 2 isolates (B3 and B14) showed excellent metal tolerance (for up to 750 mg L^-1), solubilizing (15.27-38.7 mg kg^-1) (including phosphate: 47.4 ± 1.79%), and degrading potential (22.8 ± 0.89 to 31.5 ± 1.6%) than the others. These B3 and B14 isolates were recognized as B. borstelensis UTM105 (1432 bp) and B. borstelensis AK2 (1494 bp) through molecular characterization. These isolates have produced a metal stress response protein (205-43 KDa molecular weight protein) during metal stress conditions. The phytoremediation competence of C. juncea under the influence of these bacterial isolates was assessed with various treatment (I-IV) schemes. The treatment IV (C. juncea with two bacterial isolates) showed substantial physiological and biochemical results compared with the control and the other treatments. The phytoremediation competence of C. juncea was also effective in treatment IV than the others. It reduced and extracted a reasonable quantity of metals from the bauxite mine soil. The intact results accomplished that these native metals tolerant, solubilizing, and degrading bacterial isolates, could be used as optimistic bacterial candidates in combination with C. juncea for the effective reclamation of metal enriched bauxite mine soil.

Biosorption potential of Phoenix dactylifera coir wastes for toxic hexavalent chromium sequestration

Valorization of waste phytomass into valuable components provide new functionality to these biowastes and annul problems associated with their safe disposal. In this study, date palm (Phoenix dactylifera) coir (DPC) waste was tested for its toxic hexavalent chromium (Cr(VI)) ions biosorption. The DPC biosorbent was subjected to SEM, EDX, FTIR, TGA and N₂ adsorption/desorption characterization studies. Results showed that the cellulose-rich DPC surface contained mesopores with a wide number of functional groups and possessed suitable surface attributes for Cr(VI) ions sequestration. Batch biosorption tests established the Cr(VI) ions sequestration potential of the DPC biosorbent with a maximum chromium removal efficiency of 87.2% for a 100 ppm initial feed concentration at pH 2, dosage 0.3 g, temperature 30 °C, contact time 60 min and agitation speed 100 rpm. Langmuir isotherm fitted well (R² = 0.9955) with the experimental data while the kinetic analysis showed that Cr(VI) ions sequestration by DPC followed the pseudo-second order model. Biosorption thermodynamics revealed the exothermic nature and low-temperature preference for the effective binding of chromium ions on DPC. Regeneration of the biosorbent using NaOH wash showed a nearly steady Cr(VI) ions removal efficiency (with a loss <10%) by the DPC till four recycle runs. Economic analysis showed a very low production cost of $1.09/kg for the DPC biosorbent with a total cost of $4.36/m³ for a scale-up batch process wastewater treatment plant. Thus, a low-cost, effectual and sustainable biosorbent for effective treatment of Cr(VI) ions polluted water streams has been reported.

Insights into conventional and recent technologies for arsenic bioremediation: A systematic review

Arsenic (As) bioremediation has been an economical and sustainable approach, being practiced widely under several As-contaminated environments. Bioremediation of As involves the use of bacteria, fungi, yeast, plants, and genetically modified organisms for detoxification/removal of As from the contaminated site. The understanding of multi-factorial biological components involved in these approaches is complex and more and more efforts are on their way to make As bioremediation economical and efficient. In this regard, we systematically reviewed the recent literature (n=200) from the last two decades regarding As bioremediation potential of conventional and recent technologies including genetically modified plants for phytoremediation and integrated approaches. Also, the responsible mechanisms behind different approaches have been identified. From the literature, it was found that As bioremediation through biosorption, bioaccumulation, phytoextraction, and volatilization involving As-resistant microbes has proved a very successful technology. However, there are various pathways of As tolerance of which the mechanisms have not been fully understood. Recently, phytosuction separation technology has been introduced and needs further exploration. Also, integrated approaches like phytobial, constructed wetlands using As-resistant bacteria with plant growth-promoting activities have not been extensively studied. It is speculated that the integrated bioremediation approaches with practical applicability and reliability would prove most promising for As remediation. Further technological advancements would help explore the identified research gaps in different approaches and lead us toward sustainability and perfection in As bioremediation.

Analysis of the copper removal kinetics of the Philippine giant bamboo (Dendrocalamus asper) in hydroponics

Copper is the third most utilized metal and is a versatile resource with multiple beneficial uses, but it may also become toxic to aquatic life in excess amount. Thus, there is a need to develop methods to reduce the copper contamination in the environment, particularly in bodies of water. Phytoremediation using Dendrocalamus asper may offer an environment-benign and potentially effective method for copper removal though its effectiveness may take several years to materialize for this technology to become cost-effective. By growing D. asper in synthesized contaminated water and analyzing the change in the copper content of the substrate via atomic absorption spectrophotometry, the removal was found to be optimal at 20 ppm Cu and pH 5. The rate of removal was found to have an order of 2.71 and a kinetic constant of 0.0013 ppm^-1.71 day^-1. With this, it may be possible to estimate the treatment length of phytoremediation given an initial level of copper contamination and a target concentration.

New insight into continuous recirculation-process for treating arsenate using bacterial biosorbent

In this study, a new recirculation column reactor system for arsenate removal using a polyethylenimine coated bacterial biosorbent was developed. Solution pH was the most important factor in process design and operation. In order to control and optimize solution pH favorable for arsenate removal, a pH control and recirculation system was added to a column reactor. The effects of recycle ratio, initial arsenate concentration, and flow rate on the arsenate removal performance of the developed process were examined. Thomas and Yoon-Nelson models were used to interpret the breakthrough curve of arsenate removal. The maximum arsenate adsorption amount of the new reactor was determined to be 50.86 mg/g by the Thomas model. Importantly, the new reactor showed unimpeded adsorption performance compared with that in the batch experiments. The desorption study also showed excellent reusability. The results indicated that the newly developed process could be a promising application prospect for removing arsenate.

Influence of Aquatic pH on chemical speciation, phytochelation and vacuolar compartmentalization of arsenic in Vallisneria denseserrulata (Makino)

Arsenic (As) pollution of fresh water has become a major concern worldwide. The present study reports the As accumulation potential and detoxification mechanism in a native plant, Vallisneria denseserrulata (Makino), under different aquatic acidity conditions (pH). V. denseserrulata showed maximum growth at pH ∼7.0 and accumulated ∼1700 mg/kg of As. The increase in pH from 3.5 to 7 significantly (p ≤ 0.05) increased As accumulation, thiol and total protein contents while malondialdehyde (MDA) content, soluble sugar content and percentage electrolytic leakage (%EL) of V. denseserrulata were decreased. The reduction of arsenate [As(V)] to arsenite As(III) was observed as a key step (81% reduction) of the As detoxification in V. denseserrulata. Majority of accumulated As was found in vacuoles (56-72%), while >80% of As in vacuoles was in the form of As(III). FT-IR spectra indicated the complexsation of As with carboxyl, amide, thiol, and hydroxyl groups. Our findings showed the presence of As detoxification mechanism in V. denseserrulata. Vacuolar As compartmentalization and formation of As-Phytochelatins/thiol complexes can be a part of As detoxification mechanisms in V. denseserrulata.

Confocal Volumetric μXRF and Fluorescence Computed μ-Tomography Reveals Arsenic Three-Dimensional Distribution within Intact Pteris vittata Fronds

The fern Pteris vittata has been the subject of numerous studies because of its extreme arsenic hyperaccumulation characteristics. However, information on the arsenic chemical speciation and distribution across cell types within intact frozen-hydrated Pteris vittata fronds is necessary to better understand the arsenic biotransformation pathways in this unusual fern. While 2D X-ray absorption spectroscopy imaging studies show that different chemical forms of arsenic, As(III) and As(V), occur across the plant organs, depth-resolved information on arsenic distribution and chemical speciation in different cell types within tissues of Pteris vittata have not been reported. By using a combination of planar and confocal μ-X-ray fluorescence imaging and fluorescence computed μ-tomography, we reveal, in this study, the localization of arsenic in the endodermis and pericycle surrounding the vascular bundles in the rachis and the pinnules of the fern. Arsenic is also accumulated in the vascular bundles connecting into each sporangium, and in some mature sori. The use of 2D X-ray absorption near edge structure imaging allows for deciphering arsenic speciation across the tissues, revealing arsenate in the vascular bundles and arsenite in the endodermis and pericycle. This study demonstrates how different advanced synchrotron X-ray microscopy techniques can be complementary in revealing, at tissue and cellular levels, elemental distribution and chemical speciation in hyperaccumulator plants.

Indigenous strain Bacillus XZM assisted phytoremediation and detoxification of arsenic in Vallisneria denseserrulata

The symbiosis between Vallisneria denseserrulata and indigenous Bacillus sp. XZM was investigated for arsenic removal for the first time. It was found that the native bacterium was able to reduce arsenic toxicity to the plant by producing higher amount of extra cellular polymeric substances (EPS), indole-3-acetic acid (IAA) and siderosphore. Interestingly, V. denseserrulata-Bacillus sp. XZM partnership showed significantly higher arsenic uptake and removal efficiency. The shift in FT-IR spectra indicated the involvement of amide, carboxyl, hydroxyl and thiol groups in detoxification of arsenic, and the existence of an arsenic metabolizing process in V. denseserrulata leaves. The scanning electron microscopy (SEM) images further confirmed that the bacterium colonized on plant roots and facilitated arsenic uptake by plant under inoculation condition. In plant, most of the arsenic existed as As(III) (85%) and was massively (>77%) found in vacuole of particularly leaves cells. Thus, these findings are highly suggested for arsenic remediation in the constructed wetlands.

Constructed wetlands as an alternative for arsenic removal from reverse osmosis effluent

In Argentina, drinking water for c.a. 10% of the population has arsenic (As) concentrations higher than those recommended by WHO (10 μg L^-1). Reverse osmosis (RO) appears as an immediate and effective solution for As remediation. However, this process has a residual flow known as "rejection" or "concentrate" where dissolved species are more concentrated than in the feed flow. In this study, phytoremediation with subsurface horizontal-flow constructed wetlands (CW) was proposed to reduce As concentration in the RO residues. Experiments were carried out during 419 days at room temperature and using a continuous regime (flow of 36 L d^-1, As concentration around 85 μg L^-1) of RO rejection from a water treatment plant located in Buenos Aires province, Argentina. The study was performed using prototypes planted with Cyperus haspan (PA), Juncus effusus (PB) and a mix of inert gravel and laterite (substrate) that was used as a control (PC). Results showed that after a stabilization time, As removal (%) was between 30% and 80% in the CW planted with J. effusus and between 10 and 40% with C. haspan. As concentration along CW showed similarities between the prototypes PC and PA. The cumulative mass of As was 62%, 34% and 27% for PA, PB and PC, respectively. The contribution of C. haspan and J. effusus during the experimental time was between 12 and 67% and 22 to 87%, respectively. The bioaccumulation and translocation factors indicated that for J. effusus the accumulation is more important than the translocation process (1.6 and 0.2, respectively), while for C. haspan both factors were similar (1.1 and 1.0, respectively). Results suggested that this technology has the potential for an efficient and environmentally sustainable alternative to RO rejection treatment and disposal regarding As concentration.

Non-destructive methodologies applied to track the occurrence of natural micropollutants in watering: Glycine max as a biomonitor

Groundwater is habitually used for watering purposes in rural areas where the rainfall is not enough to adequately cover the crop requirements. However, groundwater sources could be naturally contaminated with trace micropollutants like As and associated elements (B, V and F) adversely affecting the plant health. In this work, non-destructive methodologies based on reflectance and chlorophyll emission processes were applied to assess the presence of micropollutants in watering by using a widespread crop (soybean plant). One of the most substantial results is that the co-occurrence of As, V, B and F in the watering solution clearly produced a synergistic effect in the plants. In fact, both reflectance and fluorescence techniques were proved in this work to be effective in detecting non-destructively stress by multielement treatment. Particularly, for reflectance measurements the most sensitive parameters were the derivative peak area between 480 and 560 nm and the chlorophyll content. Furthermore, it was demonstrated that it is possible to successfully use a portable hyperspectral spectroradiometer instead of a conventional spectrophotometer as the determinations performed with both instruments were positively correlated. Concerning fluorescence, variable emission of chlorophyll-a was more sensitive to stress than steady-state emission. The parameter Fv/F0 was a valuable indicator of stress but the quantum yields of PSII and NPQ stood out as the most sensitive indices with variations of around 60 and 100% respectively.

Synthesis of green marine algal-based biochar for remediation of arsenic(V) from contaminated waters in batch and column mode of operation

The sorption behavior of biochar derived from green seaweed (Ulva reticulata) toward arsenic(V) ions was explored in both batch and continuous modes. The pH edge experiments indicated optimum arsenic(V) sorption observed at pH 4, with maximum sorptional capacity of 7.67 mg/g through isotherm experiments. The kinetic experimental trials indicated that arsenic(V) sorption onto biochar was a fast electrostatic attraction process, with maximum removal occurred within 30 min. The sorption isotherms were modeled using the Toth, Redlich-Peterson, Langmuir and Freundlich isotherm models while the adsorption kinetics was modeled using the pseudo-first- and pseudo-second-order kinetic equations. The three-parameter models (Redlich-Peterson and Toth) better described the isotherm data, whereas pseudo-first-order model represented kinetic data well with low error and high correlation coefficient values. Among the different alkaline and acidic elutants investigated, the solution of 0.01 M NaOH effectively desorbed arsenic(V) from spent biochar. The feasibility of the biochar in continuous remediation of arsenic(V) from contaminated waters was explored in an up-flow fixed column. The biochar exhibited arsenic(V) removal efficiency and sorptional uptake of 59.5% and 8.12 mg/g, respectively. The biochar-loaded column was effectively desorbed using NaOH (0.01 M), with desorption efficiency of 99.5%.

Simultaneous biosorption of Arsenic (III) and Arsenic (V): Application of multiple response optimizations

In this work, simultaneous biosorption of As(III) and As(V) by Sargassum glaucescens was optimized using multiple response optimizations and Doehlert experimental design. The optimum condition for simultaneous biosorption of As(III) and As(V) were: biosorbent dosage 0.47 g L-1, pH 5.9 and initial concentration 120.34 mg L-1 with maximum overall desirability of 0.94. Different isotherms were fitted to biosorption equilibrium data and the Freundlich isotherm was the most suitable model. Based on thermodynamic study, the biosorption of arsenic species onto alga was endothermic and spontaneous. Kinetic results indicated that intraparticle diffusion model was the best kinetic model. Biosorption capacity of S. glaucescens and other biosorbents were also compared.

Arsenic effects on some photophysical parameters of Cichorium intybus under different radiation and water irrigation regimes

The presence of arsenic (As) in groundwater is a major problem in several parts of Latin America. In the present work, non-destructive approaches to monitor the effects of As on plants of Cichorium intybus, an herbaceous Asteraceae, were explored. In this sense, the effects of As at different levels of water and radiation were evaluated on these crops. Plants were grown in a greenhouse, watered daily with As solutions and exposed to different water and/or light conditions for four months, using a three-factor (As, water, radiation) and two-level resource (As vs non As, field capacity vs half-field capacity condition, light vs shade condition) factorial design. The parameters most affected by this treatment were the area under the first derivative of the reflectance spectrum in the blue region, chlorophyll concentration, the Fred/Ffar-red fluorescence ratio and the quantum yield for the photophysical decay. These changes indicated the ability of this plant species to be a biomonitor for the presence of arsenic in irrigation water. Interestingly, it was further proved in this work that the biomonitoring capacity was enhanced in the presence of sunlight.

Phytofiltration of arsenic by aquatic moss (Warnstorfia fluitans)

This work investigates whether aquatic moss (Warnstorfia fluitans) originating from an arsenic (As)-contaminated wetland close to a mine tailings impoundment may be used for phytofiltration of As. The aim was to elucidate the capacity of W. fluitans to remove As from arsenite and arsenate contaminated water, how nutrients affect the As uptake and the proportion of As adsorption and absorption by the moss plant, which consists of dead and living parts. Arsenic removal from 0, 1, or 10% Hoagland nutrient solution containing 0-100 μM arsenate was followed over 192 h, and the total As in aquatic moss after treatment was analysed. The uptake and speciation of As in moss cultivated in water containing 10 μM arsenate or arsenite were examined as As uptake in living (absorption + adsorption) and dead (adsorption) plant parts. Results indicated that W. fluitans removed up to 82% of As from the water within one hour when 1 μM arsenate was added in the absence of nutrients. The removal time increased with greater nutrient and As concentrations. Up to 100 μM As had no toxic effect on the plant biomass. Both arsenite and arsenate were removed from the solution to similar extents and, independent of the As species added, more arsenate than arsenite was found in the plant. Of the As taken up, over 90% was firmly bound to the tissue, a possible mechanism for resisting high As concentrations. Arsenic was both absorbed and adsorbed by the moss, and twice as much As was found in living parts as in dead moss tissue. This study revealed that W. fluitans has potential to serve as a phytofilter for removing As from As-contaminated water without displaying any toxic effects of the metalloid.

Micro-distribution of arsenic species in tissues of hyperaccumulator Pteris vittata L

Arsenic (As) contamination and its harmful consequences have gained increasing attention in research. Phytoextraction, which uses the As hyperaccumulator Pteris vittata L., is a well-established technology adopted in many countries. However, the hyperaccumulation mechanisms of this plant remain controversial. This study investigated the species and the micro-distribution of As species in three P. vittata L. ecotypes after exposure to arsenite (AsIII) and arsenate (AsV) for 7d. Arsenic-accumulating abilities and preferences to As species varied among different ecotypes. The reduction of AsV into AsIII, oxidation of AsIII into AsV, and chelation of AsIII with thiols were all observed in P. vittata. The reduction of As mainly occurred in the rhizoid, whereas oxidation and chelation mainly occurred in the aboveground parts. Correlation analyses showed that the As concentration in pinna was significantly correlated with the AsV percentage in paraxial and abaxial epidermis (positive), AsIII-GSH percentage in paraxial epidermis (positive), and AsIII percentage in paraxial and abaxial epidermis (negative). Results indicated that oxidation and chelation reactions contributed to the accumulation of As in P. vittata.