Evaluating the mobility of polymer-stabilised zero-valent iron nanoparticles and their potential to co-transport contaminants in intact soil cores

Alleviated lead toxicity in rice plant by co-augmented action of genome doubling and TiO2 nanoparticles on gene expression, cytological and physiological changes

Lead is a very toxic and futile heavy metal for rice plants because of its injurious effects on plant growth and metabolic processes. Polyploidy or whole genome doubling increases the ability of plants to withstand biotic and abiotic stress. Considering the beneficial effects of nanoparticles and tetraploid rice, this research was conducted to examine the effectiveness of tetraploid and titanium dioxide nanoparticles (TiO2 NPs) in mitigating the toxic effects of lead. A diploid (E22-2x) and it's tetraploid (T-42) rice line were treated with Pb (200 μM) and TiO2 NPs (15 mg L-1). Lead toxicity dramatically reduced shoot length (16 % and 4 %) and root length (17 % and 9 %), biological yield (55 % and 36 %), and photosynthetic activity, as evidenced by lower levels of chlorophyll a and b (30 % and 9 %) in E-22 and T-42 rice cultivars compared to the control rice plants, respectively. Furthermore, lead toxicity amplified the levels of reactive oxygen species (ROS), such as malondialdehyde and H2O2, while decreasing activities of all antioxidant enzymes, such as superoxidase, peroxidase, and glutathione predominately in the diploid cultivar. Transmission electron microscopy and semi-thin section observations revealed that Pb-treated cells in E22-2x had more cell abnormalities than T-42, such as irregularly shaped mitochondria, cell wall, and reduced root cell size. Polyploidy and TiO2 reduced Pb uptake in rice cultivars and expression levels of metal transporter genes such as OsHMA9 and OsNRAMP5. According to the findings, genome doubling alleviates Pb toxicity by reducing Pb accumulation, ROS, and cell damage. Tetraploid rice can withstand the toxic effect of Pb better than diploid rice, and TiO2 NPs can alleviate the toxic impact of Pb. Our study findings act as a roadmap for future research endeavours, directing the focus toward risk management and assessing long-term impacts to balance environmental sustainability and agricultural growth.

Controlled-Release Materials for Remediation of Trichloroethylene Contamination in Groundwater

Groundwater contamination by trichloroethylene (TCE) presents a pressing environmental challenge with far-reaching consequences. Traditional remediation methods have shown limitations in effectively addressing TCE contamination. This study reviews the limitations of conventional remediation techniques and investigates the application of oxidant-based controlled-release materials, including encapsulated, loaded, and gel-based potassium permanganate since the year 2000. Additionally, it examines reductant controlled-release materials and electron donor-release materials such as tetrabutyl orthosilicate (TBOS) and polyhydroxybutyrate (PHB). The findings suggest that controlled-release materials offer a promising avenue for enhancing TCE degradation and promoting groundwater restoration. This study concludes by highlighting the future research directions and the potential of controlled-release materials in addressing TCE contamination challenges.

Immobilizing arsenic in soil via amine metal complex: a case study using iron-ethylenediamine

Fe-based nanomaterials have been extensively investigated for their application in mitigating arsenic (As) pollution in groundwater, sediment, and soils. Here, an iron-ethylenediamine (Fe-EDA) complex was synthesized and characterized using Fourier transform-infrared spectroscopy and X-ray photoelectron spectroscopy before its use as an amendment to ameliorate As-polluted soils. Column leaching tests at three Fe-EDA application rates (1%, 3%, and 5%) were conducted, and their results were compared with those acquired after using nano zerovalent iron (nZVI) and Fe₃O₄, to assess their efficiency to amend As-contaminated paddy soils. After leaching, stabilization efficiency and soil chemical characteristics were determined. Additionally, As fractions were measured using inductively coupled plasma-mass spectroscopy by employing a sequential extraction procedure to evaluate the performance of the treatments and understand the underlying their mechanisms. Compared with the control treatment, the Fe-EDA treatment reduced As release by more than 35.33% in the 2nd leaching cycle, whereas nZVI and Fe₃O₄ decreased the As release by 11.84% and 24.60%, respectively. Moreover, the optimal addition of the Fe-EDA chelate was 5%, which stabilized more than 50% As in the soil from the 7th to 11th leaching cycles. After sequential extraction, the Fe-Mn oxide binding fraction, which was originally 12.65%, increased to 21.5%, 18.23%, and 21.71% after the application of nZVI, Fe₃O₄, and Fe-EDA amendments, respectively. Furthermore, our treatments promoted the binding of the As fraction with crystalline Fe (III) (oxyhydr)oxide (F3); however, other fractions did not increase considerably, suggesting that the Fe-EDA complex could effectively stabilize As through electrostatic attraction between the arsenate anion and EDA, as well as As-O-Fe bond formation via a coordinating reaction. Overall, Fe-EDA was found to be a potent amendment for mitigating As-polluted soil.

A review of the influence of nanoparticles on the physiological and biochemical attributes of plants with a focus on the absorption and translocation of toxic trace elements

Trace elements (TEs) from various natural and anthropogenic activities contaminate the agricultural water and soil environments. The use of nanoparticles (NPs) as nano-fertilizers or nano-pesticides is gaining popularity worldwide. The NPs-mediated fertilizers encourage the balanced availability of essential nutrients to plants compared to traditional fertilizers, especially in the presence of excessive amounts of TEs. Moreover, NPs could reduce and/or restrict the bioavailability of TEs to plants due to their high sorption ability. In this review, we summarize the potential influence of NPs on plant physiological attributes, mineral absorption, and TEs sorption, accumulation, and translocation. It also unveils the NPs-mediated TE scavenging-mechanisms at plant and soil interface. NPs immobilized TEs in soil solution effectively by altering the speciation of TEs and modifying the physiological, biochemical, and biological properties of soil. In plants, NPs inhibit the transfer of TEs from roots to shoots by inducing structural modifications, altering gene transcription, and strengthening antioxidant defense mechanisms. On the other hand, the mechanisms underpinning NPs-mediated TEs absorption and cytotoxicity mitigation differ depending on the NPs type, distribution strategy, duration of NP exposure, and plants (e.g., types, varieties, and growth rate). The review highlights that NPs may bring new possibilities for resolving the issue of TE cytotoxicity in crops, which may also assist in reducing the threats to the human dietary system. Although the potential ability of NPs in decontaminating soils is just beginning to be understood, further research is needed to uncover the sub-cellular-based mechanisms of NPs-induced TE scavenging in soils and absorption in plants.

Assessment of shear-thinning fluids and strategies for enhanced in situ removal of heavy chlorinated compounds-DNAPLs in an anisotropic aquifer

The removal of chlorinated organic hydrocarbons (COHs) -DNAPLs was studied in permeability-contrasted sandboxes with an egg-box shaped substratum. Aqueous solutions were compared to viscous shear-thinning fluids (xanthan solution and foam). Interfacial and viscous effects were compared by increasing the capillary number of injected fluids. Non-spatially targeted DNAPL recovery (NSTR) where the driving force was the injection pressure, was compared to spatially targeted DNAPL recovery (STR) where a pumping system allowed the controlled flow. A historical contamination made of a complex mixture of COHs and hexachlorobutadiene (HCBD) as a model were used. NSTR results showed that DNAPL recovery with non-viscous liquids did not exceed 40%. The best results were obtained for xanthan solutions with surfactant ~ 1.3 ×CMC for which pure phase recovery amounted to 88% and 93% for HCBD and for the historical DNAPL, respectively. The STR strategy showed similar recovery yields, whereas xanthan concentrations were 10-times lower. Mass balances on DNAPL showed that at most, 0.15% of COHs was dissolved in the aqueous effluents. NZVI (1 g.l^-1) were delivered in xanthan in view of the chemical degradation of residual COHs and showed a 65% transmission through the low permeability soil.

Effects of nanoparticles on trace element uptake and toxicity in plants: A review

Agricultural soils are receiving higher inputs of trace elements (TEs) from anthropogenic activities. Application of nanoparticles (NPs) in agriculture as nano-pesticides and nano-fertilizers has gained rapid momentum worldwide. The NPs-based fertilizers can facilitate controlled-release of nutrients which may be absorbed by plants more efficiently than conventional fertilizers. Due to their large surface area with high sorption capacity, NPs can be used to reduce excess TEs uptake by plants. The present review summarizes the effects of NPs on plant growth, photosynthesis, mineral nutrients uptake and TEs concentrations. It also highlights the possible mechanisms underlying NPs-mediated reduction of TEs toxicity at the soil and plant interphase. Nanoparticles are effective in immobilization of TEs in soil through alteration of their speciation and improving soil physical, chemical, and biological properties. At the plant level, NPs reduce TEs translocation from roots to shoots by promoting structural alterations, modifying gene expression, and improving antioxidant defense systems. However, the mechanisms underlying NPs-mediated TEs uptake and toxicity reduction vary with NPs type, mode of application, time of NPs exposure, and plant conditions (e.g., species, cultivars, and growth rate). The review emphasizes that NPs may provide new perspectives to resolve the problem of TEs toxicity in crop plants which may also reduce the food security risks. However, the potential of NPs in metal-contaminated soils is only just starting to be realized, and additional studies are required to explore the mechanisms of NPs-mediated TEs immobilization in soil and uptake by plants. Such future knowledge gap has been highlighted and discussed.

Optimum conditions of zero-valent iron nanoparticle stabilized foam application for diesel-contaminated soil remediation involving three major soil types

Stability of foam, enhanced by nano zero-valent iron (nZVI) and its optimized constituents, may have significant potential for effective treatment of soil contaminated with diesel oil-a major environmental problem. The optimum diesel removal efficiency from distinct types of soil accomplished by the unique application of such foams as well as the optimum conditions of the foaming constituents have not been reported in literature so far. Hence, in this work, the removal of diesel contaminant from different soil types (desert, coastal, clay soil) is optimized, and the optimized results are reported for the first time, using response surface methodology (RSM), for alkylpolyglucoside phosphate (APG-Ph) foam, stabilized by nZVI. The effect of concentrations of APG-Ph (0.02, 0.04, 0.06, 0.08, and 0.1 volume %) and nZVI (2, 3, and 3.5 mg/l) on diesel removal efficacy from soil is studied using Box-Behnken design (BBD) of response surface methodology (RSM). Maximum diesel removal efficiency obtained at a concentration of 0.1 volume % APG-Ph foam with 3.5 mg/l nZVI for desert, coastal, and clay soil is 94.6, 95.3, and 57.5%, respectively. The optimum concentrations of APG-Ph and nZVI are found to be 0.98 volume % and 0.8 mg/l, respectively. Validation of this optimal condition experimentally results in highest removal efficiency of 98.3, 97.2, and 75.9% for desert, coastal, and clay soil respectively. This is in good agreement with the predicted values by RSM (98.67, 97.57, and 76.85%). The maximum diesel removal efficiency predicted at optimal concentration of APG-Ph and nZVI is significantly larger than the results reported in literature in last three years.

Low mobility of CuO and TiO2 nanoparticles in agricultural soils of contrasting texture and organic matter content

The fate of nanoparticles (NPs) in soil under relevant environmental conditions is still poorly understood. In this study, the mobility of two metal-oxide nanoparticles (CuO and TiO₂) in contrasting agricultural soils was investigated in water-saturated soil columns. The transport of TiO₂ and CuO-NPs were assessed in six soils with three different textures (from sand to clay) and two contrasted organic matter (OM) contents for each texture. TiO₂ mobility was very low in all soils, regardless of texture and OM content. Mass recoveries were always less than 5%, probably in relation with the strong homo-aggregation of TiO₂-NPs observed in all soil solutions, with apparent sizes 3-6 times larger than their nominal size. This low mobility suggests that TiO₂-NPs present a low risk of direct groundwater contamination in contrasted surface soils. Although their retention was also generally high (more than 86%), CuO nanoparticles were found to be mobile in all soils. This is probably related to their smaller apparent size and low capacity of homo-aggregation of CuO-NPs in all soil solutions. No clear influence of neither soil texture or soil total organic matter content could be observed on CuO transport. However, this study shows that in contrasted agricultural soils, CuO-NPs transport is mainly controlled by the solutes dissolved in soil solution (DOC and PO₄ species), rather than by the properties of the soil solid phase.

Porous media transport of iron nanoparticles for site remediation application: A review of lab scale column study, transport modelling and field-scale application

Injection of surface modified zero valent iron nanoparticles for in situ remediation of soil, contaminated with an array of pollutants has attracted great attention due to the high reactivity of zero valent iron towards a broad range of contaminants, its cost effectiveness, minimal physical disruption and low toxicity. The effectiveness of this technology relies on the stability and mobility of injected iron nanoparticles. Hence the development of a modelling tool capable of predicting nZVI transport is indispensable. This review provides state of the art knowledge on the mobility of iron nanoparticles in porous media, mechanisms involved in subsurface retention of nZVI based on continuum models and field scale application. Special attention is given to the identification of the influential parameters controlling the transport potential of iron nanoparticles and the available numerical models for the simulation of laboratory scale transport data.

Transport of the arsenic (As)-loaded nano zero-valent iron in groundwater-saturated sand columns: Roles of surface modification and As loading

In this study, the effects of surface modification of nZVI and arsenic (As) loading on the mobility of the three types of As-loaded nZVI (As-loaded pristine, chitosan-modified and polyaniline-modified nZVI) in quartz sand-packed columns were investigated. Breakthrough curves and retention profiles for the three types of As-loaded nZVI were analyzed by the Tufenkji-Elimelech equations and the HYDRUS-1D model. The mobility of both types of As-loaded modified nZVI was higher than the As-loaded pristine nZVI at both low and high As loadings. Compared to low As loading, the mobility of the three types of As-loaded nZVI was higher at high As loading. The values of the calculated and the fitted retention parameters of the three As-loaded nZVI were lower when As loading was higher or nZVI was modified, which were in line with the experimental column findings. The mechanisms of As-loaded nZVI transport were probably due to ripening and sedimentation. The As in the effluent was mainly from the As-loaded nZVI particles when nZVI was detected and was from the As release when no nZVI was detectable. It was evident that the mobility of the three types of As-loaded nZVI particles were severely limited (the maximum transport distance was less than 60 cm), regardless of surface modification and As loading. Therefore, the As release from the As-loaded nZVI could cause potentially wide pollution and should be paid more attention regarding to the application of nZVI in As remediation.

Transport, retention, and long-term release behavior of polymer-coated silver nanoparticles in saturated quartz sand: The impact of natural organic matters and electrolyte

This study investigated the transport and long-term release of stabilized silver nanoparticles (AgNPs), including polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs) and bare AgNPs (Bare-AgNPs), in the presence of natural organic matters (NOMs; both humic acids (HA) and alginate (Alg)) and an electrolyte (Ca²⁺) in a sand-packed column. Very low breakthrough rate (C/C₀) of AgNPs (below 0.04) occurred in the absence of NOM and the electrolyte. Increasing the concentration of NOM and decreasing the influent NOM solution's ionic strength (IS) reduced the retention of AgNPs. The reduced NP retention at high NOM and low IS was mainly attributed to the increased energy barrier between the AgNPs and the sand grain surface. Notably, the retention of PVP-AgNPs was enhanced at high Alg concentration and low IS, which mainly resulted from the improved hydrophobicity that could increase the interaction between the PVP-AgNPs and the collector. The total release amount of PVP-AgNPs (10.03%, 9.50%, 28.42%, 6.37%) and Bare-AgNPs (3.28%, 2.58%, 10.36%, 1.54%) were gained when exposed to four kinds of NOM solutions, including deionized water, an electrolyte solution (1 mM Ca²⁺), HA with an electrolyte (1 mM Ca²⁺), and a Alg (40 mg/L) solution with an electrolyte (1 mM Ca²⁺). The long-term release of retained silver nanoparticles in the quartz sand was mostly through the form of released Ag NPs. The factors that increased the mobility of AgNPs in quartz sand could improve the release of the AgNPs. The release of AgNPs had no significant change in the presence Ca²⁺ but were increased in the presence of HA. The Alg slightly decreased the release of AgNPs by increasing the hydrophobicity of AgNPs. The results of the study indicated that all the tested NOM and Ca²⁺ have prominent influence on the transport and long-term release behavior of silver nanoparticles in saturated quartz sand.

Distinguishable co-transport mechanisms of phenanthrene and oxytetracycline with oxidized-multiwalled carbon nanotubes through saturated soil and sediment columns: vehicle and competition effects

To date mechanisms underlying co-transports of engineered nanomaterials (ENMs) with contaminants have not been adequately explored, which involve complex interactions among ENMs, contaminants, and soils. This study investigated co-transport behaviors of 3 oxidized-multiwalled carbon nanotubes (o-MWCNTs) with phenanthrene (PHE) and oxytetracycline (OTC) in soil and sediment columns. Sorptions and desorptions of PHE and OTC by the o-MWCNTs were examined to facilitate the discussion of co-transport mechanisms. The results showed that mobilities of PHE and OTC in the columns were significantly enhanced by the presences of o-MWCNTs in the influents; the eluted o-MWCNTs were positively correlated to the eluted total PHE but negatively correlated to the eluted total OTC; the eluted PHE was mainly in the o-MWCNTs-associated form, while it was mainly the dissolved OTC breaking through the columns. It was thus concluded that the o-MWCNTs acted as vehicles facilitating the PHE transport, while besides the vehicle effect the o-MWCNTs also competed for the adsorption sites on soil particles with OTC and thereby enhancing the OTC mobility. These findings provide new insight into the mechanisms regulating co-transports of ENMs and contaminants in porous media.