Plant uptake is an important process in determining the transfer of pesticides through a food chain. Understanding how crops take up and translocate pesticides is critical in developing powerful models to predict pesticide accumulation in agricultural produce and potential human exposure. Herein, wheat was selected as a model plant species to investigate the uptake and distribution of eleven widely used pesticides in a hydroponic system as a function of time for 144 h. The time-dependent uptake kinetics of these pesticides were fitted with a first-order 1-compartment kinetic model. During 144 h, flusilazole and difenoconazole, with relative high log Kₒw (3.87 and 4.36, respectively), displayed higher root uptake rate constants (k). To clarify the role of root lipid content (fₗᵢₚ) in plant accumulation of pesticides, we conducted a lipid normalization meta-analysis using data from this and previous studies, and found that the fₗᵢₚ value was an important factor in predicting the root concentration factor (RCF) of pesticides. An improved correlation was observed between log RCF and log fₗᵢₚKₒw (R² = 0.748, N = 26, P < 0.001), compared with the correlation between log RCF and log Kₒw (R² = 0.686, N = 26, P < 0.001). Furthermore, the hydrophilic pesticides (e.g. log Kₒw < 2) were found to reach partition equilibrium faster than lipophilic pesticides (e.g. log Kₒw > 3) during the uptake process. The quasi-equilibrium factor (αₚₜ) was inversely related to log Kₒw (R² = 0.773, N = 11, P < 0.001) suggesting a hydrophobicity-regulated uptake equilibrium. Findings from this study could facilitate crop-uptake model optimization.

Excessive copper (Cu) in contaminated soil and groundwater has attracted continuous attentions due to the bioaccumulation and durability. In this study, the feasibility of remediation of heavy metal pollution in soil and groundwater was investigated using hydroxyapatite/calcium silicate hydrate (HAP/C–S–H) recovered from phosphorus-rich wastewater in farmland. The results show that the pH has a strong effect on copper removal from Cu-contaminated groundwater but the impact of ion strength on the removal is weak. In general, high pH and low ion strength give better results in copper removal. Kinetic and isotherm data from the study fit well with Pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The maximum adsorption capacity of HAP/C–S–H (138 mg/g) was higher than that of C–S–H (90.3 mg/g) when pH value, temperature, and ionic strength were 5, 308 K, and 0.01 M, respectively. Thermodynamics results indicate that Cu removal is a spontaneous and endothermic process. X-ray diffraction (XRD) results show that the mechanism of copper removal involves physical adsorption, chemical precipitation and ion exchange. For the remediation of Cu-contaminated soil, 76.3% of leachable copper was immobilized by HAP/C–S–H after 28 d. Acid soluble Cu, the main contributor to biotoxicity, decreased significantly while reducible and residual Cu increased. After immobilization, the acid neutralization capacity of the soil increased and the dissolution of copper was substantially reduced in near-neutral pH. It can be concluded that HAP/C–S–H is an effective, low-cost and eco-friendly reagent for in-situ remediation of heavy metal polluted soil and groundwater.

Magnetic biochars were prepared by chemical co-precipitation of Fe³⁺/Fe²⁺ onto rice straw (M-RSB) and sewage sludge (M-SSB), followed by pyrolysis treatment, which was also used to prepare the corresponding nonmagnetic biochars (RSB and SSB). The comparison of adsorption characteristics between magnetic and nonmagnetic biochars was investigated as a function of pH, contact time, and initial Cd²⁺ concentration. The adsorption of nonmagnetic biochars was better described by pseudo-second-order kinetic model, and the adsorption of RSB and SSB was better described by Langmuir and Freundlich models, respectively. Magnetization of the biochars did not change the applicability of their respective adsorption models, but reduced their adsorption capabilities. The maximum capacities were 42.48 and 4.64 mg/g for M-RSB and M-SSB, respectively, underperforming their nonmagnetic counterparts of 58.65 and 7.22 mg/g for RSB and SSB. Such a reduction was fundamentally caused by the decreases in the importance of cation-exchange and Cπ-coordination after magnetization, but the Fe-oxides contributed to the precipitation-dependent adsorption capacity for Cd²⁺ on magnetic biochars. The qualitative and quantitative characterization of adsorption mechanisms were further analyzed, in which the contribution proportions of cation-exchange after magnetization were reduced by 31.9% and 12.1% for M-RSB and M-SSB, respectively, whereas that of Cπ-coordination were reduced by 3.4% and 31.1% for M-RSB and M-SSB, respectively. These reductions suggest that for adsorbing Cd²⁺ the choice of conventional biochar was more relevant than whether the biochar was magnetized. However, magnetic biochars are easily separated from treated solutions, depending largely on initial pH. Their easy of separation suggests that magnetic biochars hold promise as more sustainable alternatives for the remediation of moderately Cd-contaminated environments, such as surface water and agriculture soil, and that magnetic biochars should be studied further.

Carbamazepine (CBZ) decay by electro-Fenton (EF) oxidation using a novel FeS₂/carbon felt (CF) cathode, instead of a soluble iron salt, was studied with the aim to accelerate the reaction between H₂O₂ and ferrous ions, which helps to produce more hydroxyl radicals (•OH) and eliminate iron sludge. First, fabricated FeS₂ and its derived cathode were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Anodes were then screened, with DSA (Ti/IrO₂–RuO₂) showing the best performance under EF oxidation regarding CBZ degradation and electrochemical characterization. Several operating parameters of this EF process, such as FeS₂ loading, current density, gap between electrodes (GBE), initial [CBZ], and electrolyte type, were also investigated. Accordingly, a nonconsecutive empirical kinetic model was established to predict changes in CBZ concentration under the given operational parameters. The contribution of different oxidation types to the EF process was calculated using kinetic analysis and quenching experiments to verify the role of the FeS₂-modified cathode. The reaction contributions of anodic oxidation (AO), H₂O₂ electrolysis (EP), and EF oxidation to CBZ removal were 12.81%, 7.41%, and 79.77%, respectively. The •OH exposure of EP and EF oxidation was calculated, confirming that •OH exposure was approximately 22.45-fold higher using FeS₂-modified CF. Finally, the 19 intermediates formed by CBZ degradation were identified by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. Accordingly, four CBZ degradation pathways were proposed. ECOSAR software was used to assess the ecotoxicity of intermediates toward fish, daphnia, and green algae, showing that this novel EF oxidation process showed good toxicity reduction performance. A prolonged EF retention time was proposed to be necessary to obtain clean and safe water, even if the targeted compound was removed at an earlier time.

The influence of intercalated anions on the structure and composition of green rusts supplies a theoretical possibility for the investigation of the structural modification of Feᴵᴵ/Feᴵᴵᴵ (oxyhydr)oxide materials. β-Cyclodextrin was intercalated into the mixed-valent iron-based hydroxide layers to synthesize new green rust materials (β-CD GRs), pursuing high-capacity uraniumⱽᴵ (Uⱽᴵ) sorption. The molar ratios of Feᴵᴵ to Feᴵᴵᴵ and the molar ratios of β-CD GR to Feᴵᴵ + Feᴵᴵᴵ had a significant effect on the synthesis of β-CD GRs. The synthesis process was further optimized by the quadric predictor and desirability function in a central composite design in combination. Both strong acidity and alkalinity were harmful to the adsorption of β-CD GRs towards Uⱽᴵ. The pseudo-first-order kinetic model and Langmuir isotherm model were appropriate in fitting the whole adsorption process. The maximum monolayer adsorption capacity of β-CD GRs was 2548.61 mg/g. The presence of mimic groundwater constituents explicitly deteriorated the interaction between β-CD GR and Uⱽᴵ species. Nanoscale nodules and particles were formed on the β-CD GR after the adsorption experiments. The peaks at 1159 and 609 cm⁻¹ vanished with the band at 1103 cm⁻¹ being left-shifted to 1117 cm⁻¹ in the FTIR spectra of β-CD GR during the heterogeneous process. The intercalation of β-CD brought obvious enhancement of Uⱽᴵ species sorption to the GR material, which was combinedly driven by several reaction pathways and different from the unmodified GRs.

Cadmium bioavailability in paddy soils is strongly affected by flooding-draining cycle. In this study, we used synchrotron-based X-ray absorption spectroscopy and a stirred-flow method to investigate the effects of flooding-draining and amendments of CaCO₃ and CaSO₄ on Cd speciation and release kinetics from a Cd-spiked paddy soil (total Cd concentration of 165 mg kg⁻¹). Extended X-ray absorption fine structure analysis showed that Cd was predominantly bound to non-iron-clay minerals (e.g. Cd-kaolinite, Cd-illite, and Cd-montmorillonite, accounting for 60–100%) in the air-dried soil and 1- or 7-day flooded samples. After prolonged flooding (30 and 120 days), Cd-iron mineral complexes (e.g. Cd bound to ferrihydrite and goethite) became the predominant species (accounting for 52–100%). Stirred-flow kinetic analysis showed that both prolonged flooding and the amendments with CaCO₃ and CaSO₄ decreased the maximum amount and the rate coefficient of Cd release. However, the effect of prolonged flooding was reversed after a short period of draining, indicating that although Cd was immobilized during flooding, it became mobile rapidly after the soil was drained, possibly due to pH decrease and rapid oxidation of CdS. The effects of the amendments on Cd uptake in rice plants were tested in a pot experiment using the same paddy soil without Cd spiking (total Cd 2.1 mg kg⁻¹). Amendment with CaCO₃ and, to a lesser extent, CaSO₄, decreased the Cd accumulation in two cultivars of rice. The combination of CaCO₃ amendment and a low Cd accumulating cultivar was effective at limiting grain Cd concentration to below the 0.2 mg kg⁻¹ limit.

In this work, ZnO–CdWO₄ nanoparticles have been synthesized by the ecofriendly green method with lemon leaf extract to favorably anchor functional groups on their surface. The prepared ZnO–CdWO₄ nanoparticles are used as adsorbent to treat Congo red (CR) dye after characterization through FT-IR, UV–Vis, TEM, SEM-EDX, and HRTEM techniques. The equilibrium partition coefficient and adsorption capacity values for CR by ZnO–CdWO₄ are estimated as 21.4 mg g⁻¹ μM⁻¹ and 5 mg g⁻¹, respectively (at an initial dye concentration of 10 mg L⁻¹). The adsorption process is found as exothermic and spontaneous, as determined by the ΔG°, ΔS°, and ΔH° values. The Boyd plot has been used as a confirmatory tool to fit the adsorption kinetics data along with intraparticle diffusion and pseudo-second-order models. Based on this research, ZnO–CdWO₄ nanoparticles are validated as an effective adsorbent for CR dye in aqueous solutions.

Ammonium molybdophosphate (AMP) exhibits high selectivity towards Cs but it cannot be directly applied in column packing, so it is necessary to prepare AMP–based adsorbents into an available form to improve its practicality. This work provided two AMP immobilized cellulose microspheres (MCC@AMP and MCC-g-AMP) as adsorbents for Cs removal by radiation grafting technique. MCC-g-AMP was prepared by radiation graft polymerization of GMA on microcrystalline cellulose microspheres (MCC) followed by reaction with AMP suspension, and MCC@AMP was synthesized by radiation hybrid grafting of AMP and GMA onto MCC through one step. The different structures and morphologies of two adsorbents were characterized by FTIR and SEM. The adsorption properties of two adsorbents against Cs were investigated and compared in batch and column experiments under different conditions. Both adsorbents were better obeyed pseudo-second-order kinetic model and Langmuir model. MCC-g-AMP presented faster adsorption kinetic and more stable structure, whereas MCC@AMP presented more facile synthesis and higher adsorption capacity. MCC@AMP was pH independent in the range of pH 1–12 but MCC-g-AMP was sensitive to pH for Cs removal. The saturated column adsorption capacities of MCC@AMP and MCC-g-AMP were 5.4 g-Cs/L-ad and 0.75 g-Cs/L-ad in column adsorption experiments at SV 10 h⁻¹. Both adsorbents exhibited very high radiation stability and can maintain an adsorption capacity of >85% even after 1000 kGy γ-irradiation. On the basis, two AMP-loaded adsorbents possessed promising application in removal of Cs from actual contaminated groundwater. These findings provided two efficient adsorbents for treatment of Cs in radioactive waste disposal.

Facile modification is a common, but effective, option to improve the uptake removal capacity of of activated carbon (AC) against diverse target volatile organic compounds (VOCs; e.g., benzene) in gaseous streams. To help design the routes for such modification, this research built strategies to generate three types of modified ACs by incorporating amine/sulfur/amino-silane groups under solvothermal or microwave (MW) thermal conditions. The adsorption performance has been tested using a total of six types of AC sorbents (three modified + three pristine forms) for the capture of 1 Pa benzene (1 atm and 298 K). The obtained results are evaluated in relation to their textural properties and surface functionalities. Accordingly, the enhancement of AC surface basicity (e.g., point of zero charge (PZC) = 10.25), attained via the silylation process, is accompanied by the reduced adsorption of benzene (a weak base). In contrast, ACs amended with amine/sulfur (electron-donating) groups using the MW technique are found to acquire high surface acidity (PZC of 5.99–6.05) to exhibit significantly improved benzene capturing capability (relative to all others). Their uplifted performance is demonstrated in terms of key performance metrics such as breakthrough volume (BTV10%: 163 → 443 L g⁻¹), adsorption capacity (Q10%: 4.82 → 13.6 mg g⁻¹), and partition coefficient (PC10%: 0.516 → 1.67 mol kg⁻¹ Pa⁻¹). Based on the kinetic analysis, the overall adsorption process is found to be governed by pore diffusion as the main rate-determining step, along with surface interaction mechanisms. The results of this research clearly support the critical role of surface chemistry of AC adsorbents and their textural properties in upgrading air/gas purification systems.

PURPOSE OF REVIEW: Hydrothermal carbonization (HTC) is an innovative technique by which a wet feedstock is converting into valuable product, hydrochar, without drying as a pretreatment step. Over all other thermal converting process, HTC is counted as the most cost-effective and environmentally friendly technique. The purpose of this review is to highlight the current research trends of HTC and the application of hydrochar derived from biomass in heavy metal removal. RECENT FINDINGS: This review provides an overview about HTC fundamentals including its ecotoxicology and the factors such as biomass type, reaction temperature, retention time, catalysis, and pH medium, which affect hydrochar composition and performance. Moreover, various modification agents in order to function the hydrochar was discussed. It is proposed that the co-hydrothermal carbonization of two or more biomasses with the addition of other materials can enhance the functional groups and change the features of the produced hydrochar. This paper also reviews the kinetic analysis and adsorption isotherm as well as the hydrochar applications in heavy metal removal. Acacia arabica waste is produced annually in huge amount, which adversely affect the environment. Up to now, it has no specific reuse in a proper way. In this respect, biomass such as Acacia arabica wastes can successfully be valorized by converting into hydrochar via hydrothermal carbonization. Moreover, application as a green adsorbent to remove heavy metal contamination from wastewater due to its high porosity and great surface area is counted as a promising technique that contributes to this field of research.